Zero-order rectal delivery of theophylline in man with an osmotic system

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Abstract
In vivoand in vitroperformances of a rectally applied osmotic delivery system containing a water-soluble derivative of theophylline were compared. The system was applied in six healthy volunteers during 72 h, and a comparison was made with two conventional dosage forms, a suppository and a solution administered orally, given once. In vitro,a perfect zero-order release rate with the osmotic system was obtained. In all subjects, application of the osmotic system resulted in a constant steady-state theophylline level just as in a long time zero-order i.v. infusion, which strongly suggests that the release rate in vivois zero-order too. The release rate was not influenced by renewing the dosage form after 36 hr or by defecation. The in vivoand in vitrorelease rates were almost identical and subjectindependent.