Signs and symptoms most often accompanying memantine overdosage in clinical trials and from worldwide marketing experience, alone or in combination with other drugs and/or alcohol, include agitation, asthenia, bradycardia, confusion, coma, dizziness, ECG changes, increased blood pressure, lethargy, loss of consciousness, psychosis, restlessness, slowed movement, somnolence, stupor, unsteady gait, visual hallucinations, vertigo, vomiting, and weakness. The largest known ingestion of memantine worldwide was 2.0 grams in a patient who took memantine in conjunction with unspecified antidiabetic medications. The patient experienced coma, diplopia, and agitation, but subsequently recovered. Fatal outcome has been very rarely reported with memantine, and the relationship to memantine was unclear.
Because strategies for the management of overdose are continually evolving, it is advisable to contact a poison control center to determine the latest recommendations for the management of an overdose of any drug. As in any cases of overdose, general supportive measures should be utilized, and treatment should be symptomatic. Elimination of memantine can be enhanced by acidification of urine.
NAMENDA (memantine hydrochloride) is contraindicated in patients with known hypersensitivity to memantine hydrochloride or to any excipients used in the formulation.
NAMENDA was evaluated in eight double-blind placebo-controlled trials involving a total of 1862 dementia (Alzheimer's disease, vascular dementia) patients (940 patients treated with NAMENDA and 922 patients treated with placebo) for a treatment period up to 28 weeks.
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.
Adverse Events Leading to DiscontinuationIn placebo-controlled trials in which dementia patients received doses of NAMENDA up to 20 mg/day, the likelihood of discontinuation because of an adverse reaction was the same in the NAMENDA group (10.1%) as in the placebo group (11.5%). No individual adverse reaction was associated with the discontinuation of treatment in 1% or more of NAMENDA-treated patients and at a rate greater than placebo.
Most Common Adverse ReactionsIn double-blind placebo-controlled trials involving dementia patients, the most common adverse reactions (incidence ≥ 5% and higher than placebo) in patients treated with NAMENDA were dizziness, headache, confusion and constipation. Table 1 lists all adverse reactions that occurred in at least 2% of patients treated with NAMENDA and at an incidence greater than placebo.
Table 1: Adverse Reactions Reported in Controlled
Clinical Trials in at Least 2% of Patients Receiving NAMENDA and at a Higher
Frequency than Placebo-treated Patients
| Adverse Reaction | Placebo (N = 922) % |
NAMENDA (N = 940) % |
| Body as a Whole | ||
| Fatigue | 1 | 2 |
| Pain | 1 | 3 |
| Cardiovascular System | ||
| Hypertension | 2 | 4 |
| Central and Peripheral Nervous System | ||
| Dizziness | 5 | 7 |
| Headache | 3 | 6 |
| Gastrointestinal System | ||
| Constipation | 3 | 5 |
| Vomiting | 2 | 3 |
| Musculoskeletal System | ||
| Back pain | 2 | 3 |
| Psychiatric Disorders | ||
| Confusion | 5 | 6 |
| Somnolence | 2 | 3 |
| Hallucination | 2 | 3 |
| Respiratory System | ||
| Coughing | 3 | 4 |
| Dyspnea | 1 | 2 |
The overall profile of adverse reactions and the incidence rates for individual adverse reactions in the subpopulation of patients with moderate to severe Alzheimer's disease were not different from the profile and incidence rates described above for the overall dementia population.
SeizuresNAMENDA has not been systematically evaluated in patients with a seizure disorder. In clinical trials of NAMENDA, seizures occurred in 0.2% of patients treated with NAMENDA and 0.5% of patients treated with placebo.
Postmarketing ExperienceThe following adverse reactions have been identified during post-approval use of memantine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These reactions include:
Blood and Lymphatic System Disorders -agranulocytosis, leukopenia (including neutropenia), pancytopenia, thrombocytopenia, thrombotic thrombocytopenic purpura.
Cardiac Disorders -cardiac failure congestive.
Gastrointestinal Disorders -pancreatitis.
Hepatobiliary Disorders – hepatitis.
Psychiatric Disorders -suicidal ideation.
Renal and Urinary Disorders -acute renal failure (including increased creatinine and renal insufficiency).
Skin Disorders -Stevens Johnson syndrome.
