Generic Symmetrel – Antiviral and AntiParkinson Drug
Symmetrel (Amantadine) is a drug used to treat Parkinson’s disease and certain viral diseases such as the flu. In 1967, it was supposed to be used precisely as an antiviral agent for the treatment of influenza caused by type A2 viruses. However, in 2011, the CDC (US Centers for Disease Control and Prevention) recommended not to use amantadine for the treatment of viral diseases, since 99% of influenza viruses are resistant to its effects. Currently, amantadine is used in medicine for the treatment of parkinsonism, neuralgia caused by herpes zoster, delayed recovery from anesthesia and extrapyramidal disorders (movement disorders) caused by taking antipsychotics. This drug is used as a pain reliever for dogs and cats. In some countries, it is used to treat influenza in horses and poultry.
In what diseases this drug is applied?
Amantadine is used to treat Parkinson’s disease as well as Parkinson’s syndromes. A 2003 Cochrane review concluded that there is insufficient evidence to support the use of this drug in Parkinson’s disease. The extended release formulation is used to treat dyskinesia, a side effect of levodopa, which is used by people with Parkinson’s disease.
Symmetrel is no longer recommended for the treatment of influenza A infection. For the 2008/2009 influenza season, the CDC found that 100% of tested samples of seasonal influenza H3N2 and 2009 pandemic influenza showed resistance to adamantanes. The CDC warned doctors to use the neuraminidase inhibitors oseltamivir and zanamivir instead of amantadine and rimantadine to treat influenza. A 2014 Cochrane review found no benefit for the prevention or treatment of influenza A.
Mode of application and dosage
Oral application, after meal. The dosage is selected individually, usually – 100 mg/day for 3 days, then up to 200 mg/day with a further increase by 100 mg per week (the last daily intake before dinner). The maximum dose is 600 mg/day.
What is the mechanism of antiviral action?
The mechanism of the antiviral action is based on the fact that this substance is an antagonist of the M2 proton channel of influenza type A viruses. Blocking these channels contributes to disruption of the viruses release from the cell and, therefore, prevents infection of other cells. In addition, amantadine stimulates the release of dopamine from neurons and increases the sensitivity of receptors to this neurotransmitter. Since the symptoms of Parkinson’s disease and extrapyramidal disorders are caused by a lack of dopamine or a decrease in sensitivity to it, generic Symmetrel is effective in these conditions. Also, this substance belongs to an antagonist of muscarinic acetylcholine receptors and a non-selective antagonist of NMDA receptors. This leads to a decrease in tremor and the analgesic effect of amantadine.
What are contraindications of this medicine?
- Prostate adenoma;
- Psychomotor agitation;
- A condition of predilirium or delirium;
- A history of psychosis;
- Acute and chronic liver and kidney diseases;
- Pregnancy (I trimester);
Pregnancy and lactation
This antiviral drug is contraindicated in the first trimester of pregnancy. During treatment, breastfeeding should be discontinued.
- The nervous system and sensory organs: mental disorders accompanied by visual hallucinations, motor or mental agitation, dizziness, sleep disorders, decreased visual acuity (very rare).
- The cardiovascular system and blood (hematopoiesis, hemostasis): heart failure, arrhythmia, tachycardia.
- The digestive tract: dry mouth, nausea.
- The genitourinary system: urinary retention (in patients with prostate adenoma).
- Others: very rarely – the appearance of a bluish skin color of the upper and lower extremities.
This drug enhances the effects (including side effects) of other antiparkinsonian drugs. It is possible to reduce the dose of levodopa with simultaneous therapy with Symmetrel. Concomitant use with diuretics containing triamterene/hydrochlorothiazide can lead to a change in the concentration of amantadine in plasma.
This drug abuse in veterinary
It was reported that in 2005, Chinese poultry farmers used amantadine to protect birds from avian influenza. In Western countries and in accordance with international animal farming regulations, amantadine is only approved for use in humans. Chickens in China have received approximately 2.6 billion doses of amantadine. Avian influenza (H5N1) strains in China and Southeast Asia are now resistant to this substance, although strains circulating elsewhere are still susceptible. If virus strains resistant to amantadine spread, the drugs of choice for an avian influenza outbreak are likely to be limited to the neuraminidase inhibitors oseltamivir and zanamivir, which block the action of the viral neuraminidase enzyme on the surface of influenza virus particles. However, there has been an increase in the incidence of oseltamivir resistance in circulating strains of influenza (eg H1N1), highlighting the urgent need for new influenza treatments.