[lou_lou]

I did not take this drug long before I had a spoltchy sp? very itchy dry -bumby/ pink rash over my arms face and neck...
this is what Amantadine is actually for influenza?


Amantadine

Bernd Sebastian Kamps and Christian Hoffmann


(Green links: Free full-text articles)

Amantadine inhibits the replication of influenza A viruses by interfering with the uncoating of the virus inside the cell. Like rimantadine, it is an M2 inhibitor which blocks the ion channel formed by the M2 protein that spans the viral membrane (Hay 1985, Sugrue 1991). The influenza virus enters its host cell by receptor-mediated endocytosis. Thereafter, acidification of the endocytotic vesicles is required for the dissociation of the M1 protein from the ribonucleoprotein complexes. Only then are the ribonucleoprotein particles imported into the nucleus via the nuclear pores. The hydrogen ions needed for acidification pass through the M2 channel. Amantadine blocks the channel (Bui 1996).

Amantadine is effective against all influenza A subtypes that have previously caused disease in humans (H1N1, H2N2 and H3N2), but not against influenza B virus, because the protein M2 is unique to influenza A viruses. For both the prevention and treatment of influenza A, amantadine has a similar efficacy to rimantadine (Stephenson 2001, Jefferson 2004). Comparative studies indicate that adverse effects were significantly more common with amantadine than rimantadine (Jefferson 2004). Amantadine is not active against the avian influenza subtype H5N1 strains which have recently caused disease in humans (Li 2004). Besides influenza, amantadine may also be indicated in the treatment of Parkinson's disease and drug-induced extrapyramidal reactions. Moreover, it may be effective as an adjunct to interferon-based combination therapy in patients with chronic hepatitis C who have failed prior hepatitis C therapy (Lim 2005).

With daily costs of 0.50 € per day in some European countries, amantadine is by far the cheapest treatment for influenza A, compared to daily costs of 5 € for rimantadine and 7 € for oseltamivir.

The use of amantadine is associated with the rapid emergence of drug-resistant variants. Resistant isolates of influenza A are genetically stable and fully transmissible, and the pathogenic potential is comparable to that of wild-type virus isolates. In immunocompromised patients, resistant virus can be shed for prolonged periods (Boivin 2002). According to a study which assessed more than 7,000 influenza A virus samples obtained from 1994 to 2005, drug resistance against amantadine and rimantadine has increased worldwide from 0.4 % to 12.3 % (Bright 2005). Virus samples collected in 2004 from South Korea, Taiwan, Hong Kong, and China showed drug-resistance frequencies of 15 %, 23 %, 70 %, and 74 %, respectively. Some authors have suggested that the use of amantadine and rimantadine should be frankly discouraged (Jefferson 2006). Recently, 109 out of 120 (91 %) influenza A H3N2 viruses isolated from patients in the US contained an amino acid change at position 31 of the M2 protein, which confers resistance to amantadine and rimantadine. On the basis of these results, the Centre for Disease Control recommended that neither amantadine nor rimantadine be used for the treatment or prophylaxis of influenza A in the United States for the remainder of the 2005-06 influenza season (CDC 2006).

Pharmacokinetics

Amantadine is well absorbed orally and maximum drug concentrations (Cmax) are directly dose-related for doses of up to 200 mg/day. Doses above 200 mg/day may result in disproportional increases in Cmax. In healthy volunteers, peak concentration were reached after 3 hours and the half-life was 17 hours (range: 10 to 25 hours). Amantadine is primarily excreted unchanged in the urine by glomerular filtration and tubular secretion.

In individuals older than 60 years, the plasma clearance of amantadine is reduced and the plasma half-life and plasma concentrations are increased. The clearance is also reduced in patients with renal insufficiency: the elimination half-life increases two to three fold or greater when creatinine clearance is less than 40 ml/min and averages eight days in patients on chronic haemodialysis. Amantadine is not removed by haemodialysis.

As 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.