NAMENDA (memantine hydrochloride) is indicated for the treatment of moderate to severe dementia of the Alzheimer's type.
Memantine showed low to negligible affinity for GABA, benzodiazepine, dopamine, adrenergic, histamine and glycine receptors and for voltage-dependent Ca2+, Na+ or K+ channels. Memantine also showed antagonistic effects at the 5HT3 receptor with a potency similar to that for the NMDA receptor and blocked nicotinic acetylcholine receptors with one-sixth to one-tenth the potency.
In vitro studies have shown that memantine does not affect the reversible inhibition of acetylcholinesterase by donepezil, galantamine, or tacrine.
Following oral administration memantine is highly absorbed with peak concentrations reached in about 3-7 hours. Memantine has linear pharmacokinetics over the therapeutic dose range. Food has no effect on the absorption of memantine.
DistributionThe mean volume of distribution of memantine is 9-11 L/kg and the plasma protein binding is low (45%).
MetabolismMemantine undergoes partial hepatic metabolism. The hepatic microsomal CYP450 enzyme system does not play a significant role in the metabolism of memantine.
EliminationMemantine is excreted predominantly (about 48%) unchanged in urine and has a terminal elimination half-life of about 60-80 hours.
The remainder is converted primarily to three polar metabolites which possess minimal NMDA receptor antagonistic activity: the N-glucuronide conjugate, 6-hydroxy memantine, and 1-nitroso-deaminated memantine. A total of 74% of the administered dose is excreted as the sum of the parent drug and the Nglucuronide conjugate. Renal clearance involves active tubular secretion moderated by pH dependent tubular reabsorption.
There are no adequate and well-controlled studies of memantine in pregnant women. NAMENDA should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Memantine given orally to pregnant rats and pregnant rabbits during the period of organogenesis was not teratogenic up to the highest doses tested (18 mg/kg/day in rats and 30 mg/kg/day in rabbits, which are 9 and 30 times, respectively, the maximum recommended human dose [MRHD] on a mg/m² basis).
Slight maternal toxicity, decreased pup weights and an increased incidence of non-ossified cervical vertebrae were seen at an oral dose of 18 mg/kg/day in a study in which rats were given oral memantine beginning pre-mating and continuing through the postpartum period. Slight maternal toxicity and decreased pup weights were also seen at this dose in a study in which rats were treated from day 15 of gestation through the postpartum period. The no-effect dose for these effects was 6 mg/kg, which is 3 times the MRHD on a mg/m² basis.
NAMENDA 2 mg/mL oral solution: clear, alcohol-free, sugar-free, and peppermint flavored.
Storage And Handling 2 mg/mL Oral Solution12 fl. oz. (360 mL) bottle NDC #0456-3202-12
Store NAMENDA oral solution at 25°C (77°F); excursions permitted to 15-30°C (59-86°F).
Manufactured for: Forest Pharmaceuticals, Inc. Subsidiary of Forest Laboratories, LLC St. Louis, MO 63045. Manufactured by: Forest Laboratories Ireland Ltd. Revised August 2014
Included as part of the PRECAUTIONS section.
PRECAUTIONS Genitourinary ConditionsConditions that raise urine pH may decrease the urinary elimination of memantine resulting in increased plasma levels of memantine.
Patient Counseling InformationSee FDA-approved patient labeling (PATIENT INFORMATION and Instructions for Use).
To assure safe and effective use of NAMENDA, the following information and instructions provided in the patient information section should be discussed with patients and caregivers.
Patients/caregivers should be instructed to follow the dose titration schedule provided by their physician or healthcare professional for NAMENDA.
If a patient misses a single dose of NAMENDA, that patient should not double up on the next dose. The next dose should be taken as scheduled. If a patient fails to take NAMENDA for several days, dosing should not be resumed without consulting that patient's healthcare professional.
Patients/caregivers should be instructed on how to use the NAMENDA oral solution dosing device. They should be made aware of the patient instruction sheet that is enclosed with the product. Patients/caregivers should be instructed to address any questions on the usage of the solution to their physician or pharmacist.
