Quinapril and its metabolite quinaprilat in human milk

Aims To measure the milk to plasma ratio (M/P) of quinapril and its active metabolite quinaprilat in lactating mothers and to assess likely infant exp osure. Methods A single dose of quinapril 20 mg was administered to six healthy mo thers who had been breastfeeding their infants for at least 2 weeks. Blood was sampled for the measurement of quinapril and quinaprilat at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 16 and 24 h. Milk was collected for measurement of quinapril and quinaprilat concentrations over the periods -4-0, 0-4, 4-8, 8 -12, 12-18, 18-24 h. The areas under the plasma and milk concentration-time curves were estimated and an M/P ratio derived for both quinapril and quin aprilat. Results The M/P ratio for quinapril was 0.12 (95% CI 0.09,0.14). No quinapr il was detected in milk after 4 h. No quinaprilat was detected in any of th e milk samples. The estimated 'dose' of quinapril that would be received by the infant was 1.6% (95% CI 1.0,2.2) of the maternal dose, adjusted for re spective weights. Conclusions Quinapril appears to be 'safe' during breastfeeding according t o conventional criteria, although as always, the risk:benefit ratio should be considered when it is to be given to a nursing mother.