Abstract
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.
Highlights
Capsule, a versatile unit solid dosage form for oral administration is designed to enclose solid, liquid or semi-solid mixture of active pharmaceutical ingredient (API) and suitable excipients in hard gelatin shells or in soft shells of gelatin [1]
hydroxypropyl methylcellulose (HPMC) capsules offered better protection against moisture-induced deterioration of the fill material as demonstrated from moisture uptake studies by dynamic vapor sorption method when compared against gelatin capsules at all relative humidity percentages up to 40% at 25 °C [35]
Studies with prolonged release radio-labelled formulations containing different viscosity grades of HPMC powder in healthy human volunteers found HPMC capsules to dissolve in 9 min as compared to 7 min for gelatin capsules
Summary
A versatile unit solid dosage form for oral administration is designed to enclose solid, liquid or semi-solid mixture of active pharmaceutical ingredient (API) and suitable excipients in hard gelatin shells or in soft shells of gelatin [1]. Change in ionic composition of the dissolution buffer medium by using potassium salt instead of sodium salt, resulted in significant delay in release of caffeine from HPMC capsules with carrageenan as gelling agent, when studied in acidic medium. Studies with prolonged release radio-labelled formulations containing different viscosity grades of HPMC powder in healthy human volunteers found HPMC capsules to dissolve in 9 min as compared to 7 min for gelatin capsules. HPMC capsules may demonstrate low correlation between the in vitro dissolution/disintegration and the in vivo performance due to observed in vitro interaction between the medium and the HPMC capsule gelling systems, which is not seen in in vivo studies in animals or human volunteers. Long-term stability studies at 40 °C and 75% relative humidity (RH) for 6 mo and at both 25 °C and 65% RH or 30 °C and 70% RH for 2 y did not reveal any alteration in disintegration and dissolution characteristics [37]
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