AMANTREL Capsules (Amantadine hydrochloride)

Table of Content

Composition

AMANTREL Capsules

Each capsule contains:

Amantadine Hydrochloride equivalent to Amantadine …….…… 100 mg

Dosage Form

Capsule

Pharmacology

Pharmacodynamics

Mechanism of Action: Parkinson’s Disease

The mechanism of action of amantadine in the treatment of Parkinson’s disease and drug-induced extrapyramidal reactions is not known. Data from earlier animal studies suggest that amantadine may have direct and indirect effects on dopamine neurons. More recent studies have demonstrated that amantadine is a weak, non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist (Ki = 10 μM). Although amantadine has not been shown to possess direct anticholinergic activity in animal studies, clinically, it exhibits anticholinergic-like side effects such as dry mouth, urinary retention and constipation.

Pharmacokinetics

Absorption

Amantadine is well-absorbed orally. Maximum plasma concentrations are directly related to dose for doses up to 200 mg/day. Doses above 200 mg/day may result in a greater than proportional increase in maximum plasma concentrations. Amantadine pharmacokinetics was determined in 24 normal adult male volunteers after the oral administration of a single amantadine hydrochloride 100 mg capsule. The mean ± SD maximum plasma concentration was 0.22 ± 0.03 μg/mL (range: 0.18 to 0.32 μg/mL). The time to peak concentration was 3.3 ± 1.5 hours (range: 1.5 to 8.0 hours).

After oral administration of a single dose of 100 mg amantadine syrup to 5 healthy volunteers, the mean ± SD maximum plasma concentration Cmax was 0.24 ± 0.04 μg/mL and ranged from 0.18 to 0.28 μg/mL. After 15 days of amantadine 100 mg b.i.d., the Cmax was 0.47 ± 0.11 μg/mL in 4 of the 5 volunteers. The administration of amantadine Capsules as a 200 mg single dose to 6 healthy subjects resulted in a Cmax of 0.51 ± 0.14 μg/mL. Across studies, the time to Cmax (Tmax) averaged about 2 to 4 hours.

Distribution

The volume of distribution determined after the intravenous administration of amantadine to 15 healthy subjects was 3–8 L/kg, suggesting tissue binding. Amantadine, after single oral 200 mg doses to 6 healthy young subjects and to 6 healthy elderly subjects has been found in nasal mucus at mean ± SD concentrations of 0.15 ± 0.16, 0.28 ± 0.26, and 0.39 ± 0.34 μg/g at 1, 4 and 8 hours after dosing, respectively. These concentrations represented 31 ± 33%, 59 ± 61%, and 95 ± 86% of the corresponding plasma amantadine concentrations. Amantadine is approximately 67% bound to plasma proteins over a concentration range of 0.1 to 2.0 μg/mL. Following the administration of amantadine 100 mg as a single dose, the mean ± SD red blood cell to plasma ratio ranged from 2.7 ± 0.5 in 6 healthy subjects to 1.4 ± 0.2 in 8 patients with renal insufficiency.

Metabolism

Eight metabolites of amantadine have been identified in human urine. One metabolite, an N-acetylated compound, was quantified in human urine and accounted for 5–15% of the administered dose. Plasma acetylamantadine accounted for up to 80% of the concurrent amantadine plasma concentration in 5 of 12 healthy volunteers following the ingestion of a 200 mg dose of amantadine. Acetylamantadine was not detected in the plasma of the remaining 7 volunteers. The contribution of this metabolite to efficacy or toxicity is not known.

There appears to be a relationship between plasma amantadine concentrations and toxicity. As concentration increases, toxicity seems to be more prevalent; however, absolute values of amantadine concentrations associated with adverse effects have not been fully defined.

