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Overdose

Memantine hydrochloride and donepezil hydrochloride are the two active ingredients of NAMZARIC. No specific antidote for memantine hydrochloride overdose is known; however, elimination of memantine can be increased by acidification of the urine. Tertiary anticholinergics such as atropine may be used as an antidote for donepezil hydrochloride overdose. In managing cases of overdose, consider the possibility of multiple drug involvement. In case of overdose, call Poison Control Center at 1-800- 222-1222 for the latest recommendation. In general, supportive measures should be utilized, and treatment should be symptomatic.

Signs and symptoms most often accompanying overdosage with other formulations of memantine 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 an individual who took memantine in conjunction with unspecified antidiabetic medications. This person experienced coma, diplopia, and agitation, but subsequently recovered.

One patient participating in a memantine hydrochloride extended-release clinical trial unintentionally took 112 mg of memantine hydrochloride extended-release daily for 31 days and experienced elevated serum uric acid, elevated serum alkaline phosphatase, and low platelet count.

No fatalities have been noted with overdoses of memantine alone. A fatal outcome has very rarely been reported when memantine has been ingested as part of overdosing with multiple drugs; in those instances, the relationship between memantine and a fatal outcome has been unclear.

Overdosage with cholinesterase inhibitors can result in cholinergic crisis characterized by severe nausea, vomiting, salivation, sweating, bradycardia, hypotension, respiratory depression, collapse, and convulsions. Increasing muscle weakness is a possibility and may result in death if respiratory muscles are involved. Tertiary anticholinergics such as atropine may be used as an antidote for donepezil hydrochloride overdosage. Intravenous atropine sulfate titrated to effect is recommended: an initial dose of 1.0 to 2.0 mg IV with subsequent doses based upon clinical response. Atypical responses in blood pressure and heart rate have been reported with other cholinomimetics when coadministered with quaternary anticholinergics such as glycopyrrolate. It is not known whether donepezil hydrochloride and/or its metabolites can be removed by dialysis (hemodialysis, peritoneal dialysis, or hemofiltration).

Dose-related signs of toxicity in animals included reduced spontaneous movement, prone position, staggering gait, lacrimation, clonic convulsions, depressed respiration, salivation, miosis, tremors, fasciculation, and lower body surface temperature.

Contraindications

NAMZARIC is contraindicated in patients with known hypersensitivity to memantine hydrochloride, donepezil hydrochloride, piperidine derivatives, or to any excipients used in the formulation.

Undesirable effects

The following serious adverse reactions are discussed below and elsewhere in the labeling.

• Cardiovascular Conditions
• Peptic Ulcer Disease and Gastrointestinal Bleeding
• Nausea and Vomiting
• Genitourinary Conditions
• Seizures
• Pulmonary Conditions

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 practice.

Memantine hydrochloride extended-release was evaluated in a double-blind, placebo-controlled trial in 676 patients with moderate to severe dementia of the Alzheimer's type (341 patients treated with memantine 28 mg/day dose and 335 patients treated with placebo) for a treatment period up to 24 weeks. Of the patients randomized, 236 treated with memantine 28 mg/day and 227 treated with placebo were on a stable dose of donepezil for 3 months prior to screening.

In the placebo-controlled clinical trial of memantine hydrochloride extended-release, the proportion of patients in the memantine hydrochloride extended-release 28 mg/day dose group and in the placebo group who discontinued treatment due to adverse reactions was 10% and 6%, respectively. The most common adverse reaction in the memantine hydrochloride extended-release treated group that led to treatment discontinuation was dizziness, at a rate of 1.5%.

The most common adverse reactions with memantine hydrochloride extended-release in patients with moderate to severe Alzheimer's disease, defined as those occurring at a frequency of at least 5% in the memantine hydrochloride extended-release group and at a higher frequency than placebo, were headache, diarrhea, and dizziness.

Table 1 lists adverse reactions that occurred at an incidence of ≥ 2% in the memantine hydrochloride extended-release treated group and occurred at a rate greater than placebo.

