Improved Traditional Phytomedicines in Current Use for the Clinical Treatment of Malaria

Table of Contents

Abstract

Phytomedicines and “green pharmacies” are promoted by some NGOs and governments as part of their efforts to control malaria. “Improved traditional medicines” (ITMs) are standardised as regards preparation and dose, although not always according to the concentration of active compounds. A systematic literature search revealed that six such phytomedicines are currently government-approved in at least one country and used on a relatively large scale nationally or internationally: Artemisia annua L. (Asteraceae), Cinchona bark (Rubiaceae), Cryptolepis sanguinolenta (Lindl.) Schltr. (Apocynaceae), “Ayush-64”, “Malarial-5” and Cochlospermum planchonii Hook. f. ex Planch. (Bixaceae). One further ITM has been developed and is in the process of being approved: Argemone mexicana decoction. Their development, phytochemistry, pharmacology, and clinical trials are reviewed, as well as priorities for future research.

Key words

malaria - herbal medicine - phytomedicine - government‐approved - clinical trials

Introduction

In spite of many valiant efforts at control and even elimination, malaria remains one of the top five causes of childhood deaths in the world. Artemisinin combination therapies (ACTs) are now recommended by the World Health Organization (WHO) as first-line treatments [1], but are still not widely available to those who most need them, especially in remote areas. It is estimated that 80 % of malaria patients are treated in the community and never come to any formal health facility [2].

Growing medicinal plants in a “green pharmacy”, for preparation at the local level (usually as herbal teas), can empower poor communities to become more self-reliant. Several Non-Governmental Organizations (NGOs) promote this approach because it has the advantage of being cheap, sustainable, available at the point of need, and does not rely on the fickle goodwill of donor agencies or on unreliable distribution networks. However, there must also be good evidence of safety and efficacy for the plants used. In a malarious area, one of the top priorities for a “green pharmacy” will always be antimalarial plants. Worldwide, over 1200 plant species are reportedly used for the treatment of malaria and fever [3]. Although many of these have been tested in the laboratory with varying results, very few have been evaluated in clinical trials [4].

Another approach is the production of standardised phytomedicines at the national level, often developed by a government-sponsored research organisation. These phytomedicines, often called “improved traditional medicines” (ITMs), are standardised as regards preparation and dose, although not always according to the concentration of active compounds. In this model, the preparation can be more complex (whether a complex mixture of plants or a more complex extraction procedure) and quality control is easier to implement. The country benefits by having a locally produced medicine which is more sustainable than imports. However, the problems of distribution and lack of infrastructure remain; and the finished product will not necessarily be cheaper than a highly subsidised ACT.

The Research Initiative on Traditional Antimalarial Methods (RITAM) (www.giftsofhealth/ritam) was established in 1999 to examine such questions and has conducted many systematic reviews on antimalarial plants [5]. This review will summarise the evidence for safety and efficacy of government-approved improved traditional phytomedicines in current clinical use for the treatment of malaria.

Methods

A literature search was performed using MEDLINE, CAB, SOCIOFILE, and EMBASE to find all articles referring to traditional herbal remedies for malaria (key words: “malaria”, “traditional medicine”, “malaria–therapy”). References of relevant articles were searched, and some journals were searched by hand to try to identify as many relevant articles as possible. The RITAM network (consisting of over 200 researchers in the field of traditional antimalarials) was consulted and conferences attended in an attempt to identify unpublished studies on herbal antimalarials. For the purposes of this review, we selected only “improved traditional medicines” which are government-approved in at least one country and which have been deployed at a relatively large scale (national or international).

Results

Six “improved traditional medicines” were identified which are government-approved, have been used on a relatively large scale and have been the subject of published research, and one further ITM which is in the process of being approved. Their composition is summarised in [Table 1], preclinical efficacy in [Table 2], and clinical efficacy (in uncomplicated P. falciparum malaria) in [Table 3].

Table 1 Government-approved improved traditional phytomedicines in current clinical use for the treatment of malaria.

Remedy	Species	Part	Preparation	Country of origin	Year developed	Countries where currently used	Level of production
Qing hao	Artemisia annua L. (Asteraceae)	aerial parts	infusion	China	340	China, Vietnam, throughout Africa	local
Totaquina	Cinchona spp (Rubiaceae)	bark	decoction	Peru	1649	India, Madagascar, Sudan, Bolivia, Colombia, Nicaragua	local and national
Phyto-laria	Cryptolepis sanguinolenta (Lindl.) Schltr. (Apocynaceae)	roots	decoction	Ghana	1974	Ghana	local and national
Ayush-64	Caesalpinia bonducella (L.) Fleming (Fabaceae)	roots seed pulp	decoction dry powder	India	1980	India	national
	Swertia chirata Buch. Ham (Gentianaceae)	whole plant	decoction
	Alstonia scholaris (L.) R. Br. (Apocyanaceae)	bark	decoction
	Picrorhiza kurrooa Royle ex Benth. (Plantaginaceae)	rhizome	decoction
Malarial-5	Cassia occidentalis L. (Caesalpinaceae) (62 %)	leaves	decoction	Mali	1982	Mali	national
	Lippia chevalieri Mold (Verbenaceae) (32 %)	leaves	decoction
	Spilanthes oleraceae L. (Compositae) (6 %)	flowerheads	decoction
N'dribala	Cochlospermum planchonii Hook. f. ex Planch. (Bixaceae)	root	decoction	Burkina Faso	2005	Burkina Faso, Ivory Coast, Nigeria	local and national
Soumafoura Tiemoko Bengaly	Argemone mexicana L. (Papaveraceae)	aerial parts	decoction	Mali	2006	Mali	local and national