Elimination

Amantadine is primarily excreted unchanged in the urine by glomerular filtration and tubular secretion. The apparent oral clearance was 0.28 ± 0.11 L/hr/kg (range: 0.14 to 0.62 L/hr/kg). The half-life was 17 ± 4 hours (range: 10 to 25 hours). Across other studies, the amantadine plasma half-life has averaged 16 ± 6 hours (range: 9 to 31 hours) in 19 healthy volunteers. Plasma amantadine clearance ranged from 0.2 to 0.3 L/hr/kg after the administration of 5 mg to 25 mg intravenous doses of amantadine to 15 healthy volunteers.  In 6 healthy volunteers, the ratio of amantadine renal clearance to apparent oral plasma clearance was 0.79 ± 0.17 (mean ± SD).

The apparent oral plasma clearance of amantadine is reduced and the plasma half-life and plasma concentrations are increased in healthy elderly individuals aged 60 years and older. After single-dose administration of 25–75 mg to 7 healthy, elderly male volunteers, the apparent plasma clearance of amantadine was 0.10 ± 0.04 L/hr/kg (range: 0.06 to 0.17 L/hr/kg) and the half-life was 29 ± 7 hours (range: 20 to 41 hours). Whether these changes are due to a decline in renal function or other age-related factors is not known. In a study of young healthy subjects (n=20), mean renal clearance of amantadine, normalised for body mass index, was 1.5-fold higher in males compared to females (p<0.032). Compared with otherwise healthy adult individuals, the clearance of amantadine is significantly reduced in adult patients with renal impairment. The elimination half-life increases 2- to 3-fold or greater when creatinine clearance is less than 40 mL/min/1.73 m2 and averages 8 days in patients on chronic maintenance haemodialysis. Amantadine is removed in negligible amounts by haemodialysis. The pH of the urine has been reported to influence the excretion rate of amantadine. Since the excretion rate of amantadine increases rapidly when the urine is acidic, the administration of urine-acidifying drugs may increase the elimination of the drug from the body.

Indications

Parkinson’s Disease/Syndrome

AMANTREL Capsules are indicated in the treatment of idiopathic Parkinson’s disease (paralysis agitans), post-encephalitic Parkinsonism and symptomatic Parkinsonism, which may follow injury to the nervous system by carbon monoxide intoxication. It is indicated in those elderly patients believed to develop Parkinsonism in association with cerebral arteriosclerosis. In the treatment of Parkinson’s disease, AMANTREL Capsules are less effective than levodopa (-)-3-(3,4-dihydroxyphenyl)-L-alanine, and their efficacy in comparison with the anticholinergic anti-Parkinson drugs has not yet been established.

Drug-Induced Extrapyramidal Reactions

AMANTREL Capsules are indicated in the treatment of drug-induced extrapyramidal reactions. Although anticholinergic-type side effects have been noted with AMANTREL Capsules when used in patients with drug-induced extrapyramidal reactions, there is a lower incidence of these side effects than that observed with the anticholinergic anti-Parkinson drugs.

Dosage and Administration

The dose of AMANTREL Capsules may need reduction in patients with congestive heart failure, peripheral oedema, orthostatic hypotension or impaired renal function.

Dosage for Parkinsonism

Adults

The usual dose of AMANTREL Capsules is 100 mg twice a day when used alone. AMANTREL Capsules have an onset of action usually within 48 hours.

The initial dose of AMANTREL Capsules is 100 mg daily for patients with serious associated medical illnesses or who are receiving high doses of other anti-Parkinson drugs. After a week to several weeks at 100 mg once daily, the dose may be increased to 100 mg twice daily, if necessary.

Occasionally, patients whose responses are not optimal with AMANTREL Capsules at 200 mg daily may benefit from an increase up to 400 mg daily in divided doses. However, such patients should be supervised closely by their physicians.

Patients initially deriving benefit from AMANTREL Capsules not uncommonly experience a fall-off of effectiveness after a few months. Benefit may be regained by increasing the dose to 300 mg daily. Alternatively, temporary discontinuation of AMANTREL Capsules for several weeks, followed by re-initiation of the drug, may result in regaining benefit in some patients. A decision to use other anti-Parkinson drugs may be necessary.

