Adults

The usual adult dose is 250 mg to 1 g every 6 hours, depending on the severity and type of infection. For most infections, 500 mg every 8 hours is common. For severe infections, the dose may be increased up to 1 g every 6 hours (4 g/day).

Elderly

No specific dose adjustment is necessary for elderly patients with normal renal function. However, renal function should be monitored, and dosage adjusted if impairment is present.

Renal_impairment

For patients with severely impaired renal function, the dose should be reduced. For creatinine clearance <10 mL/min, 250 mg every 12 hours. For creatinine clearance 10-50 mL/min, 250 mg every 8-12 hours.

Onset

Within 1 hour of administration.

Excretion

Mainly excreted unchanged by the kidneys via glomerular filtration and tubular secretion. Approximately 70-80% of the dose is excreted in the urine within 6 hours.

Half life

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

Absorption

Rapidly and almost completely absorbed from the gastrointestinal tract. Peak plasma concentrations are achieved within 1 hour after oral administration.

Metabolism

Not significantly metabolized.

Warfarin

Increased anticoagulant effect, potentially leading to bleeding.

Metformin

Increased plasma concentrations of Metformin, requiring dose adjustment.

Probenecid

Reduces renal excretion of cephalexin, leading to higher and more prolonged plasma concentrations.

Oral Contraceptives

Possible reduction in efficacy of oral contraceptives (rare).