Only limited experience with overdose is available from clinical studies and post-marketing experience.
Symptoms: Relative large overdoses (200 mg and 105 mg/day for 3 days, respectively) have been associated with either only symptoms of tiredness, weakness and/or diarrhoea or no symptoms. In the overdose cases below 140 mg or unknown dose the patients revealed symptoms from central nervous system (confusion, drowsiness, somnolence, vertigo, agitation, aggression, hallucination, and gait disturbance) and/or of gastrointestinal origin (vomiting and diarrhoea).
In the most extreme case of overdose, the patient survived the oral intake of a total of 2,000 mg memantine with effects on the central nervous system (coma for 10 days, and later diplopia and agitation). The patient received symptomatic treatment and plasmapheresis. The patient recovered without permanent sequelae.
In another case of a large overdose, the patient also survived and recovered. The patient had received 400 mg memantine orally. The patient experienced central nervous system symptoms such as restlessness, psychosis, visual hallucinations, proconvulsiveness, somnolence, stupor, and unconsciousness.
Treatment: In the event of overdose, treatment should be symptomatic. No specific antidote for intoxication or overdose is available. Standard clinical procedures to remove active substance material, e.g. gastric lavage, carbo medicinalis (interruption of potential entero-hepatic recirculation), acidification of urine, forced diuresis should be used as appropriate.
In case of signs and symptoms of general central nervous system (CNS) overstimulation, careful symptomatic clinical treatment should be considered.
Not applicable.
In clinical trials in mild to severe dementia, involving 1,784 patients treated with memantine and 1,595 patients treated with placebo, the overall incidence rate of adverse reactions with memantine did not differ from those with placebo; the adverse reactions were usually mild to moderate in severity. The most frequently occurring adverse reactions with a higher incidence in the memantine group than in the placebo group were dizziness (6.3 % vs. 5.6 %, respectively), headache (5.2 % vs. 3.9 %), constipation (4.6 % vs. 2.6%), somnolence (3.4 % vs. 2.2 %) and hypertension (4.1 % vs. 2.8 %).
The following Adverse Reactions listed in the table below have been accumulated in clinical studies with memantine and since its introduction in the market. Within each frequency grouping, undesirable effects are presented in order of decreasing seriousness.
Adverse reactions are ranked according to system organ class, using the following convention: very common (> 1/10), common (> 1/100 to < 1/10), uncommon (> 1/1,000 to < 1/100), rare (> 1/10,000 to < 1/1,000), very rare (< 1/10,000), not known (cannot be estimated from the available data).
| Infections and infestations | Uncommon | Fungal infections |
| Immune system disorders | Common | Drug hypersensitivity |
| Psychiatric disorders | Common | Somnolence |
| Uncommon | Confusion | |
| Uncommon | Hallucinations1 | |
| Not known | Psychotic reactions2 | |
| Nervous system disorders | Common | Dizziness |
| Common | Balance disorders | |
| Uncommon | Gait abnormal | |
| Very rare | Seizures | |
| Cardiac disorders | Uncommon | Cardiac failure |
| Vascular disorders | Common | Hypertension |
| Uncommon | Venous thrombosis/thromboembolism | |
| Respiratory, thoracic and mediastinal disorders | Common | Dyspnoea |
| Gastrointestinal disorders | Common | Constipation |
| Uncommon | Vomiting | |
| Not known | Pancreatitis2 | |
| Hepatobiliary disorders | Common | Elevated liver function test |
| Not known | Hepatitis | |
| General disorders and administration site conditions | Common | Headache |
| Uncommon | Fatigue |
1 Hallucinations have mainly been observed in patients with severe Alzheimer´s disease.
2 Isolated cases reported in post-marketing experience.
Alzheimer's disease has been associated with depression, suicidal ideation and suicide. In postmarketing experience these events have been reported in patients treated with memantine.
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme
Website: www.mhra.gov.uk/yellowcard
In short term studies in rats, memantine like other NMDA-antagonists have induced neuronal vacuolisation and necrosis (Olney lesions) only after doses leading to very high peak serum concentrations. Ataxia and other preclinical signs have preceded the vacuolisation and necrosis. As the effects have neither been observed in long term studies in rodents nor in non-rodents, the clinical relevance of these findings is unknown.
Ocular changes were inconsistently observed in repeat dose toxicity studies in rodents and dogs, but not in monkeys. Specific ophthalmoscopic examinations in clinical studies with memantine did not disclose any ocular changes.
