Memantine Drug Information

Memantine hydrochloride tablets are indicated for the treatment of moderate to severe dementia of the Alzheimer’s type. Memantine hydrochloride tablets are an N-methyl-D-aspartate (NMDA) receptor antagonist indicated for the treatment of moderate to severe dementia of the Alzheimer’s type.

The recommended starting dose of memantine hydrochloride tablets is 5 mg once daily. The dose should be increased in 5 mg increments to 10 mg/day (5 mg twice daily), 15 mg/day (5 mg and 10 mg as separate doses), and 20 mg/day (10 mg 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.

Memantine hydrochloride tablets can be taken with or without food. If a patient misses a single dose of memantine hydrochloride tablets, that patient should not double up on the next dose. The next dose should be taken as scheduled.

If a patient fails to take memantine hydrochloride tablets for several days, dosing may need to be resumed at lower doses and retitrated as described above. Specific Populations Renal Impairment A target dose of 5 mg twice daily is recommended in patients with severe renal impairment (creatinine clearance of 5 to 29 mL/min based on the Cockcroft-Gault equation). Hepatic Impairment Memantine hydrochloride tablets should be administered with caution to patients with severe hepatic impairment . May be taken with or without food. Initial dose is 5 mg once daily.

Increase dose in 5 mg increments to a maintenance dose of 10 mg twice daily. A minimum of 1 week of treatment with the previous dose should be observed before increasing the dose. Severe renal impairment: recommended dose is 5 mg twice daily.

Clinical Trials Experience Memantine hydrochloride 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 memantine hydrochloride 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 Discontinuation In placebo-controlled trials in which dementia patients received doses of memantine hydrochloride up to 20 mg/day, the likelihood of discontinuation because of an adverse reaction was the same in the memantine hydrochloride 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 memantine hydrochloride-treated patients and at a rate greater than placebo.

Most Common Adverse Reactions In double-blind placebo-controlled trials involving dementia patients, the most common adverse reactions (incidence ≥ 5% and higher than placebo) in patients treated with memantine hydrochloride were dizziness, headache, confusion and constipation. Table 1 lists all adverse reactions that occurred in at least 2% of patients treated with memantine hydrochloride and at an incidence greater than placebo. Table 1: Adverse Reactions Reported in Controlled Clinical Trials in at Least 2% of Patients Receiving Memantine Hydrochloride and at a Higher Frequency than Placebo-treated Patients Adverse Reaction Placebo (N = 922) % Memantine Hydrochloride (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.

Seizures Memantine hydrochloride has not been systematically evaluated in patients with a seizure disorder. In clinical trials of memantine hydrochloride, seizures occurred in 0.2% of patients treated with memantine hydrochloride and 0.5% of patients treated with placebo.

Postmarketing Experience

The 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.

Drugs that Make the Urine Alkaline

The 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) Antagonists

The combined use of memantine hydrochloride with other NMDA antagonists (amantadine, ketamine, and dextromethorphan) has not been systematically evaluated and such use should be approached with caution.

Pregnancy Risk Summary There are no adequate data on the developmental risk associated with the use of memantine hydrochloride in pregnant women. Adverse developmental effects (decreased body weight, and skeletal ossification) were observed in the offspring of rats administered memantine during pregnancy at doses associated with minimal maternal toxicity. These doses are higher than those used in humans at the maximum recommended daily dose of memantine hydrochloride . In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

The background risk of major birth defects and miscarriage for the indicated population is unknown. Data Animal Data Oral administration of memantine (0, 2, 6, or 18 mg/kg/day) to rats during the period of organogenesis resulted in decreased skeletal ossification in fetuses at the highest dose tested. The higher no-effect dose for adverse developmental effects (6 mg/kg) is 3 times the maximum recommended human daily dose (MRHD) of memantine hydrochloride (20 mg) on a body surface area (mg/m 2 ) basis.

Oral administration of memantine to rabbits (0, 3, 10, or 30 mg/kg/day) during the period of organogenesis resulted in no adverse developmental effects. The highest dose tested is approximately 30 times the MRHD of memantine hydrochloride on a mg/m 2 basis. In rats, memantine (0, 2, 6, or 18 mg/kg/day) was administered orally prior to and throughout mating and, in females, through the period of organogenesis or continuing throughout lactation to weaning.

Decreased skeletal ossification in fetuses and decreased body weight in pups were observed at the highest dose tested. The higher no-effect dose for adverse developmental effects (6 mg/kg/day) is 3 times the MRHD of memantine hydrochloride on a mg/m 2 basis. Oral administration of memantine (0, 2, 6, or 18 mg/kg/day) to rats from late gestation throughout lactation to weaning, resulted in decreased pup weights at the highest dose tested.

