BP102T Unit 5 – Biphasic Liquid Dosage Forms & Incompatibilities
Unit 5 details the preparation, bases, and compounding of semisolid dosage forms (Ointments, Creams, Pastes, Jellies) and provides a rigorous classification of Physical, Chemical, and Therapeutic Pharmaceutical Incompatibilities along with laboratory methods for their prevention and correction.
📋 Prescribed Syllabus Topics
📖 Detailed Lecture Notes & Solved Examples
11. Semisolid Dosage Forms: Ointments, Creams, Pastes & Jellies
Dedicated Webpage➔Semisolid dosage forms are intended for topical application to the skin or accessible mucous membranes for protective, emollient, or therapeutic purposes. Ointments are greasy, unctuous preparations containing < 20% water and > 50% hydrocarbons/resins. Creams are semisolid emulsions (O/W vanishing creams or W/O cold creams). Pastes contain high concentrations of finely powdered insoluble solids (20% to 50% such as Zinc Oxide paste) creating a stiff, porous, protective barrier that absorbs serous wound exudates. Jellies/Gels are transparent, non-greasy semisolids containing synthetic or natural gelling polymers (Carbopol, Sodium alginate, Methylcellulose).Ointment bohot chikna (greasy) hota hai jo sookhi aur scaly skin ke liye lagaya jata hai. Cream ek semisolid emulsion hai jo skin par gayab ho jati hai (vanishing cream). Paste me 20-50% tak sookha zinc oxide powder hota hai jo ghav ke peep aur paani ko sookh leta hai. Gel paani jaisa thanda aur transparent hota hai.
▶Classification of Ointment Bases
Four official USP/IP ointment base classes.
| Semisolid Class | Typical Composition | Physical Consistency | Key Therapeutic Application |
|---|---|---|---|
| Ointment | > 50% Hydrocarbons / Soft paraffin | Greasy, occlusive, unctuous | Dry, chronic, scaly skin lesions (Psoriasis, Eczema) |
| Cream (O/W) | Emulsion with Cetomacrogol | Smooth, non-greasy, vanishing | Acute, weeping skin conditions, cosmetic moisturizers |
| Paste | 20 - 50% insoluble solids (ZnO, Starch) | Stiff, gritty, porous, localized | Diaper rash, weeping sores, sunscreens |
| Jelly / Gel | Aqueous polymer solution (Carbopol) | Transparent, cooling, non-greasy | Lubricant for catheters, topical NSAID analgesic gels |
- •Trituration Method: Used when medicament is insoluble in base; API is finely levigated using a levigating agent (Liquid paraffin or Glycerin) on an ointment slab before geometric incorporation.
- •Fusion Method: Used when base contains solid waxes of differing melting points (Beeswax, Hard paraffin, Cetyl alcohol); ingredients are melted in descending order of melting points on a water bath.
- •Pastes vs Ointments: Pastes contain 20-50% solid powders, are less greasy, more absorbent, and less occlusive than ointments.
22. Pharmaceutical Incompatibilities: Physical, Chemical & Therapeutic
Dedicated Webpage➔A pharmaceutical incompatibility occurs when two or more substances prescribed or mixed together produce an undesirable change in the physical, chemical, or therapeutic properties of the pharmaceutical preparation, rendering it unsafe, ineffective, or physically defective. Incompatibilities are broadly categorized into: Physical Incompatibilities (Immiscibility, Insolubility, Liquefaction, Precipitation), Chemical Incompatibilities (Oxidation-Reduction, Hydrolysis, Acid-Base Neutralization, Alkaloidal precipitation), and Therapeutic Incompatibilities (Antagonism, Synergism, Contraindications, Drug-Drug interactions).Jab do dawaiyon ko ek saath milane par wo kharab ho jayein, alag ho jayein ya unka asar ulta ho jaye, toh use Incompatibility kehte hain. Physical me Camphor + Menthol pighal jate hain; Chemical me alkaloid precipitate ho jata hai; aur Therapeutic me jaise Tetracycline antibiotic ko antacid ke sath lene par wo chelate banakar shareer me absorb nahi hoti.
▶Practical Examples and Solutions for Common Incompatibilities
Specific chemical conflicts encountered in prescription dispensing.
| Type of Incompatibility | Manifestation / Example | Underlying Mechanism | Standard Dispensing Remedy |
|---|---|---|---|
| Physical: Liquefaction | Camphor + Menthol | Lowering of mutual melting point (Eutectic) | Incorporate inert absorbent (Light MgCO3) |
| Physical: Immiscibility | Castor oil + Water | Hydrophobic phase separation | Incorporate emulsifier (Acacia 4:2:1) |
| Chemical: Precipitate | Alkaloid salt + Alkaline solution | Free base alkaloid is insoluble in water | Add suspending agent (Tragacanth) + 'Shake Well' |
| Therapeutic: Chelation | Tetracycline + Calcium/Antacid | Polyvalent cation binds antibiotic | Space administration by at least 2 hours |
- •Tolerated Incompatibilities: Can be overcome by simple modification of the mixing order, dilution, or adding suspending/emulsifying agents without altering therapeutic action.
- •Adjusted Incompatibilities: Requires substituting an ingredient with another chemically equivalent compound with prescriber's approval.
- •Therapeutic Incompatibility: Involves antagonistic drug combinations, dose errors, or contraindications occurring inside the human body.
- Classify all 3 types of Incompatibilities (Physical, Chemical, Therapeutic) with at least 2 distinct clinical prescription examples each for a 10-mark question.
- List the 4 classes of ointment bases with official examples and comparative properties.