What prescription and over-the-counter drugs are dangerous during pregnancy?

Fortunately, many medications are safe just before and during pregnancy. Life’s common ailments go on even when you are pregnant. Is it safe to take antibiotics for a tooth abscess or Tylenol for a headache? Consult with your internist or gynecologist before taking anything, just to be sure, but the list of dangerous drugs is actually much shorter than most people think.

Certain categories of prescription drugs do need to be avoided if you are pregnant or trying to become pregnant. The ACE inhibitors, used to treat high blood pressure, belong to one such category. There are safe drugs for this condition, but your internist and your obstetrician should consult with each other and make sure that you are taking a safe medication.

Women who regularly take antiepileptic drugs like Dilantin should also check on appropriate medications. Some data in the scientific literature suggest that Dilantin may be associated with an increased risk of birth defects, so it is critical to check with your internist and your neurologist beforeyou become pregnant.

The FDA has divided all medications into five general categories (A, B, C, D, or X) with respect to their safety during pregnancy. The category to which a drug belongs has been determined by human and animal testing. Still, many drugs, for example those whose very nature suggests risk, have not been tested even in laboratory animals.

Category A: no risk. These drugs have been tested in carefully controlled studies on pregnant women and have shown no risk to the fetus. Almost no drugs have been rated Category A, because the FDA will not go on record as stating that a drug is safe when there is even the remotest chance of harm to a developing fetus. Therefore many drugs that do not have A ratings are perfectly safe; there simply are no tests that absolutely prove their safety.

Category B: no proven risk in humans. Drugs in category B can receive their rating one of two ways. When tested on pregnant women, the drugs show no risk, even though studies using laboratory animals, which usually involve very large dosages, may have raised the possibility of problems. Or, if adequate studies have not been carried out in humans, animal studies have shown no risk. Remember, however, that just because a certain medication does not cause problems or birth defects in rats does not mean it will be absolutely safe in humans. Thalidomide, which had been found safe in rats and rated category B, was withdrawn from the market when it was shown to cause severe birth defects in humans. It was later re-released in the United States, but only for the treatment of certain diseases including human immunodeficiency virus, leprosy, and some kinds of cancers. Stringent testing and monitoring of contraceptive methods ensure that the women who are using it are not pregnant.

The common antibiotic amoxicillin is in category B. Studies on mice and rats have shown no evidence of harm to the fetus. Nor has human experience with amoxicillin during pregnancy shown adverse effects, but there are no scientifically controlled studies on pregnant women that conclusively rule out any harmful effects.

Category C: possible risk. Drugs in this category have not been tested on pregnant women. They may have been tested in animals, usually in large doses, and the tests have shown evidence of fetal risk, or they may not have been tested in animals at all. These drugs are used only when their benefits outweigh the potential risks. The antimigraine beta-blocker Inderal (propranalol) is in Category C.

Category D: proven risk. Drugs rated D have demonstrated positive evidence of risk. They have not been tested in women and are used during pregnancy only when there is no safer alternative and when the benefits to the mother outweigh the risk to the fetus. Sometimes there is a safe alternative.

While most antibiotics are safe, tetracycline and its derivatives like doxycycline are rated category D. If you have Lyme disease, one of the common diseases for which doxycycline is used, talk to your doctor about substitute medication. If you are planning to get pregnant, you should probably take amoxicillin rather than tetracycline or doxycycline.

Category X: contraindicated in pregnancy; not to be used at all. The clear evidence of risk to the developing fetus outweighs any possible benefit to the mother. These are drugs you should avoid even if you merely think you might get pregnant. Accutane, used to treat severe acne, is rated X; women taking Accutane should not get pregnant.

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