Dosage for Concomitant Therapy

Some patients who do not respond to anticholinergic anti-Parkinson drugs may respond to AMANTREL Capsules. When AMANTREL Capsules or anticholinergic anti-Parkinson drugs are used with marginal benefit, concomitant use may produce additional benefit.

When AMANTREL Capsules and levodopa are initiated concurrently, the patient can exhibit rapid therapeutic benefits. AMANTREL Capsules should be held constant at 100 mg daily or twice daily while the daily dose of levodopa is gradually increased for optimal benefit.  When AMANTREL Capsules are added to optimal well-tolerated doses of levodopa, additional benefit may result, including smoothing out the fluctuations in improvement that sometimes occur in patients on levodopa alone. Patients who require a reduction in their usual dose of levodopa because of the development of side effects may possibly regain lost benefits with the addition of AMANTREL Capsules.

Dosage for Drug-Induced Extrapyramidal Reactions

Adults

The usual dose of AMANTREL Capsules is 100 mg twice a day. Occasionally, patients whose responses are not optimal with AMANTREL Capsules at 200 mg daily may benefit from an increase up to 300 mg daily in divided doses.

Contraindications

AMANTREL Capsules are contraindicated in patients with a known hypersensitivity to amantadine hydrochloride or to any of the other ingredients in AMANTREL Capsules.

Warnings and Precautions

Drug Interactions

Careful observation is required when AMANTREL Capsules are administered concurrently with CNS stimulants. Concurrent administration of amantadine and drugs or substances (e.g. alcohol) that act on the CNS may result in additive CNS toxicity. Close observation is recommended.

Concurrent administration of amantadine and anticholinergic agents or levodopa may increase confusion, hallucinations, nightmares, gastrointestinal disturbances, or other atropine-like side effects. Psychotic reactions have been observed in patients receiving amantadine and levodopa. In isolated cases, worsening of psychotic symptoms has been reported in patients receiving amantadine and concomitant neuroleptic medication.

Agents with anticholinergic properties may potentiate the anticholinergic-like side effects of amantadine.

Co-administration of thioridazine has been reported to worsen the tremor in elderly patients with Parkinson’s disease; however, it is not known if other phenothiazines produce a similar response.

Co-administration of triamterene/hydrochlorothiazide resulted in a higher plasma amantadine concentration in a 61-year-old man receiving amantadine 100 mg t.i.d. for Parkinson’s disease. It is not known which of the components of triamterene/hydrochlorothiazide contributed to the observation or if related drugs produce a similar response. There have been isolated reports of a suspected interaction between amantadine and combination diuretics (hydrochlorothiazide plus potassium-sparing diuretics). One or both of the components apparently reduce the clearance of amantadine, leading to higher plasma concentrations and toxic effects (confusion, hallucinations, ataxia, myoclonus).

Co-administration of quinine or quinidine with amantadine was shown to reduce the renal clearance of amantadine by about 30%.

The concurrent use of amantadine with live attenuated influenza vaccine (LAIV) intranasal has not been evaluated. However, because of the potential for interference between these products, LAIV should not be administered within 2 weeks before or 48 hours after the administration of AMANTREL Capsules, unless medically indicated. The concern about possible interference arises from the potential for antiviral drugs to inhibit replication of live vaccine virus. Trivalent inactivated influenza vaccine can be administered at any time relative to the use of AMANTREL Capsules.

Renal Impairment

Because amantadine is mainly excreted in the urine, it accumulates in the plasma and in the body when renal function declines. Thus, the dose of AMANTREL Capsules should be reduced in patients with renal impairment and in individuals who are 65 years of age or older.

Hepatic Impairment

Care should be exercised when administering AMANTREL Capsules to patients with liver disease. Rare instances of reversible elevation of liver enzymes have been reported in patients receiving amantadine, though a specific relationship between the drug and such changes have not been established.

