Previous : Critical Parameters of Formulating Drug in Hard Gelatin Capsules (Part I)

Hygroscopic compounds
Hygroscopic compounds can absorb water out of the shell, which normally has a water content of 13% to 16%. This can subsequently lead to brittleness and drying out of the shell.
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. Ideally, hygroscopic compounds should be combined with the diluent mannitol as mannitol is relatively inert where water absorption is concerned.

Adhesion of many drug actives or excipients might lead to difficulties during capsule filling, as particles stick to the surfaces of the filling machine. The consequences is that the fill substance breaks up, which leads to unacceptable fill variations. To overcome this problem, It is advisable to add a glidant or a combination of a glidant and lubricant such as Aerosil, magnesium stearate, or talcum/stearic acid.

Wetting properties
The wetting properties of the filling are of critical importance to the release of the substance. The release of hydrophobic substance can be enhanced by the addition of lactose as a diluent, or of a wetting agent such as sodium lauryl sulphate. Magnesium stearate has the opposite effect. It reduced the wetting properties and can significantly slow-down disintegration and dissolution.

When using hydrophobic drug substances, especially if they are high-dose and form the major part of the formulation, an appropriate disintegrant should be added, such as croscarmellose, crospovidone, sodium glycol starch or corn starch.

Moisture sensitivity of the drug substance
A moisture sensitive drug active might be damaged by the water contained in the capsule shell. This problem can be treated by addition of manitol. Manitol can prevent damage to the substance caused by the humidity of the shell or the environment.

Lactose hydrous is also suggested as a suitable diluent to prevent degradation of moisture sensitive drugs. However lactose anhydrous will pick up considerable amount of water to convert to the hydrated form when exposed to increasing humidity and temperature, while the lactose hydrous remains unchanged.

Lubricant prevent the powder adhering to the metal surfaces of the machine like dosing tube, dosing disk and punches as well as to optimize the powder flow and compressibility characteristics. Over lubrication not only result in a decreased dissolution but may also negatively impact the content uniformity, powder density and plug formation.It should also be noted that the time required to mix the lubricant with the formulation has a significant influence on the release profile even if the concentration remains unchanged.

Choice of hard gelatin capsule
Capsule size is the main factor in choosing an appropriate hard gelatin capsule. The determining factors are the minimum amounts of drug active and excipients required. It is possible to achieve a smaller capsule size by increasing the density of the formulation through granulation or compression. Also, get the larger size of capsule shell by increasing the amount of excipients.

`The key element of solid oral dosage form design that determines the ease swallowing by patient and consumers are size, shape, surface area and surface structure. Colour also affect people emotionally and psychologically. Orange and red are stimulating, while blue shades come across as calming.
Colours makes medicines distinctive and easy to recognize. As the number of medications increases, colours help patients with their treatment regime, and medical staff with giving out the correct medication. Product recognition can be made still easier by printing the brand name directly on the capsule.