Memantine Hydrochloride

Trade Names:
Namenda
- Tablets 5 mg
- Tablets 10 mg
- Oral solution 2 mg/mL

Pharmacology

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It is postulated that memantine exerts its therapeutic effect as a low to moderate affinity, uncompetitive nervous system N-methyl-D-aspartate (NMDA) receptor antagonist by binding preferentially to the NMDA receptor-operated cation channels.

Pharmacokinetics

Absorption

Well absorbed from the GI tract, reaching C _max in about 3 to 7 h.

Distribution

Vd is 9 to 11 L/kg. Plasma protein binding is 45%.

Metabolism

Little metabolism with 57% to 82% excreted unchanged in the urine and remainder eliminated as 3 polar metabolites that possess minimal activity.

Elimination

Terminal elimination t _½ is about 60 to 80 h. Renal elimination involves active tubular secretion moderated by pH dependent tubular reabsorption.

Special Populations

Pharmacokinetics similar in young and elderly.

Women had approximately 45% greater exposure than men; however, there was no difference in exposure when body weight was taken into account.

Indications and Usage

Treatment of moderate to severe dementia of the Alzheimer type.

Unlabeled Uses

Treatment of vascular dementia.

Contraindications

Standard considerations.

Dosage and Administration

PO Start with 5 mg daily. Increase the dose in 5 mg increments to 5 mg twice daily, 15 mg/day (5 and 10 mg as separate doses), and 10 mg twice daily. The minimum recommended interval between dose increases is 1 wk.

General Advice

• May be taken alone or in combination with other medications for Alzheimer dementia.
• Administer without regard to meals. Administer with food if GI upset occurs.
• Oral solution is sugar-free and peppermint flavored.
• To prepare oral solution dosing device, remove dosing syringe with green cap and plastic tube from protective plastic bag. Remove child-resistant cap and seal from bottle. Insert plastic tube fully into bottle and screw green cap tightly onto bottle by turning cap clockwise (to right).
• To prepare dose of oral solution, while keeping bottle upright on table remove lid to uncover opening on top of cap, insert tip of syringe (plunger fully depressed), hold syringe and gently pull the plunger of syringe to draw memantine solution into syringe. Remove syringe from opening of cap, invert syringe and slowly press plunger to level that push out any large air bubbles that may be present (tiny bubbles will not affect dose).
• Administer oral solution directly from syringe into mouth.

Storage/Stability

Store tablets and oral solution at controlled room temperature (59° to 86°F).

Drug Interactions

Plasma concentrations of both drugs may be altered.

Has not been studied; use with caution.

Renal Cl of memantine is reduced about 80% under alkaline urine conditions at pH 8.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Hypertension (4%); cardiac failure, syncope (at least 1%).

CNS

Dizziness (7%); confusion, headache (6%); hallucination, somnolence (3%); aggressive reaction, ataxia, cerebrovascular accident, hypokinesia, transient ischemic attack, vertigo (at least 1%).

Dermatologic

Rash (at least 1%).

EENT

Cataract, conjunctivitis (at least 1%).

GI

Constipation (5%); vomiting (3%).

Genitourinary

Frequent micturition (at least 1%).

Hematologic

Anemia (at least 1%).

Metabolic-Nutritional

Decreased weight, increased alkaline phosphatase (at least 1%).

Musculoskeletal

Back pain (3%).

Respiratory

Coughing (4%); dyspnea (2%); pneumonia (at least 1%).

Miscellaneous

Pain (3%); fatigue (2%).

Precautions

Pregnancy

Category B .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Renal Function

It is likely that memantine exposure will be increased in patients with moderate renal function impairment. Consider dose reduction. Administration of memantine is not recommended in severe renal function impairment.

GU conditions

Conditions that raise urine pH may decrease urinary elimination of memantine, resulting in increased plasma levels.

Seizures

Has not been studied in patients with seizure disorders.

Overdosage

Symptoms

Loss of consciousness, psychosis, restlessness, somnolence, stupor, visual hallucinations.

Patient Information

• Advise patient or caregiver that this drug does not alter the Alzheimer process and that the efficacy of the medication may decrease over time.
• Instruct patient or caregiver to continue using other medications for dementia as prescribed by health care provider.
• Advise patient or caregiver to review the patient information leaflet carefully before starting therapy and to read and check for new information each time the medication is refilled.
• Advise patient or caregiver that medication is started at a low dose and gradually increased to the max dose at intervals of at least 1 wk. Review dose escalation schedule with patient or caregiver.
• Advise patient or caregiver that doses greater than 5 mg are taken twice daily, without regard to meals, but to take with food if GI upset occurs.
• Ensure patient or caregiver using oral solution understands how to attach the green cap and plastic tube to new bottles of oral solution, withdraw prescribed dose using dosing syringe, and administer the dose.
• Advise patient or caregiver not to discontinue the drug or change the dose unless advised by health care provider.
• Caution patient or caregiver not to increase the dose of memantine if Alzheimer symptoms do not appear to be improving or appear to be getting worse, but to notify health care provider.
• Caution patient that memantine may cause drowsiness or dizziness and to use caution while driving or performing other activities requiring mental alertness or coordination until tolerance is determined.

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