Nonclinical Toxicology Carcinogenesis, Mutagenesis, Impairment Of FertilityThere was no evidence of carcinogenicity in a 113-week oral study in mice at doses up to 40 mg/kg/day (10 times the maximum recommended human dose [MRHD] on a mg/m² basis). There was also no evidence of carcinogenicity in rats orally dosed at up to 40 mg/kg/day for 71 weeks followed by 20 mg/kg/day (20 and 10 times the MRHD on a mg/m² basis, respectively) through 128 weeks.
Memantine produced no evidence of genotoxic potential when evaluated in the in vitro S. typhimurium or E. coli reverse mutation assay, an in vitro chromosomal aberration test in human lymphocytes, an in vivo cytogenetics assay for chromosome damage in rats, and the in vivo mouse micronucleus assay. The results were equivocal in an in vitro gene mutation assay using Chinese hamster V79 cells.
No impairment of fertility or reproductive performance was seen in rats administered up to 18 mg/kg/day (9 times the MRHD on a mg/m² basis) orally from 14 days prior to mating through gestation and lactation in females, or for 60 days prior to mating in males.
Use In Specific Populations Pregnancy Pregnancy Category BThere are no adequate and well-controlled studies of memantine in pregnant women. NAMENDA should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Memantine given orally to pregnant rats and pregnant rabbits during the period of organogenesis was not teratogenic up to the highest doses tested (18 mg/kg/day in rats and 30 mg/kg/day in rabbits, which are 9 and 30 times, respectively, the maximum recommended human dose [MRHD] on a mg/m² basis).
Slight maternal toxicity, decreased pup weights and an increased incidence of non-ossified cervical vertebrae were seen at an oral dose of 18 mg/kg/day in a study in which rats were given oral memantine beginning pre-mating and continuing through the postpartum period. Slight maternal toxicity and decreased pup weights were also seen at this dose in a study in which rats were treated from day 15 of gestation through the postpartum period. The no-effect dose for these effects was 6 mg/kg, which is 3 times the MRHD on a mg/m² basis.
Nursing MothersIt is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when NAMENDA is administered to a nursing mother.
Pediatric UseSafety and effectiveness in pediatric patients have not been established.
Geriatric UseThe majority of people with Alzheimer's disease are 65 years and older. In the clinical studies of NAMENDA the mean age of patients was approximately 76; over 90% of patients were 65 years and older, 60% were 75 years and older, and 12% were at or above 85 years of age. The efficacy and safety data presented in the clinical trial sections were obtained from these patients. There were no clinically meaningful differences in most adverse events reported by patient groups ≥ 65 years old and < 65 year old.
Renal ImpairmentNo dosage adjustment is needed in patients with mild or moderate renal impairment. A dosage reduction is recommended in patients with severe renal impairment.
Hepatic ImpairmentNo dosage adjustment is needed in patients with mild or moderate hepatic impairment. NAMENDA should be administered with caution to patients with severe hepatic impairment.
The recommended starting dose of NAMENDA is 5 mg (2.5 mL) once daily. The dose should be increased in 5 mg increments to 10 mg/day (2.5 mL twice daily), 15 mg/day (2.5 mL and 5 mL as separate doses), and 20 mg/day (5 mL twice daily). The minimum recommended interval between dose increases is one week. The dosage shown to be effective in controlled clinical trials is 20 mg/day (5 mL twice daily).
Dosing Titration Schedule
| Total daily dose | Strength per dose (mg) | |
| Starting Dose | 5 mg | 5mg |
| Dose after week 1 | 10 mg | 5 mg (first daily dose) 5 mg (second daily dose) |
| Dose after week 2 | 15 mg | 5 mg (first daily dose) 10 mg (second daily dose) |
| Dose after week 3 | 20 mg | 10 mg (first daily dose) 10 mg (second daily dose) |
NAMENDA can be taken with or without food. If a patient misses a single dose of NAMENDA, that patient should not double up on the next dose. The next dose should be taken as scheduled. If a patient fails to take NAMENDA for several days, dosing may need to be resumed at lower doses and retitrated as described above.
Do not mix NAMENDA oral solution with any other liquid. NAMENDA is administered with a dosing device that comes with the drug and consists of a syringe, syringe adaptor cap, tubing and other supplies a patient needs to administer the drug. The supplied syringe should be used to withdraw the correct volume of oral solution and the oral solution should be slowly squirted into the corner of the patient's mouth.
