The Former FDA Pregnancy Categories: A Historical Context
From 1979 until 2015, the FDA used a five-tiered, letter-based system (A, B, C, D, and X) to classify medication risk during pregnancy. This system, intended as a quick guide, was often misinterpreted as a simple grading scale rather than an evidence assessment. It failed to account for important factors like timing and dosage, leading to the misconception that a Category B drug was always safer than a Category C drug.
Defining What Are Category B Medications
Under the old system, Category B was assigned when either animal studies showed no fetal risk but human data was lacking, or animal studies showed risk but human studies did not confirm this, particularly later in pregnancy. This reliance on animal data was a limitation, as teratogenic effects don't always cross species.
Why the FDA Replaced the Letter System
The FDA replaced the letter categories with the Pregnancy and Lactation Labeling Rule (PLLR) in 2015 to address the old system's shortcomings. The letter system was seen as overly simple, misleading, and lacking crucial details for informed decisions. The PLLR aims to provide clearer risk-benefit assessments.
The New FDA Labeling System: PLLR
The PLLR provides detailed, narrative information in three subsections:
- 8.1 Pregnancy: Includes a Risk Summary, Clinical Considerations, and Data from human and animal studies.
- 8.2 Lactation: Details drug presence in breast milk and effects on infants.
- 8.3 Females and Males of Reproductive Potential: Covers pregnancy testing, contraception, and infertility information.
Examples of Formerly Category B Medications
These medications were previously Category B and are generally considered safe based on current evidence and PLLR guidelines. Common examples include Acetaminophen (Tylenol), Amoxicillin, Penicillins, Metformin, Cephalexin, and Loperamide (Imodium).
Comparing the Old and New Systems
| Feature | Old System (Letter Categories) | New System (PLLR) |
|---|---|---|
| Design | Single-letter, A-B-C-D-X | Detailed, narrative-based labeling with subsections |
| Focus | Overly simplistic risk assessment | Comprehensive risk-benefit assessment |
| Information | Limited; often based on animal studies or insufficient human data | Detailed Risk Summary, Clinical Considerations, and Data (human and animal) |
| Clarity | Prone to misinterpretation and confusion | Aims to minimize misinformation and provide clarity |
| Considerations | Lacked nuance on timing, dosage, etc. | Addresses specific clinical factors, including use during labor and delivery |
| Scope | Addressed pregnancy and lactation | Expanded to include Females and Males of Reproductive Potential |
Patient Guidance and Modern Practice
Pregnant individuals should not rely on the old letter categories but consult healthcare providers. Pharmacists and physicians use detailed PLLR information for informed decisions, weighing treatment benefits against potential fetal risks based on current evidence. Pregnancy exposure registries also collect data to improve knowledge.
Conclusion: Moving Beyond the Categories
The term "what are category B medications" refers to an outdated system. The shift to the PLLR provides a more accurate and comprehensive framework for assessing medication use during pregnancy. Patients should communicate openly with their providers and rely on current, detailed information rather than the old letter categories. The FDA provides an extensive list of approved drugs and other resources on their official website.
