title: Drug-drug interaction studies on first-line anti-tuberculosis drugs.
abstract: The purpose of this study was to carry out drug-drug compatibility studies on pure first line anti-tuberculosis drugs, viz., rifampicin (R), isoniazid (H), pyrazinamide (Z), and ethambutol hydrochloride (E). Various possible binary, ternary, and quaternary combinations of the four drugs were subjected to accelerated stability test conditions of 40 degrees C and 75% relative humidity (RH) for 3 months. For comparison, parallel studies were also conducted on single drugs. Changes were looked for in the samples drawn after 15, 30, 60, and 90 days of storage. Analyses for R, H, and Z were carried out using a validated HPLC method. The E was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), as it does not absorb in ultraviolet (UV). All single pure drugs were relatively stable and showed only 3%-5% degradation under accelerated conditions for 3 months. However, significant interactions were observed in case of the drug mixtures. In particular, ternary and quaternary drug combinations containing R and H along with Z and/or E were very unstable, showing 90%-95% and 70%-75% loss of R and H, respectively. In all these cases, isonicotinyl hydrazone (HYD) of 3-formylrifamycin and H was found to be the major degradation product. In case of RE and RZE mixtures, where H was absent, 3-formylrifamycin was instead the key degradation product. Another unidentified peak was observed in the mixture containing RZE. Apart from these chemical changes, considerable physical changes were also observed in pure E and the mixtures containing E, viz., RE, ZE, RHE, RZE, and RHZE. In addition, significant physical changes associated with noteworthy loss of H and E were also observed in mixtures containing HE and HZE. The present study thus amply shows that the four primary anti-tuberculosis drugs, when present together, interact with each other in a multiple and complex manner.
authors.affiliation: Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S.A.S. Nagar, Punjab 160 062, India.
authors.forename: Hemant
authors.initials: H
authors.lastname: Bhutani
authors.forename: Saranjit
authors.initials: S
authors.lastname: Singh
authors.forename: K C
authors.initials: KC
authors.lastname: Jindal
mesh_terms: D000995:Antitubercular Agents / Q000737:chemistry*; D002853:Chromatography, Liquid; D004338:Drug Combinations; D004339:Drug Compounding; D004344:Drug Incompatibility; D004355:Drug Stability; D004356:Drug Storage; D004977:Ethambutol / Q000737:chemistry; D006358:Hot Temperature; D006813:Humidity; D007538:Isoniazid / Q000737:chemistry; D013058:Mass Spectrometry; D011718:Pyrazinamide / Q000737:chemistry; D012293:Rifampin / Q000737:chemistry
chemical_list: D000995:Antitubercular Agents; D004338:Drug Combinations; D011718:Pyrazinamide; D004977:Ethambutol; D007538:Isoniazid; D012293:Rifampin