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Authors : *Dipika S. Sherkar, Vaibhav G. Bhamre, Deelip V. Derle, Minal R. Narkhede, Jitesh H. Shet and Amit Tiwari
Abstract : Objective of this work was to study the effect of ofloxacin on bioavailability and other pharmacokinetic parameters of tizanidine in rats. A single dose parallel design was used with 36 animals randomly divided in reference group and test group.  All the rats received 7 mg tizanidine orally and in test group 200 mg ofloxacin was co-administered with tizanidine. Nine blood samples were collected from each animal over a 24-hour period. Plasma tizanidine concentrations were determined by HPTLC using UV detection, and pharmacokinetic parameters were determined by non-compartmental method. The mean value of the peak plasma concentration (Cmax) of tizanidine decreased significantly (8.47%, P value <0.001; 90% CI, 91.32% -91.72%) in animals who had given the drug with ofloxacin (Cmax , 31.54 ± 0.16 µg/mL) than those who had given the drug with water (Cmax, 34.46 ± 0.07 µg/mL). The area under the plasma concentration time curve from t=0 to time of the last measureable concentration (AUC0-t) was also increased significantly (17.17%, P value <0.001; 90% CI, 116.99% -117.34%). Similarly, the value of area under the concentration-time curve from t=0 to infinity (AUC0-∞) value was increased significantly (5.24% %, P value <0.001; 90% CI, 103.77% -104.83%); these changes were not within the 90% CI range of 80.000 - 125.000 % which is the acceptable range of bioequivalence. Tmax, T1/2, terminal elimination rate constant (λz), CL/F value, Vd/F value, AUMC0-t and AUMC0-∞ values, MRT0-t and MRT0-∞ values and % relative bioavailability (Fr) value for test group were also determined and compared with reference group. Form results the values of Cmax and AUC0-∞ were not within the bioequivalence acceptable range and from statistical analysis the reference and test samples were found to be bio-in-equivalent, suggesting the improved tizanidine oral bioavailability and therapeutic efficacy due to co-administration of ofloxacin.