Memantine and donepezil

Uses

Memantine and donepezil hydrochlorides extended-release capsules are a combination of memantine hydrochloride, an NMDA receptor antagonist, and donepezil hydrochloride, an acetylcholinesterase inhibitor, used for the treatment of moderate to severe dementia of the Alzheimer’s type in patients stabilized on 10 mg of donepezil hydrochloride once daily.
Pediatric Use: Safety and effectiveness of memantine and donepezil hydrochlorides extended-release in pediatric patients have not been established.

Renal Impairment: No dosage adjustment is needed in patients with mild or moderate renal impairment.

Hepatic Impairment: No dosage adjustment is needed in patients with mild or moderate hepatic impairment. Memantine and donepezil hydrochlorides extended-release has not been studied in patients with severe hepatic impairment

Memantine and donepezil is also used to associated treatment for these conditions: Alzheimer's Disease (AD), Dementia due to Parkinson's disease, Dementia of the Alzheimer's Type, Dementia, Vascular, Diffuse Lewy Body Disease, Mild Dementia of the Alzheimer's Type, Moderate Alzheimer's Type Dementia, Severe Alzheimer's Type DementiaAlzheimer's Disease (AD), Moderate-to-severe Alzheimer's Disease, Mild Vascular dementia, Moderate Alzheimer's Type Dementia, Moderate Vascular dementia, Severe Alzheimer's Type Dementia

How Memantine and donepezil works

The commonly accepted cholinergic hypothesis proposes that a portion of the cognitive and behavioral decline associated with Alzheimer's are the result of decreased cholinergic transmission in the central nervous system. Donepezil selectively and reversibly inhibits the acetylcholinesterase enzyme, which normally breaks down acetylcholine. The main pharmacological actions of this drug are believed to occur as the result of this enzyme inhibition, enhancing cholinergic transmission, which relieves the symptoms of Alzheimer's dementia. In addition to the above, other mechanisms of action of donepezil are possible, including the opposition of glutamate-induced excitatory transmission via downregulation of NMDA receptors and the regulation of amyloid proteins, which have demonstrated significant effects on the disease process of Alzheimer's. Other possible targets for donepezil may also include the inhibition various inflammatory signaling pathways, exerting neuroprotective effects.

Continuous activation of the N-methyl-D-aspartate (NMDA) receptors in the central nervous system 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 . The pharmacological effect of memantine likely occurs via the drug's behavior as an uncompetitive (open-channel) NMDA receptor antagonist, preventing glutamate action on this receptor. Memantine has a preference for the NMDA receptor-operated cation channels. Despite these antagonist effects, memantine has not been proven to prevent or retard the neurodegeneration seen in patients diagnosed with Alzheimer’s disease .

Dosage

Memantine and donepezil dosage

For patients on donepezil hydrochloride 10 mg only, the recommended starting dose of memantine and donepezil hydrochlorides extended-release capsules is 7 mg/10 mg, taken once daily in the evening. The dose should be increased in 7 mg increments to the recommended maintenance dose of 28 mg/10 mg. The minimum recommended interval between dose increases is one week.

Patients 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 memantine and donepezil hydrochlorides extended- release capsules 28 mg/10 mg, taken once daily in the evening.

Memantine and donepezil hydrochlorides extended- release capsules can be taken with or without food, whole or sprinkled on applesauce; do not divide, chew, or crush. Severe renal impairment: the recommended maintenance dose for memantine and donepezil hydrochlorides extended-release capsules is 14 mg/10 mg once daily in the evening.

Side Effects

The most common adverse reactions, occurring at a frequency of at least 5% and greater than placebo with memantine hydrochloride extended-release 28 mg/day, were headache, diarrhea, and dizziness. The most common adverse reactions occurring at a frequency of at least 5% in patients receiving donepezil and at twice or more the placebo rate, include diarrhea, anorexia, vomiting, nausea, and ecchymosis.

Toxicity

LD50

The rat oral LD50 of donepezil is 32.6 mg/kg.

Overdose information

Signs and symptoms of overdose with cholinesterase inhibitors such as donepezil can include severe nausea and vomiting, bradycardia, hypotension, perspiration, seizures, muscle weakness respiratory depression, and collapse. Significant muscle weakness may result in death if the respiratory muscles are affected by donepezil overdose. To manage an overdose, anticholinergics can be employed as antidotes. Atropine at intravenous doses of 1.0 - 2.0 mg can be administered and titrated according to the clinical response. Consult the local poison control center for the most updated guidelines on the management of a donepezil overdose. Whether donepezil can be removed from the body with dialysis is unknown at this time.

LD50

Oral LD50, mouse 437-498 mg/kg Oral LD50, rat 328-370 mg/kg

Carcinogenesis, Mutagenesis, Impairment of Fertility

No evidence of carcinogenicity was seen in mouse and rat models administered memantine at doses equivalent to supratherapeutic human doses . Additionally, no genotoxic potential was noted when a battery of assays was performed. No effects on fertility or reproductive performance were noted in rats given to 18 mg/kg/day (equivalent to 9 times the maximum recommended human dose) orally from 14 days preceding mating through gestation and lactation in females, or for 60 preceding mating activity in males animals .

Use in pregnancy

This drug is considered a pregnancy category B drug, meaning no sufficiently controlled and adequate studies of memantine in pregnant women have been performed. This drug should be taken during pregnancy only if the potential benefit justifies the possible fetal risk .

Use in nursing

It is unknown whether memantine is excreted in human milk. Due to that fact that many drugs are found excreted in human milk, caution should be observed when this drug is taken by a nursing mother .

