Antimalarial Combinations — Current Clinical Practices 649 Antimalarial Combinations — 110 Current Clinical Practices BIRANCHI NARAYAN MOHAPATRA, CBK MOHANTY Malaria is a major public health problem of the Antimalarial combination therapy is defined as the world. An estimated 300-500 million cases and 1 to 2.7 simultaneous use of two or more blood schizonticidal million deaths occur each year due to malaria1. In India drugs with independent mode of action and thus over the past two decades malaria incidence has been unrelated by biochemical targets in the parasite4. fluctuating between 2-3 million cases each year. India has 40% of all malaria cases outside Africa2. Effective Rationale for Antimalarial Combination Quinine monotherapy for malaria has been available for Combination chemotherapy has been well estab- more than 350 years long before the causative organism lished in TB, and Leprosy which has been recently of the disease were identified3. Chloroquine remains the applied to malaria3,4. The combination is often more chief drug as monotherapy which was later joined effective. It prevents and delays the emergence of by amodiaquine, sulfadoxine-pyrimethamine and resistance by killing of mutant resistant parasite to one Mefloquine. drug by the partner drug. To achieve this, the partner Resistance to antimalarials has been documented for drug must be independently effective. The possible dis- 4 P. falciparum, P. vivax and recently P. malariae . In advantages of combination treatment are the potential P. falciparum, resistance has been observed to almost all risk or increasing adverse effect and increased cost4. currently available antimalarials (Amodiaquine, Chloro- quine, Mefloquine, Quinine and Sulfadoxine-Pyrimetha- What is not considered to be mine) except for artemisinin and its derivatives4. P. vivax Combination Therapy resistance to Chloroquine, Pyrimethamine has also been Drug combinations such as Sulfadoxine-Pyrimetha- observed, though in Indian subcontinent it is still mine, Sulfalene-Pyrimethamine, Proguanil-Dapsone, sensitive3,4. Chlorproguanil-Dapsone and Atovaquone-Proguanil Multi-drug resistance (MDR) is defined as resistance rely on synergy between the two components. The drug to three or more antimalarial compounds from different targets in the malaria parasite are linked. These chemical classes4. Generally, the first two classes are 4- combinations are operationally considered as single aminoquinolines (e.g. Chloroquine) and antifolate products and treatment with them is not considered to (Sulfadoxine-Pyrimethamine)4. MDR malaria presents be antimalarial combination therapy. Multiple-drug as the biggest therapeutic challenge to health care in therapies that include a non-antimalarial medicine to most malaria endemic area resulting in higher mortality, enhance the antimalarial effect of a blood schizontocidal morbidity and increasing the burden of malaria. To drug (Chloroquine and Chlorpheniramine) are also not counter the threat of resistance of P. falciparum to antimalarial combination therapy. monotherapy and to improve the treatment outcome, combinations of antimalarials are now recommended ANTIMALARIAL COMBINATIONS by WHO for the treatment of falciparum malaria and There are two broad groups of antimalarial combina- may be used in other type of malaria4. tions. 650 Medicine Update 1. Artemisinin based combination therapy (ACT) 1. Artemether + Lumefantrine (AL) 2. Non-artemisinin based combination therapy (Non- 2. Artesunate + Mefloquine (AS + MQ) ACT) 3. Artesunate + Sulfadoxine–Pyrimethamine (AS +SP) Artemisinin Based Combination Therapy (ACT) 4. Artesunate + Amodiaquine (AS + AQ) All the above four regimens are effective with minor Artemisinin and its derivatives (aresunate, differences in their potency and adverse effect (Table artemether, artemotil, dihydroartemisinin) preduce 1)4,5,8-10. But all are superior as antimalarial therapy in rapid clearance of parasitemia and rapid resolution of comparison to monotherapy3,4. A systematic review has P. falciparum symptoms. They act by inhibiting a encoded observed statistically insignificant rise at detection of scercoplasmic endoplasmic reticulum calcium ATpase parasite on 28 days. But fewer side effects with AL in and not by inhibiting haem metabolic pathway as comparison to AS + MQ.8 However, one study has suggested earlier3. They reduce parasite numbers by a shown irreversible hearing impairment with AL3. factor of approximately 10,000 in each a sexual cycle, which is more than other current antimalarials (which Artesunet + doxycycline/tetracycline/clindamycin reduce parasite number 100 to 1000 fold per cycle). for 7 days has been considered as a second line regimen Artemisinin and its deriveatives are eliminated rapidly. for uncomplicated