Example:- If the weight of a powder formulation is 350 mg and its bulk density is 0.75 g/ml . What is the size of capsule which can be chosen for this formulation? Volume of Capsule= Weight of the formulation in (g) / Bulk density of the formulation (g/ml). = 0.35 (g)/0.75 (g/ml) = 0.47 ml. So referring to the above table, then capsule size No. 1 having a volume of 0.48 mL can be used.
Ingredients Used in Capsule Formulations In addition to the drug(s), capsule formulations contain mainly:- 1. Diluents or fillers. 2. Lubricants & glidants . 3. Disintegrating agents. A)Diluents: They are free flowing materials, which in addition to increasing the quantity of the formulation for each capsule, they are used for their plug forming properties. The same diluents used in tablets ( organic and inorganic diluents). i) Organic Diluents: Such as anhydrous lactose , starch, hydrolyzed starch and Avicel, which is used when the ingredients are non-cohesive where it enhances their cohesiveness (compressibility). ii) Inorganic Diluents: Mainly dicalcium phosphate is used. • The diluent used should be chosen in relationship to the solubility of the active. If a soluble diluent such as lactose is added to a poorly or insoluble compound it will make the powder mass more hydrophilic, enabling it to break up more readily on capsule shell disintegration. • The converse is also true: actives that are readily soluble are best mixed with insoluble diluents such as starch or microcrystalline cellulose, because they help the powder mass to break up without interfering with their solubility in the medium.
B) Lubricants and Glidants: As capsules are automatically filled, using high speed capsules filling machine , it is essential to include a lubricant or & a glidant in the formula, to enhance powder flow & to avoid weight variations . When certain diluents such as lactose or Avicel are used, then the addition of lubricants or glidants will be essential, but when diluents such as starch or starch derivatives are used then small concentration of lubricant or no lubricant can be added . Because starch has a good lubrication & gliding properties . Also to insure excellent powder flow , glidants such as