Adults

The usual adult dose is 250-500 mg every 6 hours or 500 mg every 12 hours. For severe infections, the dose may be increased up to 4 g per day in divided doses.

Elderly

No specific dose adjustment is usually required for elderly patients with normal renal function. However, renal function should be assessed, and dose adjusted if impairment is present.

Renal_impairment

Dose adjustment is necessary for patients with renal impairment. For creatinine clearance of 30-50 mL/min, the dose should not exceed 500 mg every 8-12 hours. For CrCl 10-30 mL/min, 500 mg every 12-24 hours. For CrCl <10 mL/min, 250 mg every 12-24 hours.

Onset

Within 1 hour

Excretion

Primarily excreted unchanged by the kidneys via glomerular filtration and tubular secretion. Over 90% of the drug is excreted in the urine within 8 hours.

Half life

Approximately 0.5 to 1.2 hours in individuals with normal renal function.

Absorption

Rapidly and well absorbed from the gastrointestinal tract, even in the presence of food. Peak plasma concentrations are achieved within 1-2 hours.

Metabolism

Not significantly metabolized in the liver.

Metformin

Concomitant administration with cefalexin may increase metformin plasma concentrations. Adjust metformin dose if necessary.

Probenecid

Probenecid reduces the renal excretion of cefalexin, which may result in increased and prolonged plasma concentrations of cefalexin.

Oral Anticoagulants

Rarely, cefalexin may affect prothrombin time, necessitating monitoring in patients on oral anticoagulants.