Phenothiazines are antipsychotic medications that can cause ocular pigmentation effects. Which antihistamine is also most likely to cause pigmentation effects?

Phenothiazines are antipsychotic medications that can cause ocular pigmentation effects. Which antihistamine is also most likely to cause pigmentation effects?

• A. Promethazine
• B. Diphenhydramine
• C. Cetirizine
• D. Loratadine

Answer: (A)

Pigmentary eye changes from these drugs come from a shared chemical feature with classic phenothiazine antipsychotics—the same core structure can deposit in ocular tissues over time. Promethazine is a phenothiazine derivative, so it carries the same risk of corneal or lens pigment deposition as other drugs in that family. The other antihistamines listed are not phenothiazines: diphenhydramine is a first-generation antihistamine but not phenothiazine in structure, and cetirizine and loratadine are second-generation antihistamines with far less tendency to cause ocular pigment deposits. So promethazine is the antihistamine most likely to be associated with pigmentation effects.

Pigmentary eye changes from these drugs come from a shared chemical feature with classic phenothiazine antipsychotics—the same core structure can deposit in ocular tissues over time. Promethazine is a phenothiazine derivative, so it carries the same risk of corneal or lens pigment deposition as other drugs in that family. The other antihistamines listed are not phenothiazines: diphenhydramine is a first-generation antihistamine but not phenothiazine in structure, and cetirizine and loratadine are second-generation antihistamines with far less tendency to cause ocular pigment deposits. So promethazine is the antihistamine most likely to be associated with pigmentation effects.