In a sample of 10 units, each suppository should contain within ±15% of the average amount of active ingredient. However, if up to three individual units deviate by more than ±15% but are within ±25% of the average amount of the active ingredient, a further 20 units drawn from the same original sample as the first 10 units should be examined. The preparation under test complies only if the amount of active ingredient in not more than 3 out of 30 units deviates by more than ±15% of the average amount. None of the units should deviate by more than ±25% of the average amount.

Melting Point Determination Test

The temperature at which the partially melted substance begins to rise in the tube is regarded as the melting point.

 

Procedure: Insert one end of a glass capillary tube into the melted substance so that a column of substance column of 8–12 mm high is obtained in the tube. Cool the tube to 15°C and maintain the temperature at 15–17°C for not less than 16 hours. Attach the tube to a thermometer in a heating vessel containing water at 15°C or dip it in a water bath such that the lower end of the column of substance is 30 mm below the surface of water. Heat the water with constant stirring or regulate the temperature of the water bath slowly so that the temperature rises at a rate of 2°C per minute. Suppositories are melted rapidly at a temperature not more than 10°C above the point of complete fusion.

Liquefaction or Softening Time Test

This test is mainly performed for rectal suppositories. In this test, a standard glass rod is placed on a suppository held in a U-tube apparatus, which is immersed in a constant water bath maintained at 37°C. The time taken by the glass rod to penetrate from the surface of the suppository to the bottom end of the U-tube is recorded as the softening time.

Fragile or Breaking Test

This test is performed to determine the tensile strength of the suppository to withstand mechanical shocks during handling, transit and storage.

 

Procedure: The breaking test apparatus is used for this purpose. It consists of a double-wall chamber. Water is pumped through the walls of the chamber. The inner chamber consists of a disk, which holds the suppositories. A rod is attached to this disk. The other end of the rod consists of another disk on which weights are placed gradually and increased at one-minute intervals. The weights are added until the suppository crumbles.

All the weights used are added, which gives the tensile strength. Likewise, few more suppositories are tested and the average tensile strength is calculated. Tensile strength indicates the maximum force that the suppository can withstand during production, packing and handling. Large tensile strength indicates a lesser tendency to fracture.

Melting Range Test

It is a measure of the time taken for the entire suppository to melt when immersed in a constant-temperature (37°C) water bath. The apparatus commonly used for measuring the melting range of the entire suppository is the USP tablet disintegration apparatus.

 

Procedure: The suppository is completely immersed in the constant-temperature water bath, and the time for the entire suppository to melt or disperse in the surrounding water is measured.

The suppository is considered disintegrated under the following conditions:

1. It is completely dissolved.
2. It is dispersed into its component part.
3. There is a soft “change in shape” with the formation of core, which is not resistant to pressure with glass rod.

Both macromelting and micromelting ranges are determined.

1. Macromelting range: It is a measure of the thermal stability of the suppository. It is the time taken by the entire suppository to melt in a constant-temperature water bath. The test is conducted using the tablet disintegration apparatus. The suppository is immersed in a constant-temperature water bath and the melting range is recorded.
2. Micromelting range: The melting range of the fatty base is measured in capillary tubes.

Dissolution Studies

It is the amount of dosage form that gets dissolved in body fluid in unit time. It is a measure of the rate of drug release from the suppository. Two types of apparatus are available for testing the dissolution rate:

1. Suppository dialysis cell: Lipophilic suppositories are tested using the suppository dialysis cell, which is also known as the modified flow-through cell.
2. Stationary basket, rotating paddle, or basket apparatus (USP dissolution test apparatus): Hydrophilic suppositories are tested using stationary basket or rotating paddle apparatus.