The potential of the drug remains to be harvested by designing a suitable formulation that could overcome its inherent low bioavailability.

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The drug delivery system using solid lipid nanoparticles (SLN) came into being about two decades ago and since then lot of work has been done in this field.1-5) SLN for oral drug administration are specifically used to target the uptake of the drug by lymphatic system which prevents its first pass metabolism. Lymphatic uptake of drugs follow two routes which include transcellular transport through the enterocyte and phagocytosis of the drugs by Mast cells of payer's patches lining the intestinal mucosa. [6][7][8] The production of this nano particulate system is based on the principle of solidification of lipid nano emulsion.9) The different technologies available for the fabrication of SLN are high shear homogenization, ultrasound, high pressure homogenization (cold homogenization and hot homogenization), solvent emulsification/evaporation and microemulsion method.10) The major excipients used in the development of the SLN are fatty acids, mono, di and triglycerides, phospholipids etc., which are part of the physiological composition and thus are biocompatible to the body. [11][12][13] SLN have been shown to have superior advantages over polymeric nanoparticles, fat emulsion and liposomes.14) SLN can be produced on large scale and are also biocompatible to the body as compared to polymers, the monomeric unit of which are cytotoxic to the body.15,16) SLN exhibit sustained release effect due to the immobility of drug within lipid as compared to the emulsion formulations 17) and also exhibit better physical and chemical stability of drug compared to liposome.18) This delivery system has been extensively used as carriers for proteins, protein drugs, vaccines and lipophilic water insoluble drugs. 19) SLN are potential delivery system for lipophilic drugs where aqueous solubility of the drug is the limiting factor for its absorption. [20][21][22] Moreover, the incorporation of such drugs within SLN is easier due to their affinity for the lipid. On the other hand, entrapment of hydrophilic drug inside the hydrophobic matrix of SLN is a real challenge as the drug has maximum tendency to partition in the water during the fabrication process. Although a few hydrophilic molecules have been incorporated into SLN like thymocratin, 23) insulin, 24) diminazene 25) and thymopentin, 26) lot more scope still remains for the entrapment of hydrophilic drugs into lipid nanoparticles.Zidovudine (AZT), a hydrophilic drug has been used in the present investigation. It belongs to the class of nucleoside reverse transcriptase inhibitor and is used in the treatment of AIDS. This drug has various disadvantages like short biological half life due to extensive first pass metabolism and dose related bone marrow toxicity. AZT is a potential candidate for delivery via lipid based nanoparticulate system as this would help to improve lymphatic uptake, avoid hepatic first pass metabolism and thus reduce the dose requirement and decrease the side effects. 27) Furthermore, sustained drug release would reduce dosing frequency and at the same time ma...

Poor solubility and bioavailability of an existing or newly synthesized drug always pose challenge in the development of efficient pharmaceutical formulation. Numerous technologies can be used to improve the solubility and among them amorphous solid dispersion based spray drying technology can be successfully useful for development of product from lab scale to commercial scale with a wide range of powder characteristics. Current review deals with the importance of spray drying technology in drug delivery, basically for solubility and bioavailability enhancement. Role of additives, selection of polymer, effect of process and formulation parameters, scale up optimization, and IVIVC have been covered to gain the interest of readers about the technology. Design of experiment (DoE) to optimize the spray drying process has been covered in the review. A lot more research work is required to evaluate spray drying as a technology for screening the right polymer for solid dispersion, especially to overcome the issue related to drug re-crystallization and to achieve a stable product both in vitro and in vivo. Based on the recent FDA recommendation, the need of the hour is also to adopt Quality by Design approach in the manufacturing process to carefully optimize the spray drying technology for its smooth transfer from lab scale to commercial scale.

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