Biopharmaceutics of rectal administration of drugs in man
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Rectal absorption of acetylsalicylic acid and its calcium salt was studied in man and compared with oral absorption.
Plasma concentrations of acetylsalicylic acid and salicylic acid were measured by means ofHplc analysis, after a single dose of acetylsalicylic acid (500 mg) and after single rectal doses of acetylsalicylic acid (500 mg) and calcium acetylsalicylate (640 mg) in a cross-over study in 8 volunteers. The rectal dosage forms included fatty suppositories and aqueous solutions.
Compared with oral administration rectal absorption of acetylsalicylic acid can be equally rapid, if the volume and the pH of the aqueous micro-enema was optimized (20 ml, pH 4.0). Rectal absorption of calcium acetylsalicylate occurred very slowly. If fatty suppositories were used smaller particles favoured the rate of acetylsalicylic acid absorption. Compared with oral administration absorption from the optimized suppository dosage form proceeded significantly (P < 0.05) slower. For all rectal dosage forms, the extent to which acetylsalicylic acid reached the general circulation intact, was smaller than after oral administration.
KeywordsSalicylic Acid Dosage Form Acetylsalicylic Acid Cocoa Butter Sodium Salicylate
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