Development of leachable enalapril tablets by controlled porosity osmotic pump technique; a unique approach to enhance its sustained release effect

The present study aimed to design and evaluate controlled porosity osmotic pump (CPOP) tablets of enalapril maleate (ENP) being used for the treatment of hypertension. D-optimal response surface design was used, considering cellulose acetate and osmotic agents (lactose and fructose) as variables while physicochemical parameters of tablets were taken as responses. The asymmetric, leachable membrane of cellulose acetate on ENP tablets was applied and an increase in the thickness of core tablets from 5 ± 0.01 to 5.4 ± 0.17 mm was observed. The average weight of all CPOP formulations ranged from 376.7 ± 0.4 to 389.1 ± 0.3 mg and hardness was 6.2 ± 0.02 to 6.32 ± 0.06 Kg/cm2. The friability of all formulations was less than 1%. 89.53 ± 1.05% of ENP release was observed in phosphate buffer pH 6.8 after 12 h. Due to the smallest AIC (Akaike information criteria) and the greatest r2 values, zero-order release kinetics model with non-Fickian diffusion behavior was observed in all proposed formulations. f1 (difference factor) values were 1.28 ± 0.06 to 12.64 ± 0.41% and f2 (similarity factor) values were 59.75 ± 0.24 to 94.03 ± 1.36% in the same dissolution medium. pH-independent behavior was observed in pH-responsive study. Dissolution efficiency (DE) ranged from 51.49 ± 0.23 to 53.52 ± 0.52% and mean dissolution time (MDT) values ranged from 5.27 ± 0.05 to 5.59 ± 0.23 h. No interaction between the ingredients was found in FTIR analysis. The optimized formulation with improved drug release property was found stable in the accelerated stability study of six months. CPOP tablets of ENP can be considered as an effective substitute for immediate-release tablets to control hypertension in chronic conditions.