Chlorpheniramine dissolution and relative urinary excretion from commercial products

Dissolution profiles were determined for seven commercially available nonprescription solid dosage forms containing chlorpheniramine (four sustained release and three immediate release). An in vitro pH change method used to simulate GI transit produced dissolution profiles for some similarly labeled products which were significantly nonequivalent. One product failed to release its chlorpheniramine even when ground in a mortar and pestle in HCl solution, but did release drug in H3PO4 solution. A small (four subjects) relative bioavailability study based on average cumulative excretion of intact drug in urine gave results in parallel with substantially nonequivalent dissolution data for three products.