Memantine

INTRODUCTION

Indications

Moderate-to-severe Alzheimer's dementia.

Action

Binds to CNS N-methyl-D-aspartate (NMDA) receptor sites, preventing binding of glutamate, an excitatory neurotransmitter. Therapeutic Effects: Decreased symptoms of dementia. Does not slow progression. Cognitive enhancement. Does not cure disease.

Adverse Reactions/Side Effects

CNS: dizziness, fatigue, headache, sedation. CV: hypertension. Derm: rash. GI: weight gain. GU: urinary frequency. Hemat: anemia.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess blood pressure (BP) and compare to normal values (See Appendix F). Report a sustained increase in BP (hypertension).

• Monitor signs of anemia, including unusual fatigue, shortness of breath with exertion, pallor, and bruising. Notify physician if these signs occur.

• Assess dizziness and drowsiness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician and nursing staff, and caution the patient and family/caregivers to guard against falls and trauma.

• Periodically assess body weight and other anthropometric measures (body mass index, body composition). Report a substantial weight gain or increased body fat.

Interventions

• Guard against falls and trauma (hip fractures, head injury, and so forth) caused by drowsiness, dizziness, or other drugs; implement fall prevention strategies (See Appendix E).

• Help patient and family/caregivers explore nonpharmacologic methods to reduce combative episodes and mood disorders (exercise, structured activities, validation therapies, and so forth).

Patient/Client-Related Instruction

• Instruct patient and family/caregivers to report other bothersome side effects such as severe or prolonged headache, skin rash, or urinary frequency.

Pharmacokinetics

Absorption: Well absorbed after oral administration.

Distribution: Unknown.

Metabolism and Excretion: 57–82% excreted unchanged in urine by active tubular secretion moderated by pH- dependent tubular reabsorption. Remainder metabolized; metabolites are not pharmacologically active.

Half-life: 60–80 hr.

Contraindications/Precautions

Contraindicated in: Severe renal impairment.

Use Cautiously in: Moderate renal impairment (consider ↓ dose); Concurrent use of other NMDA antagonists (amantadine, rimantadine, ketamine, dextromethorphan); Concurrent use of drugs or diets that cause alkaline urine; Conditions that ↑ urine pH including severe urinary tract infections or renal tubular acidosis (lead to ↓ excretion and ↑ levels); OB/Lactation/Pedi: Safety not established. Discontinue drug or bottle-feed.

Interactions

Drug-Drug: Medications that ↑ urine pH lead to ↓ excretion and ↑ blood levels (carbonic anhydrase inhibitors, sodium bicarbonate).