Stability-indicating method combination drugs

To develop an HPLC stability-indicating method for Type I or II dissolution, the linearity must be wide enough, in combination with good sensitivity and minimal interference, to accommodate concentrations from low (possibly LOQ) to very high end, as the samples drawn represent the cumulative drug amount dissolved over time. As for an FiPLC method that is designed for Type VII dissolution, the linearity should accommodate the lower concentrations since it is a drug measurement of a controlled-release system. 

G.B. Chaudhari, N. Patel, P.B. Shah, Stability indicating RP-HPLC method for simultaneous determination of atorvastatin and amlodipine from their combination drug products, Chem. Pharm. Bull. 55 (2007) 241-246. 

Wahbi reported on the use of second-derivative spectroscopy for the determination of canrenone in spironolactone, and found that the method is stability-indicating for spironolactone [21]. First and second-derivative spectroscopy were also utilized for the simultaneous analysis of spironolactone in combination with either hydrochlorothiazide or frusemide [22], The drugs are extracted with ethanol and analyzed through the use of the zero-crossing method. Nowakowska [23] analyzed mixtures of spironolactone and hydrochlorothiazide in tablets by measuring the absorbance of all species at 239 nm, and that of hydrochlorothiazide at 318 nm. The recoveries for spironolactone were found to be 97.9 to 101.8%, with a coefficient of variation of less than 0.1%. 

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