Constipation and megacolon in rats related to treatment with oxodipine, a calcium antagonist.

The constipatory effects of oxodipine, a dihyrdopyridine-type calcium antagonist, have been described in a 3-mo, 12-mo, and 30-mo feeding toxicity study in rats. This paper reports the occurrence of megacolon in rats as a result of the constipatory effects of chronic administration of oxodipine. The first mortality due to oxodipine was seen after about 1 yr of treatment at a dose of 225 mg/kg/day. The toxic effects noted were dose-, time-, and sex-related. Female rats appeared more sensitive to the constipatory effects of the drug. The dose at which the effect occurred in both male and female rats was from about 75 to 675 times the recommended therapeutic dose for humans. To the best knowledge of the authors, this is the first report of a calcium channel blocker causing constipation in rats.