Toxicity

Gastrointestinal symptoms - mainly nausea but also vomiting, diarrhoea, constipation, and loss of appetite - are the major side effects. In addition, amantadine has a wide range of toxicities which may be in part attributable to the anticholinergic effects of the drug, and some reversible CNS side effects may occur during a 5-day-treatment in a substantial number of patients (van Voris 1981). As the occurrence of adverse effects is dose-related, adverse events are particularly common in the elderly and those with impaired renal function. Side effects begin within two days of the start of the drug, and usually disappear rapidly after cessation of treatment.

CNS toxicity may manifest as dizziness, nervousness, and insomnia. In a four-week prophylaxis trial, these symptoms occurred in up to 33 % of young individuals (Bryson 1980). Decreased performance on sustained attention tasks was also observed. Other CNS adverse effects include agitation, difficulty concentrating, insomnia, and lowered seizure threshold. In a direct comparison of the prophylactic use of amantadine and rimantadine, more patients receiving amantadine (13 % vs. 6% on rimantidine) withdrew from the study because of CNS side effects (Dolin 1982).

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, dream abnormality, agitation, dry nose, diarrhoea and fatigue (Symmetrel 2003).

Deaths have been reported from overdose with amantadine. The lowest reported acute lethal dose was 1 gram. In the past, some patients attempted suicide by overdosing with amantadine. As a result, it is recommended that the minimum quantity of drug is prescribed (Symmetrel 2003).

Acute toxicity may be attributable to the anticholinergic effects of amantadine. Drug overdose has therefore resulted in cardiac, respiratory, renal or central nervous system toxicity. There is no specific antidote. For more information, please check the prescribing information (Symmetrel 2003).

Efficacy

In a Cochrane review of 15 placebo-controlled trials on the prophylactic effect of amantadine, amantadine prevented 61 % of influenza cases and 25 % of cases of influenza-like illness but had no effect on asymptomatic cases (Jefferson 2006). In treatment, amantadine significantly shortened the duration of fever (by 0.99 days) but had no effect on nasal shedding of influenza A virus. The low efficacy of amantadine together with the relatively high rate of adverse events led the authors to conclude that the use of amantadine should be discouraged in seasonal and pandemic influenza (Jefferson 2006) (see also the CDC recommendation in the Introduction).

Resistance

Point mutations in the M gene lead to amino acid changes in the transmembrane region of the M2 protein and may confer high-level resistance to amantadine. The five amino acid sites known to be involved are 26, 27, 30, 31, and 34 (Holsinger 1994). The use of amantadine for treatment has been associated with the rapid emergence of resistant viruses capable of transmission, compromising its potential as a prophylaxis as well its efficacy as a treatment (Fleming 2003). The mutants are as virulent and transmissible as the wild-type virus. In an avian model, they were also genetically stable, showing no reversion to the wild-type after several passages in birds (Bean 1989). These results suggest that resistant mutants may have the potential to threaten the effective use of amantadine for the control of epidemic influenza.

Drug Interactions

Amantadine adds to the sedating effects of alcohol and other sedating drugs such as benzodiazepines, tricyclic antidepressants, dicyclomine, certain antihistamines, opiate agonists and certain antihypertensive medications. Such combinations can cause dizziness, confusion, light headedness, or fainting.

Co-administration of quinine or quinidine with amantadine has been shown to reduce the renal clearance of amantadine by about 30 % (Gaudry 1993).

Co-administration of thioridazine can worsen the tremor in elderly patients with Parkinson's disease.

Recommendations for Use

Amantadine does not completely prevent the host immune response to influenza A infection (Sears 1987) - individuals who take the drug may still develop immune responses to the natural disease or vaccination and may be protected when exposed at a later date to antigenically related viruses.

EU

In the EU, indications for influenza A treatment vary between the member states (i.e., indicated for treatment and/or prophylaxis of adults; or adults and children; or only adults and adolescents). Please check the prescribing information.

US

In the US, amantadine is indicated for the treatment of uncomplicated respiratory tract illness caused by influenza A virus strains. Treatment should be started as soon as possible, preferably within 24 to 48 hours after the onset of symptoms, and should be continued for 24 to 48 hours after the disappearance of clinical signs.

