Amantadine treats parkinsonian dyskinesia as an muscarinic antagonist and acts as a noncompetitive NMDA antagonist. Amantadine was used as an antiviral drug used to treat and prevent influenza A infections. The antiviral mechanism of action is antagonism of the influenza A surface protein M2. M2 inhibition prevents viral shedding. Due to high levels of viral resistance to amantadine and other adamantanes, these drugs are no longer used against influenza A virus.
|Metabolism||Minimal (mostly to acetyl metabolites)|
|Elimination half-life||10–31 hours|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||151.249 g/mol g·mol−1|
|3D model (JSmol)|
Amantadine (trade names Gocovri, Symadine, and Symmetrel) is the organic compound 1-adamantylamine or 1-aminoadamantane (an adamantane backbone with an amino group substituted at one of the four methyne positions). Rimantadine is a closely related derivative of adamantane with similar biological properties (both target the M2 surface protein of influenza A virus).
Amantadine is used to treat Parkinson's disease related dyskinesia and drug-induced parkinsonism syndromes. Amantadine may be used alone or combined with another anti-parkison or anticholinergic drug. The specific symptoms targeted by amatadine therapy are dyskinesia and rigidity. Levodopa and amantadine is a common combination.
Amantadine is no longer recommended for treatment or prophylaxis of influenza A in the United States. Amantadine has no effect preventing or treating influenza B infections. The Centers for Disease Control found 100% of seasonal H3N2 and 2009 pandemic flu samples were resistant to adamantanes (amantadine and rimantidine) during the 2008-2009 flu season.
The CDC guidelines updated to recommend only neuraminidase inhibitors for influenza treatment and prophylaxis. The CDC currently recommends against amantadine and rimantadine to treat influenza A infections.
Similarly, the 2011 World Health Organization virology report showed all tested H1N1 influenza A viruses were resistant to amantadine. Current WHO guidelines recommend against use of M2 inhibitors for influenza A. The continued high rate of resistance observed in laboratory testing of influenza A has reduced the priority of M2 resistance testing until further notice.
A 2014 Cochrane review did not find evidence for efficacy or safety of amantadine used for the prevention or treatment of influenza A.
Extra-pyramidal side effectsEdit
An extended release formulation is used to treat dyskinesia, a side effect of levodopa which is taken by people who have Parkinsons. WHO recommendations are currently for amantadine as a combination therapy to reduce levadopa side effects.
Fatigue in multiple sclerosisEdit
Live attenuated vaccines are contraindicated while taking amantadine. It is possible that amantadine will inhibit viral replication and reduce the efficacy of administered vaccines. The FDA recommends avoiding live vaccination and amantadine for 2 weeks prior to vaccine administration or 48 hours afterwards.
Amantadine has been associated with several central nervous system (CNS) side effects. About 10% or more of patients may experience falls, dizziness, and hallucinations. Other side effects may include constipation or dry mouth.
Serious side effects may include drowsiness (especially while driving), suicidal thoughts, actions, or depression, new or worsened hallucinations, inhibited actions (gambling, sexual activity, spending, other addictions) and diminished control over compulsions, and light headedness, falls, and hypotension (low blood pressure).
Mechanism of actionEdit
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The mechanism of its antiparkinsonian effect is poorly understood. Amantadine appears to be a weak antagonist of the NMDA-type glutamate receptor, increases dopamine release, and blocks dopamine reuptake. Amantadine probably does not inhibit monoamine oxidase (MAO) enzyme. Moreover, the drug has many effects in the brain, including release of dopamine and norepinephrine from nerve endings. It appears to be an anticholinergic antagonist (specifically a nicotinic alpha-7) like the similar pharmaceutical memantine.
In 2004, it was discovered that amantadine and memantine bind to and act as agonists of the σ1 receptor (Ki = 7.44 µM and 2.60 µM, respectively), and that activation of the σ1 receptor is involved in the dopaminergic effects of amantadine at therapeutically relevant concentrations. These findings may also extend to the other adamantanes such as adapromine, rimantadine, and bromantane, and could explain the psychostimulant-like effects of this family of compounds.
The mechanisms for amantadine's antiviral and antiparkinsonian effects are unrelated. Amantadine targets the influenza A M2 ion channel protein. The M2 protein's function is to allow the intracellular virus to replicate (M2 also functions as a proton channel for hydrogen ions to cross into the vesicle), and exocytose newly formed viral proteins to the extracellular space (viral shedding). By blocking the M2 channel, the virus is unable to replicate because of impaired replication, protein synthesis, and exocytosis.
Resistance to the drug class is a consequence of mutations to the pore-lining residues of the channel, preventing both amantadine and rimantadine from inhibiting the channel in their usual way.
Influenza B strains possess a structurally distinct M2 channel with channel-facing side chains that fully obstruct the channel vis-à-vis binding of adamantine-class channel inhibitors, while still allowing proton flow and channel function to occur; this constriction in the channels is responsible for the ineffectiveness of this drug and rimantadine towards all circulating Influenza B strains.
Drug to drug interactionsEdit
Amantadine may effect the central nervous system due to dopaminergic and anticholinergic properties. The mechanisms of action are not fully known. Because of the CNS effects, caution is required when prescribing additional CNS stimulants or anticholinergic drugs.
Amantadine was approved by the U.S. Food and Drug Administration in October 1966 as a prophylactic agent against Asian influenza. Amantadine trial experiments exposed volunteer college students to a viral challenge. The group that received amantadine (100 milligrams 18 hours before viral challenge) had less Asia influenza infections than the placebo group. Amantadine received approval for the treatment of influenza virus A in adults in 1976.
An incidental finding in 1969 prompted investigations about amantadine's effectiveness for treating symptoms of Parkinsons disease. A woman with Parkinsons was prescribed amantadine to treat her influenza infection and reported her cogwheel rigidity and tremors improved. Importantly,she also reported her symptoms worsened when she finished the course of amantadine. The published case report was not initially corroborated by any other instances by the medical literature or manufacturer data. A team of researchers looked at a group of ten patients with Parkinsons and gave them amantadine. Seven of the ten patients showed improvement, which was convincing evidence for the need of a clinical trial. The 1969 trial, lead author Robert S. Schwab, MD) included 163 Parkinsons patients and 66% experienced subjective or objective reduction of symptoms. Additional studies from Schwab's team followed patients for greater lengths of time and in different combinations of neurological drugs. The US FDA approved amantadine for use in the treatment of Parkinsons disease.
In 2017, the U.S. Food and Drug Administration approved the use of amantadine in an extended release formulation developed by Adamas Pharma for the treatment of dyskinesia, an adverse effect of levodopa, that people with Parkinson's experience.
In 2005, Chinese poultry farmers were reported to have used amantadine to protect birds against avian influenza. In Western countries and according to international livestock regulations, amantadine is approved only for use in humans. Chickens in China have received an estimated 2.6 billion doses of amantadine. Avian flu (H5N1) strains in China and southeast Asia are now resistant to amantadine, although strains circulating elsewhere still seem to be sensitive. If amantadine-resistant strains of the virus spread, the drugs of choice in an avian flu outbreak will probably be restricted to neuraminidase inhibitors oseltamivir and zanamivir which block the action of viral neuraminidase enzyme on the surface of influenza virus particles. However, there is an increasing incidence of oseltamivir resistance in circulating influenza strains (e.g., H1N1), highlighting the serious need for the development of new anti-influenza therapies.
On September 23, 2015, the US Food and Drug Administration announced the recall of Dingo Chip Twists "Chicken in the Middle" dog treats because the product has the potential to be contaminated with amantadine.
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