Oral Medication With Preparations for Prolonged Action

Historical Background Attempts to prevent gastric irritation and vomiting by enclosing irritant drugs within gastro-resistant coatings are credited to Unna and others more than 100 years ago. Some of these early coatings consisted of keratin, phenyl salicylate (salol), or gelatin hardened in formaldehyde. The preparations were called enteric, since the objective was to have them withstand gastric digestion but, nevertheless, disintegrate and undergo absorption in the intestine. These preparations were not uniformly successful, with respect to this objective. On the one hand, some soluble drugs were found able to diffuse through coatings which were satisfactorily insoluble in gastric juice, and, on the other hand, some enteric preparations were so resistant to disintegration and solution that they traversed the entire gastrointestinal tract intact. Nevertheless, such preparations continued in use and served a somewhat useful purpose. Attempts to improve upon the enteric coatings were made at sporadic intervals, but in a more