Clearance of the Antihistamine Doxylamine

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Abstract
A single oral dose of doxylamine succinate 25mg was administered to 21 young (20 to 43 years) and 22 elderly (60 to 87 years) volunteers. Multiple plasma doxylamine concentrations were determined during a 30-hour period after each dose. Elderly and young women did not differ significantly in peak plasma doxylamine concentration ( C max ) [116 vs 103 µg/L], time to C max ( t max ) [2.4 vs 2.4h], elimination half-life (12.2 vs 10.1h), volume of distribution (179 vs 176L) or clearance (191 vs 218 ml/min). C max (107 vs 108 µg/L) and t max (2.1 vs 1.6h) also did not differ between elderly and young men. However, elderly men had reduced doxylamine clearance (174 vs 240 ml/min, p < 0.02; 2.5 vs 3.2 ml/min/kg, p < 0.07) and prolonged half-life (15.5 vs 10.2h, p < 0.05). The reduced doxylamine clearance and prolonged half-life in elderly men, but not in elderly women, is similar to results for many other drugs which are transformed by oxidation.