P. falciparum malaria4. When given in combination with rapidly eliminated compounds (tetracyclines, clindamycin), a 7-days course Non-artemisinin Based Combination of treatment with artemisinin compound is required. But Therapy (Non-ACT) when given in combination with slowly eliminated antimalarials, shorter courses of treatment (3 days) are I. Sulfadoxine-Pyrimethamine + Chloroquine (SP effective4. +CQ): Chloroquine interferes with parasitic hem- In 3-day ACT regimens, the artemisinin compound degradation pathway and thereby prevents detoxi- is present in the body during only two a sexual parasite fication harmful products of metabolism whereas life-cycles(each lasting 2 days, except for P. malariae Sulfadoxine and Pyrimethamine inhibits dihydro- infections). This exposure to 3 days of artemisinin pteroate synthase (DHPS) and dihydrofolate reduc- treatment reduces the number of parasites in the body tase (DHFR) respectively, resulting in prevention by a factor of approximately one hundred million (104 × of folic acid in parasite3. 104=108). However, complete clearance of parasites is However, there is no convincing evidence that dependent on the partner medicine being effective and SP + CQ provides any additional benefit over SP, persisting at parasiticidal concentrations until all the hence not recommended3,4,6. infecting parasites have been killed. Thus, the partner II. Sulfadoxine-Pyrimethamine + Amodiaquine (SP + compounds need to be relatively slowly eliminated. As AQ): The mechanism of action of AQ is similar to result of this, the artemisinin component is protected chloroquine. In a recent systematic review SP + AQ from resistance by the partner medicine, provided it is efficacious and the partner medicine is partly protected combination has resulted in significantly lower risk of treatment failure than SP or AQ monotherapy. by the artemisinin derivative. Courses of ACTs of less 6 than 3 days are not recommended as they are less Serious adverse effects are rare . WHO recommends efficacious, and provide less protection of the slowly its use in uncomplicated P. falciparum malaria where 4 eliminated partner antimalarial4. more effective ACT is not available . The artemisinin compounds are active against all III. Quinine + tetracycline / doxycycline: tetracycline four species of malaria parasites that infect humans and and doxycycline probably act by inhibiting the are generally well tolerated. The only significant adverse binding of aminoacyl tRNA to the ribosome of effect to emerge from extensive clinical trials has been parasite. Tetracycline and doxycycline maintain rare type 1 hypersensitivity reactions (manifested activities against MDR malaria parasite. The initially by urticaria). These drugs also have gametocidal combinations have been advocated as a second line effect. This helps in preventing transmissions of therapy for uncomplicated P. falciparum malaria. malaria4. The evidence of their superiority in comparison Tetracycline and doxycycline are not recommen- to monotherapies have been clearly documented3-5. ded in pregnancy and children. Currently, there are four ACTs which have been IV. Quinine + clindamycin: The combination is recommended by WHO for treatment of uncomplicated effective against MDR malaria. Both of them have P. falciparum malaria. They are: short half life thereby reducing the selection of Antimalarial Combinations — Current Clinical Practices 651 Table 1: Dose schedule of currently available ACT tetracycline/doxycycline/clindamycin should be preferred over quinine + tetracycline/doxycycline/ Name of Regimen Dose Duration clindamycin4,11. Artemether + 1.5 mg/kg/dose 0, 8, 24, 36, 48, 60 (hr) In vivax malaria, chloroquine with primaquine is still Lumefantrine +9.0 mg/kg/dose effective but ACT can be used except AS + SP. Artesunate + 4 mg/ kg/day + Once daily for 3 days Multidrug resistant malaria parasite has forced the Mefloquine 15 mg/kg/day On 2nd day use of combinations antimalarial regimen. Artemisinin + 10mg/kg/day On 3rd day based combinations are preferred until better combi- nation regimens are found. There is no place mono- Artesunate + 4 mg/kg/day + Once daily for 3 days Amodiaquine 10 mg base/kg/day Once daily for 3 days therapy in malaria. Artesunate + 4 mg/kg/day + Once daily for 3 days REFERENCES Sulfdoxine – 25 mg/kg/day – Once on 1st day Pyrimethamine 1.25 mg/kg/day 1. WHO, 2000. WHO expert committee on malaria. Twentieth report World Health Organisation, Geneva, Technical Report Series, No. 892. resistance parasite. Clindamycin is preferred in 2. Pareek A, Nandy A, Kocher D, Patel KH, Mishra SK, Mathur pregnancy and children. It is considered as second PC. Efficacy and safety of a/b Arteether for treatment of acute line drug for uncomplicated P. falciparum