The pharmacology of cephalexin

Cephalexin has an antimicrobial spectrum that includes those pathogens most frequently encountered in clinical practice. It is useful in the treatment of infections of the upper and lower respiratory tract, skin and soft tissue, and the genitourinary tract. It can be administered in relatively high oral doses without gastrointestinal irritation, and because it is absorbed high in the intestinal tract, it does not disturb the lower bowel flora. Because of its stability and chemical configuration, it causes a very low incidence of allergy. Cephalexin is not absorbed from the stomach but is totally and rapidly absorbed in the upper intestine. Children, because of their greater body water turnover, may need higher doses per kilogram than those used in treating adults. Distribution to the tissues, other than the spinal fluid and aqueous humour, is rapidly achieved. Cephalexin does not penetrate into the host tissue cells, which probably accounts for its low incidence of side effects. Binding to human serum proteins is low, and there is no measurable destruction or metabolism of cephalexin during its sojourn in the body fluids. Cephalexin is rapidly cleared from the body by the kidneys. Seventy to 100% of the dose is found in the urine 6-8 hr after each dose. Concentrations of 500-1000 micrograms/ml of urine follow 250 to 500 mg oral doses of cephalexin, many times greater than the minimum inhibitory concentration for the usual urinary tract pathogens. Patients with creatinine clearances less than 30 ml/min require a reduction in cephalexin dosage. This reduction should be proportional to the reduced function which may be established by determination of creatinine clearance or serum creatinine.