Table 2 Summary of preclinical efficacy of antimalarial improved traditional medicines.

Remedy*	In vitro against P. falciparum		In vivo in mice (P. berghei)			References
	IC50 (µg/mL)	Extract	% parasite suppression	Extract	Dose**
Qing hao	1.5	ethanolic	33.3	aqueous infusion	8.3 mL/kg bd po for 7 d	[20], [24], [86]
Totaquina	< 10	ethanolic	100	ethanolic	500 mg/kg od po for 4 d	[26], [87]
Phyto-laria	< 6	ethanolic	59	ethanolic	100 mg/kg od po for 4 d	[43], [53]
Ayush-64	no data		0	as per Table 1	1.5 g od for 5 d	[54], [55], [88]
Malarial-5	470–600	aqueous decoction	55	aqueous decoction, lyophilised	200 mg/kg od po for 5 d	[63]
N'dribala	75	aqueous root decoction	no data			[71]
Soumafoura Tiemoko Bengaly	5.89	aqueous	0	aqueous decoction	375–3375 mg/kg po	[75], [78], [79], [84]
*  Plant species and parts as per [Table 1]. ** od = once daily; bd = twice daily; po = per os (i.e., oral)

Table 3 Summary of clinical trials of antimalarial improved traditional medicines for the treatment of uncomplicated P. falciparum malaria.

Remedy*	Dose**	Location of trial	Season	Total n of patients (P. f.)	Mean age of patients (range, in years)	Parasite clearance at d 5–7 (% of patients)	Recrudescence by d28 (% of patients)	References
Qing hao	5–9 g dried leaf infused in 1 l boiling water, 250 mL qds for 7 d	Democratic Republic of Congo	whole year	379	(≥ 18)	70–100	13–39	[89], [90], [91]
Totaquina	1.2 g daily for 5 d	Algeria, Bulgaria, China, France, India, Italy, Malaysia, Morocco, Romania, Spain	rainy	586	not reported	92–100	no data	[26, 35, 37]
Phyto-laria	2.5 g root powder per teabag, infused in 150 mL of boiling water for 5–10 mins, tds for 5 days	Ghana		58	adult	100	0	[45, 53]
Ayush-64	0.5–1 g tds for 3 d	Madhya Pradesh, India	end of rains	4	22 (7–35)	100	no data	[57]
Malarial-5	10 g bd for 4 d then od for 3 d	Sélingué and Bamako, Mali	rainy season; dry season	92	(5–60)	0	no data	[64], [65], [66]
N'dribala)	50 g dried root powder boiled in 1500 mL water for 10 minutes; 200 mL tds for 5 days	Banfora, Burkina Faso	rainy	46	23 (12–45)	52	no data	[67]
Soumafoura Tiemoko Bengaly	500 g dried aerial parts boiled in 5 L water for 3 hours, taken as 250 mL bd over 7–14 days	Sikasso, Mali	rainy	215	10 (0–65)	19	63 %	[78], [79], [84]
* Preparations used in clinical trials are those given in [Table 1]. ** tds = 3 times a day; qds = 4 times a day

Qinghao (Artemisia annua L. [Asteraceae])

Development and use of the phytomedicine: The earliest record of the medicinal use of “qing hao” dates back to 168 BC in the “Fifty-two prescriptions”, which recommended it for the treatment of haemorrhoids [6]. Ge Hong was the first to recommend “qing hao” for the treatment of “intermittent fevers” (many of which were probably malaria). His “Handbook of Prescriptions for Emergency Treatment”, written in 340 AD, recommends the following preparation: “Take a bunch of qing hao and two sheng (two times 0.2 L) of water for soaking it, wring it out to obtain the juice and ingest it in its entirety” [7].

Although there is some debate as to whether “qing hao” was in fact Artemisia annua or A. apiacea [7], it was from A. annua that Chinese scientists isolated artemisinin, the most powerful antimalarial compound ever discovered, in 1971. Since then, several NGOs have recommended the use of Artemisia annua as a herbal remedy ([Fig. 1]). Anamed (Action for Nature and Medicine, www.anamed.org) has distributed seeds of a recently developed artemisinin-rich genetic variety of Artemisia annua [8] for cultivation and preparation as a herbal antimalarial to 240 partner organisations in developing countries. Other NGOs such as IFBV in Luxembourg (http://www.iwerliewen.org/) and ICEI in Italy (http://www.icei.info/) are involved in similar programmes. Artemisia annua leaf infusion was officially approved by the Ministry of Health in the Democratic Republic of Congo in 2007.

