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The pharmacokinetics of cefoxitin were studied in 6 healthy volunteers and in 5 patients with pleural effusion of varied etiologies. The antibiotic was administered in a multiple dosage regimen of 30 mg/kg every 8 hours. Cefoxitin concentrations in serum and pleural fluid were determined after administration of the third dose corresponding to the levels of steady-state in both fluids. The elimination half-life of the antibiotic from the pleural fluid comes to 3.51 +/- 1.15 h, which is significantly greater than the serum half-life, (t 1/2 = 1.42 +/- 0.51 h). This kind of multiple dosage regimen ensures therapeutic levels of cefoxitin in the pleural fluid during the entire treatment.

The pharmacokinetics off cefoxitin were studied after a single i.v. and i. m. dose of 15 mg/kg of cefoxitin to 15 younger people (15-55 years) and to 16 geriatric patients (66-94 years). The kinetics of the antibiotic follow an open two-compartment model for both administration routes. After i.m. administration of the antibiotic, there are modifications in the distribution with respect to i.v. administration, and there is a decrease in beta K21 and as a consequence, an increase in Vp. In geriatric patients, pharmacokinetic modifications take place with respect to those recorded in the younger people in both administration routes, there being a decrease in the following pharmacokinetic parameters: alpha, beta, K12, K21, K13 and Clp, together with an increase in the apparent distribution volume Vdss. A linear relationship has been established between the constant beta and the age of the patient. In spite of the pharmacokinetic modifications observed as a function of age, given the wide safety margin of the antibiotic, it is not necessary to modify the dosage regimen of cefoxitin in geriatric patients.

The pharmacokinetics of cefoxitin was studied in 14 patients with a pleural effusion, 8 of which had normal renal function and the other 6 varying degrees of renal impairment. All patients received a single dose of 30 mg/kg i.v. bolus of the antibiotic. The serum and pleural fluid concentrations of cefoxitin were determined microbiologically. The serum elimination half-life of the antibiotic in the group of patients with normal renal function had a mean value of 1.35 +/- 0.56 h while that of the second group ranged between 2.00 h and 40.79 h, according to the deterioration in renal function. The disappearance half-life of cefoxitin from pleural fluid increased parallel to the degree of renal impairment, reaching a value of 30.09 h for a creatinine clearance (Ccr) of 5.8 ml/min. From the data obtained, dosage regimens were programmed according to the degree of renal function with the aim of achieving safe and efficient cefoxitin levels in both biological fluids.