Abstract
Electrochemical behavior of rifampicin (RIF) as an anti-tuberculosis drug was studied in detail in water/ethanol mixture using different voltammetric techniques. The results indicate that rifampicin is oxidized in two steps, the first step is related to the reversible oxidation of hydroquinone moiety to benzoquinone and the second one is related to the irreversible oxidation of phenolic ring of RIF. In this work, the adsorption activity and diffusion coefficient of RIF was also determined and shows that the first oxidation step is diffusion control while second one is a diffusion/adsorption control process. Furthermore, our results show that the oxidation of RIF (especially in the first step) is complex and highly pH-dependent. The Pourbaix diagram was drawn for this drug and useful information was obtained regarding the oxidized and reduced forms of RIF and the acid/base properties of the species obtained from RIF and its oxidized form (RIF-Q). The first line of tuberculosis drug treatment currently includes the simultaneous use of rifampicin, isoniazid, pyrazinamide and ethambutol (Fixed Dose Combinations, FDCs). Understanding the mechanism of drug-drug interactions is not only useful in preventing drug toxicity or side effects, but also in devising safer treatments for diseases. In this study, based on the obtained electrochemical data, we suggest plausible mechanisms for the reaction of RIF-Q with the medicines prescribed in FDC. The obtained results show that the mentioned drugs through their free amino group can react with RIF-Q. Our findings also show that the rate of these reactions is low in acidic environments such as the stomach and high in neutral or alkaline environments such as the small intestine. In these reactions, ethambutol has the highest rate and pyrazinamide has the lowest rate for the reaction with RIF.
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