Amantadine is also indicated for prophylaxis against the signs and symptoms of influenza A virus infection when early vaccination is not feasible or when the vaccine is contraindicated or not available. Prophylactic dosing should be started in anticipation of an influenza A outbreak and before or after contact with individuals with influenza A virus respiratory tract illness.

Amantadine should be continued for at least 10 days following known exposure. When prophylaxis is started with inactivated influenza A virus vaccine, it should be administered for 2 to 4 weeks after the vaccine has been given (i.e., until protective antibody responses develop). When inactivated influenza A virus vaccine is unavailable or contraindicated, amantadine should be administered for the duration of known influenza A infection in the community because of repeated and unknown exposure.

The daily dosage of amantadine for adults is 200 mg; two 100 mg tablets (or four teaspoonfuls of syrup) as a once daily dose. The daily dosage may be split into one tablet of 100 mg twice a day. If central nervous system effects develop on a once daily dosage, a split dosage schedule may reduce such complaints. In persons of 65 years of age or older, the daily dosage of amantadine is 100 mg. Low-dose amantadine (100 mg/day) can reduce toxicity and may maintain the prophylactic efficacy seen with 200 mg/day (Sears 1987). In an experimental challenge study on 78 subjects, using doses of 50 mg, 100 mg or 200 mg/day, there was no significant difference between the groups in influenza illness or viral shedding (Reuman 1989).

In elderly institutionalised patients, individualised dosing of amantadine, based upon a patient's creatinine clearance, seems to be effective while reducing adverse reactions (Kolbe 2003).

In paediatric patients, lower total daily doses should be calculated on the basis of 4.4 to 8.8 mg/kg/day (2 to 4 mg/lb/day). However, given the relatively low efficacy of amantadine and the high risk of occurrence of gastrointestinal and CNS adverse effects, the authors do not recommend the administration of amantadine in children.

Warnings

Amantadine is contraindicated in severe renal impairment and patients with epilepsy. In addition, it should be used cautiously in elderly patients (impaired renal function?).

Amantadine may cause mydriasis and should therefore not be given to patients with untreated closed-angle glaucoma.

The safety of amantadine in pregnant women has not been established.

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 (Symmetrel 2003).



Summary

Amantadine is available as 100 mg tablets or capsules and as a syrup containing 50 mg/5ml.

Drug class: M2-inhibitor.

Indications: treatment and prevention of Influenza A.

Dosage: 100 mg qd both for treatment and prophylaxis. For prophylaxis, amantadine should be started as soon as possible after exposure and continued for at least 10 days.

Special Dosage: persons with reduced kidney function and elderly persons may need lower doses (or less frequent doses).

Pharmacokinetics: good absorption with peak concentration after 3 hours and a half-life of 17 hours. Excreted unchanged in the urine by glomerular filtration and tubular secretion. Reduced clearance in individuals > 60 years and in patients with renal insufficiency: half-life is increased when creatinine clearance is less than 40 ml/min. Amantadine is not removed by haemodialysis.

Contraindications: psychosis. Patients with insufficiently treated epileptic episodes.

Interactions: central nervous system stimulants; quinine and quinidine; thioridazine.

Side effects: gastrointestinal and CNS symptoms.

Comments/Warnings: no well-controlled studies have been done in pregnant women to evaluate the safety of amantadine. Amantadine should not be prescribed to pregnant women.

Amantadine is excreted in breast milk in low concentrations. Although no information is available on the effects in infants, the manufacturer recommends that amantadine be used cautiously in nursing mothers.

Patients receiving amantadine who note central nervous system effects or blurring of vision should be cautioned against driving or working in situations where alertness and adequate motor co-ordination are important.

Store amantadine at room temperature between 15 and 30°C (59 and 86°F).