Table 1: Adverse reactions with memantine hydrochloride extended-release in patients with moderate to severe Alzheimer's disease

In controlled clinical trials of donepezil hydrochloride, the rate of discontinuation due to adverse reactions for patients treated with donepezil hydrochloride was approximately 12%, compared to 7% for patients treated with placebo. The most common adverse reactions leading to discontinuation, defined as those occurring in at least 2% of donepezil hydrochloride patients and at twice or more the incidence seen with placebo, were anorexia (2%), nausea (2%), diarrhea (2%) and urinary tract infection (2%).

The most common adverse reactions reported with donepezil hydrochloride in controlled clinical trials in patients with severe Alzheimer's disease, defined as those occurring at a frequency of at least 5% in the donepezil hydrochloride group and at twice or more the placebo rate, were diarrhea, anorexia, vomiting, nausea, and ecchymosis. The most common adverse reactions reported with donepezil hydrochloride in controlled clinical trials in patients with mild to moderate Alzheimer's disease were insomnia, muscle cramp, and fatigue.

Table 2 lists adverse reactions that occurred at an incidence of ≥ 2% in the donepezil hydrochloride group and at a rate greater than placebo in controlled trials in patients with severe Alzheimer's disease.

Table 2: Adverse reactions with donepezil hydrochloride in patients with severe Alzheimer's disease

The following adverse reactions have been identified during post-approval use of memantine hydrochloride and donepezil hydrochloride. 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.

Acute renal failure, agranulocytosis, cardiac failure congestive, hepatitis, leukopenia (including neutropenia), pancreatitis, pancytopenia, Stevens-Johnson syndrome, suicidal ideation, thrombocytopenia, and thrombotic thrombocytopenic purpura.

Abdominal pain, agitation, cholecystitis, confusion, convulsions, hallucinations, heart block (all types), hemolytic anemia, hepatitis, hyponatremia, neuroleptic malignant syndrome, pancreatitis, and rash.

Therapeutic indications

NAMZARIC is indicated for the treatment of moderate to severe dementia of the Alzheimer's type in patients stabilized on 10 mg of donepezil hydrochloride once daily.

Pharmacokinetic properties

NAMZARIC was bioequivalent to co-administration of individual memantine hydrochloride extendedrelease and donepezil hydrochloride.

Exposure (AUC and Cmax) of memantine and donepezil following NAMZARIC administration in the fed or fasted state was similar. Further, exposure of memantine and donepezil following NAMZARIC administration as intact capsule or capsule contents sprinkled on applesauce was similar in healthy subjects.

Memantine is well absorbed after oral administration and has linear pharmacokinetics over the therapeutic dose range. It is excreted predominantly unchanged in urine and has a terminal elimination half-life of about 60-80 hours. In a study comparing 28 mg once-daily memantine hydrochloride extended-release to 10 mg twice-daily memantine hydrochloride, Cmax and AUC0-24 values were 48% and 33% higher for the memantine hydrochloride extended-release dosage regimen, respectively.

After multiple dose administration of memantine hydrochloride extended-release, memantine peak concentrations occur around 9-12 hours postdose. There is no difference in the absorption of memantine hydrochloride extended-release when the capsule is taken intact or when the contents are sprinkled on applesauce.

After single-dose administration, there is no difference in memantine exposure, based on Cmax or AUC, for memantine hydrochloride extended-release when the drug product is administered with food or on an empty stomach. However, peak plasma concentrations are achieved about 18 hours after administration with food versus approximately 25 hours after administration on an empty stomach.

The mean volume of distribution of memantine is 9-11 L/kg and the plasma protein binding is low (45%).

Memantine undergoes partial hepatic metabolism. The hepatic microsomal CYP450 enzyme system does not play a significant role in the metabolism of memantine.

Memantine is excreted predominantly in the urine, unchanged, and has a terminal elimination half-life of about 60-80 hours. About 48% of administered drug is excreted unchanged in urine; 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 N-glucuronide conjugate. Renal clearance involves active tubular secretion moderated by pH dependent tubular reabsorption.

