Artesunate is a semi-synthetic derivative of artemisinin, a naturally occurring sesquiterpene endoperoxide. It is difficult to detect and identify by standard spectrophotometric methods. The standard method used to determine artesunate in tablets involves high-performance liquid chromatography (HPLC). In many countries, such equipment is not available.
Antimalarials such as chloroquine and sulfadoxine have particular chemical groups that react with certain compounds to give colour reactions. Artesunate does not possess these reactive groups, but an alkali-decomposition product of it can react with diazonium salts to produce a visually distinct yellow product. This product absorbs visible light at 420 nm and the absorbance intensity corresponds linearly to the artesunate concentration.
Quantitative Determination of Artesunate in Tablets
It was found that optimum yield of ARTS290, the alkali-decomposition product occurs after incubation in 1 N NaOH. This product reacts with Fast red TR salt (a diazonium salt) to produce a colored reaction product (ARTS420) which can be measured by spectrophotometry at 420 nm. The color reaction takes place under a wide range of pH, but is more specific for artesunate at acidic pH.
Quantitative analysis of artesunate tablets can be accomplished by measuring the absorbance of the ethyl acetate extracts. Measurements can be made in the field with the aid of a hand-held portable photometer fitted with a 420-nm filter.
The method was evaluated for artemisinin, artemether, chloroquine, quinine, primaquine, sulfadoxine, and pyrimethamine at pH 4, 6, and 8. It was found that the method is specific for artesunate at a pH of 4 (see figure in box). At pH>6, the method has possible applications for colorimetric verification of other antimalarial drugs such as artemisinin, primaquine and sulfadoxine.
Only 1% of the tablet (assuming 50mg artesunate) is required for the assay, so the remaining tablet can be used as an antimalarial. Fast TR Red Salt can be requested temporarily from the office of the WHO Representative in Cambodia. We look forward to receiving articles from readers about their experience with the tests. WHO considers developing a kit for this purpose.
Margin Highlights: It was found that the method is specific for artesunate at a pH of 4.