This study reports the use of para-sulphonato calixarene to produce stable complexes with improved bioavailability for nifedipine, a calcium-channel blocker that is practically insoluble in water. Thermal analysis and electrospray ionisation mass spectroscopy confirmed that nifedipine formed complexes with the calixarenes in a size dependent way. The most stable, soluble complexes was formed with para-sulphonato calixarene. Complexation was weakest with the calixarene while complexation with the calixarene was intermediate. However, the calix[4 and 6]arenes changed the chemical stability of the drug in solution because significant amounts of the nitroso-pyridine derivative was produced, proposing an interaction between the nifedipine bearing a H substituent at the N-1 position and the calixarenes. This oxidative degradation of the drug was greatest when combined with the calixarene. Simultaneous oral ingestion of the calix[6 or 8]arenes significantly increased the bioavailability of the drug after oral administration in male Sprague-Dawley rats while not influencing CYP3A activities in the liver. The pharmacokinetic parameters of the nifedipine: para-sulfonato calixarene complexes showed it was bioequivalent to a nifedipine PEG-solution. The absolute bioavailability for both formulations was ca. 60 %.
Keywords: Para-sulphonato calix[n]arenes, nifedipine, solubility, stability, pharmacokinetics
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