The relative infant dose (RID) may be of concern for breastfeeding infants if RID exceeds which percentage?

• A. 2%
• B. 5%
• C. 10%
• D. 15%

Answer: (C)

Understanding how much drug a breastfeeding infant could receive through milk is captured by the relative infant dose. Clinically, if the RID exceeds about 10%, the infant’s exposure is considered potentially clinically relevant, warranting caution. This threshold exists because, at or above this level, there’s a greater chance of adverse effects in neonates whose metabolism and excretion are immature. The RID is an estimate based on the drug concentration in milk and typical infant daily intake, and real-world variations in both can change actual exposure. So when RID goes beyond 10%, clinicians may consider alternative therapies, adjust maternal dosing, or monitor the infant more closely, while RID below 10% is generally viewed as low risk, keeping in mind drug-specific data still matter.