Capsules (Types of Capsules)

Capsules are solid dosage forms in which the drug substance is enclosed within either a hard or soft soluble shell. Generally, the shells are formed from gelatin. The capsule may be regarded as a “container” drug delivery system, which provides a tasteless/odorless dosage form without the need of a secondary coating step, as may be required for tablets.

Capsules (Types of Capsules)

Types of Capsules:

Generally, capsules are of two types:

1. Hard gelatin capsules.

2. Soft gelatin capsules.

1. Hard gelatin capsules.

Hard gelatin capsule consists of two parts namely ‘cap’ and ‘body’. The diameter of the cap is slightly larger than the body. But the length of the cap is smaller than the body. The drug is filled in the body and is inserted into the cap to give the final form capsule.

Advantages of Hard Gelatin Capsules:

  • They are more elegant.
  • They are easy to transport.
  • They are tasteless and odorless shells.
  • They are suitable for drugs possessing unpleasant taste and odor.
  • Provide ready bioavailability of drug because of minimal excipients and little pressure applied during manufacturing.
  • Provide enteric effect.
  • They are uniquely suitable for blinded clinical trials and are widely used in preliminary drug studies.

Disadvantages of Hard Gelatin Capsules:

  • They are not suitable for extremely soluble materials, such as potassium chloride, potassium bromide, and ammonium chloride, because the sudden release of these drugs may irritate the gastric mucosa.
  • They are not suitable for efflorescent materials because they absorb moisture and cause softening of capsules.
  • They are not suitable for aqueous or hydroalcoholic solutions.
  • The filling process is laborious and time-consuming. Therefore production rate is slower than tableting.

Formulation of Gelatin Shell

Gelatin shell contains:

1. Gelatin (main ingredient),

2. Plasticizers,

3. Opacifying agents,

4. Colouring agents,

5. Flavouring agents,

6. Sweetening agents,

7. Preservatives,

8. Water,

9. Acids.

1. Gelatin: Gelatin is a heterogeneous product derived by irreversible hydrolytic extraction of treated animal collagen.

Properties of gelatin depend on:

  • Parent collagen,
  • Method of extraction,
  • pH value,
  • Thermal degradation,
  • Electrolyte content.

Sources of Gelatin:

(i) Animal bones,

(ii) Frozen pork skin,

(iii) Hide portion.

Types of Gelatin:

(i) Type A: It is derived from acid-treated precursors. This type of gelatin possesses an isoelectric point in the region of pH 9.0.

(ii) Type B: it is derived from an alkali-treated precursor of bones. This type of gelatin possesses an isoelectric point in the region of pH 4.7.

The film of capsules made from bone gelatin is tough and firm. But film tends to be hazy and brittle. Capsules made from pork skin gelatin possess plasticity and clarity, these are responsible for reducing hazy or cloudiness. In practice, both types of gelatine are used in combination to give all the desired properties to capsules.

2. Plasticizers: It increases the plasticity of the film. E.g. glycerine, sorbitol, propylene glycol.

3. Colouring Agents: These are used to impart color to the body and cap. E.g. water-soluble dyes, certified lakes, and vegetable colors. They are used either alone or in combination.

4 Opacifying agents: These are used to give opacity to the gelatin film. E.g. Titanium dioxide.

5. Flavouring agents: These are used in a concentration of not more than 2%. E.g. ethyl vanillin, essential oils.

6. Sweetening agents: E.g. Sugar is not more than 5%.

7. Preservatives: E.g. methylparaben, potassium bisulfite.

Formulation of Capsule Content

Capsules mostly contain active ingredients, however, the following ingredients are also used in the manufacturing of capsules:

1. Glidants: e.g. talc, magnesium stearate, colloidal silica.

2. Fillers (diluents): e.g. lactose, starch, dicalcium phosphate.

3. Disintegrants: e.g. crospovidone, croscarmellose sodium.

4. Surfactants: e.g. sodium lauryl sulfate, sodium locusta.

5. Hydrophilic agents: e.g. methylcellulose, hydroxyl ethyl cellulose.

Manufacturing of Hard Gelatin Capsule Shell

1. Dipping: Pairs of stainless steel pins are dipped into the dipping solution to simultaneously form the caps and bodies. The pins are lubricated with a proprietary mold-release agent. The pins are at ambient temperature. (about 228o C), whereas the dipping solution is maintained at a temperature of about 508o C in a heated, jacketed dipping pan. The length of time to cast the film has been reported to be about 12 seconds, with larger capsules requiring longer dipping times.