Internet sources:

USA: http://influenzareport.com/link.php?id=6










References


Bean WJ, Threlkeld SC, Webster RG. Biologic potential of amantadine-resistant influenza A virus in an avian model. J Infect Dis 1989; 159: 1050-6. Abstract: http://amedeo.com/lit.php?id=2723453


Boivin G, Goyette N, Bernatchez H. Prolonged excretion of amantadine-resistant influenza a virus quasi species after cessation of antiviral therapy in an immunocompromised patient. Clin Infect Dis 2002; 34: Abstract: http://amedeo.com/lit.php?id=11807683 - Full text at http://www.journals.uchicago.edu/CID...57/010857.html


Bright RA, Medina MJ, Xu X, et al. Incidence of adamantane resistance among influenza A (H3N2) viruses isolated worldwide from 1994 to 2005: a cause for concern. Lancet 2005; 366: 1175-81. Epub 2005 Sep 22. Abstract: http://amedeo.com/lit.php?id=16198766


Bryson YJ, Monahan C, Pollack M, Shields WD. A prospective double-blind study of side effects associated with the administration of amantadine for influenza A virus prophylaxis. J Infect Dis 1980; 141: 543-7. Abstract: http://amedeo.com/lit.php?id=7373087


CDC 2006. CDC Recommends against the Use of Amantadine and Rimantadine for the Treatment or Prophylaxis of Influenza in the United States during the 2005-06 Influenza Season. Available from http://www.cdc.gov/flu/han011406.htm - Accessed 13 February 2006.


Demicheli V, Jefferson T, Rivetti D, Deeks J. Prevention and early treatment of influenza in healthy adults. Vaccine 2000; 18: 957-1030. Abstract: http://amedeo.com/lit.php?id=10590322


Dolin R, Reichman RC, Madore HP, Maynard R, Linton PN, Webber-Jones J. A controlled trial of amantadine and rimantadine in the prophylaxis of influenza A infection. N Engl J Med 1982; 307: 580-4. Abstract: http://amedeo.com/lit.php?id=7050702


Fleming DM. Zanamivir in the treatment of influenza. Expert Opin Pharmacother 2003; 4: 799-805. Abstract: http://amedeo.com/lit.php?id=12740002


Gaudry SE, Sitar DS, Smyth DD, McKenzie JK, Aoki FY. Gender and age as factors in the inhibition of renal clearance of amantadine by quinine and quinidine. Clin Pharmacol Ther 1993; 54: 23-7. Abstract: http://amedeo.com/lit.php?id=8330461


Hay AJ, Wolstenholme AJ, Skehel JJ, Smith MH. The molecular basis of the specific anti-influenza action of amantadine. EMBO J 1985; 4: 3021-4. Abstract: http://amedeo.com/lit.php?id=4065098 - Full text at http://www.pubmedcentral.gov/article...bmedid=4065098


Holsinger LJ, Nichani D, Pinto LH, Lamb RA. Influenza A virus M2 ion channel protein: a structure-function analysis. J Virol 1994; 68: 1551-63. Abstract: http://amedeo.com/lit.php?id=7508997 - Full text at http://www.pubmedcentral.gov/article...bmedid=7508997


Jefferson T, Deeks JJ, Demicheli V, Rivetti D, Rudin M. Amantadine and rimantadine for preventing and treating influenza A in adults. Cochrane Database Syst Rev 2004; 0: Abstract: http://amedeo.com/lit.php?id=15266442


Jefferson T, Demicheli V, Rivetti D, Jones M, Di Pietrantonj C, Rivetti A. Antivirals for influenza in healthy adults: systematic review. Lancet 2006; 367: 303-13. Abstract: http://amedeo.com/lit.php?id=16443037


Kolbe F, Sitar DS, Papaioannou A, Campbell G. An amantadine hydrochloride dosing program adjusted for renal function during an influenza outbreak in elderly institutionalized patients. Can J Clin Pharmacol 2003; 10: 119-22. Abstract: http://amedeo.com/lit.php?id=14506511


Li KS, Guan Y, Wang J, et al. Genesis of a highly pathogenic and potentially pandemic H5N1 influenza virus in eastern Asia. Nature 2004; 430: 209-13. Abstract: http://amedeo.com/lit.php?id=15241415


Lim JK, Wooten D, Siegel R, Cheung RC. Amantadine in treatment of chronic hepatitis C virus infection? J Viral Hepat 2005; 12: 445-55. Abstract: http://amedeo.com/lit.php?id=16108758


