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PASTES AND GELS

A Pharmaceutical Sciences Assignment

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TABLE OF CONTENTS

1. Introduction to Semisolid Dosage Forms
2. Pastes — Definition, Classification, Formulation, Preparation, Uses
3. Gels — Definition, Classification, Formulation, Preparation, Uses
4. Differences Between Pastes and Gels
5. Summary
6. References

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1. INTRODUCTION TO SEMISOLID DOSAGE FORMS

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2. PASTES

2.1 Definition

"Pastes are stiff preparations intended for application to the skin. They differ from ointments in that they contain a large proportion of finely powdered material." — British Pharmacopoeia (BP)

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2.2 Classification of Pastes

• Fatty base (soft paraffin, hard paraffin, lard) + high powder content
• Examples: Zinc Oxide Paste (Lassar's Paste), Compound Zinc Paste

• Water or glycerin as vehicle
• Used in dentistry and on mucous membranes
• Examples: Triamcinolone Dental Paste, Carmellose Gelatin Paste (Orabase)

• Contain active pharmaceutical ingredients (APIs)
• Examples: Dithranol Paste, Salicylic Acid Paste

• Protective/emollient only; no active drug
• Example: Plain Zinc Oxide Paste

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2.3 Formulation Components (Ingredients) of Pastes

• Zinc oxide — protective, astringent, mild antiseptic
• Starch — absorbent, soothing
• Calamine — cooling, antipruritic
• Kaolin — absorbent
• Titanium dioxide — photoprotective

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2.4 Preparation Methods of Pastes

Method 1: Fusion / Melting Method (Fatty Pastes)

1. Melt higher-melting base components (hard paraffin, beeswax) on a water bath.
2. Add lower-melting components (soft paraffin, liquid paraffin) to the melt.
3. Finely powder medicaments; pass through 150 µm sieve.
4. Gradually incorporate powders into the melted base with continuous stirring.
5. Stir throughout cooling to prevent powder settling.
6. Fill into airtight containers.

Key Point: Continuous stirring during cooling is essential for uniform powder dispersion.

Method 2: Trituration / Levigation Method

1. Levigate powders with a small amount of liquid paraffin or glycerin to a smooth paste.
2. Incorporate the remaining base in small portions, mixing thoroughly each time.
3. Final product should be smooth and free of gritty particles.
4. Spatula-and-slab method can be used for small-scale preparation.

Method 3: Machine Mixing (Industrial Scale)

• Triple-roller mills or planetary mixers
• Ensures fine, homogeneous powder-base dispersion

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2.5 Uses and Applications of Pastes

• Protective barrier (nappy rash, skin excoriation)
• Absorptive for exuding/weeping wounds
• Astringent (zinc oxide contracts tissues)
• Anti-inflammatory (corticosteroid pastes)
• Keratolytic (salicylic acid softens/removes hyperkeratotic skin)
• Dental adhesive and therapeutic applications

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3. GELS

3.1 Definition

"Gels are semisolid systems consisting of either small inorganic particles or large organic molecules interpenetrated by a liquid." — USP

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3.2 Classification of Gels

• Topical (skin), Ophthalmic, Nasal, Vaginal, Rectal, Oral mucosal

• Elastic/reversible gels (agar, gelatin) — regain structure after distortion
• Rigid/irreversible gels (silica gel) — do not revert once broken

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3.3 Formulation Components (Ingredients) of Gels

Gelling Agents (most critical component)

Other Excipients

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3.4 Preparation Methods of Gels

Method 1: Dispersion & Neutralization Method (Carbomer Gels) — Most Common

1. Disperse carbomer powder slowly onto the surface of purified water (do not add in bulk). Allow hydration for 30–60 minutes. The dispersion is acidic (pH ~3–4).
2. Dissolve API, preservatives, and humectants in a small portion of water separately.
3. Add the drug solution to the carbomer dispersion; mix gently.
4. Neutralize dropwise with triethanolamine (TEA) with slow stirring until a clear, viscous gel forms (target pH 6–7).
5. Adjust volume with purified water. Package in collapsible tubes or pump dispensers.

Key Points:

• Sprinkle carbomer gradually onto water; never add water to carbomer
• Avoid high-shear mixing — breaks polymer chains and reduces viscosity
• Degree of neutralization controls viscosity and clarity

Method 2: Heat-and-Cool Method (HPMC / Methylcellulose / Gelatin Gels)

1. Heat one-third of purified water to 80–90°C.
2. Disperse gelling agent (e.g., HPMC) in hot water with stirring.
3. Add the remaining cold water (ice-cold) to the hot dispersion while stirring — cools and gels the mixture.
4. Dissolve API in a suitable solvent and incorporate into the cooled gel base.
5. Adjust pH, add excipients, fill into containers.

