NOTES FOR UPSC DRUG INSPECTOR 2026

PHARMACEUTICAL CAPSULE TECHNOLOGY

Comprehensive Industrial Technical Notes: Shell Composition, Manufacturing, Filling Technologies, Quality Control & Plant GMP Compliance

1. Definition & Industrial Overview

A Capsule is defined as a solid unit dosage form in which active pharmaceutical ingredients (APIs) with or without suitable pharmaceutical excipients are enclosed within a small, soluble shell or container, typically manufactured from gelatin or synthetic non-gelatin polymers (e.g., HPMC).

Industrial Advantages of Capsules

• Taste & Odor Masking: Shell completely encloses offensive or bitter APIs, significantly improving patient compliance.
• Formulation Versatility: Can accommodate diverse fill materials including dry powders, granules, pellets, mini-tablets, non-aqueous liquids, suspensions, and pastes.
• Faster Dissolution Kinetics: Requires no high compaction pressure (unlike compressed tablets); the shell disintegrates rapidly in GI fluid, leading to prompt API liberation and absorption.
• Design & Brand Flexibility: Easily recognizable by distinct color combinations, bandings, and high-precision brand printings.

Industrial Limitations

• Cost Factor: Capsule shell manufacturing process and specialized high-speed filling machinery increase overall unit production cost compared to standard compressed tablets.
• Incompatibility with Moisture-Sensitive / Liquid APIs: Hygroscopic drugs absorb moisture from gelatin, making shells brittle and prone to cracking. Efflorescent drugs release water into gelatin, causing shell softening, tackiness, and leakage.
• Environmental Sensitivity: Requires strict environmental controls during manufacturing and storage (35%-55% RH and 15°C – 25°C).

2. Classification and Types of Pharmaceutical Capsules

• Hard Gelatin Capsules (HGC): Two-piece telescoping structure consisting of a narrower Body (holds fill material) and a shorter, wider Cap (locks over body). Formulated primarily for dry powders, granules, pellets, or non-aqueous pastes.
• Soft Gelatin Capsules (SGC / Softgels): One-piece, hermetically sealed, flexible shell formed, filled, and sealed simultaneously in a continuous rotary die process. Ideal for liquid APIs, oil solutions, suspensions, and self-emulsifying systems.
• Non-Gelatin / Vegetarian Capsules (HPMC / Hypromellose / Pullulan): Shells made from plant-derived polymers. Feature lower equilibrium moisture content (3%-7%) compared to gelatin (13%-16%), making them highly suitable for moisture-sensitive APIs and vegetarian/halal/kosher requirements.
• Enteric-Coated / Gastro-Resistant Capsules: Shells coated or formulated with acid-resistant polymers (e.g., Cellulose Acetate Phthalate / CAP, Eudragit L100) that remain intact in gastric fluid (pH 1.2) but dissolve rapidly in intestinal fluid (pH > 5.5).
• Modified / Sustained-Release Capsules: Hard capsules filled with multi-particulate systems (e.g., enteric-coated or sustained-release coated beads/pellets) or matrix mini-tablets to deliver steady plasma drug levels over 12-24 hours.

3. Capsule Shell Composition & Manufacturing (Lachman Framework)

A. Raw Material Composition of Capsule Shells

• Gelatin Types & Sources: Type A Gelatin is produced by acid hydrolysis of pigskin collagen (Isoelectric Point / pI = 7.0 – 9.0). Type B Gelatin is produced by alkali hydrolysis of bovine bone/hide collagen (pI = 4.7 – 5.2). Industrial standard is a blend of bone gelatin (provides firmness/clarity) and pork skin gelatin (provides flexibility).
• Gelatin Quality Parameters:
  • Bloom Strength (Gel Strength): Measure of cohesive strength of cross-linked gelatin. Hard capsules require 200-250 g; Soft capsules require 150-200 g.
  • Viscosity: Maintained at 25-45 millipoise (2.5-4.5 mPa s) measured at 60°C in a 6.67% aqueous gelatin solution.
• Plasticizers (Essential for Softgels): Added to impart elasticity, flexibility, and softness to softgel shells. Common examples: Glycerol, Sorbitol, Propylene Glycol.
• Plasticizer-to-Gelatin (P:G) Ratio Guidelines:
  • Hard Gelatin Shells: 0.0 to 0.4 : 1
  • Hard Softgel Shells: 0.4 : 1
  • Medium Softgel Shells: 0.6 : 1
  • Soft/Flexible Softgel Shells: 0.8 to 1.0 : 1
• Equilibrium Moisture Content: Hard Gelatin Shells contain 13.0% – 16.0% w/w water (acts as essential structural plasticizer). Softgel Shells (post-drying) contain 6.0% – 10.0% w/w water.
• Functional Additives: Opacifiers (Titanium Dioxide / TiO2, 0.2% – 1.2% to block light transmission), Preservatives (Methylparaben and Propylparaben in 4:1 ratio to inhibit microbial growth), Colorants (FD&C dyes and Iron Oxides).