Name of the medicinal product

Qualitative and quantitative composition

Special warnings and precautions for use

Included as part of the PRECAUTIONS section.

Donepezil hydrochloride, an active ingredient in NAMZARIC, as a cholinesterase inhibitor, is likely to exaggerate succinylcholine-type muscle relaxation during anesthesia.

Because of their pharmacological action, cholinesterase inhibitors may have vagotonic effects on the sinoatrial and atrioventricular nodes. This effect may manifest as bradycardia or heart block in patients both with and without known underlying cardiac conduction abnormalities. Syncopal episodes have been reported in association with the use of donepezil hydrochloride, an active ingredient in NAMZARIC.

Through their primary action, cholinesterase inhibitors may be expected to increase gastric acid secretion due to increased cholinergic activity. Clinical studies of donepezil hydrochloride in a dose of 5 mg/day to 10 mg/day have shown no increase, relative to placebo, in the incidence of either peptic ulcer disease or gastrointestinal bleeding. Patients treated with NAMZARIC should be monitored closely for symptoms of active or occult gastrointestinal bleeding, especially those at increased risk for developing ulcers, e.g., those with a history of ulcer disease or those receiving concurrent nonsteroidal anti-inflammatory drugs (NSAIDs).

Donepezil hydrochloride, an active ingredient in NAMZARIC, when initiated, as a predictable consequence of its pharmacological properties, has been shown to produce diarrhea, nausea, and vomiting. Although in most cases, these effects have been mild and transient, sometimes lasting one to three weeks, and have resolved during continued use of donepezil hydrochloride, patients should be observed closely at the initiation of treatment.

Although not observed in clinical trials of donepezil hydrochloride, an active ingredient in NAMZARIC, cholinomimetics may cause bladder outflow obstruction.

Conditions that raise urine pH may decrease the urinary elimination of memantine, an active ingredient in NAMZARIC, resulting in increased plasma levels of memantine.

Cholinomimetics, including donepezil hydrochloride, an active ingredient in NAMZARIC, are believed to have some potential to cause generalized convulsions. However, seizure activity also may be a manifestation of Alzheimer's disease.

Because of their cholinomimetic actions, cholinesterase inhibitors should be prescribed with care to patients with a history of asthma or obstructive pulmonary disease.

Advise the patient to read the FDA-approved patient labeling (PATIENT INFORMATION).

• Instruct patients and caregivers to take NAMZARIC only once daily in the evening, as prescribed.
• If a patient misses a single dose of NAMZARIC, that patient should not double up on the next dose. The next dose should be taken as scheduled.
• Instruct patients and caregivers that NAMZARIC capsules should be swallowed whole. Alternatively, NAMZARIC capsules may be opened and sprinkled on applesauce and the entire contents should be consumed. The capsules should not be divided, chewed, or crushed. Warn patients and caregivers not to use any capsules of NAMZARIC that are damaged or show signs of tampering.

Advise patients and caregivers that NAMZARIC may cause headache, diarrhea, dizziness, anorexia, vomiting, nausea, and ecchymosis.

There was no evidence of carcinogenicity in a 113-week oral study in mice at doses up to 40 mg/kg/day (7 times the dose of memantine at the maximum recommended human dose [MRHD] of NAMZARIC [28 mg/10 mg] 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 (14 and 7 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 (6 times the dose of memantine at the MRHD of NAMZARIC 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.

No evidence of carcinogenic potential was obtained in an 88-week carcinogenicity study of donepezil conducted in mice at oral doses up to 180 mg/kg/day (approximately 90 times the dose of donepezil at the MRHD of NAMZARIC on a mg/m² basis), or in a 104-week carcinogenicity study in rats at oral doses up to 30 mg/kg/day (approximately 30 times the dose of donepezil at the MRHD of NAMZARIC on a mg/m² basis).