2. Rotation: After dipping, the pins are withdrawn from the dipping solution, and as they are done so, they are elevated and rotated two and a half times until they are facing upward. This rotation helps to distribute the gelatin over the pins uniformly and to avoid the formation of a bead at the capsule ends. After rotation, they are blasted cool air to set the film.

3. Drying: The racks of gelatin-coated pins then pass into a series of four drying ovens. Drying is done mainly by dehumidification bypassing large volumes of dry air over the pins. Only a temperature elevation of a few degrees is permissible to prevent film melting. Drying must not be so rapid as to cause “case hardening” of the outer surface of the forming shells that would impede further moisture removal. Overdrying must be avoided as this could cause films to split on the pins due to shrinkage or at least make them too brittle for the later trimming operation. Under drying will leave the films too pliable or sticky for subsequent operations.

4. Stripping: A series of bronze jaws (softer than stainless steel) strip the cap and body portions of the capsules from the pins.

5. Trimming: The striped cap and body portions are delivered to collets in which they are firmly held. As the collets rotate, knives are brought against the shells to trim them to the required length.

6. Joining: The cap and body portions are aligned concentrically in channels, and the two portions are slowly pushed together. The entire cycle takes about 45 minutes, however, about two-thirds of this time is required for the drying step alone.

7. Sorting: During sorting, the capsules passing on a lighted moving conveyor are examined visually by inspectors. Any defective capsules spotted are thus manually removed. Defects are generally classified according to their nature and potential to cause problems in usage. The most serious of these defects are the ones that could cause stoppage of a filling machine such as imperfect cuts, dented capsules, or those with holes. Other defects may cause problems on usage, such as capsules with splits, long bodies, or grease inside. Many less important, cosmetic faults, which only detract from appearance, also may occur (small bubbles, specks in the film, marks on the cut edge, etc.).

8. Printing: In general, capsules are printed before filling. Empty capsules can be handled faster than filled capsules, and should there be any loss or damage to the capsules during printing, no active ingredients would be involved. Generally, printing is done on offset rotary presses having throughput capabilities as high as three or four million capsules per hour. Available equipment can print either axially along the length of capsules or radially around the circumference of capsules.

Sizes and Shapes of Hard Gelatin Capsule Shell

Empty gelatin capsules are manufactured in eight sizes for human use, ranging from 000 (the largest) to 5 (the smallest). The volumes and approximate capacities for the traditional eight sizes are listed below.

Sizes and Shapes of Hard Gelatin Capsule Shell

Although the standard shape of capsules is the traditional, symmetrical, cylindrical shape, some manufacturers have employed distinctive proprietary shapes. Lilly’s Pulvule-1 is designed with a characteristic body section that tapers to a bluntly pointed end. Glaxo Smith Kline’s Spansule1 capsules exhibit a characteristic taper at both the cap and body ends.

Filling of Hard Gelatin Capsules

Rectification: The empty capsules are oriented so that all point in the same direction, that is, the body ends downward. In general, the capsules pass one at a time through a channel just wide enough to provide a frictional grip at the cap end. A specially designed blade pushes against the capsule and causes it to rotate about its cap end as a fulcrum. After two pushes (one horizontally and one vertically downward), the capsules will always be aligned body end downward, regardless of which end entered the channel first.

Separation of caps from bodies: This process also depends on the difference in diameters between cap and body portions. Here, the rectified capsules are delivered body end first into the upper portion of split bushings or split-filling rings. A vacuum applied from below pulls the bodies down into the lower portion of the split bushing. The diameter of the caps is too large to allow them to follow the bodies into the lower bushing portion. The split bushings are then separated to expose the bodies for filling.