Phospholipidosis in pulmonary macrophages due to accumulation of memantine in lysosomes was observed in rodents. This effect is known from other active substances with cationic amphiphilic properties. There is a possible relationship between this accumulation and the vacuolisation observed in lungs. This effect was only observed at high doses in rodents. The clinical relevance of these findings is unknown.
No genotoxicity has been observed following testing of memantine in standard assays. There was no evidence of any carcinogenicity in life long studies in mice and rats. Memantine was not teratogenic in rats and rabbits, even at maternally toxic doses, and no adverse effects of memantine were noted on fertility. In rats, foetal growth reduction was noted at exposure levels, which are identical or slightly higher than at human exposure.
Treatment of patients with moderate to severe Alzheimer's disease.
Pharmacotherapeutic group: Other Anti-dementia drugs, ATC code: N06DX01.
Mechanism of action
There is increasing evidence that malfunctioning of glutamatergic neurotransmission, in particular at NMDA-receptors, contributes to both expression of symptoms and disease progression in neurodegenerative dementia.
Memantine is a voltage-dependent, moderate-affinity uncompetitive NMDA-receptor antagonist. It modulates the effects of pathologically elevated tonic levels of glutamate that may lead to neuronal dysfunction.
Clinical efficacy and safety
A pivotal monotherapy study in a population of patients suffering from moderate to severe Alzheimer's disease (mini mental state examination (MMSE) total scores at baseline of 3 − 14) included a total of 252 outpatients. The study showed beneficial effects of memantine treatment in comparison to placebo at 6 months (observed cases analysis for the clinician´s interview based impression of change (CIBIC-plus): p = 0.025; Alzheimer´s disease cooperative study - activities of daily living (ADCS-ADLsev): p = 0.003; severe impairment battery (SIB): p = 0.002).
A pivotal monotherapy study of memantine in the treatment of mild to moderate Alzheimer's disease (MMSE total scores at baseline of 10 to 22) included 403 patients. Memantine-treated patients showed a statistically significantly better effect than placebo-treated patients on the primary endpoints: Alzheimer´s disease assessment scale (ADAS-cog) (p = 0.003) and CIBIC-plus (p = 0.004) at week 24 (last observation carried forward (LOCF)). In another monotherapy study in mild to moderate Alzheimer's disease a total of 470 patients (MMSE total scores at baseline of 11 − 23) were randomised. In the prospectively defined primary analysis statistical significance was not reached at the primary efficacy endpoint at week 24.
A meta-analysis of patients with moderate to severe Alzheimer's disease (MMSE total scores < 20) from the six phase III, placebo-controlled, 6-month studies (including monotherapy studies and studies with patients on a stable dose of acetylcholinesterase inhibitors) showed that there was a statistically significant effect in favour of memantine treatment for the cognitive, global, and functional domains. When patients were identified with concurrent worsening in all three domains, results showed a statistically significant effect of memantine in preventing worsening, as twice as many placebo-treated patients as memantine-treated patients showed worsening in all three domains (21 % vs. 11 %, p < 0.0001).
Absorption:
Memantine has an absolute bioavailability of approximately 100 %. Tmax is between 3 and 8 hours. There is no indication that food influences the absorption of memantine.
Distribution:
Daily doses of 20 mg lead to steady-state plasma concentrations of memantine ranging from 70 to 150 ng/ml (0.5 - 1 μmol) with large interindividual variations. When daily doses of 5 to 30 mg were administered, a mean cerebrospinal fluid (CSF)/serum ratio of 0.52 was calculated. The volume of distribution is around 10 l/kg. About 45 % of memantine is bound to plasma-proteins.
Biotransformation:
In man, about 80 % of the circulating memantine-related material is present as the parent compound. Main human metabolites are N-3,5-dimethyl-gludantan, the isomeric mixture of 4- and 6-hydroxy-memantine, and 1-nitroso-3,5-dimethyl-adamantane. None of these metabolites exhibit NMDA-antagonistic activity. No cytochrome P 450 catalysed metabolism has been detected in vitro.
In a study using orally administered 14C-memantine, a mean of 84 % of the dose was recovered within 20 days, more than 99 % being excreted renally.
Elimination:
Memantine is eliminated in a monoexponential manner with a terminal t½ of 60 to 100 hours. In volunteers with normal kidney function, total clearance (Cltot) amounts to 170 ml/min/1.73 m2 and part of total renal clearance is achieved by tubular secretion.
