Kinetics of drug decomposition. Part 74. Kinetics of degradation of minocycline in aqueous solution.

Under anaerobic conditions within the pH range 0.38-9.35 (at 343 K) and in the presence of air oxygen within the pH range 0.83-5.42 (at 323 K) the degradation of minocycline (MC) in aqueous solutions follows the first order kinetics. In neutral and alkaline solutions in the presence of air oxygen the autocatalytic first order reaction takes place. The degradation of MC both under anaerobic and aerobic conditions is catalyzed by buffer components of formate, acetate, phosphate and borate buffers. Under anaerobic conditions the degradation of MC is a result of water evoked spontaneous reaction. The rate of this reaction depends on the charge of MC. The specific rate constants of degradation for particular ionic species of MC under anaerobic conditions have been determined. The rate of oxidation of MC is also charge-dependent. The most susceptible to oxidation are the ionic species MC+-, MC+-- and MC--. Effects of temperature, metal ions and stabilizers on the stability of MC were also investigated.