Special Populations Renal ImpairmentA target dose of 5 mg (2.5 mL) twice daily is recommended in patients with severe renal impairment (creatinine clearance of 5 – 29 mL/min based on the Cockcroft-Gault equation).
Hepatic ImpairmentNAMENDA should be administered with caution to patients with severe hepatic impairment.
NAMENDA was evaluated in eight double-blind placebo-controlled trials involving a total of 1862 dementia (Alzheimer's disease, vascular dementia) patients (940 patients treated with NAMENDA and 922 patients treated with placebo) for a treatment period up to 28 weeks.
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.
Adverse Events Leading to DiscontinuationIn placebo-controlled trials in which dementia patients received doses of NAMENDA up to 20 mg/day, the likelihood of discontinuation because of an adverse reaction was the same in the NAMENDA group (10.1%) as in the placebo group (11.5%). No individual adverse reaction was associated with the discontinuation of treatment in 1% or more of NAMENDA-treated patients and at a rate greater than placebo.
Most Common Adverse ReactionsIn double-blind placebo-controlled trials involving dementia patients, the most common adverse reactions (incidence ≥ 5% and higher than placebo) in patients treated with NAMENDA were dizziness, headache, confusion and constipation. Table 1 lists all adverse reactions that occurred in at least 2% of patients treated with NAMENDA and at an incidence greater than placebo.
Table 1: Adverse Reactions Reported in Controlled
Clinical Trials in at Least 2% of Patients Receiving NAMENDA and at a Higher
Frequency than Placebo-treated Patients
| Adverse Reaction | Placebo (N = 922) % |
NAMENDA (N = 940) % |
| Body as a Whole | ||
| Fatigue | 1 | 2 |
| Pain | 1 | 3 |
| Cardiovascular System | ||
| Hypertension | 2 | 4 |
| Central and Peripheral Nervous System | ||
| Dizziness | 5 | 7 |
| Headache | 3 | 6 |
| Gastrointestinal System | ||
| Constipation | 3 | 5 |
| Vomiting | 2 | 3 |
| Musculoskeletal System | ||
| Back pain | 2 | 3 |
| Psychiatric Disorders | ||
| Confusion | 5 | 6 |
| Somnolence | 2 | 3 |
| Hallucination | 2 | 3 |
| Respiratory System | ||
| Coughing | 3 | 4 |
| Dyspnea | 1 | 2 |
The overall profile of adverse reactions and the incidence rates for individual adverse reactions in the subpopulation of patients with moderate to severe Alzheimer's disease were not different from the profile and incidence rates described above for the overall dementia population.
SeizuresNAMENDA has not been systematically evaluated in patients with a seizure disorder. In clinical trials of NAMENDA, seizures occurred in 0.2% of patients treated with NAMENDA and 0.5% of patients treated with placebo.
Postmarketing ExperienceThe following adverse reactions have been identified during post-approval use of memantine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These reactions include:
Blood and Lymphatic System Disorders -agranulocytosis, leukopenia (including neutropenia), pancytopenia, thrombocytopenia, thrombotic thrombocytopenic purpura.
Cardiac Disorders -cardiac failure congestive.
Gastrointestinal Disorders -pancreatitis.
Hepatobiliary Disorders – hepatitis.
Psychiatric Disorders -suicidal ideation.
Renal and Urinary Disorders -acute renal failure (including increased creatinine and renal insufficiency).
Skin Disorders -Stevens Johnson syndrome.
DRUG INTERACTIONS Drugs That Make The Urine AlkalineThe clearance of memantine was reduced by about 80% under alkaline urine conditions at pH 8. Therefore, alterations of urine pH towards the alkaline condition may lead to an accumulation of the drug with a possible increase in adverse effects. Urine pH is altered by diet, drugs (e.g. carbonic anhydrase inhibitors, sodium bicarbonate) and clinical state of the patient (e.g. renal tubular acidosis or severe infections of the urinary tract). Hence, memantine should be used with caution under these conditions.
Use With Other N-methyl-D-aspartate (NMDA) AntagonistsThe combined use of NAMENDA with other NMDA antagonists (amantadine, ketamine, and dextromethorphan) has not been systematically evaluated and such use should be approached with caution.
