Hygroscopic compound is the ability of a substance or compound to absorb water molecules from the environment either through absorption or adsorption. Examples of hygroscopic substances are honey, glycerin, ethanol, methanol, concentrated sulfuric acid, and sodium hydrochloride.

Hygroscopic and deliquescent components pose problems when filled into gelatin capsules in that they absorb moisture from the gelatin, leaving the latter moisture depleted and often in a brittle or deformed state, susceptible to breakage and leakage.

Hygroscopic compounds can have negative influence on the formulation of hard gelatin capsules :
  1. Hygroscopic compounds can absorb water out of the shell. (normally water content of capsule shell is 13-16%)
  2. The absorption of moisture during production can lead to the build-up of a sorption film that affects the fluidity of the powder mix filling.
Therefore, ideally hygroscopic compounds should be combined with the diluents mannitol, as mannitol is relatively inert where water absorption is concerned.

Many pharmaceutically active compounds are hygroscopic or deliquescent and, where the hygroscopicity thereof is particularly marked, they have been unsuitable for formulation in gelatin capsule form, a form recognised normally as beingconvenient both for the pharmaceutical formulator and patient user.

One of Hygroscopic or even very deliquescent compounds are Chondroitin and Glucosamine. Chondritin and Glucosamine are chondroprotective agents which have found application in the treatment and/or prevention of osteoarthritis and related disease of the joints, commonly used as dietary supplements.

You can click here to read more about How to Make Glucosamine And Chondroitin Capsule

Thus, with slightly hygroscopic products, that is products with a hygroscopicity of less than 10% waterabsorption at 43% relative humidity, the problem can be overcome.

Capsules containing a hygroscopic or deliquescent component are stabilized by :
a) forming a mixture of the hydrogscopic or deliquescent compound with a sufficient quantity of water to achieve an equilibrium,
b) adding a thickening agent and
c) heating the solution or suspension; and introducing the heated composition so formed into the capsule as to provide a gelatin capsule having reduced susceptibility to subsequent water transfer from the capsule gelatin to the hygroscopic or deliquescent component.