Formulation, Optimization, and Evaluation of Solid-lipid Formulation for Bioavailability Enhancement Utilizing Diltiazem Hydrochloride

Background: Cardiac arrhythmia is a health concern, requiring effective medication for proper treatment. Diltiazem hydrochloride (DTZ.HCL), a class IV anti-arrhythmic calcium channel blocker, was used as a model drug due to its ability to block Ca++ channels in the SA and AV nodes, reducing calcium entry into cardiac cells and subsequently decreasing the force of contraction and oxygen consumption by the heart. Despite its good oral absorption, DTZ.HCL bioavailability is reduced to approximately 40% due to extensive first-pass metabolism. A nano-enabled drug delivery system has the advantage of incorporating both lipophilic and hydrophilic drugs with improved physical stability and enhanced bioavailability. Objective: The objective of this study was to develop a solid-lipid formulation utilizing diltiazem hydrochloride and evaluate it for its bioavailability enhancement. Methods: In the experimental study, SLNs were prepared using the microemulsion technique. A blend ratio (1:1) of lipid (stearic acid: compritol 888 ATO), span 80, PEG 200, and water was selected based on the microemulsion region obtained from the Triplot (4.1) ternary phase diagram. The hydrophilic drug diltiazem hydrochloride was incorporated into the lipid blend, and a preheated Smix was maintained at 80°C to obtain a transparent microemulsion, which then crystallized to form SLNs upon subsequent dispersion in cold water (1:25). Critical process parameters, including magnetic stirring speed, homogenizer speed, and probe sonication cycle, were optimized using Design Expert 10 software to achieve the desired particle size diameter, PDI, and entrapment efficiency. Results: The results revealed that the particle size and PDI were significantly influenced by the span 80 and PEG 200. An increase in the concentration of the lipid blend resulted in large particle sizes. The optimized formulation showed a particle size of 415.4±0.2 nm, PDI of 0.184±0.01, and zeta potential of -24.19±0.12 mV. These results were corroborated by DSC thermograms, which indicated reduced enthalpy associated with the reduced particle size of SLNs. Given that diltiazem hydrochloride is a hydrophilic drug with high water solubility, the entrapment efficiency was relatively 30.6% ±0.45. In vitro release studies demonstrated an initial burst release, followed by a sustained release of 85% over 24 hours. The optimized SLNs followed the Higuchi matrix model, with a coefficient of correlation (R²) value of 0.9369. Conclusion: Results concluded successful development of SLNs with improved bioavailability when compared by way of in-vitro method with marketed preparations.