Fig. 1 Pastor George Okuto is one of Anamed's local partners in Kisumu, Kenya. He has distributed seedlings of Artemisia annua to over 200 families for use in their herbal home gardens (reproduced by the author).

The doses recommended by Anamed are based on the Chinese pharmacopoeia: an infusion of 5 g dried leaves on which 1 L of boiling water is poured and left to cool for 15 minutes, of which 250 mL is taken every six hours for seven days. A reduced dose is recommended for children, according to weight [9]. However, alternative preparations may be more effective. The most effective preparation in the literature was a crude ethanolic extract suspended in oil and presented in capsules [10]. A similar preparation is currently being developed by the Equator Foundation in the Netherlands (http://artemisia-for-all.org/). Preliminary studies show this can provide a much larger dose of artemisinin in a much smaller volume than the tea. Other suggestions are to use dried A. annua powder mixed in porridge, biscuits, or honey, to improve palatability for young children [11].

Phytochemistry and pharmacology: Artemisia annua contains many different classes of compounds: at least 28 monoterpenes, 30 sesquiterpenes, 12 triterpenoids and steroids, 36 flavonoids, 7 coumarins, 4 aromatic and 9 aliphatic compounds [12]. Several of these have some antimalarial activity, but the most active is undoubtedly the sesquiterpene lactone artemisinin, found in the leaves and flowers. Artemisinin has been found in only two other species, Artemisia apiacea and A. lancea [13]. Some other sesquiterpenes occur in much greater concentrations than artemisinin in wild strains of the plant: arteannuin B (2–4 ×) and artemisinic acid (7–8 ×). Arteannuin B used alone is ineffective and toxic in rat malaria, but it potentiates the effect of artemisinin [14]. A. annua also produces at least 36 flavonoids, five of which have been shown selectively to potentiate the in vitro activity of artemisinin against Plasmodium falciparum [15]. Casticin, at a concentration of 5 µmol/L, induces a 3- to 5-fold reduction in the IC₅₀ for artemisinin [16]. Chrysosplenol-D has the strongest potentiating effect, and this is also the most abundant flavone in plant material [15]. An aqueous infusion can extract up to 86 % of the artemisinin into the water, whereas as little as 30 % is extracted in a decoction (when the plant is boiled in water for several minutes), because artemisinin is not heat-stable [17]. Using full fat milk rather than water can increase the proportion of artemisinin extracted [18]. Recent research has shown that the traditional method of soaking then wringing out or pounding the juice of the plant results in much higher artemisinin concentrations than the infusion (up to 293 mg/L compared to 14.5 mg/L, respectively), although the extraction efficiency (total amount of artemisinin extracted) is less (14.9 % compared to 53.8 %, respectively) [19].

In vivo and in vitro studies have also shown that the whole Artemisia annua extract has a much greater antimalarial activity than the equivalent dose of artemisinin [19], [20]. Furthermore the bioavailability of artemisinin from a crude plant extract is much greater than from pure tablets (Rezelman, unpublished data).

Artemisinin has now been used in several million patients, with only one report of neurological side effects following artesunate treatment [21], [22]. Artemisinin is generally considered to be safe in the second and third trimesters of pregnancy [22] and now artesunate is recommended as the first line treatment for pregnant women with severe malaria [1]. However, early studies showed that relatively low doses of artemisinin (13–25 mg/kg or 1/200–1/400 of the LD50) cause fetal resorption in rodents, therefore use in the first trimester is not recommended [23] except in severe cases [1].

Clinical trials: Ethanolic extracts have been tested mainly against P. vivax in China, but the results seem promising, with 100 % parasite clearance and fever clearance reported although recrudescence occurred in up to 33 % [10], [14]. One study claimed a 100 % “cure” rate for P. falciparum malaria [14].

Herbal infusions (according to the Anamed recipe) are the preparation most widely tested in Africa, in six trials. These report rates of parasite clearance ranging from 70 % to 100 %, with recrudescence rates up to 39 % [24] ([Table 2]). The only side-effect reported was nausea in 3–25 % of patients. However, none of these studies included children, who are the group at greatest risk of severe malaria and death. A recent pilot pharmacovigilance study has confirmed that the only significant adverse event observed was that of miscarriage in the first trimester of pregnancy [25].

