FDA pregnancy risk categories and the CPS

The FDA pregnancy risk categories

In response to the thalidomide tragedy, the FDA implemented labeling requirements in 1979 with the aim of providing evidence-based information about use of medication in pregnancy. Each drug is classified into 1 of 5 categories based on the absence or presence of data on the safety of its use during pregnancy, the type of study subjects, and the study results (Table 1). Each category has designated sentences to be included in the drug label. The FDA categories are intended to guide drug choice before fetal exposure, rather than provide information on how to manage the pregnancy following exposure.4 Critics of the FDA classification pointed out that, although the system is easy to use, it might oversimplify the complexity of weighing risks to the fetus against the need to adequately manage maternal medical conditions. The system does not fully address the fact that the benefits of treatment of some conditions (eg, diabetes, asthma, pregnancy-induced hypertension, and psychiatric conditions) might outweigh the risk of fetal drug exposure.5

There is also a misunderstanding that the successive categories represent increasing severity of malformation and that all medications in the same category have the same risk and type of malformations. Furthermore, this system does not make a distinction between the sources of data for medications within the same risk category. For example, a medication can be listed as class B based on the failure of animal studies to show fetal risk but without well-controlled human studies; or based on the failure of animal studies to show fetal risk but with adequate and well-controlled human studies demonstrating safety in pregnancy. Classifying these 2 types of data in the same category implies that both have the same rigour of safety information in human pregnancy, when the most important data should always be derived from human studies.6 There are also concerns that the generic statements provide insufficient information for clinicians to properly counsel pregnant patients in the event of inadvertent fetal drug exposures.5

In response to these concerns, the FDA made an announcement in May 2008, stating that they will replace the A, B, C, D, and X classification system with a narrative framework consisting of 3 sections. The new labeling information will contain a risk summary section that incorporates human and animal data and a clinical consideration section that addresses risk assessment and how to handle inadvertent fetal drug exposure. In addition, there will be therapeutic alternatives and a data section summarizing the evidence discussed in the other 2 sections.7 However, to date, the pregnancy risk categories are still in effect and are still being used by physicians.

Compendium of Pharmaceuticals and Specialties

The Compendium of Pharmaceuticals and Specialties (CPS) is the most frequently used reference for evaluating safety when prescribing medication to pregnant women in Canada.8 However, its contents are legal product monographs provided by the manufacturers and are not designed for physicians to advise pregnant women about the safety of medication use in pregnancy. Therefore, information obtained from the CPS might provide the physician with incomplete or misleading information with regards to safety. For example, to date, there have been many studies involving thousands of women exposed to fluoxetine during pregnancy, which have reported reassuring information. 9–11 However, the product monograph for fluoxetine (Prozac) in the 2009 CPS edition states the following: “Safe use of fluoxetine during pregnancy has not been established. Therefore PROZAC should not be administered to women of childbearing potential unless, in the opinion of the treating physician, the expected benefits to the patient markedly outweigh the possible hazards to the fetus or the child.”12 Consequently, after reading this statement in the CPS, it is not surprising that physicians are hesitant to advise their pregnant patients to take this drug during pregnancy, even if their conditions warrant its use.

Motherisk approach

Owing to the limitations of the current FDA pregnancy risk classification system and pregnancy information contained in the CPS, additional resources are required to assess the safety of medication use in pregnancy. Counselors at the Motherisk Program use peer-reviewed, in-house statements prepared from published primary literature, including materials such as abstracts from meetings. The strengths and limitations of the various types of study designs are discussed in a paper by a Motherisk team member,13 as it is important to understand how studies are conducted in order to critically evaluate the literature.

When evaluating the literature there are many considerations to be made about the risk-benefit profile of taking a drug during pregnancy. In addition to congenital malformations, other neonatal outcomes, such as prematurity, low birth weight, abnormal neurodevelopment, functional abnormalities, miscarriage, and stillbirth, are also important and might affect the physician’s and patient’s decisions on how to proceed with the pregnancy. As well, items such as timing of exposure are important to know, as some drugs might be safe for use in one trimester and contraindicated in another.

Some women and their health care providers, overestimate the teratogenic risk associated with drug use during pregnancy, resulting in unnecessary termination of a wanted pregnancy or not using needed medications to manage serious maternal conditions.14 In addition, in some cases, such as depression and bipolar disorder, inadequate maternal treatment might lead to poor pregnancy outcomes and negatively affect maternal-infant interaction.15

Conclusion

Physicians frequently rely upon the FDA pregnancy risk category system and the CPS to evaluate the safety of medications in pregnancy; however, both the FDA classification system and the product monographs of the CPS are inadequate to address the complexity of weighing the benefits of treatment against the possible risk of drug exposure. The Motherisk Program is a reliable source for physicians to receive evidence-based, unambiguous information, assisting physicians in counseling their pregnant patients and ensuring appropriate treatment of the mother while at the same time protecting her unborn child. For more information, please visit www.motherisk.org.