Dosing of fill material: Various methods are employed, which are described below.

Filling (dosing of material) can be done by:

1. Auger fill principle (Gravitational forces)

2. Vibratory fill principle (Overfill/Scrape-off excess)

3. Piston tamps principle (Pressured measured): Again there are two types of fillers:

(a) Dosator machine, and

(b) Dosing disc machine.

View looking down on the dosing (Capsules)
(a) View looking down on the dosing
Side view (projected) showing progressive plug formation Note the placement of strain gauges on the piston to measure tamping and plug ejection forces
(b) Side view (projected) showing progressive plug formation Note the placement of strain gauges on the piston to measure tamping and plug ejection forces

Fig.1: Dosing-disc filling principle

Dosator-filling principle (Capsules)
Fig.2: Dosator-filling principle

Replacement of caps and ejection of filled capsules: The cap and body bushing portions are rejoined. Pins are used to pushing the filled bodies up into the caps for closure and push the closed capsules out of the bushings. Compressed air also may be used to eject the capsules.

Sealing and Locking of Capsules

1. Bodies are moistened with brush and painted with acacia mucilage.

2. Caps are placed on wet paper before fixing

3. Hard-gelatin capsules are made self-locking by forming indentations or grooves on the inside of the cap and body portions. Thus when they are fully engaged, a positive interlock is created between the cap and body portions.

Examples include Posilok1 (Qualicaps, Inc., Whitsett, North Carolina, U.S.) and Coni-Snap1 (Capsugel, Div. Pfizer Inc., Greenwood, South Carolina, U.S.). The rim of the body portion of Coni-Snap capsules is tapered to help guide the cap onto the body. In high-speed automatic capsule filling machines, this feature can reduce or eliminate snagging or splitting of capsules. Both brands of locking capsules are closed by a pre-lock feature based on indentations formed further down on the cap that keeps the caps and body pieces of the empty capsules together during shipping and handling but allows their easy separation for capsule filling. The Coni-Snap principle with pre lock feature is illustrated in Fig.3.

Sealing and Locking of Capsules
1. The tapered rim prevents faulty joins. 2. These indentations prevent the pre-closed capsule from opening too early. 3. These grooves lock the two halves together after filling (SNAP-FIT principle)


Finishing of Capsules

1. Pan Polishing: The accelacota tablet coating pan is issued to dust and polish capsules. A polyurethane or cheesecloth liner is placed in the pan and the liner is used to trap the removed dust as well as to impart a glossy texture to the capsules.

2. Cloth Dusting: In this method, the filled capsules are rubbed with a cloth that may or may not be impregnated with inert oil. This method is hand operation and improves glossy to the capsules.

3. Brushing: In the automatic polishing equipment capsules are fed under rotating soft brushes. Brushes remove dust from the surface of the capsule. This equipment is also connected to a vacuum which removes the dust immediately. During operation, scratches may develop on the capsules or sometimes deformation takes place.


It is a mechanical sorting machine that removes unfilled powder or unfilled bodies or loose caps. Rotofil is a capsule filling machine that is specifically designed to fill pellets.

Storage and Stability

Finished hard-gelatin capsules normally contain an equilibrium moisture content of 13% to 16%. This moisture acts as a plasticizer and thus is critical to the physical properties of the shells. At lower moisture contents (< 12%), shells become too brittle; at higher moisture contents (> 18%), they become too soft. It is best to avoid extremes of temperature and to maintain a relative humidity of 40% to 60% when handling and storing capsules.

