Regional gastrointestinal permeability of rifampicin and isoniazid (alone and their combination) in the rat
DESIGN: Permeability of RMP and INH (alone and in combination) was determined in various segments of rat GIT (stomach, duodenum, jejunum and ileum) at concentrations of respectively 2.4 and 1.2 mg/ml, using a ligated loop technique. Drug analysis was performed by HPLC. Extent of absorption was considered as the total drug disappearing from the loop. Permeability was correlated with solubility and decomposition data at pH corresponding to different GIT sites.
RESULTS: RMP was well absorbed from the stomach due to its solubility, which was maximum between pH 1–2. INH was poorly absorbed from the stomach, but was well absorbed from all three segments of the intestine. In combination, RMP disappearance was enhanced in the presence of INH in the stomach and jejunum, but INH disappearance was not influenced by RMP.
CONCLUSION: The study shows higher in situ RMP disappearance in the presence of INH, attributable to drug degradation due to catalysis by INH. As the two drugs show regional specific permeability, FDCs without reduced RMP bioavailability resulting from its decomposition in the presence of INH can be designed by segregating delivery of the two drugs by around 3–4 h. RMP should be released in the stomach and INH in the intestine.
Document Type: Regular Paper
Affiliations: Department of Pharmaceutical Analysis, NIPER, SAS Nagar, India
Publication date: 01 August 2003
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