Monto AS, Gunn RA, Bandyk MG, King CL. Prevention of Russian influenza by amantadine. JAMA 1979; 241: 1003-7. Abstract: http://amedeo.com/lit.php?id=368354


Reuman PD, Bernstein DI, Keefer MC, Young EC, Sherwood JR, Schiff GM. Efficacy and safety of low dosage amantadine hydrochloride as prophylaxis for influenza A. Antiviral Res 1989; 11: 27-40. Abstract: http://amedeo.com/lit.php?id=2712549


Sears SD, Clements ML. Protective efficacy of low-dose amantadine in adults challenged with wild-type influenza A virus. Antimicrob Agents Chemother 1987; 31: 1470-3. Abstract: http://amedeo.com/lit.php?id=3435099


Stephenson I, Nicholson KG. Influenza: vaccination and treatment. Eur Respir J 2001; 17: 1282-93. Abstract: http://amedeo.com/lit.php?id=11491177 - Full text at http://erj.ersjournals.com/cgi/content/full/17/6/1282


Sugrue RJ, Hay AJ. Structural characteristics of the M2 protein of influenza A viruses: evidence that it forms a tetrameric channel. Virology 1991; 180: 617-24. Abstract: http://amedeo.com/lit.php?id=1989386


Symmetrel (package insert). Endo Pharmaceuticals Inc., Chadds Ford, 2003. http://influenzareport.com/link.php?id=6


Van Voris LP, Betts RF, Hayden FG, Christmas WA, Douglas RG Jr. Successful treatment of naturally occurring influenza A/USSR/77 H1N1. JAMA 1981; 245: 1128-31. Abstract: http://amedeo.com/lit.php?id=7007668


hope this helps you both!

[lou_lou]

Indications
Amandatine is useful in the treatment of Parkinson's syndrome and in the short-term management of drug-induced extrapyramidal symptoms.

In Parkinson's Disease, amantadine has been used alone and in combination with anticholinergic antiparkinson drugs and with levodopa. The final therapeutic benefit seen with amantadine is significantly less than that seen with levodopa. The maximal therapeutic benefit to be obtained with amantadine is usually seen within 1 week. However, initial benefits may diminish with continued dosing.

Amantadine is useful as an adjunct in patients who do not tolerate optimal doses of levodopa alone or in combined therapy with a decarboxylase inhibitor. In these patients, the addition of amantadine may result in better control of Parkinson's syndrome and may help to smooth out fluctuations in performance.

The comparative efficacy of amantadine and anticholinergic antiparkinson drugs has not yet been established. When amantadine or anticholinergic antiparkinson drugs are each used with marginal benefit, concomitant use may permit the same degree of control, often with a lower dose of the anticholinergic medication.

Amantadine is effective in reducing severity or abolishing drug-induced extrapyramidal reactions including parkinsonism disease, dystonia and akathisia. It is not effective in the management of tardive dyskinesia.

Although anticholinergic-type side effects have been noted when used in patients with drug-induced extrapyramidal reactions, there appears to be a lower incidence of these side effects than that observed with anticholinergic antiparkinson drugs.

Antiparkinsonian agents should not usually be used prophylactically during neuroleptic administration. However, they may be given when needed to suppress extrapyramidal symptoms. Therefore, amantadine may be used in the management of extrapyramidal symptoms which cannot be controlled by reduction of neuroleptic dosage, but should be discontinued as soon as it is no longer required. Amantadine should be withdrawn after a period of time to determine whether there is recrudescence of extrapyramidal symptoms.

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Contraindications
Known hypersensitivity to amantadine.

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Warnings
A small number of suicidal attempts, some of which have been fatal, have been reported in patients treated with amantadine. The incidence of suicidal attempts is not known and the pathophysiologic mechanism is not understood. Suicidal attempts and suicidal ideation have been reported in patients with and without prior 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 behavior, 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 treatment. Because some patients have attempted suicide by overdosing with amantadine, prescriptions should be written for the smallest quantity consistent with good patient management.

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

Patients with a history of CHF or peripheral edema 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.

