Tuesday, 11 July 2017

Formulation of Capsules: Hard and Soft Gelatin Capsules

In the GPAT examination, you will find fair amount of questions asked from the capsule section. Here in this section you will find the detail of formulation of hard and soft gelatin capsules.

Capsules are defined as the solid dosage form which contains the drug substances enclosed in the hard or soft container usually made up of the gelatin.


1. Gelatin: It is prepared by the hydrolysis of collagen obtained from animal connective tissue. 
  • On hydrolysis, gelatin gives 18 amino acids (glycine and alanine most common).
  • There are two types of gelatin:
  • a) TYPE A (Acid hydrolysed gelatin): Produced by acid hydrolysis (Isoelectric point near to pH 9.
  • TYPE B (Base hydrolysed gelatin): Produced by alkaline hydrolysis (Isoelectric point near to pH 4.5.
2. Opacifing agent: Titanium dioxide.

                  TESTS FOR GELATIN: Picric acid test & Tannic acid test

Solubility limits of empty capsule:

  • a) Water resistance : Fails to dissove in water at 20 – 30 Degree c in 15 minutes.
  • b) Acid solubility : dissolve in less than 5 minutes in 0.5% aqueous HCL at 36-38 degree Celsius.

Capsule Size

Equipment for filling of HGC :

  • 1. Lilly park devis
  • 2.Rotofil
  • 3.Hofiger
  • 4.Macofar
  • 5.MG2
  • 6.Osaka
  • 7.Zanasi
  • 8.Perry /Accofil

Equipment for de-dusting of HGC :

  • Rotosort ; Mechanically sorts out unfilled joined capsules, loose caps
  • Erweka KEA : For both de dusting and polishing
  • Seidender equipment: uses a belt for visual inspection

Rotary bottle Method is used for dissolution rate studies in capsules.


Soft gelatin capsules (SGC) contain a drug that is encapsulated dissolve, solublize or suspended in liquid vehicle 
In suspension that has to  be filled in SGC uses wetting agent lecithin.

Composition of SGC: 

1. Plasticizer used for softening the capsules. (Sorbitol, Glycerin & Propylene Glycol)
  • The ratio of dry plasticizer to dry gelatin measures the hardness of the capsule shell. 
  • Hardness of gelatin shell: Dry weight of plasticizer/Dry weight of gelatin (0.4 = hard, 0.6 = medium, 0.8 = soft).
2. Preservatives: In the concentration of 0.2% and most common combination is a 4 parts of methyl paraben and 1 part of propyl paraben. 

3. Opacifier: Titanium dioxide in the concentration range 0.2- 1.2 %.

4. 1% Fumaric acid: To increase the acid solubility and reduce the aldehydic tanning of gelatin.

5. 5%  Sugar: To produce  chew-able shell and taste.

6. Essential  Oils:  2% for odour and taste.

  •  Iron and content should not be more than 15PPM.
  • Various coating like salol, shellac, cap also modifies the solubility of gelatin. 

The physicochemical properties of gelatin which are of most important for manufacturers:

1.Bloom strength:
  • It is an empirical  gel strength measure, molecular weight of gelatin , which gives an identification of the firmness of the gel. 
  • It is measured in a bloom gelometer, which determine the weight in grams required to depress a standard plunger ( 0.5 inches in diameter)  a fixed distance into 4 mm deep into 6.66% w/w gel held at 10 degree c for 17 hr.
  • Bloom strengths in the range of 150-280 g are considered suitable for capsules.
  • Viscosity is determined using 6.66% w/w of gelatin solution in water at 60 degree c using capillary pipette.The range Must be in 25-45 mill poise.
3.  Sealing temperature of the gelatin film is between 37-40 degree C.

4. Minimum fill volume in capsulation is calculated from specific gravity of liquid.

5 Capsules at equilibrium with 20-30 % relative humidity at 21-24 degree C  are considered by the shell of such capsule contains 6-10% water depending upon the gelatin formula used.

6. Moisture content of the shell is determine  by toluene distillation method.

Base Absorption: 
  • Base absorption is defined as the minimum amount of base or vehicle in grams required per gram of solid drug to from a mixture which easily can be encapsulated in SGC. 
  • Base absorption : weight of base (grams)/ Weight of drug 
Minimum per gram factor :

  • M/G Factor = (BA+S/D) * 16.23 minims
  • BA = Base absorption Value
  • S = Solid Drug
  • D = Density of Mixture

If you have any doubt or any query feel free to make a comment below. We will be happy enough to solve all your queries.

You can also check our other sections which will help you in your preparation:

5.  Miscellaneous topics for GPAT

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