Manufacturing Defects

The manufacturing of hard gelatin capsules involves several steps like Dipping of stainless steel, trimming, stripping, joining of the cap, and body of the capsule. So, during several operations few defects are formed at this stage only like:

Major defects:

1. Capsules are not specified type i.e hard shell formation.

2. It may have cracks, breaks, pinholes, or splits, losing its integrity.

3. Color variation, and non-uniformity of appearance.

4. Surface spots and embedded particles on capsules.

5. Body and cap are not uniform and do not fit properly.

Minor defects:

1. Capsule’s surface is not smooth.

2. Opacity not proper.

3. There are pits, dents, thin areas, specks, spots, or blemishes.

4. Capsules not free of adhering surface spots.

Quality Control Test

Disintegration Test: According to B.P., which applies to both hard and soft capsules:

  • Introduce one capsule in each tube and suspend the apparatus in a beaker containing 60 ml water at 37 C.
  • If hard capsules float on the surface of the water, then a disc may be added.
  • Operate the apparatus for 30 minutes. Remove the assembly from the liquid.
  • The capsules pass the test if no residue remains on the screen of the apparatus.

Weight variation:

  • Weigh 20 capsules individually and determine the average weight.
  • The individual wt should be within the limit of 90-110% of average weight.
  • If not all of the capsules fall within the limit, weigh, weigh 20 capsules individually again.
  • Remove the net content of each capsule with the aid of a small brush.
  • Weight the empty shell individually. Net weight of contents individually = Weight of shell − Gross weight.
  • Determine the average net content from the sum of individual net weight.
  • Then determine the differences between each net content and average net content.

Limits: Not more than 2 of the differences are greater than 10% of the average net content.

Content Uniformity:

  • 10 capsules are taken and subjected to assay.
  • 9 of 10 capsules should be in the range of 15% (85 – 115%).
  • 10th capsule is beyond the ± 15% range, the 20 capsules are assayed.
  • All capsules within range of ± 25% (75 – 125%).

Moisture Permeation Test

  • The degree and rate of moisture penetration are determined by packaging the dosage unit together with color is revealing the desiccant pellet.
  • Expose the packed unit to known relative humidity over a specified time.
  • Observe the desiccant pellet for color change.
  • Any color change indicates absorption of moisture.
  • By measuring pre-test weight and protest weight of pellet, the amount can be calculated.

Bloom Strength of Gelatin

  • Gelatin is weighed into the water to typically create a 6.67% solution in standard bloom bottles.
  • The mix is then stirred and kept for 3 hours at room temp.
  • Bottles are placed in a 65 oC bath for 20 minutes,
  • Allow the bloom jars to cool for 15 minutes at room temperature
  • They are then conditioned for 16 hrs in a 10 oC water bath.
  • When conducting a gelatin bloom test, the bloom jar is centered with the probe just above the sample surface.
  • The probe penetrates the gelatin to a target depth of 4 mm at a speed of 0.5 mm/sec and then retracts.
  • The peak force is a gel strength in grams bloom.
  • Bloom may range between 150 – 250 g.

Viscosity: The viscosity for gelatin may range from 25 – 45 milipoise.

Iron content: Gelatin used in manufacturing gelatin capsules should not be more than 15 ppm of iron.

Soft Gelatin Capsules

Definition: Soft gelatin capsules are made of gelatin to which glycerin or polyhydric alcohol such as sorbitol has been added. Soft gelatin capsules, which contain more moisture than hard capsules, may have a preservative, such as methylparaben and/or propylparaben, to retard microbial growth. These are solid dosage forms in which powder, paste, or liquid medicaments are enclosed in a soft, globular gelatin shell. They may be round, oval, or oblong.

Nature of Shell and Capsules Contents

Typically, soft gelatin is made up of gelatin, plasticizer, and materials that impart the desired appearance (colorants and/or opacifiers), and sometimes flavors. The formulation of the capsules content for each product is individually developed to fulfill the specification and end-use requirements of the products.

1. Gelatin: A large number of different shell formulations are available, depending on the nature of the liquid filling material. Most commonly the gelatin is alkali (base) processed (type B) and it normally constituents 40% of the wet molten gel mass. Type-A acid processed gelatin can be also used.

2. Plasticizers: It is used to make soft gelatin capsule shell elastic and pliable. The most commonly used plasticizer in soft gelatin is glycerol, although sorbitol and propylene glycol are also used often in combination with glycerol. The amount of plasticizer contributes to the hardness of the final product and may even affect the dissolution and disintegration characteristics, as well as its chemical and physical stability. They are selected based on their compatibility with the fill formulation, ease of processing, and the desired properties of the final products, including hardness, appearance, handling, and physical stability.

