Dental Hygiene Pharmacology Practice Exam

The main idea is that methemoglobinemia risk from benzocaine is highest in the youngest patients. Infants under 2 years have an immature methemoglobin-reducing enzyme system (lower activity of NADH-cytochrome b5 reductase), so when benzocaine oxidizes hemoglobin from Fe2+ to Fe3+ (forming methemoglobin), the body’s ability to revert it back is limited. This allows methemoglobin to accumulate, reducing oxygen delivery to tissues and potentially causing hypoxia. That’s why benzocaine-containing products are avoided in this age group.