Understanding the former FDA pregnancy risk categories
Prior to 2015, the U.S. Food and Drug Administration (FDA) used a five-letter system (A, B, C, D, and X) to classify medications based on their potential risks to a developing fetus. This system, in use since 1979, was a quick reference for healthcare providers discussing medication use with pregnant patients, though it was often misinterpreted. Despite its replacement, understanding this system is still important for interpreting older medical records and literature.
The definition of a Class B medication
A medication was classified as Category B if animal reproduction studies showed no risk, but there were no adequate, controlled studies in pregnant women. This indicated a seemingly lower risk than Category C, but without the strong human data of Category A.
Why the old system was replaced
The FDA replaced the letter-based system with the new Pregnancy and Lactation Labeling Rule (PLLR) in 2015 due to several limitations. The old system was criticized for oversimplification, leading to misinterpretations of risk. It also lacked the specific details needed for a proper risk-benefit analysis, such as the timing of exposure or specific adverse effects. Additionally, relying heavily on animal studies was problematic because teratogenicity doesn't reliably generalize across species. The simple letter label didn't provide enough clinical context for evidence-based decision-making.
The modern replacement: The Pregnancy and Lactation Labeling Rule (PLLR)
The PLLR, implemented in 2015, offers a more detailed and narrative approach to drug labeling. Instead of a single letter, drug labels now include specific subsections:
- Pregnancy (includes Labor and Delivery): This section provides a Risk Summary, Clinical Considerations, Data, and information on the Pregnancy Exposure Registry.
- Lactation (includes Nursing Mothers): This includes details on drug presence in human milk and potential effects on the breastfed child.
- Females and Males of Reproductive Potential: This addresses issues like pregnancy testing, contraception, and infertility related to the medication.
A list of medications formerly classified as Category B
Examples of medications previously classified as Category B include:
- Antibiotics: Amoxicillin, penicillins, and metronidazole.
- Analgesics: Acetaminophen (Tylenol).
- Anti-nausea medication: Ondansetron (Zofran).
- Diabetes medication: Metformin (Glucophage).
- Antifungals: Certain topical clotrimazole products.
Other meanings of 'Class B' medications
The term 'Class B' can have different meanings outside of pregnancy risk. For example, in some legal systems, 'Class B substances' refer to controlled, illegal drugs like cocaine and methamphetamines. The Centers for Medicare & Medicaid Services (CMS) uses 'Part B Drugs and Biologicals' for certain outpatient prescription drugs covered under Medicare Part B, often infused or injected medications administered by a physician. It's crucial to understand the context when encountering this term.
Comparison of former FDA pregnancy categories
The former FDA pregnancy risk categories provided a quick, though often misinterpreted, assessment of potential fetal risk. These categories ranged from A (no risk shown in controlled human studies) to X (clear risks outweigh benefits and are contraindicated in pregnancy). Category B indicated no fetal risk in animal studies but lacked sufficient human data. Category C involved animal studies showing adverse effects with no controlled human data, where benefits might outweigh risks. Category D showed positive evidence of human fetal risk, but use might be acceptable in certain critical situations. A table detailing the former FDA pregnancy categories can be found on {Link: Drugs in Pregnancy https://jfmo.cchs.ua.edu/files/2013/09/Drugs_Pregnancy.pdf}.
Conclusion
While the concept of what are class B medications appears on older drug labels, it refers to an outdated FDA pregnancy risk classification system. This system, which relied on animal data and limited human studies, was replaced by the PLLR in 2015. The PLLR provides a more detailed approach to evaluating drug safety during pregnancy and lactation, enabling more informed decisions.