3. Water: It is the most important component of soft gelatin capsules. It usually accounts for 30 – 40% of the wet gel formulation and its presence is important to ensure proper processing during gel preparation and soft gelatin encapsulation. The levels of water are important for good physical stability because in harsh storage conditions soft gelatin capsules will become either too soft and fuse, or too hard and embrittled.

4. Colourants/Opacifiers: Colourants (soluble dyes, or insoluble pigments or lakes) and opacifiers are typically used at low concentrations in the wet formulation. They can be either synthetic or natural and are used to impart the desired shell color for product identification. An opacifier, usually Titanium dioxide, may be added to produce an opaque shell when the fill formulation is a suspension, or to prevent photo-degradation of light-sensitive fill material. Titanium dioxide is used singly to give a white opaque shell and with combination, it gives a colored opaque shell.

5. Bloom Strength: Bloom strength is a measurement of cohesive strength of the cross-linking that occurs between gelatin molecules and is proportional to the molecular weight of gelatin. And it is also known as gel strength or gel rigidity of gelatin.

Bloom’s strength is determined by measuring the weight in grams required to move a plastic plunger (0.5 inches diameter). 4 mm held at 10°C for 17 days. It may be a range of 150 – 250.

6. Viscosity: Viscosity is a measure of the molecular chain length and determines the manufacturing characteristics of the gelatin film. The viscosity for gelatin can be in the range of 25 -45 milipoise.

7. Flavouring Agent: It may be used in a concentration of not more than 2% are used. Examples are essential oil, ethyl vanillin.

8. Sweetening Agent: These agents like sugar can be used in a concentration of not more than 5%.

9. Preservatives: Gelatin is stable when it is dry. Micro-organisms attack gelatin only in presence of moisture. Hence, preservatives are essential. For example, Methylparaben, propylparaben, sodium met bisulfite, potassium bisulfate, etc.

Capsule Size

For Human use, empty capsules ranging in size from 000 the largest to 5 smallest.

Capsule Size

Importance of Base Adsorption and Minim/gram

Based adsorption is expressed as the number of grams of liquid base required to produce a capsulate mixture when mixed with one gram of solid. The base adsorption of solid is influenced by such factors as the solid’s particle size and shape, its physical states (fibrous, amorphous, or crystalline), its density, its moisture content, and its oleophilic or hydrophilic nature.

Importance of Base Adsorption and Minimgram

The base adsorption is used to determine the “minim per gram” factor (m/g) of the solid. The minim per gram factor is the volume in minims that is occupied by one gram of the solid plus the weight of liquid base (BA) required to make a capsulate mixture. The minim per gram factor is calculated by dividing the weight of base plus the gram of solid (BA + S) by the weight of mixture (W) per cubic centimeter minims.


  • It helps to determine the base adsorption and fluidity of a mixture.
  • It is used to determine the minim per gram factor (M/g) of the solid.
  • It is also important of establishing specifications for the control of the physical properties of solid.
  • The convenience of using M/g factors is particularly evident in the vitamin field, where there may be many ingredients and numerous combinations.
  • They are used to rapidly calculate capsules size.

BA and M/g Factors of Some Typical Solids:

BA and Mg Factors of Some Typical Solids

Production of Soft Gelatin Capsules

Composition of the shell:

  • The basic component of a soft gelatin shell is gelatin; however, the shell has been plasticized.
  • The ratio of dry plasticizer to dry gelatin determines the “hardness” of the shell and can vary from 0.3 – 1.0 for the very hard shell to 1.0 – 1.8 for the very softshell.
  • Up to 5% of sugar may be included to give a “chewable” quality to the shell.
  • The residual shell moisture content of finished capsules will be in the range of 6-10%.


