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Inhibitor

The anti-influenza A compound amantadine acts by blocking the M2 ion channel which is required for uptake of protons into the interior of the virus to permit acid-promoted viral uncoating (decapsidation).

Definition

ChEBI: A member of the class of adamantanes that is used as an antiviral and antiparkinson drug.

Biological Functions

Amantadine was originally introduced as an antiviral compound, but it is modestly effective in treating symptoms of parkinsonism. It is useful in the early stages of parkinsonism or as an adjunct to levodopa therapy. Its mechanism of action in parkinsonism is not clear, but amantadine may affect dopamine release and reuptake. Additional sites of action may include antagonism at muscarinic and N-methyl-Daspartate (NMDA) receptors. Adverse effects include nausea, dizziness, insomnia, confusion, hallucinations, ankle edema, and livedo reticularis. Amantadine and the anticholinergics may exert additive effects on mental functioning

Synthesis Reference(s)

Journal of the American Chemical Society, 91, p. 6457, 1969 DOI: 10.1021/ja01051a047Synthesis, p. 457, 1976

Antimicrobial activity

It inhibits influenza A virus replication at concentrations of 0.2– 0.6 mg/L, but has little or no activity against influenza B or C.

Acquired resistance

Resistance is the consequence of mutations in amino acid positions 27, 30 and 31 in the M2 transmembrane sequence. Cross-resistance between amantadine and rimantadine is universal. Influenza H3N2 strains worldwide are now resistant, but seasonal H1N1 strains remain susceptible. Postexposure family prophylaxis results in the prompt emergence of drug resistance after onset of treatment.

General Description

Amantadine has been used for years as a treatment for Parkinson disease. The adamantanamines have twomechanisms in common:they inhibit an early step in viralreplication, most likely viral uncoating,and in somestrains, they affect a later step that probably involves viral assembly,possibly by interfering with hemagglutinin processing.The main biochemical locus of action is the influenzatype A virus M2 protein, which is an integral membrane proteinthat functions as an ion channel. The M2 channel is a protontransport system. By interfering with the function of theM2 protein, the adamantanamines inhibit acid-mediated dissociationof the ribonucleoprotein complex early in replication.They also interfere with transmembrane proton pumping,maintaining a high intracellular proton concentrationrelative to the extracellular concentration and enhancingacidic pH-induced conformational changes in the hemagglutininduring its intracellular transport at a later stage. The conformationalchanges in hemagglutinin prevent transfer of thenascent virus particles to the cell membrane for exocytosis.

Flammability and Explosibility

Flammable

Pharmaceutical Applications

A symmetrical synthetic C-10 tricyclic amine with an unusual cage-like structure, supplied as the hydrochloride for oral administration.

Mechanism of action

Amantadine hydrochloride (1-adamantanamine hydrochloride) is a symmetric, tricyclic, primary amine that inhibits penetration of RNA viral particles into the host cell. It also inhibits the early stages of viral replication by blocking the uncoating of the viral genome and the transfer of nucleic acid into the host cell.

Pharmacokinetics

Oral absorption: >90% Cmax 200 mg oral per day: 0.4–0.9 mg/L after c. 4–6 h Plasma half-life: 9.7–14.5 h Volume of distribution: 10.4 L/kg Plasma protein binding: 65% Absorption and distribution Absorption after oral administration is almost complete. Levels in secretions approach plasma concentrations. Metabolism and excretion About 56% of a single oral dose is excreted unchanged within 24 h by the kidney. Altogether 90% of an oral dose is excreted in the urine with a mean elimination half-life of 11.8 h in subjects with normal renal function. In elderly men, the half-life is 28.9 h and in patients with renal insufficiency half-lives of 18.5 h to 33.8 days have been observed. The renal clearance is around 398 mL/min (range 112–772 mL/min), indicating active secretion as well as glomerular filtration. Less than 5% of a dose is removed during hemodialysis and average half-lives of 8.3 and 13 days have been reported in patients on chronic hemodialysis. Extreme care must be taken to ensure that drug does not accumulate to toxic levels.

Side effects

Embryotoxicity and teratogenicity have been observed in rats receiving 50 mg/kg per day, about 15 times the usual human dose. Neurological side effects include drowsiness, insomnia, light-headedness, difficulty in concentration, nervousness, dizziness and headache in up to 20% of individuals. Other side effects include anorexia, nausea, vomiting, dry mouth, constipation and urinary retention. All develop during the first 3–4 days of therapy and are reversible by discontinuing the drug. An exception to rapid onset of adverse reactions is livedo reticularis. Convulsions, hallucinations and confusion are dose related, usually occurring at levels in excess of 1.5 mg/L; convulsions may occur at a lower threshold in patients with a history of epilepsy and the drug is best avoided in such patients.

Safety Profile

Poison by intraperitoneal route.Moderately toxic by ingestion. Mutation data reported.When heated to decomposition it emits toxic fumes ofNOx. Used as an antiviral agent.

Synthesis

Amantadine, 1-adamantanamine (10.1.12), is synthesized from adamantane. It is directly brominated to 1-bromadamantane (10.1.10), which in Ritter reaction conditions when heated with a mixture of acetonitrile and concentrated sulfuric acid transforms into 1-acetylaminoadamantane (10.1.11). Hydrolysis of this product using alkali leads to the formation of amantadine (10.1.12) [16,17].

Purification Methods

Dissolve the amine in Et2O, dry it over KOH, evaporate and sublime it in vacuo. [Stetter et al. Chem Ber 93 226 1960.]