Pregnancy

The effect of amantadine on embryofoetal and peri- and postnatal development has not been adequately tested, i.e. in studies conducted under the Good Laboratory Practices (GLP) and according to current recommended methodology. There are no adequate and well-controlled studies in pregnant women. Human data regarding teratogenicity after maternal use of amantadine is scarce, but amantadine-related complications during pregnancy have been reported. AMANTREL Capsules should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or foetus.

Lactation

Amantadine is excreted in human milk. Use of AMANTREL Capsules is not recommended in nursing mothers.

Paediatric Use

The safety and efficacy of amantadine in newborn infants and infants below the age of 1 year have not been established.

Geriatric Use

Because amantadine is primarily excreted in the urine, it accumulates in the plasma and in the body when renal function declines. Thus, the dose of AMANTREL Capsules should be reduced in patients with renal impairment and in individuals who are 65 years of age or older. The dose of AMANTREL Capsules may need reduction in patients with congestive heart failure, peripheral oedema, or orthostatic hypotension.

Deaths

Deaths have been reported from overdose with amantadine. The lowest reported acute lethal dose was 1 gram. Acute toxicity may be attributable to the anticholinergic effects of amantadine. Drug overdose has resulted in cardiac, respiratory, renal or CNS toxicity. Cardiac dysfunction includes arrhythmia, tachycardia and hypertension.

Suicide Attempts

Suicide attempts, some of which have been fatal, have been reported in patients treated with amantadine, many of whom received short courses for influenza treatment or prophylaxis. The incidence of suicide attempts is not known and the pathophysiologic mechanism is not understood. Suicide attempts and suicidal ideation have been reported in patients with and without a history of psychiatric illness. Amantadine can exacerbate mental problems in patients with a history of psychiatric disorders or substance abuse. Patients who attempt suicide may exhibit abnormal mental states, which include disorientation, confusion, depression, personality changes, agitation, aggressive behaviour, hallucinations, paranoia, other psychotic reactions and somnolence or insomnia. Because of the possibility of serious adverse effects, caution should be observed when prescribing amantadine to patients being treated with drugs having CNS effects, or for whom the potential risks outweigh the benefit of the treatment.

As some individuals have attempted suicide with amantadine, prescriptions should be written for the smallest quantity consistent with good patient management.

CNS Effects

Patients with a history of epilepsy or other ‘seizures’ should be observed closely for possible increased seizure activity.

Patients receiving amantadine, who report CNS effects or blurring of vision, should be cautioned against driving or working in situations where alertness and adequate motor coordination are important.

Neuroleptic Malignant Syndrome (NMS)

Sporadic cases of possible neuroleptic malignant syndrome (NMS) have been reported in association with dose reduction or withdrawal of amantadine therapy. Therefore, patients should be observed carefully when the dosage of amantadine is reduced abruptly or discontinued, especially if the patient is receiving neuroleptics.

NMS is an uncommon but life-threatening syndrome characterised by fever or hyperthermia; neurologic findings including muscle rigidity, involuntary movements, altered consciousness; mental status changes; other disturbances such as autonomic dysfunction, tachycardia, tachypnoea, hyper- or hypotension; laboratory findings such as creatine phosphokinase elevation, leucocytosis, myoglobinuria, and increased serum myoglobin.

The early diagnosis of this condition is important for the appropriate management of these patients. Considering NMS as a possible diagnosis and ruling out other acute illnesses (e.g. pneumonia, systemic infection, etc.) is essential. This may be especially complex if the clinical presentation includes both serious medical illness and untreated or inadequately treated extrapyramidal signs and symptoms (EPS). Other important considerations in the differential diagnosis include central anticholinergic toxicity, heat stroke, drug fever and primary CNS pathology.

