Abstract
When isosorbide 5‐mononitrate was intravenously infused at a rate of 4 mg h ^−1^ for 2.5 h to five human subjects, its concentrations in plasma increased slowly to 185 ng ml^−1^ ± 5 per cent C.V. at 2.5 h and a steady‐state plasma level was not reached during the infusion. When the infusion was discontinued, plasma drug concentrations declined with an elimination half‐life of 4.2 h ± 6 per cent C.V. The systemic clearance after the infusion doses was 132 ml min^−1^ ± 18 per cent C.V. and the volume of distribution was 48.4 1 ± 16 per cent C. V. After equal oral doses of 10 mg, the peak plasma isosorbide 5‐mononitrate concentration of 191 ng ml^−1^ ±16 per cent C.V. was reached at 1.1 h ± 30 per cent C.V., and plasma levels declined with a terminal half‐life of 4.9 h. The complete systemic availability of isosorbide 5‐mononitrate indicated that pre‐systemic elimination after the oral doses was negligible. A one‐compartment open model appeared adequate to describe the plasma level data after intravenous infusion and oral doses. After single oral doses of 10 mg isosorbide dinitrate, the peak plasma concentration of the 5‐mononitrate metabolite of 72 ng ml^−1^ ± 27 per cent C. V. occurred at l.7h.41 per cent C.V. Approximately 50 per cent (range 22–68 per cent) of the oral dose of isosorbide dinitrate circulated in plasma as the 5‐mononitrate metabolite. The pharmacokinetics of isosorbide mononitrates are markedly different to those of the parent dinitrate and these differences follow from the greater systemic availability and volume of distribution of the mononitrates.