Precaution

• Memantine and donepezil hydrochlorides extended-release is likely to exaggerate succinylcholine-type muscle relaxation during anesthesia.
• Memantine and donepezil hydrochlorides extended-release may have vagotonic effects on the sinoatrial and atrioventricular nodes manifesting as bradycardia or heart block.
• Monitor patients for symptoms of active or occult gastrointestinal bleeding, especially those at increased risk for developing ulcers.
• Memantine and donepezil hydrochlorides extended-release can cause diarrhea, nausea, and vomiting.
• Memantine and donepezil hydrochlorides extended-release may cause bladder outflow obstructions.
• Conditions that raise urine pH may decrease the urinary elimination of memantine, resulting in increased plasma levels of memantine.

Interaction

Combined use with NMDA antagonists: use with caution. Memantine and donepezil hydrochlorides extended-release may interfere with anticholinergic medications. Concomitant administration of succinylcholine, similar neuromuscular blocking agents, or cholinergic agonists may lead to synergistic effect.

Volume of Distribution

The volume of distribution of donepezil is 11.8 ± 1.7 L/kg for a 5-mg dose and 11.6 ± 1.91 L/kg for a 10-mg dose. It is largely distributed in the extravascular compartments. Donepezil crosses the blood-brain barrier and cerebrospinal fluid concentrations at the above doses have been measured at 15.7%. The volume of distribution at steady-state according to the FDA label for donepezil ranges from 12 - 16 L/kg.

The mean volume of distribution of memantine is 9-11 L/kg .

Elimination Route

Donepezil is slowly absorbed via the gastrointestinal tract after oral administration. Tmax is 3 to 4 hours with a bioavailability of 100% and steady-state concentrations are attained within 15 to 21 days of administration. The Tmax in one pharmacokinetic study determined a Tmax of 4.1 ± 1.5 hours. The Cmax of 5 mg donepezil tablets is estimated to be 8.34 ng/mL, according to the Canadian monograph. The AUC of 5 mg donepezil tablets has been determined to be 221.90-225.36 ng.hr/mL.

After an oral dose, memantine is well absorbed. Its peak drug concentrations are attained in about 3-7 hours. Memantine shows linear pharmacokinetics when given at normal therapeutic doses. This drug can be taken without regard to food, as there is no effect of food on memantine absorption .

Half Life

The average elimination half-life of donepezil is about 70 hours according to the results of various studies and the FDA label for donepezil.. One pharmacokinetic study determined the average terminal half-life to be 81.5±22.0 h

Within the range of 60-100 hours .

The terminal elimination half-life was significantly increased in patients with moderate to severe renal impairment, in comparison with patients with normal renal function . Exercise caution when this drug is administered to patients with renal dysfunction.

Clearance

According to the FDA label, the average apparent plasma clearance of this drug is 0.13 – 0.19 L/hr/kg. A 5 mg dose of donepezil in healthy patients was shown to have a plasma clearance of 0.110±0.02 L/h/kg. In 10 patients diagnosed with alcoholic cirrhosis, showed a mean decrease in clearance by 20% when compared to the clearance in 10 healthy subjects. In 4 patients with severe renal impairment compared to 4 healthy subjects, no significant change in clearance was noted.

This drug is cleared by active tubular secretion in the kidneys. Tubular reabsorption of this drug is pH dependent .

Elimination Route

In a study of radiolabeled administration donepezil in healthy adults, 57% of measured radioactivity was identified in the urine, and 5% was identified in the feces.

This drug is mainly excreted in the urine. Approximately 48% of administered memantine is excreted unchanged in urine .

The remainder of the drug is metabolized to three main metabolites. These metabolites are the N-glucuronide conjugate, 6-hydroxy memantine, and 1-nitroso-deaminated memantine, which show minimal NMDA receptor antagonist activity .

Pregnancy & Breastfeeding use

There are no adequate data on the developmental risk associated with the use of memantine and donepezil hydrochlorides extended-release capsules or its active ingredients (memantine hydrochloride and donepezil hydrochloride) in pregnant women. There are no data on the presence of memantine or donepezil in human milk, the effects on the breastfed infant, or the effects of memantine and donepezil hydrochlorides extended-release capsules or its metabolites on milk production.

Contraindication

Memantine and donepezil hydrochlorides extended-release capsules are contraindicated in patients with known hypersensitivity to memantine hydrochloride, donepezil hydrochloride, piperidine derivatives, or to any excipients used in the formulation.

Special Warning

In case of renal & hepatic impairment: A similar dose schedule can be followed for patients with renal or mild to moderate hepatic impairment as clearance of donepezil hydrochloride is not affected by these conditions.

In case of children: There are no adequate and well controlled trials in document to safety and efficacy of donepezil hydrochloride in any illness occurring in children. Donepezil is not recommended for use in children.

In case of renal impairment: A target dose of 5 mg BID is recommended in patients with severe renal impairment (creatinine clearance: 5-29 ml/min).

In case of hepatic impairment: No dosage adjustment is needed in patients with mild or moderate hepatic impairment. Memantine should be administered with caution to patients with severe hepatic impairment.

Acute Overdose

Overdose may result in cholinergic crisis; symptoms include severe nausea, vomiting, salivation, hypotension, bradycardia, resp depression, collapse and seizures. Muscle weakness may increase and death may occur if resp muscles are involved. Treatment includes supportive measures and use of tertiary anticholinergics (such as atropine).

Symptoms: Agitation, asthenia, bradycardia, vomiting, dizziness, vertigo, ECG changes, increased BP, visual hallucinations, confusion, lethargy, restlessness, slowed movement, somnolence, stupor, unsteady gait, weakness, loss of consciousness, psychosis, coma.

Management: Symptomatic and supportive treatment. May increase elimination by urinary acidification.

Storage Condition

Keep below 30°C temperature, away from light & moisture. Keep out of the reach of children.

Innovators Monograph

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