Totaquina (bark of Cinchona species [Rubiaceae])

Development and use of the phytomedicine: It is not known how long Cinchona bark had been used by indigenous communities in South America before its “discovery” by Jesuit priests in Peru in the early part of the 17th century [26]. Indeed, it is not known whether malaria even existed there before the arrival of European settlers. The first probable reference to the use of Cinchona in medical practice came in Belgium in 1643, when a public health official in Ghent recommended a powder, Pulvis indicus, for the treatment of tertian fevers [27]. The first indisputable reference, however, is the Schedula Romana, a handbill issued by the Pharmacy of the Collegio Romano in 1649 and again in 1651, containing precise instructions on dosage and administration. In 1649, at a gathering in Rome of the Jesuit Order, the influential Spanish Cardinal Juan de Lugo recommended the powder to the assembled delegates, ensuring the remedy's dissemination to missions throughout Europe [28]. In the nineteenth century, colonial powers established plantations of Cinchona throughout the tropics [29]. Today Cinchona trees are still cultivated in many parts of the tropics, for example the Congo, Madagascar, Guatemala, the Philippines, Vietnam, Indonesia and India.

Several crude extracts of Cinchona bark were in common use in the first half of the 20th century [26]. Totaquina type I (or quinetum) was prepared as a total alkaloid extract of C. succirubra Pav. Ex Klotzsch (Rubiaceae) or C. robusta (Rubiaceae) by dissolving the soluble constituents of powdered bark with hydrochloric acid, then precipitating the alkaloids with sodium hydroxide and drying the crude deposit. Totaquina type II (or residual alkaloids) was left over from the bark of C. ledgeriana (Howard) Bern. Moens ex Trimen (Rubiaceae) after the extraction of quinine. Sometimes “Cinchona febrifuge” was made from the total alkaloids of C. ledgeriana, without the prior extraction of quinine. Today, a processed powder of C. ledgeriana bark is still sold as a phytomedicine in Madagascar under the name of “Totaquina” by the Institut Malgache de Recherches Appliquées ([Fig. 2]).

Fig. 2 “Totaquina”: powdered bark of Cinchona ledgeriana sold as a phytomedicine in Madagascar (reproduced by the author).

Phytochemistry and pharmacology: Almost 30 alkaloids have now been described in Cinchona bark [30], several of which are active against plasmodia in vitro, and some of which are not [31]. The four best-known alkaloids are quinine with its d-isomer quinidine, and cinchonine with its l-isomer cinchonidine, all of which have antiplasmodial activity. They are found in varying proportions in different barks. Interestingly, quinine is not the most potent of the alkaloids: quinidine, dihydroquinidine, and cinchonine all have a consistently lower IC₅₀ in vitro. The combination of quinine with quinidine and cinchonine is 2–10 times more effective against quinine-resistant strains, and the mixture of alkaloids has a more consistent effect than any of the alkaloids used singly [32]. Cinchonine also inhibits P-glycoprotein, a transmembrane pump which pumps toxins (including drugs) out of cells, and is overexpressed in cancer cells, contributing to multidrug resistance. Cinchonine has been used to good effect in combination with chemotherapy for patients with lymphoproliferative syndromes [33]. It is possible that similar mechanisms are involved in malaria drug resistance [34], and cinchonine may therefore be able to counteract this.

Clinical trials: Several clinical trials were conducted of crude Cinchona preparations in India in the 1920s and 1930s [26]. The largest was a multicentre trial of totaquina conducted under the auspices of the League of Nations in 1933 [35]. 421 patients were given totaquina type I, and 634 were given totaquina type II. The outcome measure was parasite and fever clearance on the fifth (and last) day of treatment; there was no further follow-up to look for relapses. There was an attempt at standardising the composition of the totaquina used and the doses administered, but there was still quite a wide variation in the actual doses given. In spite of the variation in dosage, the parasite clearance achieved was surprisingly uniform, and as good as quinine. As regards safety, the League of Nations concluded that “the case records contain no cogent evidence that Totaquina is more toxic than quinine in the doses given” [36].

A small trial published in 1935 compared the response of P. falciparum infections to treatment with either quinine, totaquina type I (42 patients) or type II (31 patients). They found no significant difference in parasite or fever clearance times between the groups, with 100 % clearance of both fever and parasites by day 4 of treatment [37]. Unfortunately there was no longer term follow-up to look at relapse rates. No further clinical trials of totaquina have been published since 1935. However, trials on individual Cinchona alkaloids have shown that they are all effective antimalarials. Quinidine is at least as effective as quinine and more so in the case of resistant infections [38]. Cinchonine and cinchonidine, when used in isolation, are also as effective as quinine [39], [40]. A standardised mixture of Cinchona alkaloids has been developed and marketed as “Quinimax” (71.4 % quinine with 18.6 % quinidine and 5 % cinchonine). It is as effective as quinine in the treatment of malaria, but with a lower incidence of side-effects [41]. There have been no published studies comparing its efficacy with that of quinine in areas with significant quinine resistance.

