Gelatin capsules, hard, moisture

A hard gelatin capsule exhibited moisture sorption depending on humidity, the hysteresis of which was analyzed by the Young-Nelson hypothesis. This allowed the formation of a monolayer of adsorbed moisture to be distinguished from normal condensation of moisture and from absorption of moisture (Fig. 185).72S... 

Finished hard gelatin capsules normally contain an equilibrium moisture content of 13-16%. This moist-... 

JH Bell, NA Stevenson, JE Taylor. A moisture transfer effect in hard gelatin capsules of sodium cromoglycate. J Pharm Pharmacol 25 (suppl) 96P-103P, 1973. 

P York. Studies of the effect of powder moisture content on drug release from hard gelatin capsules. Drug Dev Ind Pharm 6 605-627, 1980. 

O. Bemtsson, G. Zackrisson and G. Ostling, Determination of moisture in hard gelatin capsules using near-infrared spectroscopy applications to at-line process control of pharmaceutics, J. Pharm. Biomed. Anal, 15, 895-900 (1997). 

York, P. Analysis of moisture sorption hysteresis in hard gelatin capsules, maize starch, and maize starch drug powder mixtures. J. Pharm. Sci. 1981, 33, 269-273. 

Table 1 lists some of the examples where dissolution problems have been reported with hard gelatin capsules. Fig. 7 depicts the behavior in one such case. Hard capsules normally contain 13%-16% water, which acts as a plasticizer and imparts flexibility. The moisture variations in the range of 12%-18% do not seriously impair the shell structure, however, below 12%, the shells beeome brittle and get easily ruptured. The capsules beeome moist, soft, and distorted when... 

The most commonly used capsule shells are the hard gelatin capsules that are made of gelatin, sugar, and water. On average, hard gelatin capsules contain between 13%i and 16% moisture, which acts as a plasticizer. This moisture content should be maintained for optimum capsule shell performance. Capsule shells that are too dry can become brittle and fracture easily, while capsule shells that are too moist become soft and tacky. 

Iron oxides have been reported to make hard gelatin capsules brittle at higher temperatures when the residual moisture is 11-12%. This factor affects the use of iron oxides for coloring hard gelatin capsules, and will limit the amount that can be incorporated into the gelatin material. 

Good flow properties are a prerequisite for the successful manufacture of both tablets and powder-filled hard gelatin capsules. It is a property of all powders to resist the differential movement between particles when subjected to external stresses. This resistance is due to the cohesive forces between particles. Three principal types of interparticle force have been identified (Harnby et al. 1985) forces due to electrostatic charging, van der Waals forces and forces due to moisture. 

Hard gelatin capsules should be evaluated for appearance (including brittleness), color, odor of contents, assay, degradation products, dissolution, moisture, and microbial limits. Testing of soft gelatin capsules should include appearance, color, odor of contents, assay, degradation products, dissolution, microbial limits, pH, leakage, and pellicle formation. In addition, the till medium should be examined for precipitation and cloudiness. 

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