Pharmaceutical quality control of acid and neutral drugs based on competitive self-assembly in amphiphilic systems

An aggregation parameter-based methodology for determining acid and neutral drugs in pharmaceutical dosage forms is presented. The method is based on competitive self-assembly in ternary dye-surfactant-drug aqueous mixtures. Dyes bearing charge of opposite sign to that of surfactants bind to surfactant to form mixed dye-surfactant aggregates, which are monitored from changes in the spectra features of the dye. The drug competes with the dye to interact with the surfactant to form drug-surfactant aggregates, which results in a decrease in the surfactant to dye binding degree proportional to the drug concentration in the aqueous solution. Coomassie Brilliant Blue G (CBBG) and didodecyldimethylammonium bromide (DDABr) were the dye and surfactant reactant used, respectively. The suitability of the surfactant to dye binding degree (SDBD) method to determine drugs with very different molecular structure: propionic (flurbiprofen, ibuprofen, naproxen and ketoprofen) and acetic (diclofenac, felbinac and zomepirac) acids, indolines (indomethacin and sulindac), glycyrrhetinic acid derivatives (carbenoxolone and enoxolone), salicylates (diflunisal and phenyl salicylate), oxicams (meloxicam, piroxicam and tenoxicam), pyrazolones (phenylbutazone and sulfinpyrazone) and hydrocortisones (dexamethasone and prednisolone) has been proved. The proposed method was successfully applied to the determination of drugs in commercial formulates (effervescent granulates, tablets, suppositories, gels and blisters) with a minimum sample treatment (dilution of liquid samples and dissolution of solid samples).