The higher no-effect dose (6 mg/kg/day) is approximately 3 times the MRHD of memantine hydrochloride on a mg/m 2 basis.

Pediatric Use Safety and effectiveness in pediatric patients have not been established. Memantine failed to demonstrate efficacy in two 12-week controlled clinical studies of 578 pediatric patients aged 6 to 12 years with autism spectrum disorders (ASD), including autism, Asperger’s disorder and Pervasive Development Disorder - Not Otherwise Specified (PDD-NOS). Memantine has not been studied in pediatric patients under 6 years of age or over 12 years of age. Memantine treatment was initiated at 3 mg/day and the dose was escalated to the target dose (weight-based) by week 6. Oral doses of memantine 3 mg, 6 mg, 9 mg, or 15 mg extended-release capsules were administered once daily to patients with weights < 20 kg, 20 kg to 39 kg, 40 kg to 59 kg and ≥ 60 kg, respectively.

In a randomized, 12-week double-blind, placebo-controlled parallel study (Study A) in patients with autism, there was no statistically significant difference in the Social Responsiveness Scale (SRS) total raw score between patients randomized to memantine (n=54) and those randomized to placebo (n=53). In a 12-week responder-enriched randomized withdrawal study (Study B) in 471 patients with ASD, there was no statistically significant difference in the loss of therapeutic response rates between patients randomized to remain on full-dose memantine (n=153) and those randomized to switch to placebo (n=158). The overall risk profile of memantine in pediatric patients was generally consistent with the known risk profile in adults . In Study A, the adverse reactions in the memantine group (n=56) that were reported in at least 5% of patients and at least twice the frequency of the placebo group (N=58) are listed in Table 2: Table 2: Study A Commonly Reported Adverse Reactions with a Frequency ≥ 5% and Twice That of Placebo Adverse Reaction Memantine N=56 Placebo N=58 Cough 8.9% 3.4% Influenza 7.1% 3.4% Rhinorrhea 5.4% 0% Agitation 5.4% 1.7% Discontinuations due to adverse reactions a Aggression 3.6% 1.7% Irritability 1.8% 3.4% a Reported adverse reactions leading to discontinuation in more than one patient in either treatment group. The adverse reactions that were reported in at least 5% of patients in the 12 to 48 week open-label study to identify responders to enroll in Study B are listed in Table 3: Table 3: 12 to 48 Week Open Label Lead-In study to Study B Commonly Reported Adverse Reactions with a Frequency ≥ 5% Adverse Reaction Memantine N=903 Headache 8.0% Nasopharyngitis 6.3% Pyrexia 5.8% Irritability 5.4% Discontinuations due to adverse reactions a Irritability 1.2% Aggression 1.0% a At least 1% incidence of adverse reactions leading to premature discontinuation. In the randomized withdrawal study (Study B), the adverse reaction in patients randomized to placebo (n=160) and reported in at least 5% of patients and at twice the frequency of the full-dose memantine treatment group (n=157) was irritability (5.0% vs 2.5%). Juvenile Animal Study In a study in which memantine (0, 15, 30 or 45 mg/kg/day) was orally administered to rats during the juvenile period of development (postnatal days 14 through 70), delays in sexual maturation were noted in males and females at all but the lowest dose tested, and body weight was reduced at the high dose.

In rats orally administered memantine as a single dose (PND 14) or three daily doses (PND 14 to 16), neuronal lesions were observed in several areas of the brain at all but the lowest dose tested. Adverse neurobehavioral effects (decreased auditory startle habituation) were observed at the high dose. The no-effect dose for developmental toxicity was the lowest dose tested (15 mg/kg/day). In a second juvenile animal study, memantine (0, 1, 3, 8, 15, 30, and 45 mg/kg/day) was orally administered to male and female rats beginning on PND 7 and continuing for various periods during postnatal development.

Because of early memantine-related mortality, the 30 and 45 mg/kg/day groups were terminated without further evaluation. Apoptosis or neuronal degeneration in the brain was observed on PNDs 8 to 17 at a dose of 15 mg/kg/day. The no-effect dose for apoptosis and neuronal degeneration was 8 mg/kg/day.

In animals in which memantine (0, 1, 3, 8, or 15 mg/kg/day) was orally administered on PNDs 7 to 70, adverse neurobehavioral effects (increased locomotor motor activity, increased auditory startle response and decreased habituation, and deficit in learning and memory) were observed at all but the lowest dose tested. Effects on auditory startle persisted after drug discontinuation. The no-effect dose for developmental toxicity was the lowest dose tested (1 mg/kg/day).

Memantine hydrochloride tablets are contraindicated in patients with known hypersensitivity to memantine hydrochloride or to any excipients used in the formulation. Memantine hydrochloride tablets are contraindicated in patients with known hypersensitivity to memantine hydrochloride or to any excipients used in the formulation.

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 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.