Donepezil was negative in a battery of genotoxicity assays (in vitro bacterial reverse mutation, in vitro mouse lymphoma tk, in vitro chromosomal aberration, and in vivo mouse micronucleus).

Donepezil had no effect on fertility in rats at oral doses up to 10 mg/kg/day (approximately 10 times the dose of donepezil at the MRHD of NAMZARIC on a mg/m² basis) when administered to males and females prior to and during mating and continuing in females through implantation.

There are no adequate data on the developmental risk associated with the use of NAMZARIC or its active ingredients (memantine hydrochloride and donepezil hydrochloride) in pregnant women. Adverse developmental effects (mortality and decreased body weight and skeletal ossification) were observed in the offspring of rats administered memantine or donepezil during pregnancy at doses associated with minimal maternal toxicity. These doses are higher than those used in humans at the recommended daily dose of NAMZARIC.

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown.

Animal Data

Memantine Hydrochloride

Oral administration of memantine (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 2 times the dose of memantine at the recommended human daily dose (RHD) of NAMZARIC (28 mg memantine/10 mg donepezil) on a body surface area (mg/m²) basis.

Oral administration of memantine to rabbits (3, 10, or 30 mg/kg/day) during the period of organogenesis resulted in no adverse developmental effects. The highest dose tested is approximately 20 times the dose of memantine at the RHD of NAMZARIC on a mg/m basis. In rats, memantine (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 2 times the dose of memantine at the RHD of NAMZARIC on a mg/m² basis.

Oral administration of memantine (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 2 times the dose of memantine at the RHD of NAMZARIC on a mg/m² basis.

Donepezil Hydrochloride

Oral administration of donepezil to rats and rabbits during the period of organogenesis resulted in no adverse developmental effects. The highest doses (16 and 10 mg/kg/day, respectively) were approximately 15 and 7 times, respectively, the dose of donepezil at the RHD of NAMZARIC on a mg/m² basis.

Oral administration of donepezil (1, 3, or 10 mg/kg/day) to rats during late gestation and throughout lactation to weaning resulted in an increase in stillbirths and offspring mortality at the highest dose tested. The higher no-effect dose (3 mg/kg/day) is approximately 3 times the dose of donepezil at the RHD of NAMZARIC on a mg/m² basis.

There are no data on the presence of memantine or donepezil in human milk, the effects on the breastfed infant, or the effects of NAMZARIC or its metabolites on milk production.

The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for NAMZARIC and any potential adverse effects on the breastfed infant from NAMZARIC or from the underlying maternal condition.

Safety and effectiveness of NAMZARIC in pediatric patients have not been established.

Memantine failed to demonstrate efficacy in two 12-week controlled clinical studies of 578 pediatric patients aged 6-12 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 (weightbased) by week 6. Oral doses of memantine 3, 6, 9, or 15 mg extended-release capsules were administered once daily to patients with weights < 20 kg, 20-39 kg, 40-59 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 3:

Table 3: Study A Commonly Reported Adverse Reactions With a Frequency ≥ 5% and Twice That of Placebo

The adverse reactions that were reported in at least 5% of patients in the 12-48 week open-label study to identify responders to enroll in Study B are listed in Table 4:

Table 4: 12-48 Week Open Label Lead-In study to Study B Commonly Reported Adverse Reactions with a Frequency ≥ 5%

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%).

In a juvenile animal study, male and female juvenile rats were administered memantine (15, 30, and 45 mg/kg/day) starting on postnatal day (PND) 14 through PND 70. Body weights were reduced at 45 mg/kg/day. Delays in sexual maturation were noted in male and female rats at doses ≥ 30 mg/kg/day. Memantine induced neuronal lesions in several areas of the brain on PND 15 and 17 at doses ≥ 30 mg/kg/day. Behavioral toxicity (decrease percent of auditory startle habituation) was noted for animals in the 45 mg/kg/day dose group. The 15 mg/kg/day dose was considered the No-Observed- Adverse-Effect-Level (NOAEL) for this study.

