The present paper describes the effect of metals ions on the in vitro availability of enoxacin (a second generation quinolone antibiotic) owing to drug-metal interaction. These interaction studies were performed at 37 °C in different pH environments simulating human body compartments and were studied by UV spectroscopic technique. In order to determine the probability of these reactions different kinetic parameters (dissolution constants (K) and free energy change (ΔG)) for these reactions were also calculated. It is proposed that the structure of enoxacin contains various electron donating sites which facilitate its binding with metallic cations forming chelates. Hence taking food products, nutritional supplements or multivitamins containing multivalent cations at the same time as enoxacin, could reduce the absorption of the drug into the circulation and thus would decrease the effectiveness of the drug. In addition, the MIC of enoxacin for various microorganisms before and after interaction with metal ions was calculated which in most cases was increased which possibly could impair the clinical efficacy of the drug.

Patients diagnosed with diabetes are prescribed a large number of medications for appropriate therapy, increasing risk of side effects or drug interactions. Metformin, a guanidine derivative is commonly used as a drug of choice for the treatment of non insulin dependent diabetes mellitus. There are a number of interactions reported for metformin. On the other hand, NSAIDs are generally used for the treatment of pain, fever and inflammation, particularly arthritis. Since the former drug is used in long term therapy, it may be co-administered with other drugs. In the present paper, we investigated the in-vitro availability of metformin in presence of commonly used NSAIDs, like diclofenic sodium, flurbiprofen, ibuprofen, mefenamic acid, meloxicam and tiaprofenic acid. These studies were carried out using modified BP 2007 dissolution test apparatus in simulated body environments at 37°C. These drug interactions were analyzed by UV/ VIS spectroscopy and the effect on the availability of both metformin and NSAIDs in presence of each other was calculated by applying simultaneous equation which was derived by modifying Beers law. The interactions were further studied by RP-HPLC with mobile phase consisting of methanol and water (80:20 v/v) maintained at a flow rate of 1 mLmin-1 at isobestic point 241 nm (metformin, diclofenac sodium, flurbiprofen, tiaprofenic acid, ibuprofen, meloxicam and mefenamic acid) respectively The results showed that the in vitro availability of NSAIDs and metformin owing to interaction was depressed through the formation of charge transfer complexes which was found to be associated with inter- and intra-molecular rearrangement of the electronic cloud of the interacting drugs. Henee it is envisaged that concurrent administration of metformin and NSAIDs could alter the bio-availability and impair the clinical efficacy of both drugs. Effect of pH is also studied on these drug-drug interactions.

In the present paper, we describe the in vitro availability of simvastatin, a potent HMG-CoA reductase inhibitor, in presence of losartan potassium, which is a non-peptide angiotensin II receptor antagonist. These studies were carried out at 37, 48 and 60°C in different pH environments simulating human body compartments. The reactions were studied by UV spectroscopy and the availability of both drugs in presence of each other was determined by deriving a simultaneous equation for two component system through modifcation of Beer`s law. The interactions were further characterized by IR and H¹NMR spectroscopic techniques. It was observed that availability of simvastatin in presence of losartan at 37 ºC in simulated gastric juice, at pH 7.4 and pH 9.0 was blocked by losartan through the formation of a charge-transfer complex while the availability of losartan in turn was immensely increased. In pH 4.0 these effects were reversed, availability of simvastatin increased and the availability of losartan was depressed. Similar results were observed at higher temperatures.