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Uses

Alzheimer's Disease

Memantine hydrochloride is used for the palliative treatment of moderate to severe dementia of the Alzheimer's type (Alzheimer's disease). The current indication is based principally on 2 short-term (24 or 28 weeks) randomized, controlled clinical studies in adults (50-93 years of age) with a diagnosis of probable Alzheimer's disease that was moderate to severe. In both studies, patients treated with memantine hydrochloride received an initial dosage of 5 mg once daily, with weekly increases in increments of 5 mg daily until a dosage of 20 mg daily (10 mg twice daily) was reached. Patients enrolled in the 24-week study had received donepezil hydrochloride (a reversible acetylcholinesterase inhibitor) for at least 6 months (at a stable dosage for the preceding 3 months) and continued to receive donezepil hydrochloride in addition to either memantine hydrochloride or placebo during the study period. Various instruments were used to assess efficacy. In both studies, changes from baseline in cognitive performance were assessed using the Severe Impairment Battery (SIB) scale. Changes from baseline in overall daily function and overall clinical effects (including information from caregivers) were assessed using the modified Alzheimer's disease Cooperative Study Activities of Daily Living inventory (ADCS-ADL) and the Clinician's Interview Based Impression of Change (CIBIC plus), respectively. In both studies, patients receiving memantine hydrochloride experienced less deterioration in cognitive and daily function than patients receiving placebo. In the 24-week study, patients receiving memantine experienced less decline in CIBIC plus scores than patients receiving placebo; however, while improvements in CIBIC plus scores were observed in patients receiving memantine in the 28-week study, the difference from placebo (intent-to-treat analysis) was not statistically significant. In an unpublished 24-week open-label extension of the 28-week trial, improvement relative to the projected rate of continued decline in cognition, daily function, and overall clinical impression of change was observed in patients who were switched from placebo to memantine.

A third randomized, controlled clinical study of 12 weeks' duration was conducted in nursing home patients with severe dementia (Alzheimer's disease or vascular dementia). In patients randomized to receive memantine hydrochloride, therapy was initiated at a dosage of 5 mg once daily and increased to 10 mg once daily after one week. In this study, daily function was assessed using the care dependency subscale of the Behavioral Rating Scale for Geriatric Patients (BGP), and overall clinical effects were assessed using the Clinical Global Impression of Change scale (CGI-C); cognitive function was not evaluated. In a subset of patients diagnosed as having Alzheimer's disease, memantine hydrochloride was more effective than placebo, as assessed by changes from baseline in both the BGP and CGI-C scales.

Dosage and Administration

Administration

Memantine hydrochloride is administered orally (as a tablet or oral solution) without regard to meals. Memantine hydrochloride tablets and oral solution are equivalent on a mg-per-mg basis. The oral solution should be administered using the dosing device with oral syringe provided by the manufacturer, referring to the accompanying patient information for instructions. Memantine hydrochloride oral solution should not be mixed with any other liquid.

Dosage

The recommended initial adult dosage of memantine hydrochloride is 5 mg once daily. The dosage of memantine hydrochloride shown to be effective in clinical trials and the recommended target dosage is 20 mg daily, given in 2 divided doses (10 mg twice daily). Dosage should be increased to the target dosage in increments of 5 mg daily at intervals of not less than 1 week. Following initiation of therapy at a dosage of 5 mg once daily, dosage should be increased to 10 mg daily (5 mg twice daily), with subsequent increases to 15 mg daily (5 mg and 10 mg as separate doses) and then to 20 mg daily (10 mg twice daily).

Special Populations

No dosage adjustment is needed in patients with mild to moderate renal impairment. However, in patients with severe renal impairment (i.e., creatinine clearance of 5-29 mL/minute), a target dosage of 5 mg twice daily is recommended. Creatinine clearance may be estimated using the following formulas:

Ccr male = [(140 - age) x weight (in kg)] / [72 x serum creatinine (in mg/dL)]Ccr female = 0.85 x Ccr male

Cautions

Contraindications

Known hypersensitivity to memantine hydrochloride or any ingredient in the formulation.

Warnings/Precautions

General Precautions

Seizures

Mematine has not been systematically evaluated in patients with a seizure disorder. In clinical studies, seizures occurred in 0.2% of patients receiving memantine and in 0.5% of patients receiving placebo.

