Standard Sizes of Two-Piece Capsules

Capsule Size System

• Pharmaceutical hard-shell capsules are standardized by an internationally accepted numbering system.
  • Integer alone (e.g., 5, 4, 3 … 000) = regular length.
  • Suffix "el" = "elongated" (longer body, same diameter; slightly larger fill capacity).
  • Suffix "el+" & "xel" = progressively more elongated versions of size 0.
• Manufacturer referenced in the transcript: ACG Associated Capsules Pvt. Ltd. (major global supplier of empty hard capsules).
• Material is usually hard gelatin or
  HPMC (= hydroxy-propyl-methyl-cellulose) for vegetarian/halal grades; physical size standards, however, are identical.

Tabulated Dimensional Data

(Values are directly from the transcript; tolerances not shown.)

• Size-linked parameters
  • Nominal fill volume (at bulk density 1.0 g·mL⁻¹) → in $\text{mL}$.
  • Locked length (overall length when cap is fully pressed onto body) → in $\text{mm}$.
  • External diameter (widest outer diameter, usually measured at cap end) → in $\text{mm}$.

Observations & Trends

• Inverse numbering: smaller numerical value ⇒ larger capsule (e.g., 0 is bigger than 1, 000 is largest).
• Length ↑ & diameter ↑ with larger capacity, but diameter remains constant within the same “family” of elongated variants; only the length extends to give extra volume.
• Rough density rule: For most powdered APIs & excipients with tapped density ≈ 0.6\,\text{g·mL}^{-1}, fill weight ≈ $0.6 \times \text{volume}$. Example: Size 0 ($0.68\,\text{mL}$) can hold $\approx 0.41\,\text{g}$ of such powder.

Practical Selection Guidelines

• Patient acceptability:
  • Sizes 4–2 favored for pediatrics & geriatrics due to swallowability.
  • Sizes 0–00 common in adult prescription & supplement markets.
• Formulation density drives final choice:
  • High-density actives (e.g., metallic salts) may use smaller numbers.
  • Low-density blends (e.g., herbals) often require elongated or 000.
• Multi-particulate / pellets: elongated shells (0el, 0xel) helpful to maintain diameter for coating uniformity while adding length.
• Combination products: filling two API layers or tablets inside often prompts use of 0xel–00el.

Manufacturing & Regulatory Notes

• Tolerances for length and diameter are specified in pharmacopeial monographs (e.g., USP ⩵ ±$0.4\,\text{mm}$ for diameter). Always verify supplier’s CoA.
• Capsules are delivered joined pre-locked (aka “pre-closed”); length in the table represents that locked state.
• Typical fill machinery settings are calibrated using the locked length and internal volume—not the external diameter.

Memorization Aids

• "5-4-3: Think of childhood years—tiny kids, tiny capsules."
• "0 family: same diameter $7.66\,\text{mm}$; just keep stretching (el → el+ → xel)."
• "Triple-0 = 1.37 mL ≈ 2 × size-0 volume."
• Visual mnemonic: arrange empty shells from 5 to 000; the staircase left-to-right gets both longer and fatter.

Example Calculation

Suppose a powder has true density \rhot = 1.2\,\text{g·mL}^{-1} and Carr’s compressibility index 18 % (giving approximate tapped density \rhotap \approx 0.75\,\text{g·mL}^{-1}).
Desired dose = $300\,\text{mg}$.
Required volume $V = \frac{m}{\rho} = \frac{0.300}{0.75} = 0.40\,\text{mL}$.
Size choice: 2el (0.41 mL) or regular 2 (0.37 mL) depending on fill variations.

Links to Previous Pharmaceutical Technology Topics

• Powder flow & density (lecture 3): directly informs capsule size selection.
• Gelatin cross-linking & brittleness (lecture 7): more critical in larger shells; moisture monitoring essential.
• Encapsulation equipment types (lecture 9): dosator vs. tamping pin set-ups align with capacities listed above.

Ethical & Practical Implications

• Choosing smaller capsules whenever feasible improves patient compliance and reduces choking risk.
• Oversizing can waste gelatin resources and increase storage/packaging volume (sustainability concern).
• Accurate sizing also minimizes the need for excipient over-filling, thereby reducing potential allergen exposure.