Cryptolepis sanguinolenta (Lindl.) Schltr. (Apocynaceae)

Development and use of the phytomedicine: Cryptolepis sanguinolenta (Lindl.) Schltr. (Apocynaceae) is a scrambling shrub native to West Africa and used for the treatment of malaria in Ghana and in the Democratic Republic of Congo [42], [43]. In 1974, C. sanguinolenta was introduced to the Centre for Scientific Research into Plant Medicine (CSRIPM) in Mampong-Akwapim, Ghana. Decoctions of the roots of this plant have since then been used to treat malaria and some bacterial infections [44]. It has been developed and sold in standardized teabags under the brand name of “Phyto-laria” by the company Phyto-Riker ([Fig. 3]) and is approved by Ghana's drug regulatory agency, the Food and Drugs Board [45]. Each teabag contains 2.5 g of Cryptolepis root powder and is also standardized using total content of alkaloids. Instructions to patients are to steep the teabag in one cup (about 150 mL) of boiling water for 5–10 minutes and to take one cup three times a day for 5 days. WHO is currently collaborating with CSRIPM to develop a standardized form of the extract for use in African countries [46].

Fig. 3 “Phyto-laria”: a standardized teabag formulation of Cryptolepis sanguinolenta on sale in Ghana (reproduced by the author).

Phytochemistry and pharmacology: The roots of C. sanguinolenta contain approximately 0.5 % of alkaloids [47]. The major alkaloid is cryptolepine, an N-methyl derivative of the indoloquinoline compound, quindoline. In vitro this alkaloid has antimalarial activity comparable to chloroquine [48], [49]. However cryptolepine intercalates into DNA [50] and causes cell death by inhibiting the action of poly (ADP-ribose) polymerase [51]. Daily administration of 30 mg/kg cryptolepine to mice resulted in extensive necrosis of liver cells after 6 weeks but not after 2 weeks [52].

Ethanolic extracts of the root are very effective against P. falciparum in vitro and against P. berghei in vivo ([Table 2]). In an acute toxicity assessment of this product, up to 2 g/kg body weight of the dry extract (corresponding to 1754-fold the human dose of the product) was given orally to groups of mice, rats, and rabbits. No adverse effects were observed in any of the animals [46].

Clinical trials: A controlled clinical trial compared an aqueous root extract of Cryptolepis sanguinolenta with chloroquine in patients with P. falciparum malaria [53]. Twelve patients were treated with Cryptolepis extract (25 mg/kg body weight three times daily) and 10 were given chloroquine (25 mg/kg over 3 days). Parasite clearance time was only one day longer than with chloroquine (3.3 vs. 2.2 days) and symptom clearance was faster (36 vs. 48 hours). Fewer side effects were reported by patients taking the extract than by those on chloroquine. No significant changes were detected in the blood and urine samples analysed. No cases of recrudescence were reported in any of the participants in the follow-up 28-day period. A larger trial in 46 patients confirmed a parasite clearance time of 82.3 h and a fever clearance time of 25.4 h [45].

Ayush-64

Development and use of the phytomedicine: Widespread resurgence of malaria in India during the 1970s prompted the Indian government to develop an Ayurvedic remedy for malaria. Scientists at the Central Council for Research in Ayurveda and Siddha (CCRAS), an autonomous institution of the Ministry of Health and Family Welfare, selected four plants to prepare a formulation named “Ayush-64”. CCRAS further developed the drug in collaboration with 20 laboratories in the country and patented Ayush-64 as a new antimalarial herbal compound. The herbs were all traditionally used for the treatment of fevers including malaria [54].

Aqueous decoctions of the constituent herbs ([Table 1]) are prepared separately, then boiled to reduce the volume, cooled and filtered. The filtrate is then evaporated to dryness by steam. The powders obtained from the aqueous extract are meshed (two parts of C. bonducella seed pulp and one part of all the others) and mixed with adhesives like starch and gum acacia. Tablets of 500 mg are strip packed. The recommended dosages are as follows: adults should take 1 g (2 tablets) three times a day for 5 to 7 days. For children aged 5–12 years, the dose is 500 mg twice daily for 5–7 days, and for infants below 5 years, œ tablet of 500 mg powdered and mixed with honey twice a day for 5–7 days [54].

Ayush-64 was used on a large scale in public health programmes in the 1980s [55], but this has been scaled back since the results of recent clinical trials were deemed unsatisfactory [54], [56]. However, very similar preparations are still produced by Ayurvedic companies in India.

Phytochemistry and pharmacology: The active principles of Alstonia scholaris (echitamine chloride), Swertia chirata (swerchirin), and Caesalpinea bonducella (β-caesalpin) have been tested on albino rats infected with P. berghei. Echitamine chloride was effective at 320 mcg/kg subcutaneously, β-caesalpin was effective at 1.6 mg/kg orally, and swerchirin was effective at both levels and by both routes [55]. However, mouse studies of Ayush-64 itself revealed that there was neither any decrease in parasitaemia nor any increase in the survival time [55]. The acute and subacute toxicity animal studies showed Ayush-64 was safe even at high dosages (100 mg to 10 g/kg), so it was recommended for clinical trials.