The management of NMS should include the following: 1) intensive symptomatic treatment and medical monitoring; and, 2) treatment of any concomitant serious medical problems for which specific treatments are available. Dopamine agonists, such as bromocriptine, and muscle relaxants, such as dantrolene, are often used in the treatment of NMS; however, their effectiveness has not been demonstrated in controlled studies.

Melanoma

Epidemiological studies have shown that patients with Parkinson’s disease have a higher risk (2- to approximately 6-fold higher) of developing melanoma than the general population. Whether the increased risk observed was due to Parkinson’s disease or other factors, such as drugs used to treat Parkinson’s disease, is unclear. For the reasons stated above, patients and providers are advised to monitor for melanomas frequently and on a regular basis when using amantadine for any indication. Ideally, periodic skin examinations should be performed by appropriately qualified individuals (e.g. dermatologists).

Other

Amantadine should be used with caution in patients with confusional or hallucinatory states or underlying psychiatric disorders, in patients with liver or kidney disorders, and those suffering from, or who have a history of, cardiovascular disorders. Caution should be applied when prescribing amantadine with other medications having an effect on the CNS. Peripheral oedema (thought to be due to an alteration in the responsiveness of peripheral vessels) may occur in some patients during continual treatment (not usually before 4 weeks) with amantadine. This should be taken into account in patients with congestive heart failure.

Patients with a history of congestive heart failure or peripheral oedema should be followed closely as there are patients who developed congestive heart failure while receiving amantadine. Patients with Parkinson’s disease improving on amantadine should resume normal activities gradually and cautiously, consistent with other medical considerations, such as the presence of osteoporosis or phlebothrombosis. Because amantadine has anticholinergic effects and may cause mydriasis, it should not be given to patients with untreated angle-closure glaucoma.

The dose of amantadine may need careful adjustment in patients with congestive heart failure, peripheral oedema, or orthostatic hypotension. Care should be exercised when administering amantadine to patients with a history of recurrent eczematoid rash, or to patients with psychosis or severe psychoneurosis not controlled by chemotherapeutic agents. Serious bacterial infections may begin with influenza-like symptoms or may coexist with or occur as complications during the course of influenza. Amantadine has not been shown to prevent such complications.

Discontinuation

Amantadine should not be discontinued abruptly in patients with Parkinson’s disease since a few patients have experienced a parkinsonian crisis, i.e. a sudden marked clinical deterioration, when this medication was suddenly stopped. The dose of anticholinergic drugs or of amantadine should be reduced if atropine-like effects appear when these drugs are used concurrently.

Abrupt discontinuation may also precipitate delirium, agitation, delusions, hallucinations, paranoid reaction, stupor, anxiety, depression and slurred speech.

Undesirable Effects

The adverse reactions reported most frequently at the recommended dose of amantadine (5–10%) are: nausea, dizziness (light-headedness), and insomnia.

Less frequently (1–5%) reported adverse reactions are depression, anxiety and irritability, hallucinations, confusion, anorexia, dry mouth, constipation, ataxia, livedo reticularis, peripheral oedema, orthostatic hypotension, headache, somnolence, nervousness, dream abnormality, agitation, dry nose, diarrhoea, and fatigue.

Infrequently (0.1–1%) occurring adverse reactions are congestive heart failure, psychosis, urinary retention, dyspnoea, skin rash, vomiting, weakness, slurred speech, euphoria, thinking abnormality, amnesia, hyperkinesia, hypertension, decreased libido, and visual disturbance, including punctate sub-epithelial or other corneal opacity, corneal oedema, decreased visual acuity, sensitivity to light, and optic nerve palsy.

Rare (less than 0.1%) occurring adverse reactions are instances of convulsion, leucopaenia, neutropaenia, eczematoid dermatitis, oculogyric episodes, suicidal attempt, suicide, and suicidal ideation.

