Investigation of nifedipine absorption in different regions of the human gastrointestinal (GI) tract after simultaneous administration of C-13- and C-12-nifedipine

Objective: To evaluate the absorption of nifedipine in man from four different sites of the gastrointestinal tract. Methods: On separate occasions, nifedipine solution was administered locally to the stomach, the small intestine and two sites in the colon in 4 healthy male volunteers (age 29-34 y weight 73-82 kg, nonsmokers) using a remote controlled drug delivery device (HF-capsule). In order to assess absolute and relative bioavailabilities, an intravenous infusion was given on a separate occasion and all treatments were accompanied by a simultaneous oral dose of a stable-isotope labelled nifedipine solution. This allowed to minimise the influence of intra-individual variability. Plasma samples were collected up to 24 h post dose and faeces for 72 h. A new method of analysis of nifedipine in plasma and faeces using gas chromatography with mass-selective detection (GCMS) was employed. Results: Dissolved nifedipine was found to enter the systemic circulation completely along the intestine, being absorbed from jejunum to colon. Absorption was less rapid from the colon than from the upper part of the gut, but this was not associated with a decrease in absorption and/or bioavailability: Absolute bioavailability, calculated from the normalised AUC values, ranged from 42 to 56%, and bioavailability relative to oral solution was 100 to 126% (medians of the application sites). Conclusion: The absence of an absorption window in the intestinal tract suggests that nifedipine is well suited for use in controlled-release formulations.