Clinical trials: Almost all clinical trials of Ayush-64 have been conducted on patients with P. vivax malaria [4], [55], [56]. Only one trial included patients with P. falciparum malaria, and in even in this trial there were only four patients with asexual P. falciparum parasites [57] ([Table 3]). Several uncontrolled field trials found that 82–86 % of patients were cleared of P. vivax parasites by day 7–9 [55], [57]. Four randomised controlled trials have been carried out, of which three were double-blind [4]. These showed that parasite clearance was achieved by day 6 in 72–95 % of patients [55], but there was significant recrudescence so that by day 28, only 48.9 % of patients remained free of parasites (compared to 100 % of those treated with chloroquine) [56]. Two studies suggested that symptomatic improvement was good [55] whereas the third reported that it was slower with Ayush-64 than with chloroquine, and that patients complained about the frequency and duration of dosing and the size of the tablets [56].

Malarial-5

Development and use of the phytomedicine: “Malarial” was first formulated by Prof. Mamadou Koumaré at the Department for Traditional Medicine in Mali, based on a recipe used in his family. It has been produced as an “improved traditional phytomedicine” in Mali since 1982, and is now government-approved and included in the Malian National Formulary [58] as a treatment for fevers and malaria in patients aged 15 years and above.

Phytochemistry and pharmacology: Cassia occidentalis L. (Caesalpinaceae) is a pantropical plant widely used for the treatment of malaria [59] and is active in vitro against malaria parasites [60]. Lippia chevalieri Mold. (Verbenaceae) is an aromatic herb which is used in West Africa to flavour tea and treat fevers [61]. Spilanthes oleracea L. (Asteraceae) is a sprawling plant with yellow flowers which have a variety of uses in traditional medicine, including as a local anaesthetic for toothache, and as an antipyretic. They contain spilanthol, which is effective against Plasmodium falciparum [62]. “Malarial” was evaluated against malaria parasites in vitro and in mice. It was not very active in vitro (IC₅₀ = 470–600 µg/ml) but prolonged the survival of malaria-infected mice by 2–3 days compared to the untreated controls [63]. It was also non-toxic to mice.

Clinical trials: Three clinical studies were carried out to evaluate the safety and efficacy of Malarial. The first was a randomised controlled trial comparing it to chloroquine [64]. There were 53 patients included, of which 36 were randomised to “Malarial” and 17 to chloroquine. Follow-up to day 21 was completed by 75 % of the Malarial group, and 59 % of the chloroquine group. Fever clearance was not significantly different between the two groups. However, parasite clearance was better in the chloroquine group, but there was still a substantial reduction in parasitaemia in the Malarial group (geometric mean = 17 975 at day 0 and 154 at day 7). Malarial was better tolerated than chloroquine.

A second comparative study was conducted one year later, with the same inclusion criteria, except that patients were required to have a temperature of 38 °C or higher. Fifty-three patients were included, and parasitaemia at inclusion was higher than in the first study (geometric mean 46 024 at day 0). The reduction in parasitaemia was slower for patients on Malarial, and their mean parasitaemia never went below 5000 parasites/mm³ [65]. The higher initial parasitaemia in this study may explain the poorer result than in the first study. Patients in this study were febrile at inclusion, with high parasite counts, so their immunity to malaria may have been less than that of the patients in the first study. It was felt that the amount of Spilanthes oleraceae (4 %) present in this formulation of Malarial was insufficient for a truly effective schizonticidal activity.

It was therefore decided to increase the amount of Spilanthes oleraceae in Malarial to 6 %, and this was tested in an observational cohort study of patients with uncomplicated malaria [66]. Thirty patients were included, aged 5 years or above, with a temperature of > 37.5 °C and a parasitaemia of > 3000 per mcl P. falciparum. There was no control group. Parasitaemia declined (from a geometric mean of 5465 at day 0 to 629 at day 7) and symptoms improved. Parasitaemia at day 7 remained higher in patients aged 8–19 years than in older patients. This suggests that patient immunity was playing a role in clearing the parasites.

N'dribala (Cochlospermum planchonii Hook. f. ex Planch. [Bixaceae])

Development and use of the phytomedicine: A decoction of the roots of Cochlospermum planchonii Hook. f. ex Planch. (Bixaceae) is traditionally used for the treatment of fevers and malaria in Burkina Faso [67], Ivory Coast [68], Niger [69], and Nigeria [70]. A company in Burkina Faso (Phytofla, Inc.) produces sachets of 70 g of Cochlospermum planchonii root, sold as an improved traditional medicine in pharmacies, which obtained government approval in Burkina Faso in 2005. It is estimated that over 85 000 patients are treated with this preparation every year. Conservation measures are needed to protect the wild sources of this plant.

Phytochemistry and pharmacology: In vitro the IC₅₀ of antiplasmodial activity of Cochlospermum planchonii aqueous root decoction against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum was 75 µg/mL [71]. Cytotoxicity in vitro was low (Francoise Benoit-Vical, personal communication).