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

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Precautions
General:
Amantadine should not be discontinued abruptly since a few patients with Parkinson's Disease experienced a parkinsonian crisis, i.e., sudden marked clinical deterioration, when this medication was suddenly stopped.

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

The diagnostic evaluation of patients with this syndrome is complicated. In arriving at a diagnosis, it is important to identify cases where the clinical presentation includes both serious medical illness (e.g., pneumonia, systemic infection, etc.) 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: Intensive symptomatic treatment and medical monitoring; and treatment of any concomitant serious medical problems for which specific treatments are available. There is no general agreement about specific pharmacological treatment regimens for uncomplicated NMS.

Patients with Special Diseases and Conditions:
Because amantadine is not metabolized and is mainly excreted in the urine, it may accumulate in the plasma and in the body when renal function declines. The dose of amantadine should be reduced in patients with renal impairment and in patients who are 65 years of age or older (see Dosage). The dose of amantadine may need careful adjustment in patients with congestive heart failure, peripheral edema, or orthostatic hypotension.

Care shoud be exercised when administering amantadine to patients with liver disease, a history of recurrent eczematoid rash, or to patients with psychosis or severe psychoneurosis not controlled by chemotherapeutic agents. Rare instances of reversible elevation of liver enzyme levels have been reported in patients receiving amantadine, though a specific relationship between the drug and such changes has not been established.

Pregnancy:
Amantadine has been shown to be embryotoxic and teratogenic in rats at 50 mg/kg/day, approximately 12 times the recommended human dose, but not at 37 mg/kg/day. Embryotoxic and teratogenic drug effects were not seen in rabbits that received up to 25 times the recommended human dose.

There are not adequate and well controlled studies in pregnant women. Therefore, amantadine should not be used in women with childbearing potential, unless in the opinion of the physician, the expected benefit to the patient outweighs the possible risk to the fetus.

Lactation:
Since amantadine is secreted in human milk, its use is not recommended in nursing mothers.

Children:
The safety and efficacy of use of amantadine in neonates and infants less than 1 year old have not been established.

Drug interactions:
The dose of anticholinergic drugs or of amantadine should be reduced if atropine-like effects appear when these drugs are used concurrently.

Careful observation is required when amantadine is administered concurrently with CNS stimulants.

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Adverse Effects
Adverse reactions reported below have occurred in patients while receiving amantadine alone or in combination with anticholinergic antiparkinsonian drugs and/or levodopa.

The adverse reactions reported most frequently (5 to 10%) are: nausea, dizziness (lightheadedness) and insomnia.

Less frequently reported (1 to 5%) are: depression, anxiety and irritability, hallucinations, confusion, anorexia, dry mouth, constipation, ataxia, livedo reticularis, peripheral edema, orthostatic hypotension, headache, somnolence, nervousness, dream abnormality, agitation, dry nose, diarrhea and fatigue.

Infrequently occurring adverse reaction (0.1 to 1%) are: CHF, psychosis, urinary retention, dyspnea, skin rash, vomiting, weakness, slurred speech, euphoria, confusion, thinking abnormality, amnesia, hyperkinesia, hypertension, decreased libido, and visual disturbance, including punctuate subepithelial or other corneal opacity, corneal edema, decreased visual acuity, sensitivity to light, and optic nerve palsy.

Rarely occurring adverse reactions (less than 0.1%) are: instances of convulsion, leukopenia, neutropenia, ezcematoid dermatitis and oculogyric episodes. Other rare occurring adverse reactions are: suicidal attempt, suicide, and suicidal ideation (see Warnings).

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Overdose
Symptoms:
Deaths have been reported from overdose with amantadine. The lowest reported acute lethal dose was 2 g. An elderly patient with Parkinson's syndrome who took an overdose of 2.8 g of amantadine in a suicidal attempt, developed acute toxic psychosis, urinary retention, and a mixed acid-base disturbance. The toxic psychosis was manifested by disorientation, confusion, visual hallucinations and aggressive behavior. Convulsions did not occur, possibly because the patient had been receiving phenytoin prior to the acute ingestion of amantadine.

