Displacement value & its calculations

• Displacement value (D.V.) is a crucial concept in the preparation of suppositories, particularly when using the fusion molding method.
• It helps determine the amount of suppository base required to incorporate a specific amount of active pharmaceutical ingredient (API) while maintaining the desired weight of the suppository.

Key Concepts:

• Displacement Value (D.V.): The amount of suppository base displaced by a given amount of API.
• It ensures proper dosage and uniformity in prepared suppositories.

Importance of Displacement Value:

• The displacement value is essential for:
  • Calculating the correct amount of suppository base needed.
  • Maintaining the intended weight and dosage of each suppository.
  • Ensuring uniformity across all suppositories.

Calculating the Displacement Value (D.V.):

Formula:

$$\text{D.V.} = \frac{\text{Weight of base displaced by the API (B)}}{\text{Weight of API in each suppository (A)}}$$

Information Needed:

1. Desired weight of each suppository (W)
2. Weight of API in each suppository (A)
3. Weight of base displaced by the API (B)

Calculating the Weight of the Base:

• Once the displacement value (D.V.) is known, the weight of the base required for each suppository can be calculated using the following formula:
• $\text{Base_wt} = \text{Desired weight of each suppository (W)}$$-\left( \text{Weight of API in each suppository (A)} \times \text{Displacement value (D.V.)} \right)$
• This formula ensures accurate determination of the base quantity needed to prepare suppositories with the correct dosage and uniform weight.

Example:

If you have:

• Desired suppository weight (W) = 2 g
• Weight of API in each suppository (A) = 0.5 g
• Displacement value (D.V.) = 1.5

Then:

• $\text{Base _wt} = 2\,\text{g} – (0.5\,\text{g} \times 1.5) = 2\,\text{g} – 0.75\,\text{g} = 1.25\,\text{g}$
• So, you will need 1.25 g of base for each suppository.

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