Clinical trial: “N'dribala” was evaluated in the clinical treatment of uncomplicated falciparum malaria in Banfora Hospital, Burkina Faso [67] ([Table 3]). 46 patients on N'dribala were compared to 21 treated with chloroquine (which was at the time the standard treatment, with 12 % of patients experiencing clinical resistance). Both treatments resulted in similar parasite clearance rates at day 5 (52 % and 57 %, respectively) although more patients on N'dribala remained febrile at day 5. Only minor side effects were reported in both groups.

Soumafoura Tiemoko Bengaly (Argemone mexicana L. [Papaveraceae])

Development and use of the phytomedicine: Argemone mexicana L. (Papaveraceae) is a pantropical weed with a long history of use in traditional medicine, dating back to the Aztecs [72]. It is used as an antimalarial in several African countries, including Benin, Mali, and Sudan [73], [74], [75].

It is currently being developed as a standardized phytomedicine by the Department for Traditional Medicine in Mali, and named after the traditional healer Tiemoko Bengaly who has participated in its development ([Fig. 4]). The current official phytomedicine (Malarial-5) is felt not to be sufficiently effective and has never been trialled in children [59]. In the quest for a new official phytomedicine, two large areas of the south-east of Mali were surveyed. A retrospective treatment-outcome study was conducted to identify the herbal preparation most often correlated with successful outcomes in cases of presumed malaria [75], [76], [77]. The most promising herbs were also tested in vitro, and Argemone mexicana had the greatest antimalarial activity [75].

Fig. 4 Chief Tiemoko Bengaly holds Argemone mexicana, the source of the phytomedicine which now bears his name in Mali (reproduced by the author).

The decoction was then studied in a prospective dose escalating clinical trial following a local recipe in patients with uncomplicated malaria. This found a dose-response correlation and a good safety profile [78]. The optimal dose was then compared in a randomized controlled trial to artesunate-amodiaquine for the home-based management of presumed malaria [79]. Following positive results, it is being considered for approval as an “Improved Traditional Medicine” for malaria in Mali, to supercede the current Malian ITM for malaria (“Malarial-5”).

Phytochemistry and pharmacology: IC₅₀ values of the aerial parts of this plant against the chloroquine-resistant K1 strain of Plasmodium falciparum were 5.89 and 1.00 µg/mL for the aqueous decoction and methanol extracts, respectively [75]. The plant contains several alkaloids with in vitro antimalarial activity, including berberine, allocryptopine, and protopine [80]. However animal studies suggest that the crude aqueous extract is not effective against P. berghei, and that berberine is not well absorbed orally (Falquet, unpublished data). Studies are underway to identify which compounds are active in humans.

Clinical trials: These were the only trials of ITMs included in this review which reported the rate of adequate clinical response (ACR), which is the outcome measure recommended by the World Health Organization [81], [82], and adapted by RITAM for the assessment of herbal remedies [83]. ACR occurred in only 35 % of patients treated with a low dose (one dose daily for three days), compared to 72.5 % of patients treated with a higher dose (twice daily for seven days). Although parasite counts decreased, they were cleared completely in only 9 % of patients [78]. The randomized controlled trial in 300 patients with presumed malaria showed that the remedy is safe and well tolerated, even in children. 89 % of patients recovered clinically, although the proportion of patients with parasitaemia at day 28 was 63–76 % in the AM group and 21–49 % in the ACT group. Deterioration to severe malaria was 1.9 % in both groups in children aged ≤ 5 years (there were no cases in patients aged > 5 years) and 0 % had coma/convulsions [79]. Patients were followed for three months to see whether the lack of parasite clearance would be a problem. From day 29 to day 84, there were no significant differences between treatment groups in the incidence of new uncomplicated malaria (0.33 vs. 0.31 episodes/patient), severe malaria (< 6 % per month of patients aged ≤ 5 years) or moderate anaemia (hematocrit < 24 %: 1.1 % in both groups at d84). Total parasite clearance at day 28 was not correlated with incidence of uncomplicated or severe malaria or of moderate anaemia over the subsequent two months [84].

Discussion

The seven phytomedicines presented here are only a small fraction of the huge potential for development of herbal medicines for malaria. Many other remedies have never been researched thoroughly in spite of strong anecdotal evidence of safety and efficacy. Further research is needed, both on the phytomedicines reported here and on new potential phytomedicines. Although these phytomedicines are produced according to standard recipes, in most cases their quality (in terms of key phytochemicals) is not controlled. Clinical trials have often been small and of variable quality. Except for trials of Argemone mexicana, they have excluded young children, who are those at greatest risk of malaria. In semi-immune adults, it is expected that many patients will improve even without treatment, so it is possible that the reported efficacy rates are greater than would be observed in non-immune patients. These results should be interpreted with care and not extrapolated inappropriately.

