Excretion of doxepin and N-desmethyldoxepin in human milk.

Doxepin and N-desmethyldoxepin concentrations in plasma and breast milk from a lactating mother and in plasma from her infant were measured during an 8 week period using high performance liquid chromatography. Plasma concentrations ranged from 35-68 microgram l-1 for doxepin and 65-131 microgram l-1 for N-desmethyldoxepin. Mean pre-feed milk/plasma ratios were 1.08 and 1.02 for doxepin and N-desmethyldoxepin respectively and increased to 1.66 and 1.53 at the post-feed samples. Only N-desmethyldoxepin (15 microgram l-1) was detectable in the infant's plasma sampled after 43 days of maternal therapy.