Treatment:
There is no specific antidote. Slowly administered i.v. physostigmine in 1 and 2 mg doses at 1 to 2 hour intervals in an adult, and 0.5 mg doses at 5 to 10 minute intervals in a child 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 i.v.

Hemodialysis does not remove significant amounts of amantadine hydrochloride in patients with renal failure; a 4 hour hemodialysis removed 7 to 15 mg after a single 300 mg oral dose.

The pH of the urine has been reported to influence the excretion rate of amantadine. Since the excretion rate of the drug increases rapidly when the urine is acidic, the administration of urine-acidifying fluids 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 the possible development of arrhythmias, hypotension, hyperactivity, and convulsions; if required, appropriate therapy should be administered. The blood electrolytes, urine pH and urinary output should be monitored. If there is no record of recent voiding, catheterization should be done. The possibility of multiple drug ingestion by the patient should be considered.

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Dosage
Parkinson's Disease:
The initial dose of amantadine is 100 mg daily for patients with serious associated medical illnesses or who are receiving high doses of other antiparkinson drugs. After one to several weeks at 100 mg once daily, the dose may be increased to 100 mg twice daily. When amantadine and levodopa are initiated concurrently, amantadine should be held constant at 100 mg daily or twice daily while the daily dose of levodopa is gradually increased to optimal dose. When used alone, the usual dose of amantadine is 100 mg twice a day.

Patients whose responses are not optimal with amantadine at 200 mg daily may benefit from an increase to 300 mg daily in divided doses. Patients who experience a fall-off of effectiveness may regain benefit by increasing the dose to 300 mg daily; such patients should be supervised closely by their physicians.

Drug-Induced Extrapyramidal Symptoms:
The usual dose of amantadine is 100 mg twice a day. Occasionally, patients whose responses are not optimal with amantadine at 200 mg daily may benefit from an increase up to 300 mg daily in divided doses.

In the Presence of Impaired Renal Function:
Table I outlines the recommended dosage adjustments dependent upon creatinine clearance, based upon the current National Advisory Committee on Immunization (NACI) Canada Communicable Disease Report, May 29, 1992.

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Table I
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Creatinine Clearance
(mL/min/1.73m(2)) Dosage
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>=80 100 mg twice daily
60-79 Alternating daily doses of 200 and 100 mg
40-59 100 mg once daily
30-39 200 mg twice weekly
20-29 100 mg thrice weekly
10-19 Alternating weekly doses of 200 and 100 mg
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The recommended dosage for patients on hemodialysis is 20 mg every 7 days.

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Supplied
Capsules:
Each red, soft gelatin capsule contains: Amantadine HCl 100 mg. Also contains parabens. Alcohol-free, lactose-free, sodium-free, sulfite-free and tartrazine-free. Bottles of 100. Store at room temperature (15 to 30°C).

Syrup:
Each 5 mL of clear colorless syrup contains: Amantadine HCl 50 mg. Also contains parabens. Alcohol-free, lactose-free, sodium-free, sulfite-free and tartrazine-free. Bottles of 500 mL. Store at room temperature (15 to 30°C).

Information from MentalHealth.com

[Virginia Therese]

Tena...for some reason, I seemed to have missed your second response to my post related to Amandatine...just read it, now in its entirety, and it certainly answered many questions that I still have about this medication. Thank you so much for taking the time to send such a comprehensive report. Reading this, it is obvious that it is not as benign as I had thought...and it supports my feelings about NOT wanting to Doreen's dose to be increased to the 300 mg. daily...not yet, anyway. It was particularly important for me to read that Amantadine should NOT be discontinued abruptly...I have questioned this, too, especially in view of the fact that Doreen had such a horrendous reaction to the Cogentin...actual withdrawal symptoms which made me think that the titration off the medication had been a tad too abruptly. I have also questioned what "abruptly" means other than not stopping the medication "cold turkey"...4-5 days...a week...10 days...what is the general criteria for titrating off a medication? Or, is there a general criteria? Does it depend on which "medication"?

Thank you again, Tena...so much...we can always depend on you to give us comprehensive responses.

Therese