Drugs, pregnancy, and lactation: GI agents: part I.(Obstetrics)

Gastrointestinal complaints are common in pregnancy and the postpartum period. They include conditions such as nausea and vomiting, constipation, diarrhea, heartburn, and erosive gastroesophageal reflux disease, which may be treated with the following products:

Antiemetics. Nausea and vomiting is the most frequent GI complaint in pregnancy. A wide range of oral and parenteral antiemetics is available to treat nausea and vomiting of pregnancy (NVP). All are considered low risk for developmental toxicity (growth retardation, structural defects, functional and behavioral deficits, or death). The most commonly prescribed over-the-counter agent for this condition is doxylamine (Unisom), usually combined with vitamin [B.sub.6] (pyridoxine). These two drugs were the components of Bendectin, which was removed from the market by its manufacturer in 1983, but classified by the Food and Drug Administration as safe and effective. Other common oral medications for NVP include prochlorperazine (Compazine), metoclopramide (Reglan), trimethobenzamide (Tigan), promethazine (Phenergan), and ondansetron (Zofran).

Hyperemesis gravidarum, requires intravenous antiemetics, such as droperidol (Inapsine), prochlorperazine, and ondansetron.

Laxatives. There are seven types of products that act as laxatives: saline (phosphates and magnesium hydroxide and its salts), stimulants/irritants (cascara, bisacody1, casanthranol, senna, and castor oil), bulking agents (methylcellulose, polycarbophil, and psyllium), emollient (mineral oil), fecal softeners (docusate), hyperosmotics (glycerin, lactulose), and tegaserod (Zelnorm).

With the exception of lactulose and tegaserod, these products are available over the counter. Most do not cause direct embryo/fetal toxicity. However, castor oil, which is converted to ricinoleic acid in the gut, is an irritant that may induce premature labor. Improper use of saline laxatives can cause electrolyte imbalances, and mineral oil will prevent absorption of fat-soluble vitamins.

Of the laxatives, bulking agents and fecal softeners are the best in pregnancy. Cascara sagrada and senna are excreted into breast milk and are compatible with breast-feeding, although they may cause diarrhea in a nursing infant.

Tesgaserod, a serotonin type-4 receptor agonist, is approved for women with irritable bowel syndrome whose primary bowel symptom is constipation (and for idiopathic constipation in those under age 65). Limited animal and human data suggest a low risk for embryo/fetal toxicity.