Key Point: HPMC and methylcellulose are reverse-thermal polymers — they gel on cooling, not heating.

Method 3: Direct Dissolution Method (Tragacanth / CMC / Alginate Gels)

• Gelling agent dissolved directly in water at room temperature
• Drug and excipients added and mixed uniformly
• No neutralization or special temperature control needed

Method 4: Industrial Manufacturing

• Jacketed vessels with planetary or high-shear mixers
• Vacuum mixing to remove entrapped air
• In-line quality checks: pH, viscosity, clarity, drug content uniformity
• Aseptic processing for ophthalmic gels (sterile, preservative-free)

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3.5 Uses and Applications of Gels

• Anti-inflammatory — topical NSAID gels
• Antimicrobial — antibiotic gels for acne, vaginal infections
• Local anaesthetic — urethral catheterization, dental procedures
• Ophthalmic — prolonged corneal contact time
• Hormonal transdermal delivery — testosterone, estrogen gels
• Wound management — hydrogels maintain moist healing environment
• Antacid — aluminium/magnesium hydroxide gels

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4. DIFFERENCES BETWEEN PASTES AND GELS

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5. SUMMARY

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6. REFERENCES

1. Aulton, M.E. & Taylor, K.M.G. (2021). Aulton's Pharmaceutics: The Design and Manufacture of Medicines (6th ed.). Elsevier.
2. Lachman, L., Lieberman, H.A. & Kanig, J.L. (2019). The Theory and Practice of Industrial Pharmacy (4th ed.). CBS Publishers.
3. Banker, G.S. & Rhodes, C.T. (2002). Modern Pharmaceutics (4th ed.). Marcel Dekker.
4. Allen, L.V., Popovich, N.G. & Ansel, H.C. (2014). Ansel's Pharmaceutical Dosage Forms and Drug Delivery Systems (10th ed.). Lippincott Williams & Wilkins.
5. British Pharmacopoeia 2023. MHRA, London.
6. United States Pharmacopeia (USP 46–NF 41). USP Convention.
7. Rowe, R.C., Sheskey, P.J. & Quinn, M.E. (2022). Handbook of Pharmaceutical Excipients (9th ed.). Pharmaceutical Press.
8. Sinko, P.J. (2017). Martin's Physical Pharmacy and Pharmaceutical Sciences (7th ed.). Lippincott Williams & Wilkins.

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• Pastes — 4 classification types, 7 ingredient categories with examples, 3 preparation methods (fusion, levigation, machine mixing), clinical uses table
• Gels — 4 classification systems, 10 excipient categories including gelling agents table with concentrations, 4 preparation methods with step-by-step procedures and key points, clinical uses table
• Comparison table — 16 parameters comparing both dosage forms side by side
• All sections include pharmacopoeia definitions (BP, USP), named examples, and referenced standard textbooks

Assignment: Dispensing of Pastes and Gels

For Pharmacy Students (B.Pharm)

1. Introduction

• safe and effective therapy
• proper stability of product
• prevention of contamination
• better patient adherence and outcomes

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2. Overview of Pastes and Gels in Dispensing

2.1 Pastes

• Zinc oxide paste
• Salicylic acid paste
• Triamcinolone dental paste

• usually protective/absorptive
• often difficult to spread
• need clear counseling on application thickness and frequency

2.2 Gels

• Diclofenac gel
• Clindamycin gel
• Lidocaine gel
• Miconazole oral gel

• elegant, non-greasy, easy to spread
• may contain alcohol or volatile solvents
• require proper closure to avoid drying

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3. Objectives of Dispensing Pastes and Gels

1. Supply the correct drug and strength in correct dosage form
2. Maintain product quality and stability
3. Prevent microbial and physical contamination
4. Provide complete and understandable patient instructions
5. Monitor safety issues (allergy, contraindications, interactions, misuse)

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4. Stepwise Dispensing Procedure

4.1 Prescription Screening

• patient details (name, age, sex, weight if pediatric)
• diagnosis/indication
• drug name, strength, and dosage form (paste vs gel)
• route of administration (skin/oral mucosa/eye/vaginal/rectal)
• frequency and duration
• prescriber signature/date

• hypersensitivity history
• pregnancy/lactation status
• pediatric/geriatric suitability
• interacting medicines (e.g., acne combinations, steroid overuse risk)

4.2 Product Selection

• Choose prescribed brand/generic equivalent
• Verify concentration (e.g., 1%, 2%, 5%)
• Check base suitability (occlusive paste vs non-greasy gel)
• Confirm intended site compatibility (e.g., ophthalmic gel must be sterile)

4.3 Compounding/Extemporaneous Dispensing (if required)

• calculate quantity accurately
• use geometric dilution and proper levigation
• ensure uniform mixing
• avoid contamination and cross-contamination
• record batch sheet and formula

