Influenza
The mechanisms for amantadines antiviral and antiparkinsonian effects are unrelated. Amantadine targets the influenza A M2 ion channel protein. The M2 proteins 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.Amantadine and rimantadine function in a mechanistically identical fashion, entering the barrel of the tetrameric M2 channel and blocking pore function—i.e., proton translocation.Resistance to the drug class is a consequence of mutations to the pore-lining amino acid residues of the channel, preventing both amantadine and rimantadine from binding and inhibiting the channel in their usual way. Pharmacokinetics
Amantadine is well absorbed orally. The onset of action is usually within 48 hours when used for parkinsonian syndromes, including dyskinesia. As plasma concentrations of amantadine increase, there is a greater risk for toxicity.Half-life elimination averages eight days in patients with end-stage kidney disease. Amantadine is only minimally removed by hemodialysis.Amantadine is metabolized to a small extent (5-15%) by acetylation. It is mainly excreted (90%) unchanged in urine by kidney excretion. Medical uses
Parkinsons disease
Amantadine is used to treat Parkinsons disease-related dyskinesia and drug-induced parkinsonism syndromes. Amantadine may be used alone or in combination with another anti-Parkinsons or anticholinergic drug. The specific symptoms targeted by amantadine therapy are dyskinesia and rigidity.
The reference standard was a large batch of impure penicillin kept in Oxford. The assay was later modified by Floreys group to a more reproducible "cup assay": in this assay, a penicillin solution was defined to contain one unit/ml of penicillin when 339 microlitres of the solution placed in a "cup" on a plate of solid agar produced a 24 millimetre zone of inhibition of growth of Oxford Staphylococcus. : 107 
First International Standard (1944). A single 8 gram batch of pure crystalline penicillin G sodium was stored at The National Institute for Medical Research at Mill Hill in London (the International Standard). One penicillin unit was defined at 0.6 micrograms of the International Standard. An impure "working standard" was also defined and was available in much larger quantities distributed around the world: one unit of the working standard was 2.7 micrograms (the amount per unit was much larger because of the impurities). At the same time, the cup assay was refined, where instead of specifying a zone diameter of 24 mm, the zone size were instead plotted against a reference curve to provide a readout on potency. Second International Standard (1953). A single 30 gram batch of pure crystalline penicillin G sodium was obtained: this was also stored at Mill Hill. One penicillin unit was defined as 0.5988 micrograms of the Second International Standard.There is an older unit for penicillin V that is not equivalent to the current penicillin V unit.