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We have developed a Bioanalytical method for the determination of
sildenafil and N-desmethyl sildenafil. During the method validation
all parameters were found to be well within the acceptable limits as
mentioned in the USFDA guidelines.After study sample analysis ISRA
(incurred sample reanalysis) was performed for both sildenafil and its
metabolite N-desmethyl sildenafil. The ISRA results of sildenafil were
found to be matching with initial concentration, but ISRA results of
N-desmethyl sildenafil has shown 20 to 50% increase in the
concentration when compared to initial concentration. Same bulk
spiked Calibration standards and QCs were were used for both study
sample analysis and ISRA. Calibration standards and Quality control
samples were comfortably passing for both sildenafil and N-desmethyl
sildenafil. Using same samples second ISRA was performed.During second
ISRA the values of sildenafil were matching with initial values, but
N-desmethyl sildenafil results has shown 50 to 100% increase in the
concentration when compared to the concentration of initial analysis.
Using same bulk spiked calibration standards and QC samples ISRA was
performed for 6 times on different days. The concentration of
sildenafil was found to be matching with initial analysis during all
six times, but N-desmethyl sildenafil concentration was found to be
increasing 20 to 50% during each analysis. The N-desmethyl sildenafil
ISRA results of 5th and 6th time analysis were matched and found to
be with in 20%.
Please share yours experience to resolve this problem.
Freeze thaw stability has been proved for 6 cycles by spiking the
sildenafil and N-desmethyl sildenafil to harvested plasma.
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