Atovaquone/Proguanil : A New Drug Combination to Combat Malaria

Investigation of pre-clinical pharmacokinetic parameters of atovaquone nanosuspension prepared using a pH-based precipitation method and its pharmacodynamic properties in a novel artemisinin combination

OBJECTIVES

Recently, a growing resistance to antimalarial drugs such as chloroquine, sulfadoxine-pyrimethamine, artemisinin derivatives and mefloquine has been observed. The pharmacokinetic limitation of the current therapy and multi-drug resistance has resulted in an urgent need to study the new antimalarial combinations with existing drugs. This study investigated the activity of a novel triple combination of atovaquone (nanosized)-proguanil-artesunate as an alternative artemisinin combination therapy. Atovaquone in this combination was formulated as a freeze-dried nanosuspension and its pharmacokinetic parameters were also evaluated.

METHODS

The suppressive and curative effect of atovaquone nanosuspension, proguanil, and artesunate were studied in a murine model. The in vivo pharmacokinetics of the newly developed atovaquone nanosuspension with particle size less than 200 nm was investigated.

RESULTS

Prophylactic efficacy of atovaquone nanosuspension alone at 1/80th the therapeutic dose was proven. In the curative test, atovaquone nanosuspension and proguanil at 1/10th the therapeutic dose was the minimum effective dose that resulted in complete cure of parasitaemia. As a triple combination, atovaquone nanosuspension in combination with proguanil at 1/80th the therapeutic dose of each and 1/5th the therapeutic dose of artesunate resulted in a complete cure. The in vivo pharmacokinetics of the nanosuspension showed a significant (three times) reduction in T_max value and the area under the curve of the nanosuspension was 1.9 times greater as compared with the plain suspension.

CONCLUSIONS

The potential of the synergistic combination of atovaquone nanosuspension-proguanil-artesunate in curing the multi-drug resistant malarial infection at reduced doses of all three drugs could be a solution to pill burden observed with the current therapy.

Artemisinin-naphthoquine combination: A directly observed treatment option in malaria

Resistance to standard antimalarials has led to the need for newer options. Artemisinin-based combination therapies (ACTs), which require a tedious three-day treatment schedule, have been introduced for the treatment of drug-resistant malaria. Of late, the new generation artemisinin-naphthoquine (ANQ) combination has been developed, which requires a single dose treatment. Artemisinin initiates the action through the cleavage of the endoperoxide bridge while naphtoquine maintains the process by getting concentrated in the digestive vacuole of the parasite. One ANQ tablet contains 50 mg naphthoquine and 125 mg of artemisinin in the ratio of 1:2.5. The optimal dosage in adults is 400 mg of naphthoquine and 1000 mg artemisinin; which amounts to 8 tablets in a single dose. The dosage for children is adjusted based on the body-weight. The combination has been found to be quite effective with and safe. Studies have demonstrated an adequate clinical and parasitologic response of 98.1-100% in both adults and children. However, further trials are required to confirm its non-inferiority with other ACTs. Adverse reactions with ANQ have been mild. Further studies are needed before safety can be established during pregnancy. ANQ increases the compliance rates because of single dosage. It may be administered by the peripheral health workers as a directly observed therapy, which would be of special benefit to troops in the North-Eastern Sector.