BP102T • Unit 4Topic 3 of 3⏱ 5 Min Read

3. Suppositories & Pessaries: Bases, Displacement Value & Molding

💡 Core Concept & Clinical Context:

Suppositories are solid unit dosage forms of various shapes and weights adapted for insertion into body cavities (rectum, vagina, urethra) where they melt at body temperature (37°C) or dissolve in mucosal secretions to exert localized or systemic pharmacological actions. Rectal suppositories weigh approx. 1-2 g (torpedo-shaped), while vaginal suppositories (pessaries/globules) weigh 3-5 g. Suppository bases are classified into: (1) Fatty/Oleaginous bases (Theobroma oil / Cocoa butter), (2) Water-soluble/Hydrophilic bases (Polyethylene Glycol - PEG / Macrogols), and (3) Water-miscible bases (Glycerogelatin base: 14% Gelatin, 70% Glycerin, 16% Purified Water).

Clinical Scenarios & Pharmacopoeial Examples:

1Displacement Value Calculation & Compounding Formula

Displacement Value ($DV$) is the number of parts by weight of medicament that displaces 1 part by weight of the suppository base.

Step-by-Step Breakdown:

•Mathematical Formula:

•DV = [ (W_drug) ] / [ (Weight of pure base mold) - (Weight of medicated suppository - W_drug) ]

•Worked Example:

•Prepare 6 suppositories of Paracetamol (0.2 g each) using a 1 g Cocoa butter mold. (DV of Paracetamol = 1.5).

•1. Total drug required for 6 units (plus 2 extra for overage = 8 units):

•Drug required = 8 * 0.2 g = 1.6 g Paracetamol.

•2. Weight of Cocoa butter displaced by drug:

•Displaced base = 1.6 g / 1.5 (DV) = 1.067 g.

•3. Total Cocoa butter required:

•Base required = (8 * 1.0 g) - 1.067 g = 6.933 g Cocoa butter.

Comparison & Reference Table:

Suppository Base	Melting / Dissolution Mechanism	Key Advantages	Critical Precautions
Theobroma Oil (Cocoa butter)	Melts sharply at body temp (30-35°C)	Non-irritating, excellent soothing effect	Do NOT overheat > 36°C (polymorphic transition)
Glycerogelatin Base	Dissolves in mucous secretions	Ideal for vaginal pessaries, prolonged action	Hygroscopic; moisten with water before insertion
Polyethylene Glycol (PEG)	Dissolves in body fluids (high m.p.)	Does not require refrigeration, clean insertion	May cause rectal stinging if not moistened

📋Key Takeaways & Exam Highlights

Theobroma Oil (Cocoa Butter): Melts at 30-35°C; exhibits polymorphism ($\alpha, \beta, \beta', \gamma$ forms). Overheating above 36°C produces the unstable low-melting $\alpha$ form (m.p. 24°C) which fails to solidify at room temp.
Glycerogelatin Base: Prepared by soaking gelatin in water, adding glycerin, and heating gently on water bath; requires lubrication with liquid paraffin.
PEG (Macrogols): Do not melt at body temperature; dissolve slowly in mucosal secretions, avoiding messy leakage.

🇮🇳 हिन्दी व्याख्या (3. Suppositories & Pessaries: Bases, Displacement Value & Molding)

सपोसिटरी (Suppository) गुदा या योनि मार्ग में रखी जाने वाली ठोस दवा है जो शरीर के 37°C तापमान पर पिघल जाती है। कोकोआ बटर (Theobroma oil) सबसे मुख्य बेस है। डिस्प्लेसमेंट वैल्यू से बेस की सही मात्रा तय होती है।