Spectral analysis of severely overlapping spectra based on newly developed mathematical filtration techniques and ratio spectra manipulations: An application to the concurrent determination of dapoxetine and sildenafil in combined dosage form.

BACKGROUND

Dapoxetine hydrochloride (DAP) and sildenafil citrate (SIL) have proven clinically effective in the treatment of comorbid conditions like erectile dysfunction and premature ejaculation. The analysis of DAP and SIL combinations represents a challenge because of the severe overlap of these compounds' spectra. Six newly developed methods were proven effective for resolving such a challenging overlap. They also exhibited the advantage of simplicity as they depend on the zero-order spectrum and only require simple mathematical handling.

OBJECTIVE

We suggested six simple, precise, and sensitive spectrophotometric methods based on mathematical filtration techniques and ratio spectra manipulations to resolve the spectra of DAP and SIL in their bulk and combined pharmaceutical dosage form and estimate the relevant individual concentrations.

METHODS

The first three methods were based on the zero-order range and involved modest mathematical manipulations. They are the induced dual-wavelength, Fourier self-deconvolution, and absorptivity factor spectrophotometric methods. Three other methods that are based on ratio spectra manipulation were developed: ratio difference, mean centering of the ratio spectra, and derivative ratio spectrum.

RESULTS

We determined the performance of the suggested methods for estimating DAP and SIL in their laboratory mixtures and their combined pharmaceutical dosage form. The linear ranges for DAP and SIL were 1-40 µg/ml and 2-60 µg/ml, respectively. The detection limits were in the 0.18-1.10 µg/ml range for DAP and in the 0.68-1.11 µg/ml range for SIL. The developed methods were validated as per the ICH guidelines for linearity, detection limit, quantitation limit, selectivity, precision, and accuracy. Normal probability, interval, and Tukey's simultaneous significant difference plots were utilized to confirm and better visualize the analysis of variance test results. Statistically, no significant difference was observed to exist between results obtained from the hereby developed and the previously reported methods.