Hyperamylasemia in response to ritodrine or ephedrine administered to pregnant women.

BACKGROUND: Ritodrine and ephedrine can induce hyperamylasemia in pregnant women. The incidence of these beta-agonist-induced hyperamylasemias and their interaction on serum amylase activity are not known. STUDY DESIGN: Serum amylase activity was determined 12 to 24 hours after the administration of ritodrine alone (n = 140), ephedrine alone (n = 160), ephedrine and ritodrine simultaneously (n = 34), and ephedrine after prolonged (> or = 7 days) use of ritodrine (n = 101). RESULTS: A significantly higher incidence of hyperamylasemia (amylase > 215 IU/L) was seen in a group treated with ritodrine alone (60/140, 43 percent), ephedrine alone (54/160, 34 percent), or ephedrine plus ritodrine (24/34, 71 percent) compared with untreated pregnant women (21/426, 4.9 percent). There was no difference in the incidence of hyperamylasemia among the untreated pregnant women and women who received ephedrine after long-term ritodrine (8/101, 7.9 percent). Isozyme patterns, examined in 72 out of the 146 women with hyperamylasemia after such medications, indicated that salivary-type amylase exclusively was hypersecreted. CONCLUSIONS: Clinical doses of beta-agonists such as ephedrine or ritodrine induce hypersecretion of salivary-type amylase in approximately one-third of women who are pregnant. Desensitization to beta-agonists may occur after prolonged use of ritodrine.