Memantine Flashcards
What are the indications for memantine?
Moderate to severe dementia in Alzheimer’s disease
Oscillopsia in MS
What is the pharmacodynamic of memantine?
NMDA receptor antagonist
Continuous activation of NMDA receptors in the CNS caused by glutamate is thought to cause some of the Alzheimer’s disease symptoms
This overactivation is thought to contribute to neurotoxicity due to the excitatory properties of glutamate
Minimal effect on GABA, benzo, dopamine, adrenergic, histamine, and glycine receptors & Ca2+, Na+ or K+ channels
What is the pharmacokinetic of memantine?
Bioavailability = ?
Protein binding = ~ 45%
Half-life = 60-80 hours (terminal half-life)
Metabolism = partially metabolised in liver (CYP450 does not majorly contribute to its metabolism)
Excretion = 48% kidney via urine (unchanged drug)
What dose of memantine is usually prescribed?
Initially 5mg OD
Increased in steps of 5mg at weekly intervals to a max of 20mg daily
What dose of memantine is prescribed for those with hepatic impairment?
Dose depends on the eGFR
eGFR is 30–49 mL/minute/1.73 m2 = reduce dose to 10 mg daily. If well tolerated after at least 7 days, the dose can be increased in steps to 20 mg daily
eGFR is 5–29 mL/minute/1.73 m2 = reduce dose to 10 mg daily
eGFR < 5 mL/minute/1.73 m2 = avoid memantine
What are the contraindications for memantine?
Hypersensitivity to drug and any of its excipients (inc. people with rare hereditary problems of lactose intolerance, the Lapp lactase deficiency, or glucose-galactose malabsorption)
Severe hepatic impairment
Severe renal impairment - avoid if eGFR < 5mL/min/1.73m^2
What are the cautions for memantine?
Hx of convulsions or predisposing factors for epilepsy
What are the common adverse effects of memantine?
Constipation
HTN
Dyspnoea
Headache
Dizziness
Impaired balance
Drowsiness
What are the less common adverse effects of memantine?
Vomiting
Thrombosis
HF
Confusion
Fatigue
Hallucinations
Abnormal gait
What are the very rare adverse effects of memantine?
Seizures
Pancreatitis
Psychosis
Depression
Suicidal ideation
What are the possible drug interactions with memantine hydrochloride?
Antimuscarinics - memantine possible enhances effects of antimuscarinics
Antipsychotics - memantine possibly reduces the effects of antipsychotics
Barbiturates - memantine may reduce the effects of barbiturates
Baclofen and dantrolene - memantine possibly reduces the effects of these drugs. A dose adjustment may be necessary
Dopaminergics - memantine possibly enhances the effects of dopaminergic drugs e.g., cabergoline
NMDA-antagonists e.g., amantadine, ketamine, or dextromethorphan - increased risk of toxicity with memantine. Avoid concomitant use
Warfarin - memantine possibly enhances anticoagulant effect of warfarin. Monitor INR closely during concurrent use
What should you advice patients to do if they miss their dose?
Skip the missed dose and take the next one at the right time
Do not take 2 doses to make up for a forgotten dose
If you regularly forget set an alarm to remind you or ask your pharmacist for ways to help you remember to take your meds
When should you advise patients to call 999 or go to A&E?
If they have taken more than their prescribed dose of memantine and:
- have hallucinations
- pass out or have a seizure or fit
When should you advise patients to call 111?
If they have taken more than their prescribed dose of memantine and:
- start to get any symptoms
- have vomiting or diarrhoea
Sources
https://cks.nice.org.uk/topics/dementia/prescribing-information/memantine-hydrochloride/
https://www.nhs.uk/medicines/memantine/how-and-when-to-take-memantine/
https://www.nice.org.uk/guidance/NG97/chapter/Recommendations#pharmacological-management-of-alzheimers-disease
https://bnf.nice.org.uk/drugs/memantine-hydrochloride/
https://go.drugbank.com/drugs/DB01043
