More than one half of all pregnant women have symptoms of gastroesophageal reflux, particularly during the third trimester. Although conservative measures such as avoiding substances that precipitate or exacerbate symptoms and elevating the head of the bed may be successful, more than one third of pregnant women also report taking antacid medications with varying degrees of success in alleviating symptoms. Larson and colleagues investigated the ability of the histamine H₂-receptor blocker ranitidine to relieve symptoms of gastroesophageal reflux during pregnancy.

Patients who were at more than 20 weeks of gestation attending a university prenatal clinic were asked to volunteer for the study if they had persistent heartburn despite use of conservative measures and antacid medications. Patients with known esophageal and gastric disease and liver conditions, and those requiring medication for chronic psychiatric conditions were excluded from the study. Patients were required to read and sign a statement concerning the testing of ranitidine in pregnant animals.

During the first week of the study, baseline data were collected, including an extensive questionnaire on gastrointestinal symptoms and general health, a symptom diary and a visual analog scale to evaluate the level of discomfort. Patients used only antacids during this initial week and then were randomly assigned to one of three treatment groups: placebo twice daily; placebo in the morning plus ranitidine, 150 mg, in the evening; and ranitidine, 150 mg twice daily. Diaries were collected each week. Patients also completed global assessments weekly and gave counts of pills and antacid medications used.

Complete data were available for 18 of the 20 women who completed the study. Patients reported significant improvement in heartburn symptoms when they took placebo, as well as when they took either regimen of ranitidine. The greatest improvement was reported with twice-daily ranitidine, which was associated with a 55.6 percent improvement over baseline and a 44.2 percent improvement compared with placebo. The improvement associated with the single daily dose of ranitidine was not statistically superior to either placebo or baseline. The number of antacid tablets consumed was significantly lower in patients receiving either of the ranitidine regimens. Only one patient reported the need for heartburn medication after delivery.

The authors conclude that ranitidine taken in a dosage of 150 mg twice daily provides effective relief of gastroesophageal reflux symptoms. They note the substantial placebo effect and the limited benefit provided by a single evening dose of 150 mg of ranitidine. Although ranitidine is a category B1 agent for pregnancy (indicating that no adequate studies have been performed in humans to assess pregnancy risk), it is available without a prescription as a 75-mg tablet, and no adverse effects have been reported in animal studies or case reports.