4.4 Packaging

• collapsible aluminum/laminated tubes
• wide-mouth ointment jars (for stiff pastes)
• light-resistant containers (if photosensitive)
• sterile ophthalmic tubes for eye gels

• minimize air exposure
• use tight closure
• avoid reactive containers
• provide applicator/spatula if needed

4.5 Labeling

• patient name
• drug name and strength
• dosage form (paste/gel)
• route: “For external use only” where applicable
• directions: amount, frequency, duration
• storage instructions
• beyond-use date/expiry
• cautionary statements

• “Do not apply on broken skin unless advised”
• “Avoid contact with eyes”
• “Wash hands before and after use”
• “For ophthalmic use only” (if eye preparation)
• “For vaginal use only” / “For rectal use only” (site-specific)

4.6 Patient Counseling

• indication and expected benefit
• exact method of application
• amount to use (thin film/pea-sized/fingertip unit)
• frequency and duration
• whether to rub gently or leave as protective layer
• whether area should be cleaned before application
• when not to occlude with dressing
• adverse effects and warning signs
• missed dose advice
• storage and handling

4.7 Documentation

• prescription copy
• product name/batch/expiry
• quantity dispensed
• pharmacist intervention (if any)
• counseling provided
• refill details

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5. Special Dispensing Considerations for Pastes

1. Consistency: very stiff; counsel patient to apply in small portions.
2. Spreadability: low; may need gentle warming in hands (if appropriate).
3. Occlusion: fatty pastes are occlusive; avoid over-application in infected lesions unless prescribed.
4. Absorbent nature: good for weeping lesions; clarify use on dry vs wet lesions.
5. Removal: may be difficult; advise use of cotton with suitable cleansing agent.
6. Jar contamination risk: recommend spatula instead of fingers for repeated use.

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6. Special Dispensing Considerations for Gels

1. Volatile components: close cap tightly to prevent drying.
2. Alcohol-containing gels: may sting on inflamed skin; warn patient.
3. Clear appearance: phase separation/discoloration indicates instability.
4. Site-specific use: ophthalmic, oral, vaginal gels are not interchangeable.
5. Drug release: generally faster than pastes; avoid overuse.
6. Cosmetic acceptability: improves adherence; still emphasize correct dose.

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7. Common Errors in Dispensing Pastes and Gels

• dispensing wrong strength (e.g., 0.025% vs 0.05%)
• confusion between cream/ointment/gel/paste
• missing “external use only” label
• inadequate counseling on quantity and duration
• not warning about steroid-containing pastes/gels
• dispensing expired or near-expiry product
• wrong storage advice (especially heat-sensitive gels)
• failure to assess contraindications (broken skin, allergy, pediatric age)

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8. Patient Counseling Example (Practical)

1. Apply thin layer to affected area 3-4 times daily.
2. Do not apply on cuts/wounds.
3. Wash hands after application.
4. Avoid tight bandage unless doctor advised.
5. Stop and report if severe redness/rash occurs.
6. Keep tube tightly closed; store below recommended temperature.

1. Clean and dry area before each application.
2. Apply thick protective layer; do not rub vigorously.
3. Reapply after each diaper change.
4. Seek medical advice if rash worsens or fever appears.

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9. Storage and Stability During Dispensing

• Store in cool, dry place away from direct sunlight
• Avoid freezing unless specifically allowed
• Keep cap tightly closed
• Prevent microbial contamination
• Follow FEFO (First Expiry First Out) in pharmacy stock management
• Check appearance before dispensing (odor, color, separation, grittiness)

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10. Legal and Ethical Aspects

• dispense against valid prescription for Rx-only products
• maintain confidentiality
• provide unbiased counseling
• avoid unauthorized substitution where not permitted
• document interventions and medication errors
• report adverse drug reactions when indicated

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11. Role of Pharmacist in Optimizing Outcomes

• selecting appropriate semisolid dosage form based on lesion/site
• preventing misuse of steroid-containing products
• teaching correct application technique
• improving adherence through practical counseling
• monitoring efficacy and safety during refill visits

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12. Conclusion

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13. Short Viva/Review Questions

1. Why are pastes preferred for weeping skin lesions?
2. Give three counseling points for alcohol-based gels.
3. What labels are essential for topical semisolid preparations?
4. Differentiate dispensing concerns of ophthalmic gel and topical gel.
5. What steps reduce contamination while dispensing semisolids?

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14. References (Suggested)

1. Aulton ME, Taylor K. Aulton’s Pharmaceutics: The Design and Manufacture of Medicines.
2. Allen LV. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems.
3. British Pharmacopoeia (latest edition).
4. USP-NF (latest edition).
5. Remington. The Science and Practice of Pharmacy.

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• a ready-to-submit handwritten style format (with simpler headings), or
• a 5-7 page classroom assignment format with cover page, index, and diagram placeholders.