Adults

Initially 5 mg once daily, increasing gradually by 5 mg increments at weekly intervals to a target maintenance dose of 20 mg once daily. Max dose 20 mg/day.

Elderly

No dosage adjustment needed based on age. Follow adult dosage. However, monitor renal function.

Renal_impairment

Moderate (Creatinine Clearance 30-49 mL/min): Max dose 10 mg once daily. Severe (Creatinine Clearance 5-29 mL/min): Max dose 5 mg once daily.

Onset

Clinical effects may take several weeks to become apparent. Maximum benefit usually observed after consistent use for several months.

Excretion

Primarily via the kidneys, largely as unchanged drug (48%) and metabolites. Renal excretion accounts for approximately 75% of total clearance.

Half life

Approximately 60 to 80 hours.

Absorption

Well absorbed orally, with absolute bioavailability of approximately 100%. Peak plasma concentration is reached within 3 to 7 hours.

Metabolism

Memantine undergoes partial hepatic metabolism, primarily by N-glucuronidation and N-demethylation, resulting in three polar metabolites. However, a significant portion is excreted unchanged.

Hydrochlorothiazide

Memantine may decrease the clearance of hydrochlorothiazide, potentially leading to increased levels of the diuretic.

N-methyl-D-aspartate (NMDA) antagonists

Concomitant administration with other NMDA-receptor antagonists (amantadine, ketamine, dextromethorphan) should be avoided due to the risk of potentiation of central nervous system effects.

Drugs excreted by renal tubular secretion

Cimetidine, ranitidine, quinidine, and nicotine are cleared by the same renal cation transport system as memantine. Co-administration could theoretically alter the plasma levels of either or both drugs.