Abstract
The biological half‐life in the blood of a new anticonvulsive drug, NSD 3004, was studied in various species. The half‐life in man was about 120 days and from 2–30 days in 3 other mammalian species. The substance is a carbonic anhydrase inhibitor and is bound strongly to the carbonic anhydrase in human red blood cells with a dissociation constant of about 10‐8 M. The receptor (drug) concentration is about 100–133 μM in red blood cells which corresponds to the concentration of carbonic anhydrase. The data presented indicate that NSD 3004 is bound to human carbonic anhydrases B and C (HCAB and HCAC) and that the strongest binding is to the C fraction. More than 90% of the NSD 3004 in the plasma is protein bound. This, and the high affinity to the red blood cells, explains the extremely long half‐life of the substance in human blood.
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