NAMENDA XR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NAMENDA XR (NAMENDA XR).
Memantine is an uncompetitive, moderate-affinity N-methyl-D-aspartate (NMDA) receptor antagonist that binds preferentially to NMDA receptor-operated cation channels. It blocks the effects of excess glutamate, which can lead to neuronal excitotoxicity, without interfering with normal synaptic transmission.
| Metabolism | Memantine undergoes partial hepatic metabolism via CYP450 enzymes, but is primarily excreted unchanged in urine. About 75-80% of the drug is eliminated unchanged; minor metabolites include N-gluduronide conjugate, 6-hydroxy memantine, and 1-nitroso memantine. |
| Excretion | Renal elimination of unchanged drug (57-82%) and metabolites, with ~20% fecal excretion. Total renal clearance is predominantly via tubular secretion. |
| Half-life | Terminal elimination half-life is 60-80 hours (mean 70 h) in young adults, prolonged to 80-120 h in elderly due to reduced renal function; steady-state is achieved in 3-4 weeks. |
| Protein binding | 45% bound to plasma proteins (mainly albumin). |
| Volume of Distribution | Vd is 7-10 L/kg, indicating extensive tissue distribution beyond plasma volume. |
| Bioavailability | Oral bioavailability is ~100% (extensive absorption); no significant first-pass metabolism. |
| Onset of Action | Oral: Clinical effects (cognitive improvement) typically observed after 2-4 weeks of daily dosing; no immediate effect. |
| Duration of Action | Duration of action is sustained due to long half-life; once-daily dosing maintains therapeutic concentrations. Clinical response persists with continued administration; effects may wane over months. |
28 mg orally once daily, after titration; initial dose 7 mg once daily, increase by 7 mg every 7 days to target dose.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | GFR 30-49 mL/min: 14 mg once daily; GFR 15-29 mL/min: 7 mg once daily; GFR <15 mL/min or dialysis: not recommended. |
| Liver impairment | Child-Pugh Class A or B: no adjustment; Child-Pugh Class C: not studied, use with caution. |
| Pediatric use | Not approved for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No specific dose adjustment; use standard adult dosing with careful monitoring for adverse effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NAMENDA XR (NAMENDA XR).
| Breastfeeding | Unknown if memantine is excreted in human milk. Present in rat milk at concentrations higher than maternal plasma (M/P ratio not reported). Caution should be exercised when administered to a nursing woman. |
| Teratogenic Risk | Pregnancy Category B. In animal studies, memantine showed no evidence of teratogenicity at doses up to 10 times the maximum human dose. There are no adequate and well-controlled studies in pregnant women. In the first trimester, risk cannot be ruled out; second and third trimester potential risks include possible effects on fetal NMDA receptor development. Use only if clearly needed. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to memantine hydrochloride or any components of the formulation."]
| Precautions | ["Seizures: Use with caution in patients with a history of seizure disorders.","Genitourinary conditions: Conditions that raise urine pH (e.g., severe urinary tract infections, renal tubular acidosis) may decrease elimination, leading to increased plasma concentrations.","Concomitant use with other NMDA antagonists (e.g., amantadine, ketamine, dextromethorphan) should be avoided due to risk of adverse effects."] |
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| Fetal Monitoring | Monitor maternal renal function (creatinine clearance) as dosing is adjusted; fetal monitoring via ultrasound for growth and development if exposed during pregnancy. |
| Fertility Effects | No human data on fertility. In animal studies, no impairment of fertility was observed at doses up to 10 times the human dose. |