In a second juvenile rat toxicity study, male and female juvenile rats were administered memantine (1, 3, 8, 15, 30, and 45 mg/kg/day) starting on postnatal day (PND) 7 through PND 70. Due to early memantinerelated mortality, the 30 and 45 mg/kg/day dose groups were terminated without further evaluation. Memantine induced apoptosis or neuronal degeneration in several areas of the brain on PND 8, 10, and 17 at a dose of 15 mg/kg/day. The NOAEL for apoptosis and neuronal degeneration was 8 mg/kg/day. Behavioral toxicity (effects on motor activity, auditory startle habituation, and learning and memory) was noted at doses ≥ 3 mg/kg/day during treatment, but was not seen after drug discontinuation. Therefore, the 1 mg/kg/day dose was considered the NOAEL for the neurobehavioral effect in this study.

The majority of people with Alzheimer's disease are 65 years and older. In the clinical study of memantine hydrochloride extended-release, the mean age of patients was approximately 77 years; over 91% of patients were 65 years of age and older, 67% were 75 years of age and older, and 14% were 85 years of age and older. The efficacy and safety data presented in the clinical trials section were obtained from these patients. There were no clinically meaningful differences in most adverse events reported by patients ≥ 65 years old and < 65 years old.

The mean age of patients enrolled in the clinical studies with donepezil hydrochloride was 73 years; 80% of these patients were between 65 and 84 years of age, and 49% of patients 75 years of age and older. The efficacy and safety data presented in the clinical trials section were obtained from these patients. There were no clinically significant differences in most adverse events reported by patients ≥ 65 years old and < 65 years old.

A dosage reduction is recommended in patients with severe renal impairment. No dosage adjustment is needed in patients with mild or moderate renal impairment.

No dosage adjustment is needed in patients with mild or moderate hepatic impairment. NAMZARIC has not been studied in patients with severe hepatic impairment.

Dosage (Posology) and method of administration

The recommended dose of NAMZARIC is 28 mg/10 mg once daily.

For patients stabilized on donepezil hydrochloride 10 mg and not currently on memantine hydrochloride, the recommended starting dose of NAMZARIC is 7 mg/10 mg, taken once a day in the evening. The dose should be increased in 7 mg increments of the memantine hydrochloride component to the recommended maintenance dose of 28 mg/10 mg once daily. The minimum recommended interval between dose increases is one week. The dose should only be increased if the previous dose has been well tolerated. The maximum dose is 28 mg/10 mg once daily.

Patients stabilized on memantine hydrochloride (10 mg twice daily or 28 mg extended-release once daily) and donepezil hydrochloride 10 mg once daily can be switched to NAMZARIC 28 mg/10 mg, taken once a day in the evening. Patients should start NAMZARIC the day following the last dose of memantine hydrochloride and donepezil hydrochloride administered separately.

If a patient misses a single dose of NAMZARIC, the next dose should be taken as scheduled, without doubling up the dose.

NAMZARIC can be taken with or without food. NAMZARIC capsules can be taken intact or may be opened, sprinkled on applesauce, and swallowed without chewing. The entire contents of each NAMZARIC capsule should be consumed; the dose should not be divided.

Except when opened and sprinkled on applesauce, as described above, NAMZARIC capsules should be swallowed whole. NAMZARIC capsules should not be divided, chewed, or crushed.

For patients with severe renal impairment (creatinine clearance 5-29 mL/min, based on the Cockcroft- Gault equation) stabilized on donepezil hydrochloride 10 mg once daily and not currently on memantine hydrochloride, the recommended starting dose of NAMZARIC is 7 mg/10 mg taken once a day in the evening. The dose should be increased to the recommended maintenance dose of 14 mg/10 mg once daily in the evening after a minimum of one week.

Patients with severe renal impairment, stabilized on memantine hydrochloride (5 mg twice daily or 14 mg extended-release once daily) and donepezil hydrochloride 10 mg once daily, can be switched to NAMZARIC 14 mg/10 mg, taken once daily in the evening.