  • Formulation of soft gelatin capsules involves liquid, rather than powder technology.
  • Material is generally formulated to produce the smallest possible capsules consistent with maximum stability, therapeutic effectiveness, and manufacturing efficiency.
  • The liquid is limited to those that do not harm the gelatin shell.
  • The pH of liquid can be in the range of 2.5 – 7.5.

Soft Gelatin Capsules are manufactured by following four methods:

1. Plate process,

2. Rotary die process,

3. Reciprocating die,

4. Accogel machine.

1. Plate Process:

  • Place the gelatin sheet over a die plate containing numerous die pockets.
  • Application of vacuum to draw the sheet into the die pockets.
  • Fill the pockets with liquid or paste.
  • Place another gelatin sheet over the filled pockets, and
  • Sandwich under a die press where the capsules are formed and cut out.

2. Rotary Die Process:

  • In this machine the soft gelatin capsules are prepared and then filled immediately with liquid medicaments, it is having two hoppers and two rotating dies
  • The liquid mixture is placed in one hopper and the liquid medicament in another Hopper.
  • The two rotating dies rotate in opposite directions when the fluid gelatin mixture enters the machine from the hopper it produces two continuous ribbons.
  • These half-shells of the capsule are formed.
  • At this stage the measured quantity of the medicament is filled into it with the stroke of a pump with the subsequent movement of them dies, the other half capsule is formed.
  • The two halves of the capsules are sealed together by the heat and pressure of the rotating dies.
  • As the die rolls rotate, the convergence of the matching dies pockets seals and cuts out the filled capsules.
Rotary Die Process (Capsules)

3. Reciprocating Die Process:

  • The early success of the rotary die process led others to develop continuous methods of soft gelatin capsules manufacture.
  • One such method, known as the reciprocating die process, was announced in 1949 and was developed by the Nortan Company, Worchester, MA.

Quality Control Tests

1. Disintegration Test: The disintegration test for hard and soft gelatin capsules follows the same procedure and uses the same apparatus described in the next chapter for uncoated tablets. The capsules are placed in the basket rack assembly, which is immersed 30 times per minute into a thermostatically controlled fluid at 37°C and observed over the time described in the individual monograph. To satisfy the test, the capsules disintegrate completely into a soft mass having no palpably firm core and only some fragments of the gelatin shell.

Weight variation: The gross weight of 10 intact capsules is determined individually. Then each capsule is cut open and the contents are removed by washing with a suitable solvent. The solvent is allowed to evaporate at room temperature over about 30 minutes, with precautions to avoid uptake or loss of moisture. The individual shells are weighed and the net contents calculated. From the results of the assay directed in the individual monograph, the content of the active ingredient in each of the capsules is determined.

Content Uniformity: Unless otherwise stated in the USP monograph for an individual capsule, the amount of active ingredient, determined by assay, is within the range of 85% to 115% of the label claim for 9 of 10 dosage units assayed, with no unit outside the range of 70% to 125% of the label claim. Additional tests are prescribed when two or three dosage units are outside of the desired range but within the stated extremes.

2. Dissolution Test:

  • The dissolution test is carried out using the dissolution apparatus official in both the U.S.P and IP.
  • The capsule is placed in a basket, and the basket is immersed in the dissolution medium and caused to rotate at a specified speed.
  • The dissolution medium is held in a covered 1000 ml glass vessel and maintained at 370°C ± 0.5°C using a constant temperature suitable water bath.
  • The stirrer speed and type of dissolution medium are specified in the individual monograph.


  • Six capsules are tested and are accepted if each of them is not less than the monograph specified i.e. +5%.
  • If it fails then additional six capsules are tested. The result is accepted if the average of 12 capsules is greater than or equal to p and none of them is less than p − 15%.
  • If the capsule still fails the test the additional 12 capsules are tested and are accepted if the average of 24 is greater than the top, if not more than two less than p − 15%, and none of them is less than p − 25%.

3. Physical Quality Control:

Finally, physical control processing and packaging may be accomplished by the following in continuous operations:

  • A capsule diameter sorter allows passing to the next unit of any capsule within ± 0.020 inches of theoretical diameter.
  • A capsule color: The capsules are fed to it automatically from the diameter sorter by a pneumatic conveyor. In this unit, any capsule whose color does not conform to the reference color standard for that particular product is discarded others pass the test.

