Understanding the impact of drug input rate on its pharmacokinetic-pharmacodynamic relationship may lead to a more optimal drug therapy. The aim of the present study was to investigate the influence of the rate of administration on tolerance development to frusemide, by giving the drug at four different infusion rates.Methods
Eight healthy volunteers were given 10 mg of frusemide on four different occasions, as a constant-rate intravenous infusion during 10, 30, 100 and 300 min, respectively. Urinary volume and contents of frusemide and sodium were measured in samples collected over 8 h.Results
The four different infusion rates systematically influenced the frusemide excretion rate versus diuretic and natriuretic response relationship. Counter-clockwise hysteresis occurred for the most rapid infusion rate, whereas a progressive clockwise hysteresis was observed for the slower infusions, indicating development of tolerance. For each subject, diuresis and natriuresis were modeled for all four treatments simultaneously, using a feedback tolerance model. It was not possible to describe the data using a model without tolerance. The time course of tolerance development showed remarkable differences between the infusion rates. The intensity of maximum tolerance development was significantly less for the slowest infusion rate compared with the more rapid infusions and it appeared significantly later. However, no differences in diuretic or natriuretic response were found between the treatments.Conclusions
The direction of the hysteresis loop is dependent on the input rate of frusemide. After the administration of a single low dose of frusemide, the time course of tolerance, rather than the integrated time course of tolerance, is influenced by the drug input rate.