The medications we prescribe for pregnant women should always be safe for the developing fetus. The weight of our management should always be more of a benefit than a risk. We allow ourselves to be guided by our sound judgment and the Food and Drug Administration pregnancy categories, because we do not want to be the culprit of bringing the teratogens to the patients.If we could, we review our pharmacology books whenever we deal with pregnant women.
According to Dr. Cagayan, an obstetrician-gynecologist from the University of the Philippines, we could first consider the available supportive treatment as much as possible.If the drug therapy is absolutely needed, we could opt for the one with a known safety profile. Generally, we choose the topical or inhalational agents over the oral and the intravenous routes because they don’t circulate around the patients’ bodies. We decide to give the lowest possible dose and duration of treatment to reduce fetal exposure to the agent. If the prescription of a risky medication is needed,the weight of the benefits and the presence teratogenic risk should be well-explained to the patient and their relatives.In my practice, however, I request pregnancy test prior to the prescription of any medication to women in the reproductive age group.
The FDA categories are named A, B, C. D, and X. The MIMS Manual showed that the classification is based on the results of the animal and human studies of the drugs and the potential risk it could give to the fetus. Category A are those that are truly safe for all pregnant patients. The results of the controlled studies among human subjects show absence of risk. Among this group are the multivitamins, and other prenatal supplements such as the ferrous sulfate and calcium tablets.
Dr. Cagayan wrote that the Category B includes the penicillins, macrolides,ranitidine and beta-lactams. The MIMS Manual said that the medications under this category have no evident risk in humans because there was nothing found in human studies, or the studies made on human subjects are inadequate.The research on animals showed no risk.
In the Category C, in which the Metronidazole belongs, the risk for the teratogenicity cannot be ruled out. The studies made on humans are lacking. however, the researches on animal subjects either show fetal risk or are inadequate. The benefits may be justified against the risk involved in giving the drug.
The prescription of Category D medications also involves much thought on the weight of the benefit effects of these drugs on the patients’ condition versus the risk of their teratogenicity because the investigational or post-marketing data are linking them to the well-known congenital anomalies. Included here are the antiepileptic drugs,such as the carbamazepine and phenytoin.
The medications in the X category are absolutely contraindicated to pregnancy. Animal and human studies and investigational and postmarketing reports show fetal risks which outweigh the benefits to the patient. This include the thalidomide, diethylstilbestrol, cytotoxic agents and isotretinoin.
The doctors face numerous cases when the women took the medications without knowing that they were pregnant. Counseling must be done. The physician has to have the current, best evidence on the medications they took before he gives any advice. He should make it known that there is a 3% risk for the occurrence of congenital anomalies, even if the patient has no exposure to any teratogens.
List of Sources:
Cagayan, MSF. Drugs,Medications and Immunizations During Pregnancy. In:Sumpaico WW, Ocampo-Andres IS, Capito LRB, Diamante AN, Carnero S, Gamilla Z. Textbook of Obstetrics, 3rd ed. 2002 . Association of Writers of Philippine Textbook of OBGYN,Inc. Quezon City.
MIMS Manual. 2009