Uptake of metronidazole by human erythrocytes

In studies performed with equilibrium dialysis metronidazole was found to bind closely to human erythrocytes. In blood of haematocrit value approximately 50% of the drug was bound to erythrocytes. The ratio of bound and unbound metronidazole was influenced by the concentration of the drug and the erythrocytes. Of the intracellular proteins of erythrocytes it was the carbonic anhydrase enzyme in the first place which was responsible for binding; binding to haemoglobin was negligible. Besides binding to it, metronidazole reduced the carbonic anhydrase activity by almost 50%.