It is useful to have a range of evidence-based options for use in “green pharmacies” because no plant will grow well in all conditions. Artemisia annua grows well in many tropical areas but needs adequate rainfall and some shade. It does not grow well in semi-arid areas, where Argemone mexicana thrives.

What is the best way of prioritising other plants or remedies for development into phytomedicines? Except for the case of Argemone mexicana, which was selected following a logical process of prioritisation among available antimalarial plants in Southern Mali [76], the other phytomedicines were developed more as a result of historical circumstances. However, now it is known that over 1200 plant species are used worldwide for the treatment of malaria and fevers, and many have been tested in vitro and/or in vivo. RITAM has developed a score taking into account existing ethnobotanical and laboratory data to prioritise remedies for future development [85].

In this process it is important to start out with traditional methods of preparation which have been found empirically to be effective. Recent experiments have shown that traditional methods of soaking and crushing produce the most concentrated extracts of Artemisia annua [19]. However subsequent research has shown that an ethanolic extract may be a good alternative. Ayush-64, which turned out not to be very effective, is not really an Ayurvedic treatment for malaria. It was produced by scientists from traditional plants but using modern methods which are far removed from the traditional preparation, and may have destroyed active ingredients.

What are the most appropriate outcome measures for clinical trials of herbal antimalarials? As shown in [Table 3], most trials to date have used parasite clearance at day 5–7 as the principle outcome measure. Parasite clearance is important in low transmission areas where patients are not readily re-infected and have little or no immunity to malaria. In areas of high malaria transmission, populations develop a level of immunity to malaria by the age of five years, and re-infection happens fast, so the importance of parasite clearance is debatable. Furthermore, the accurate confirmation of parasite clearance requires high-quality microscopy, and it is not clear that this was used in all the trials. Adequate clinical response (ACR) is a composite outcome measure which requires the patient to be afebrile and/or clear of parasites at day 14, without previously having any danger signs or treatment failure [81], [82]. WHO first recommended ACR as the best outcome measure for clinical trials on uncomplicated malaria in 1996 [82], so it was never used in trials before then, and was not even used in all subsequent trials. The prevention of severe malaria and death are the most important outcomes but require large sample sizes, larger than practical in many trials. A sample size of 300 patients was required to show that there was no significant difference in these outcomes between patients treated with Argemone mexicana decoction and those treated with artesunate/amodiaquine [79]. Interestingly, the herbal medicine prevented severe malaria and death without totally clearing parasites [79], [84].

Safety outcomes are equally important. While caution is important, dangers are sometimes overplayed by opponents of herbal medicine. It is important to remember the ancient dictum “sola dosis facit venenum”: only the dose makes a poison. It is easy to be scared by the “toxic” constituents of plants, but most effective medicines are toxic if given at too high a dose. The time-honoured antimalarial quinine is highly toxic in overdose. In contrast Artemisia annua and Argemone mexicana are remarkably safe. Some researchers have expressed doubts about the continued use of Cryptolepis sanguinolenta extracts because of the cytotoxicity of cryptolepine, and it seems from animal experiments that long-term use may indeed lead to hepatotoxicity. However, when used as a short-term treatment for one or two weeks, there is no observed toxicity. Further clinical trials should carefully monitor markers of toxicity (in particular liver function tests), and data is needed on the absorption, metabolism and excretion of the alkaloids of C. sanguinolenta.

Some scientists view plants purely as a source of new compounds, to be developed into modern pharmaceuticals. Why then do totaquina and qing hao remain in use as herbal remedies, when highly effective chemical compounds have been isolated and developed as pharmaceuticals from these plants? Firstly, the herbal remedies can be produced locally, and are thus more readily available, affordable, and sustainable than manufactured medicines. Secondly, (especially in the case of totaquina) the herbal remedy may be better tolerated, with fewer side effects than the pharmaceutical. Thirdly, the herbal remedies are natural combinations, containing several antimalarial constituents and therefore may delay the development of resistance. Fourthly, they may be as effective as pure compounds. All the available evidence suggests that crude extracts of Cinchona bark, in spite of variability in composition, are as effective as quinine in the treatment of both P. vivax and P. falciparum malaria, and indeed may be more effective in areas where P. falciparum has evolved resistance to quinine. There is also mounting evidence that Artemisia annua herbal preparations have greater efficacy and bioavailability than equivalent doses of pure artemisinin.

In the context of the current public health war on malaria, is there still a role for phytomedicines? It is an unwise general who discards any weapons from his arsenal. While ACTs are highly efficacious they still cannot easily be deployed, reliably and consistently, in all malarious areas. Supplies are likely always to be limited, so it makes sense to keep ACTs for those at greatest risk (children and pregnant women) while using phytomedicines as a first-line for lower risk patients. Many areas have only intermittent supplies of ACTs with more or less frequent stock-outs. Other areas are still beyond the reach of drug distribution networks. In such areas a “green pharmacy” may help to provide a sustainable solution in the short to medium term.

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