Cell: 1 mm.

Solution— Place a volume of Oral Solution, equivalent to about 200 mg of amantadine hydrochloride, in a vessel, dissolve in 0.1 N hydrochloric acid, and filter. Transfer the filtrate to a separator, add 10 mL of 0.5 N sodium hydroxide, and extract with 5 mL of methylene chloride. Filter the extract through anhydrous sodium sulfate, and rinse the anhydrous sodium sulfate with 2 mL of methylene chloride.

Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Amantadine Hydrochloride Capsules.

Assay preparation— Pipet 5.0 mL of the Oral Solution into a 250-mL conical flask, and add 45 mL of 1.0 N sodium hydroxide and 50.0 mL of Internal standard solution. Shake for 60 minutes, and collect the hexane layer (Assay preparation).

Procedure— Proceed as directed in the Assay under Amantadine Hydrochloride Capsules. Calculate the quantity, in mg, of amantadine hydrochloride (C10H17N·HCl) in the portion of Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Amantadine Hydrochloride RS in the Standard preparation; and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.