OBJECTIVE To determine the pharmacokinetics of cefuroxime axetil in malnourished rats using a diet with a restriction in energy and nutrients (group M), a diet with a low quality protein (group K) and a good quality diet (group C) as a control. METHODS The rats were fed with the corresponding diet during 21 days. After this period a single oral dose of cefuroxime axetil (equivalent to a 2.2 mg dose of cefuroxime) was administered, and plasma samples were taken at 0, 5, 10, 30, 45, 60, 90, 120, 180, 240, 300 and 360 minutes; samples were assayed using an HPLC assay. Biochemical parameters were also measured an a microscopy study of the small intestine was done. After a 21 day period of recovery of the malnourished groups a second pharmacokinetic study was performed using the same sample times as in the first study. RESULTS In malnourished animals of group K the levels of plasma proteins were low, and showed higher concentrations of fat in the liver. The relative bioavailability of cefuroxime was 78.2% for group M and 64.4% for group K. Groups M and K presented lower values of area under the curve, which means that the amount of antibiotic absorbed was lower than group C. In the second pharmacokinetic study although the animals received a good quality diet, it was observed that the area under the curve of group K was lower, and the relative bioavailability was 54.3%, while group M had similar pharmacokinetic values than control group. CONCLUSIONS The pharmacokinetics of cefuroxime was affected by malnutrition, suggesting that the absorption process via the transporter was modified in the malnourished groups, specially in the group fed with a low quality protein.