The quality of essential antimicrobial and antimalarial drugs marketed in Rwanda and Tanzania: influence of tropical storage conditions on in vitro dissolution

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Abstract
The quality of 33 formulations of essential antimicrobial and antimalarial drugs (amoxicillin capsules, metronidazole tablets, sulfamethoxazole/trimethoprim tablets, quinine tablets and sulphadoxine/pyrimethamine tablets) marketed in Rwanda and Tanzania was assessed and the influence of tropical storage conditions on potency and in vitro dissolution investigated. Drug content and in vitro dissolution were determined immediately after purchase and during 6-month storage under simulated tropical conditions (75% relative humidity, 40 degrees C) using the methods described in the USP 24 monographs on the drugs concerned. At the time of purchase, the drug content of all the formulations was within the limits recommended by the USP 24, but after 6-month storage, the drug content of one sulfamethoxazole/trimethoprim and one quinine formulation were found to be substandard. Immediately after purchase, four formulations (three sulfamethoxazole/trimethoprim and one sulphadoxine/pyrimethamine combination) failed the USP 24 dissolution test. Except for three metronidazole and one quinine formulations, dissolution tests performed after 6 months of storage under simulated tropical conditions showed that drug release remained within the USP 24 recommended values. In both countries, essential drug formulations met pharmacopoeial potency requirements, but some had a poor in vitro drug release profiles. Some of the formulations tested were not stable upon storage under simulated tropical conditions.