A rapid and sensitive spectrophotometric method has been developed for the quantitative analysis of three antiviral, anti-parkinsonism drugs, namely amantadine (AMA), memantine (MET), and rimantadine (RIM). The method is based on the usage of 1,3-indandione (IDO) as a chromogenic reagent to form charge transfer complexes with the studied drugs and produce colored reaction products with an absorbance maximum at 522 nm, allowing quantitative analysis of these drugs. In addition, the study was validated according to the official guidelines that permits usage in quality control laboratories. Many factors (reagent volume, diluting solvent, temperature, reaction and stability time) influencing the reactions were studied and optimized. The results showed that this method is able to detect AMA, MET, or RIM over a linear range between 10–140 µg/mL with high selectivity and robustness. Furthermore, the study results were applied to analyze the drugs in their pharmaceutical preparations with acceptable accuracy and precision.