B. Capsule Shell Manufacturing Technology

Hard Gelatin Capsule Manufacturing (Pin-Dipping Process):

1. Dipping: Temperature-controlled stainless steel pin bars dipped into molten gelatin sol (50°C – 55°C).
2. Spinning: Pin bars rotated 360° horizontally to distribute gelatin film uniformly across pin heads.
3. Drying: Passed through controlled drying kilns with dehumidified air (20°C – 25°C, 40% – 50% RH).
4. Stripping & Trimming: Dried gelatin caps and bodies stripped off pins by brass jaws and trimmed to exact lengths by stationary knives.
5. Joining: Caps and bodies pre-joined into self-locking designs (e.g., Coni-Snap feature with locking grooves to prevent separation).

Soft Gelatin Capsule Manufacturing (Rotary Die Process – RP Scherer): Two continuous molten gelatin ribbons are fed between counter-rotating die cylinders containing pocket molds. Liquid fill material is precisely injected under pressure between ribbons at the exact moment die pockets meet. Heat and pressure simultaneously seal, shape, cut, and eject individual softgels, followed by immediate tumble drying and tray tunnel drying.

4. Capsule Shell Sizes & Preformulation Studies

A. Standard Hard Capsule Shell Sizes (8 Human Sizes)

Capsule Size	Volume Capacity (mL)	Powder Fill Capacity (mg)	Relative Size Category
000	1.37 mL	800 – 1400 mg	Largest Human Size
00	0.95 mL	500 – 900 mg	Very Large
0	0.68 mL	350 – 700 mg	Standard Large
1	0.50 mL	250 – 500 mg	Medium
2	0.37 mL	200 – 400 mg	Medium Small
3	0.30 mL	150 – 300 mg	Small
4	0.21 mL	100 – 200 mg	Very Small
5	0.13 mL	60 – 100 mg	Smallest Human Size

Note: Actual fill weight depends on powder bulk density (0.6 – 1.0 g/mL). Veterinary sizes include 10, 11, and 12 (volume up to 30 mL).

B. Preformulation & Fill Compatibility

• Suitable Fill Materials for Hard Capsules: Dry powders, granules, multi-unit coated pellets, mini-tablets, non-aqueous liquids, and thermo-softened pastes.
• Suitable Fill Materials for Softgels: Lipophilic liquids (vegetable oils, mineral oils), water-miscible non-aqueous liquids (PEG 400, Propylene Glycol), self-emulsifying microemulsion systems (SEDDS), and liquid suspensions.
• Incompatible Fill Materials:
  • High Moisture Liquids (> 5% water): Dissolves or softens the gelatin shell causing structural failure.
  • Low Molecular Weight Aldehydes: Causes gelatin cross-linking (tanning), rendering the shell insoluble in gastric fluids.
  • Extreme pH Liquids: Liquids with pH < 2.5 induce acid hydrolysis and leakage; pH > 7.5 induces shell hardening.

5. Capsule Filling Mechanisms & Industrial Equipment

• Tamping Pin Mechanism (e.g., Bosch, Zanasi Presses): A rotating dosing disc with 5 or 6 cavities maintains a constant powder bed depth. Tamping pins compress powder into a light plug in 5 successive steps before the final dosed plug is transferred into the capsule body.
• Dosator Mechanism (e.g., MG2 Presses): A dosator tube equipped with an internal movable piston plunges directly into an open powder bed. The piston compresses powder into a plug, the tube retracts, rotates over the open capsule body, and the piston descends to eject the plug.
• Liquid & Semi-Solid Filling Assembly: Precision volumetric dosing pumps inject thermo-softened pastes or non-aqueous liquids into HGC bodies. Immediately followed by Banding / Micro-Sealing (Quali-Seal / LEMS technology) at the cap-body junction to prevent leakage and tampering.