Packaging and Storage of Soft Gelatin Capsules

  • Capsules should be packed in well-closed glass or plastic containers and stored in a cool place.
  • These types of containers have an advantage over cardboard boxes in that they are more convenient to handle and transport and protect the capsules from moisture and dust.
  • To prevent the capsules from rattling a tuft of cotton is placed over and under the capsules in the vials.
  • In vials containing very hygroscopic capsules, a packet-containing desiccant like silica gel or anhydrous calcium chloride may be placed to prevent the absorption of excessive moisture by the capsules. Nowadays capsules are strip packaged which provide sanitary handling of medicines, ease in counting and identification.
  • Plastic bottle with screw cap (most popular package in the USA).
  • Clamshell blister (one-piece plastic that folds over and locks itself; no heating required.
  • Blister pack (heat-sealed blister on cardboard).
  • Plastic pail/bucket (economical bulk package).
  • Plastic pouch zip-locked (for sale via retail stores or route trucks must be packed in outer case for shipping).

Stability Testing of Soft Gelatin Capsules

1. Moisture Permeation Test: The USP requires the determination of the moisture permeation characteristics of single-unit and unit-dose containers to ensure their suitability for packaging capsules. The degree and rate of moisture penetration are determined by packaging the dosage unit together with a color-revealing desiccant pellet, exposing the packaged unit to known relative humidity over a specified time interval, observing the desiccant pellet for color change (indicating the absorption of moisture), and comparing the pretest and posttest weight of the packaged unit.

Physical Stability: Unprotected soft gelatin capsules rapidly reach equilibrium with the atmospheric conditions under which they are stored.

  • This inherent characteristic warrants a brief discussion of the effects of temperature and humidity on the products.
  • General statements relative to the effects of temperature and humidity on soft gelatin capsules must be confined to a control capsule that contains mineral oil with a gelatin shell having dry glycerin to dry gelatin ratio of 0.5 – 1 and a water to dry gelatin ratio of 1 – 1 and that is dried to equilibrium with 20 – 30% RH and 21 – 24°C
  • The physical stability of soft gelatin capsules is associated primarily with the pick-up or loss of water by the capsule shell.
  • If these are prevented by proper packaging, the above-controlled capsule should have satisfactory physical stability at a temperature ranging from just above freezing to as high as 600°C.
  • As the humidity increases the moisture content pickup of capsules increases. For example: At 30% RH at room temperature shows that gelatin retains about 12% (48 mg) of water and glycerin 7% (14 mg) of water at 60% RH the moisture content should be 17.4%. High humidity (> 60% RH at 21 – 240°C) produce more lasting effects on the capsule shell. The capsule manufacturer routinely conducts accelerated stability tests on new products as an integral part of the product development program.
  • The successful results are obtained by conducting at test conditions like

(a) 80% RH at room temperature in an open container

(b) 400°C in an open container

(c) 400°C in a closed container.

  • Before testing, the capsule should be equilibrated to known humidity at many conditions, preferably 20 – 30% RH at 21 – 24°C.
  • Evaluation of the results of the previously described heat test should be made only after the capsules have returned to equilibrium to room temperature.

Stability: 20 to 30 % RH at 21 to 24°C.

Stability Testing of Soft Gelatin Capsules

Applications of Soft Gelatin Tablets

  • As an oral dosage form.
  • As a suppository dosage form.
  • As a specialty package in tube form, for human and veterinary use, single-dose application for topical, ophthalmic, and rectal ointments.
  • It is used in water-immiscible, volatile, and non-volatile liquids such as vegetable and aromatic oils, aromatic and aliphatic hydrocarbons, ether, esters, alcohol, and organic acids.
  • Solid is also encapsulated into soft gelatin capsules as a solution in one of the suitable liquid solvents, as suspension, or as dry powder, granules, or pelletized materials.
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