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The most common instability problem of gelatin capsules arises from negative impact of extremes of temperature and especially atmospheric relative humidity on the mechanical integrity of the capsule shells with adverse effect extended even to the fill material. Moreover, choice of fill materials is highly restricted either due to their specific chemical structure, physical state or hygroscopicity. Additional reports of unpredictable disintegration and dissolution of filled hard gelatin capsules in experimental studies have prompted the search for a better alternative capsule shell material. The present review aims to provide an overview on the physicochemical, pharmaceutical and biopharmaceutical properties of hydroxypropyl methylcellulose (HPMC) as capsule shell material and perform comparative evaluation of HPMC and gelatin in terms of in vitro/in vivo performance and storage stability. HPMC capsule provides a highly flexible and widely acceptable platform capable of solving numerous challenges currently facing the pharmaceutical and nutraceutical industries and expands the possibilities for selection of different types of fill materials. The current topic introduces a new section on influence of various factors on in vitro dissolution of HPMC capsules. Delayed in vitro disintegration/dissolution of HPMC capsules in aqueous medium does not produce any negative effect in vivo. However, advancements in the processes of production and filling of HPMC capsule shells and detailed studies on effects of various parameters on their in vitro/in vivo dissolution would establish their supremacy over hard gelatin capsules in future.

Topical hydrogel preparations are applied on skin to obtain local or systemic action. NSAID's are non-steroidal drugs having excellent anti-inflammatory and analgesic activity but it produces GIT ulceration when used orally. To overcome that problem with oral formulations, many NSAID's are preferred to be administered by topical route. The present investigation is aimed to formulate the hydrogel of Diclofenac potassium with different ratio of Carbopol of different grades along with guar gum for application over the skin. Fourier transform Infrared (FT-IR) spectrophotometer has been used to notice drug -polymer interaction. After getting satisfactory combinations of polymers, hydrogel formulations of Diclofenac potassium were subjected to different physicochemical studies. Evaluation tests for visual appearance, pH, viscosity, spreadability, swelling index etc. were found satisfactory. To investigate the drug permeation kinetics and permeability coefficient from the goat abdominal skin, pieces of goat skin were fixed on the Franz diffusion cell, in a way that the upper surface of abdominal skin faced the donor chamber. The experiment was carried out with 2 gm of the drug loaded hydrogel spreaded on the skin surface at 32 o C in phosphate buffer pH-5.8. A distinct correlation between % swelling index and permeability coefficient of the formulations through goat abdominal skin has been observed. With increase in % swelling index over a period of 8 h the permeability coefficient decreased. It indicates that swelling of hydrogel forms a sticky, gelatinous mass that retards the permeation of Diclofenac potassium through goat abdominal skin. There are significant co relations between viscosity of hydrogel, % swelling index and permeation coefficient. It has been found that with increase in viscosity, permeability coefficient increased whereas permeability coefficient of drug decreased with increase in % swelling index of the formulations.

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