Other adverse reactions reported during postmarketing experience with amantadine usage include the following:

Nervous System/Psychiatric: Coma, stupor, delirium, hypokinesia, hypertonia, delusions, aggressive behaviour, paranoid reaction, manic reaction, involuntary muscle contractions, gait abnormalities, paraesthesia, EEG changes, and tremor. Abrupt discontinuation may also precipitate delirium, agitation, delusions, hallucinations, paranoid reaction, stupor, anxiety, depression and slurred speech.

Cardiovascular: Cardiac arrest, arrhythmias, including malignant arrhythmias, hypotension, and tachycardia.

Respiratory: Acute respiratory failure, pulmonary oedema, and tachypnoea.

Gastrointestinal: Dysphagia.

Haematologic: Leucocytosis; agranulocytosis.

Special Senses: Keratitis and mydriasis.

Skin and Appendages: Pruritus and diaphoresis.

Miscellaneous: Neuroleptic malignant syndrome (see WARNINGS AND PRECAUTIONS), allergic reactions (including anaphylactic reactions), oedema, fever, pathological gambling, increased libido (including hypersexuality), and impulse control symptoms.

Laboratory Test: Elevated CPK, BUN, serum creatinine, alkaline phosphatase, LDH, bilirubin, GGT, SGOT, and SGPT.

Overdosage

Deaths have been reported from overdosage with amantadine. The lowest reported acute lethal dose was 1 gram. Because some patients have attempted suicide by overdosing with amantadine, prescriptions should be written for the smallest quantity consistent with good patient management.

Acute toxicity may be attributable to the anticholinergic effects of amantadine. Drug overdose has resulted in cardiac, respiratory, renal or CNS toxicity. Cardiac dysfunction includes arrhythmia, tachycardia and hypertension. Pulmonary oedema and respiratory distress (including adult respiratory distress syndrome ) have been reported. Renal dysfunction, including increased BUN, decreased creatinine clearance and renal impairment can occur. CNS effects have been reported, including insomnia, anxiety, agitation, aggressive behaviour, hypertonia, hyperkinesia, ataxia, gait abnormality, tremor, confusion, disorientation, depersonalisation, fear, delirium, hallucinations, psychotic reactions, lethargy, somnolence and coma. Seizures may be exacerbated in patients with a history of seizure disorders. Hyperthermia has also been observed in cases where a drug overdose has occurred.

There is no specific antidote for an overdose of amantadine. However, slowly administered intravenous physostigmine in 1 mg and 2 mg doses in an adult at 1- to 2-hour intervals and 0.5 mg doses in a child at 5- to 10-minute intervals up to a maximum of 2 mg/hour have been reported to be effective in the control of CNS toxicity caused by amantadine hydrochloride.

For acute overdosing, general supportive measures should be employed along with immediate gastric lavage or induction of emesis. Fluids should be forced and, if necessary, given intravenously. The pH of the urine has been reported to influence the excretion rate of amantadine. Since the excretion rate of amantadine increases rapidly when the urine is acidic, the administration of urine-acidifying drugs may increase the elimination of the drug from the body. The blood pressure, pulse, respiration and temperature should be monitored. The patient should be observed for hyperactivity and convulsions; if required, sedation, and anticonvulsant therapy should be administered. The patient should be observed for the possible development of arrhythmias and hypotension; if required, appropriate anti-arrhythmic and anti-hypotensive therapy should be given. Electrocardiographic monitoring may be required after ingestion, since malignant tachyarrhythmia can appear after overdose.

Care should be exercised when administering adrenergic agents, such as isoproterenol, to patients with amantadine overdose, since the dopaminergic activity of amantadine has been reported to induce malignant arrhythmias.

The blood electrolytes, urine pH and urinary output should be monitored. If there is no record of recent voiding, catheterization should be done.

Incompatibility

Not applicable

Storage and Handling Instructions

Store below 30ºC.

Packaging Information

AMANTREL Capsules: Blister pack of 15 Capsules

Last Updated: July 2018

Last Reviewed: July 2018