Renal handling also involves tubular reabsorption, probably mediated by cation transport proteins. The renal elimination rate of memantine under alkaline urine conditions may be reduced by a factor of 7 to 9. Alkalisation of urine may result from drastic changes in diet, e.g. from a carnivore to a vegetarian diet, or from the massive ingestion of alkalising gastric buffers.
Linearity:
Studies in volunteers have demonstrated linear pharmacokinetics in the dose range of 10 to 40 mg.
Pharmacokinetic/pharmacodynamic relationship:
At a dose of memantine of 20 mg per day the CSF levels match the ki-value (ki = inhibition constant) of memantine, which is 0.5 μmol in human frontal cortex.
Caution is recommended in patients with epilepsy, former history of convulsions or patients with predisposing factors for epilepsy.
Concomitant use of N-methyl-D-aspartate (NMDA)-antagonists such as amantadine, ketamine or dextromethorphan should be avoided.).
Some factors that may raise urine pH may necessitate careful monitoring of the patient. These factors include drastic changes in diet, e.g. from a carnivore to a vegetarian diet, or a massive ingestion of alkalising gastric buffers. Also, urine pH may be elevated by states of renal tubulary acidosis (RTA) or severe infections of the urinary tract with Proteus bacteria.
In most clinical trials, patients with recent myocardial infarction, uncompensated congestive heart failure (NYHA III-IV), or uncontrolled hypertension were excluded. As a consequence, only limited data are available and patients with these conditions should be closely supervised.
This medicinal product contains lactose. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Moderate to severe Alzheimer's disease usually causes impairment of driving performance and compromises the ability to use machinery. Furthermore, Memantine LEK has minor or moderate influence on the ability to drive and use machines such that outpatients should be warned to take special care.
Treatment should be initiated and supervised by a physician experienced in the diagnosis and treatment of Alzheimer's dementia. Therapy should only be started if a caregiver is available who will regularly monitor the intake of the medicinal product by the patient. Diagnosis should be made according to current guidelines. The tolerance and dosing of memantine should be reassessed on a regular basis, preferably within three months after start of treatment. Thereafter, the clinical benefit of memantine and the patient's tolerance of treatment should be reassessed on a regular basis according to current clinical guidelines. Maintenance treatment can be continued for as long as a therapeutic benefit is favourable and the patient tolerates treatment with memantine. Discontinuation of memantine should be considered when evidence of a therapeutic effect is no longer present or if the patient does not tolerate treatment.
Posology
Adults:
Dose titration
The maximum daily dose is 20 mg per day. In order to reduce the risk of undesirable effects, the maintenance dose is achieved by upward titration of 5 mg per week over the first 3 weeks as follows.
To facilitate the up-titration other tablet strengths are available.
Week 1 (day 1-7):
The patient should take half a 10 mg film-coated tablet (5 mg) per day for 7 days.
Week 2 (day 8-14):
The patient should take one 10 mg film-coated tablet (10 mg) per day for 7 days.
Week 3 (day 15-21):
The patient should take one and a half 10 mg film-coated tablets (15 mg) per day for 7 days.
From Week 4 on:
The patient should take two 10 mg film-coated tablets (20 mg) per day.
Maintenance dose
The recommended maintenance dose is 20 mg per day.
Elderly: On the basis of the clinical studies, the recommended dose for patients over the age of 65 years is 20 mg per day (two 10 mg film-coated tablets once a day) as described above.
Children and adolescents: Memantine LEK is not recommended for use in children below 18 years due to a lack of data on safety and efficacy.
Renal impairment: In patients with mildly impaired renal function (creatinine clearance 50 − 80 ml/min) no dose adjustment is required. In patients with moderate renal impairment (creatinine clearance 30 - 49 ml/min) daily dose should be 10 mg per day. If tolerated well after at least 7 days of treatment, the dose could be increased up to 20 mg/day according to standard titration scheme. In patients with severe renal impairment (creatinine clearance 5 - 29 ml/min) daily dose should be 10 mg per day.
Hepatic impairment: In patients with mild or moderate hepatic impaired function (Child-Pugh A and Child-Pugh B), no dose adjustment is needed. No data on the use of memantine in patients with severe hepatic impairment are available. Administration of Memantine LEK is not recommended in patients with severe hepatic impairment.
Method of administration
Memantine LEK should be administered once a day and should be taken at the same time every day. The film-coated tablets can be taken with or without food.
No special requirements.