Urinary Excretion

Conditions that increase urinary pH (e.g., dietary changes [e.g., from a high-protein to a vegetarian diet], concomitant use of drugs that alkalinize urine [e.g., carbonic anhydrase inhibitors, sodium bicarbonate], renal tubular acidosis, severe urinary tract infections) may decrease elimination of memantine, resulting in increased plasma memantine concentrations; use with caution under such conditions.

Specific Populations

Pregnancy

Category B.

Lactation

Not known whether memantine is distributed into human milk. However, since many drugs are distributed into human milk, caution is advised if memantine is administered in nursing women.

Pediatric Use

Safety and efficacy not established in children.

Geriatric Use

Clinical studies have been conducted principally in older patients since dementia of the Alzheimer's type occurs mainly in an older patient population. Memantine pharmacokinetics were similar in elderly patients and younger adults.

Hepatic Impairment

Although pharmacokinetics have not been evaluated in patients with hepatic impairment, only a modest effect on clearance would be expected.

Renal Impairment

The area under the plasma concentration-time curve AUC was increased by 4, 60, or 115% in individuals with mild (creatinine clearance exceeding 50 but less than 80 mL/minute), moderate (creatinine clearance 30-49 mL/minute), or severe (creatinine clearance 5-29 mL/minute) renal impairment, respectively. Terminal elimination half-life was increased by 18, 41, or 95% in those with mild, moderate, or severe renal impairment, respectively. Dosage adjustment is recommended in patients with severe renal impairment, but not in those with mild or moderate renal impairment. (See Dosage and Administration: Special Populations.)

Common Adverse Effects

Adverse effects occurring in 2% or more of patients receiving memantine in clinical studies and more frequently than with placebo include dizziness (7%), confusion (6%), headache (6%), constipation (5%), cough (4%), hypertension (4%), back pain (3%), hallucination (3%), pain (3%), somnolence (3%), vomiting (3%), dyspnea (2%), and fatigue (2%).

Drug Interactions

Drugs Affecting Hepatic Microsomal Enzymes

Inhibitors or inducers of cytochrome P-450 (CYP) system; pharmacokinetic interaction unlikely.

Drugs Metabolized by Hepatic Microsomal Enzymes

Minimal inhibition of CYP isoenzymes 1A2, 2A6, 2C9, 2D6, 2E1, or 3A4 by memantine observed in vitro. No induction of CYP isoenzymes 1A2, 2C9, 2E1, or 3A4/5 observed in vitro at concentrations exceeding those associated with therapeutic efficacy. Pharmacokinetic interaction unlikely.

Protein-bound Drugs

Because plasma protein binding of memantine is low (45%), a pharmacokinetic interaction with drugs that are highly protein bound (e.g., digoxin, warfarin) is unlikely.

Drugs Secreted by Renal Tubular Cationic Transport

Potential pharmacokinetic interaction (altered plasma concentrations of both drugs) when memantine is used with drugs secreted by the same renal cationic system (e.g., cimetidine, hydrochlorothiazide, metformin, nicotine, quinidine, ranitidine, triamterene). However, concomitant use of memantine with a fixed combination of hydrochlorothiazide and triamterene did not affect bioavailability of either memantine or triamterene, and maximum plasma concentrations and area under the plasma concentration-time curve (AUC) of hydrochlorothiazide decreased by only 20%. In addition, concomitant use of memantine with a fixed combination of glyburide and metformin hydrochloride did not affect the pharmacokinetics of memantine, metformin, or glyburide, and the hypoglycemic effects of the glyburide-metformin combination were not affected.

Alkalinizing Agents

Potential decreased memantine clearance with resulting increases in adverse effects when the drug is used concomitantly with agents that increase urine pH (e.g., carbonic anhydrase inhibitors, sodium bicarbonate). Use with caution. Memantine clearance was decreased by approximately 80% at alkaline urine conditions (i.e., pH 8).

Cholinesterase Inhibitors

Concomitant use of memantine with the acetylcholinesterase inhibitor donepezil did not affect the pharmacokinetics of either drug or substantially alter acetylcholinesterase inhibition by donepezil. In a 24-week clinical study in patients with moderate to severe Alzheimer's disease, adverse effects observed with combination therapy with memantine and donepezil were similar to those observed with donepezil alone. In vitro and animal studies indicate that memantine does not affect the reversible inhibition of acetylcholinesterase produced by donepezil, galantamine, or tacrine.

N-Methyl-d-aspartate (NMDA) Antagonists

Concomitant use of memantine hydrochloride with other NMDA antagonists (e.g., amantadine, ketamine, dextromethorphan) has not been systematically evaluated. Use with caution.