Adults

The 25 mg strength is unusually low for typical adult systemic acyclovir dosing. Standard adult doses for treatment usually range from 200 mg to 800 mg, 2-5 times daily depending on the indication. For this specific 25 mg tablet, consult a physician for precise dosage recommendations, which might be for very specific pediatric or unique clinical situations.

Elderly

Elderly patients may have reduced renal function, requiring dosage adjustment based on creatinine clearance. Consult a physician for appropriate dose modifications.

Renal_impairment

Dosage should be adjusted in patients with renal impairment. Severe impairment (creatinine clearance <10 mL/min) may require significant dose reduction. Consult a physician for dose titration based on renal function.

Onset

Clinical effects typically begin within a few days of initiating therapy, depending on the infection type and severity. For rapid relief, IV formulations are used.

Excretion

The primary route of elimination is renal excretion, via both glomerular filtration and tubular secretion. Approximately 62% to 91% of the dose is excreted unchanged in the urine.

Half life

The plasma half-life of acyclovir in adults with normal renal function is approximately 2.5 to 3 hours. This is significantly prolonged in patients with renal impairment.

Absorption

Oral absorption of acyclovir is poor and variable, with bioavailability ranging from 15% to 30%. Peak plasma concentrations occur 1.5 to 2 hours after oral administration.

Metabolism

Acyclovir is primarily excreted unchanged by the kidneys. A minor metabolite, 9-carboxymethoxymethylguanine, accounts for approximately 10-15% of the dose.

Probenecid

Significantly increases acyclovir plasma concentrations and prolongs its half-life by reducing renal excretion. Concurrent use requires caution and often a reduction in acyclovir dosage.

Nephrotoxic drugs

Coadministration with other nephrotoxic drugs (e.g., cyclosporine, aminoglycosides) may increase the risk of renal dysfunction. Close monitoring of renal function is advised.

Mycophenolate Mofetil

Increases plasma concentrations of both acyclovir and the active metabolite of mycophenolate mofetil. Monitor patients for increased toxicity and adjust doses if necessary.