Use of gentamicin physiologically-based model for individual dosing

A new approach to fixing initial doses of gentamicin (GM) for i.m. administration (that is most commonly used anyway) is discussed. This approach is based on a physiologically-based model allowing to reproduce individual patterns of GM concentration change in the patient's blood. This approach was used to reproduce the individual pattern of GM concentration change after the initial i.m. administration of 80 mg to 19 male patients (age-range 21 to 73 years, weight range 50-94 kg, creatinine concentration in the blood 0.4-1.6 mg/d). The GM concentration levels, obtained with the help of this model, were afterwards compared to the results of FPIA measurement of GM concentrations in the blood of the patients 0.5, 1, 2, 3, 5 and 7 h after administration. It proved that the average deviation of the predicted values from the actual was equal to 20 per cent for all the measuring time-points. For comparison we used individual patterns of GM distribution in blood calculated according to the one-compartment model from the same values of Vd, Cl and dose. In this case the error of pharmacokinetic prediction exceeded the 20 per cent and amounted to 43 per cent by 0.5 and 7 hours. Thus, the new approach with the physiologically-based model provides better accuracy for stable pharmacokinetic prediction for longer stretches of time upon administration, which is especially important for the correct establishment of dosing intervals.