It also may interfere with penetration of the cell wall by adsorbed virus. To prevent a viral infection, the drug should be present before exposure to the virus, but, if given within 24-48 hours of onset of symptoms, the influenza may be less severe. Absorption from the GI tract appears to be rapid and complete. Peak plasma concentrations are achieved in about 2-4 hours following oral administration. Ninety percent of amantadine is excreted in the urine via glomerular filtration and tubular secretion.
Renal impairment reduces protein binding.
Acidifying the urine increases the rate of excretion. Only a small amount of amantadine is removed by dialysis. Because amantadine is primarily excreted unchanged in the urine, patients with renal impairment should receive lower doses. Renal function should be monitored closely and the dose adjusted accordingly. Peripheral edema and congestive heart failure can be precipitated by amantadine, which is thought to induce a redistribution of fluid within the body rather than an increase in total body water.