Prescription Medication Use in Pregnancy
Prescription Medication Use in Pregnancy
Choosing the best therapy for a pregnant patient is complicated by a lack of information. Counseling a patient may be even more difficult. The current pregnancy labeling with its accompanying letter codes of A, B, C, D, and X appears as a quick and simple guide to relative safety among medications. This implied hierarchy of risk can be misleading.
When the U.S. Food and Drug Administration (FDA) approves a medication for marketing in the United States, the pregnancy section of the medication label is written based on preclinical studies and, perhaps, a small number of inadvertent human exposures occurring during clinical trials. Given the information available at approval, most medications are assigned to Pregnancy Category C. This designation indicates that human data are lacking and animal studies were positive or not done. With no requirements for systematic review and label updates, 66% of all medications with a pregnancy category are now in Category C. A handful of medications are labeled Pregnancy Category X, including not only frank human teratogens such as thalidomide but also nonteratogens that provide no known benefit to pregnant women. Similarly, less than 1% of medications have the Pregnancy Category "A" rating, as this degree of safety needs to be documented by well-controlled human studies.
Despite the limited human data on medication safety in pregnancy and the standard label warning to avoid use in pregnancy "unless the benefits outweigh the risks," women need and indeed and were prescribed medications at 38% of these visits. Physicians reported prescribing 3 or more medications to their pregnant patients at 1.1 million office visits.
Pregnant women are exposed to much the same classes of drugs as nonpregnant women, though the relative prevalence differs. Prenatal vitamins are the most commonly filled prescriptions during pregnancy. After multivitamins, anti-infectives are the next most frequently filled prescriptions among pregnant (and nonpregnant) women, followed by analgesics, dermatologics, and antiasthmatics. Based on the 1994 National Disease and Therapeutic Index Survey, psychotherapeutic agents and contraceptives were the third and sixth most commonly mentioned medications at physician office visits made by women aged 15-44, regardless of pregnancy status. While prescriptions for medications in these therapeutic classes are less frequently filled by pregnant women in a managed-care setting, contraceptives remained among the top 10 and psychotherapeutics within the top 20 filled prescriptions among women whose pregnancies ended in spontaneous or induced abortions.
Not all the medications used during pregnancy are well classified, and some may be unsafe. In Sweden, a pregnancy category system similar to the FDA's A, B, C system is used, but with subcategories within a particular letter category denoting finer gradations in risk. In a population-based study, this Swedish system of classification was applied to more than 34,000 prescriptions filled by pregnant women in Denmark; 26.6% of the prescriptions were for medications classified as potentially harmful. Perhaps more importantly, 28.7% of the prescriptions were written for agents that had not been given a pregnancy category classification. Similar percentages were reported for lactating women as well.
Given the historic lack of well-controlled studies of medications in human pregnancy, a variety of initiatives were started in the 1990s. Today many of these projects are beginning to show results. From simple follow-up of exposures to a single medication to multisponsor consortiums studying entire therapeutic classes, almost a dozen studies are now recruiting participants and collecting data. The FDA is responsible for numerous initiatives, ranging from a complete overhaul of the pregnancy section of the medication label to discussions with the Centers for Disease Control and Prevention (CDC) on developing a national surveillance program.
Choosing the best therapy for a pregnant patient is complicated by a lack of information. Counseling a patient may be even more difficult. The current pregnancy labeling with its accompanying letter codes of A, B, C, D, and X appears as a quick and simple guide to relative safety among medications. This implied hierarchy of risk can be misleading.
When the U.S. Food and Drug Administration (FDA) approves a medication for marketing in the United States, the pregnancy section of the medication label is written based on preclinical studies and, perhaps, a small number of inadvertent human exposures occurring during clinical trials. Given the information available at approval, most medications are assigned to Pregnancy Category C. This designation indicates that human data are lacking and animal studies were positive or not done. With no requirements for systematic review and label updates, 66% of all medications with a pregnancy category are now in Category C. A handful of medications are labeled Pregnancy Category X, including not only frank human teratogens such as thalidomide but also nonteratogens that provide no known benefit to pregnant women. Similarly, less than 1% of medications have the Pregnancy Category "A" rating, as this degree of safety needs to be documented by well-controlled human studies.
Despite the limited human data on medication safety in pregnancy and the standard label warning to avoid use in pregnancy "unless the benefits outweigh the risks," women need and indeed and were prescribed medications at 38% of these visits. Physicians reported prescribing 3 or more medications to their pregnant patients at 1.1 million office visits.
Pregnant women are exposed to much the same classes of drugs as nonpregnant women, though the relative prevalence differs. Prenatal vitamins are the most commonly filled prescriptions during pregnancy. After multivitamins, anti-infectives are the next most frequently filled prescriptions among pregnant (and nonpregnant) women, followed by analgesics, dermatologics, and antiasthmatics. Based on the 1994 National Disease and Therapeutic Index Survey, psychotherapeutic agents and contraceptives were the third and sixth most commonly mentioned medications at physician office visits made by women aged 15-44, regardless of pregnancy status. While prescriptions for medications in these therapeutic classes are less frequently filled by pregnant women in a managed-care setting, contraceptives remained among the top 10 and psychotherapeutics within the top 20 filled prescriptions among women whose pregnancies ended in spontaneous or induced abortions.
Not all the medications used during pregnancy are well classified, and some may be unsafe. In Sweden, a pregnancy category system similar to the FDA's A, B, C system is used, but with subcategories within a particular letter category denoting finer gradations in risk. In a population-based study, this Swedish system of classification was applied to more than 34,000 prescriptions filled by pregnant women in Denmark; 26.6% of the prescriptions were for medications classified as potentially harmful. Perhaps more importantly, 28.7% of the prescriptions were written for agents that had not been given a pregnancy category classification. Similar percentages were reported for lactating women as well.
Given the historic lack of well-controlled studies of medications in human pregnancy, a variety of initiatives were started in the 1990s. Today many of these projects are beginning to show results. From simple follow-up of exposures to a single medication to multisponsor consortiums studying entire therapeutic classes, almost a dozen studies are now recruiting participants and collecting data. The FDA is responsible for numerous initiatives, ranging from a complete overhaul of the pregnancy section of the medication label to discussions with the Centers for Disease Control and Prevention (CDC) on developing a national surveillance program.
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