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Pharmacokinetic analysis fo arithmetic mean concentration data can lead us to selection of an inappropriate deterministic compartmental model and biased pharmacokinetic parameter estimates. The terminal phase disposition rate constant estimated by fitting a deterministic model to mean data is in all cases an underestimate of the expected value of this rate constant. The area under the mean data curve calculated via the linear trapezoidal rule from time zero to the last detectable concentration sampling point is equal to the mean of the individual subject areas under the curve for the same time span. This equality supports the use of mean data for determination of model-independent pharmacokinetic parameters.

The pharmacokinetics of chloramphenicol (CAP) and total chloramphenicol succinate (CAPS) were studied in eight hospitalized adult patients with normal renal and hepatic function receiving intravenous chloramphenicol sodium succinate therapy. The steady-state peak concentrations of CAP (8.4-26.0 micrograms/ml) occurred at an average of 18.0 min (range 5.4-40.2) after cessation of the chloramphenicol sodium succinate infusion. Unhydrolyzed CAPS prodrug, representing 26.0 +/- 7.0% of the dose, was recovered unchanged in the urine indicating that the bioavailability of CAP from a dose of intravenous chloramphenicol succinate is not complete. A pharmacokinetic model was developed for simultaneous fitting of CAP and CAPS plasma concentration data. Pharmacokinetic parameters determined by simultaneous fitting were: V, 0.81 +/- 0.18 liters/kg; t1/2, 3.20 +/- 1.02 hr; CLB, 3.21 +/- 1.27 ml/min/kg for chloramphenicol; and V, 0.38 +/- 0.13 liters/kg; t1/2, 0.57 +/- 0.12 hr; CLB, 7.72 +/- 1.87 ml/min/kg for total chloramphenicol succinate.