6. Quality Control & Quality Assurance Tests

A. Non-Pharmacopoeial (Unofficial) Quality Tests

• Bloom Strength Test: Measured using a Bloom Gelometer or Texture Analyzer (6.67% gelatin solution chilled at 10°C for 16-18 hours; force in grams required to depress a 0.5-inch plunger by 4 mm).
• Moisture Content Determination: Verified using Loss on Drying (LOD) at 105°C or Karl Fischer (KF) Titration.
• Shell Locking Integrity: Evaluated by verifying proper engagement of Coni-Snap locking grooves and band seal dimensions.
• Softgel Seal Leakage Test: Softgels subjected to vacuum pressure or placed on absorbent paper under 40°C thermal stress to ensure no liquid seam leakage.

B. Pharmacopoeial (Official) Quality Tests (IP / BP / USP)

Weight Variation Test Protocol:

• Hard Capsules: 20 intact capsules weighed individually. Body opened, contents emptied completely, shell cleaned with air/ether, empty shell weighed. Net fill mass calculated.
• Soft Capsules: 20 intact capsules weighed. Shell sliced open, contents washed thoroughly with a suitable solvent (ether/petroleum spirit), solvent evaporated at room temperature, empty shell weighed.

Average Fill Weight (IP / BP / USP)	Maximum Allowed Deviation (%)
Less than 300 mg	±10.0%
300 mg or more	±7.5%

Pass Criteria: Not more than 2 individual capsule weights deviate from average weight by more than the allowed percentage, and NONE deviate by more than double the specified percentage.

Content Uniformity Test: Mandatory when active API is < 25 mg or < 25% of total capsule fill mass. 10 individual capsules assayed; active drug content must lie within 85.0% - 115.0% of labeled claim with Relative Standard Deviation (RSD) ≤ 6.0%.

Disintegration Test (DT): Evaluated using USP Basket-Rack Assembly at 37 ± 2°C with plastic discs added to prevent floating.

Capsule Category	Test Medium	Official DT Time Limit
Hard Gelatin Capsules	Water at 37 ± 2°C	< 30 minutes
Soft Gelatin Capsules	Water at 37 ± 2°C	< 60 minutes
Enteric Coated Capsules	0.1 N HCl (2 hrs) → pH 6.8 Buffer (1 hr)	0 disintegration in HCl (2 hrs); < 60 min in pH 6.8 Buffer

Dissolution Testing:

• USP Apparatus 1 (Basket, 50-100 rpm): Prevents lightweight capsules from floating to the fluid surface.
• USP Apparatus 2 (Paddle, 50 rpm): Used with wire sinkers to keep capsules submerged at the bottom of the vessel.
• Enzymatic Dissolution Addition: If gelatin cross-linking (pellicle formation) occurs due to thermal/humidity storage stress, USP permits adding Pepsin (in acidic media) or Pancreatin (in pH 6.8 buffer) to digest pellicles.

7. Post-Formulation & Industrial Plant Requirements

A. Storage & Environmental Controls

• Filling Room Temperature: Maintained at 15°C – 25°C.
• Relative Humidity (RH) Controls: Kept strictly between 35% – 55% RH in capsule filling and packaging suites.
• Critical Impact of Relative Humidity on Capsules:
  • If RH < 35%: Shell loses structural water content (< 10%), becoming highly brittle and cracking during handling.
  • If RH > 60%: Shell absorbs excess moisture (> 18%), becoming soft, sticky, losing mechanical shape, and adhering together.

B. Primary Packaging Systems

• Blister Packaging (Alu-Alu vs PVC/PVDC): Cold-form Alu-Alu blisters provide 100% moisture barrier protection for moisture-sensitive capsule formulations; PVC/PVDC used for general stability.
• HDPE Bottle Packaging: High-Density Polyethylene containers equipped with induction-sealed foil liners, child-resistant caps, and silica gel desiccant canisters.

C. GMP & Manufacturing Facility Compliance

• Cleanroom Standards: Capsule processing and packaging conducted in Grade D (ISO Class 8) cleanroom suites equipped with HEPA filtration (99.97% efficiency @ 0.3 micron).
• Air Differential Pressure Gradient: Positive pressure differential maintained inside processing cubicles relative to adjoining corridors to eliminate airborne cross-contamination.
• ICH Stability Testing (ICH Q1A):
  • Accelerated Stability: 40°C ± 2°C / 75% RH ± 5% RH for 6 months.
  • Real-Time Stability: 25°C ± 2°C / 60% RH ± 5% RH OR 30°C ± 2°C / 75% RH ± 5% RH for 12 to 36 months.