Does Namenda (Memantine) Cause Hyponatremia?
No, memantine (Namenda) does not cause hyponatremia based on available evidence. Hyponatremia is not listed among the recognized adverse effects of this medication in clinical studies or guidelines.
Evidence from Clinical Studies
The side effect profile of memantine is well-characterized and does not include electrolyte disturbances:
- Common adverse effects of memantine include constipation, dizziness, headache, and confusion, which are typically mild and transient 1
- These effects differ substantially from the cholinesterase inhibitors (donepezil, rivastigmine, galantamine), which primarily cause gastrointestinal side effects like nausea, diarrhea, vomiting, and weight loss 1
- Memantine is generally well tolerated with rare undesired effects 1
Mechanism and Pharmacology
Memantine's mechanism of action does not predispose to hyponatremia:
- It functions as a moderate-affinity, uncompetitive, voltage-dependent NMDA-receptor antagonist that inhibits excessive calcium influx 2
- The drug's pharmacokinetic profile shows no interaction with renal sodium handling, though dosing adjustments are needed in severe renal impairment (creatinine clearance 5-29 mL/min) due to reduced drug clearance, not electrolyte effects 3
Clinical Context: Actual Causes of Hyponatremia in Dementia Patients
If a patient on memantine develops hyponatremia, consider these common culprits instead:
- Thiazide diuretics are the most frequent cause (41% of severe hyponatremia cases), particularly in elderly patients with low body weight 4, 5
- SIADH accounts for 38% of severe hyponatremia cases 4
- Proton pump inhibitors can increase hyponatremia risk through multiple mechanisms 6
- Other diuretics, particularly loop diuretics, can lead to sodium depletion 6
Important Clinical Considerations
Risk factors for hyponatremia in elderly patients (the typical memantine population) include:
- Advanced age (each 10-year increment doubles the risk) 5
- Low body weight (each 5 kg decrease increases risk by 27%) 5
- Low serum potassium levels 5
- Concomitant use of thiazide diuretics 4, 5
If hyponatremia develops in a patient taking memantine, investigate alternative causes rather than attributing it to the medication, focusing on diuretics, SIADH, volume status, and other medications known to cause electrolyte disturbances 6, 4.