Self-Microemulsifying Drug Delivery Systems : A Comprehensive Review
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Abstract
The formulation and delivery of poorly water-soluble drugs remain a significant challenge in pharmaceutical development. Self-Microemulsifying Drug Delivery Systems (SMEDDS) have emerged as a promising solution to overcome solubility and bioavailability limitations, particularly for Biopharmaceutics Classification System (BCS) Class II drugs. SMEDDS are isotropic mixtures of oils, surfactants, and co-surfactants that spontaneously form oil-in-water microemulsions upon contact with gastrointestinal fluids, producing nano-sized droplets that enhance drug dissolution, absorption, and lymphatic transport. This review provides a comprehensive overview of SMEDDS, starting with the principles of lipid-based drug delivery and the mechanism of self-emulsification. The selection of formulation components—including oils (e.g., medium-chain triglycerides), surfactants (e.g., Tween 80, Cremophor EL), and co-surfactants (e.g., Transcutol P, PEG 400)—is discussed in detail, emphasizing their role in microemulsion formation and drug solubilization. The formulation development process, including pseudo-ternary phase diagram construction, excipient screening, and optimization via design of experiments (DoE), is elaborated to illustrate systematic approaches in SMEDDS design. Key characterization techniques such as droplet size analysis, zeta potential measurement, thermodynamic stability testing, and phase behavior studies are highlighted to ensure formulation robustness. The advantages of SMEDDS—such as improved oral bioavailability, ease of manufacturing, and protection from enzymatic degradation—are contrasted with limitations like surfactant-induced toxicity and drug precipitation risks. The review also explores the diverse applications of SMEDDS across oral, topical, ocular, and parenteral routes, supported by case studies of marketed products such as Neoral® and Norvir®. Recent advances, including solid and supersaturated SMEDDS, targeted delivery strategies, and stimuli-responsive systems, are presented as future directions. Overall, SMEDDS represent a versatile and effective platform for enhancing the therapeutic performance of hydrophobic drugs, with continued innovation paving the way for broader clinical application
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