Enprostil (methyl 7-[(1 R,2R,3R)-3-hydroxy-2-[(E)-(3R)-3-hydroxy-4- phenoxy-1-butenyl]-5-oxocyclopentyl]-4,5-heptadienoate), an E-type prostaglandin exhibiting anti-ulcer activity, is formulated as a propylene carbonate solution filled into soft elastic gelatin (SEG) capsules. Enprostil SEG capsules were maintained for timed intervals at 50 degrees C, 30 degrees C, and room temperature, and the quantity of drug released upon complete capsule dissolution was determined as a function of storage condition. The dissolution test adhered to USP XXI guidelines (paddle method) and used a multidimensional HPLC technique to provide a sensitive and selective enprostil assay. Parallel HPLC assays determined the enprostil concentration in the propylene carbonate fill that was physically expressed from initially manufactured and from aged capsules. This corrected for any enprostil loss via chemical degradation on storage. The study included six different aged samples (six replicates each), and for all six samples, the enprostil recovered from dissolved capsules averaged 104 +/- 1.4% of the enprostil physically expressed from the capsules. Similarly, the enprostil recovered from dissolved, aged capsules averaged 103 +/- 5% of the enprostil physically expressed from capsules at the initial time point. These findings exclude the possibility that interactions with the SEG capsule wall reduce drug availability during storage under normal conditions. The multidimensional HPLC technique should generally extend to analysis of other noncationic drugs formulated into soft gelatin capsules.