Drugs and medications during pregnancy
Drugs in pregnancy
Incidence
- Of women 20–25% report using medications on a regular basis throughout pregnancy.
- Major congenital anomalies occur in 3–4% of live births and 70% of such anomalies have no known cause. It is estimated that 2–3% are due to medications and 1% to environmental toxins.
Drug trials in pregnancy
- Drug trials are difficult to carry out in pregnancy because of concern over the fetus. As such, many drugs have not been validated for use or safety in human pregnancy.
- Recommendations often rely on data from animal models. The occurrence of thalidomide-associated embryopathy has led to the belief that human teratogenicity cannot be predicted by animal studies. However, every drug that has since been found to be teratogenic in humans has caused similar effects in animals.
Pharmacokinetics during pregnancy
- Pharmacokinetics is the study of how a drug moves through the body.
- Drug absorption is altered in pregnancy. Gastric emptying and gastric acid secretion are reduced. Intestinal motility is decreased. Pulmonary tidal volume is increased which may affect the absorption of inhaled drugs.
- The volume of distribution changes in pregnancy. Plasma volume rises by 40%, total body water increases 7–8 L, and body fat increases 20–40%. Despite these changes (which would be expected to decrease drug levels), albumin concentrations decline, and free fatty acid and lipoprotein values rise. As a result, protein binding of many drugs is lower in pregnancy, leading to an increase in circulating free (biologically active) drug levels.
- Metabolism and elimination are also altered in pregnancy. High steroid hormone levels affect hepatic metabolism and prolong the half-life of some drugs. Glomerular filtration rate rises 50–60%, thereby increasing the renal clearance of other drugs.
