In vitro release of tetracyclines in presence of H2-receptor antagonists

There are a number of drug interactions reported for tetracyclines with many other drugs. In present study in vitro release of five different tetracyclines i.e., tetracycline, demeclocycline, oxytetracycline, methacycline and doxycycline in presence of cimetidine and ranitidine has been studied by USP XX dissolution method. The release of almost all tetracyclines was depressed in presence of cimetidine and ranitidine while in some cases the value were greatly increased due to the formation of charge transfer complexes of the antibiotic with H2-receptor antagonists, which gave absorbance at same wavelengths but with much higher molar absorptivity. An attempt was made to elucidate the mechanism of this effect.