Studies on sustained-release dosage forms. III. Preparation of nifedipine suppositories and bioavailability in rabbits.

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Abstract
By the use of solid dipersion systems, suppositories having both a fat release and a sustained release of nifedipine were developed. Namely, cellulose acetate phthalate (CAP)-polyethylene glycol (PEG) matrix was prepared as a suppository base by using PEG 4000 as a water-soluble carrier and CAP as a poorly soluble carrier. Conventional suppositories (use of PEG 4000 alone as a base: C-O), three kinds of CAP-PEG matrix suppositories (use of 5, 10 and 15% (w/w) CAP in the matrix: M-5, M-10 and M-15) and double layer suppositories including nifedipine only in the outside layer (use of 15% CAP in the matrix a a base: D-15) were prepared, and the sustained-release effect and bioavailability of each suppository were examined in rabbits. The M-5 as well as C-0 produced a sharp peak of plasma concentration of nifedipine and did not give a sustained-release effect. The M-10 gave a sustained-release effect, but it was not a desirable preparation because it developed many cracks and broke easily. The M-15 gave a low and plateau plasma level of nifedipine and had no cracks, but the extent of bioavailability was very small. The D-15 enhanced the bioavailabilty of nifedipine and also gave a sustained-release plasma level of nifedipine. Therefore, it appeared that D-15 was a suitable preparation for our purpose.

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