Capsule Defects and Remedies During Filling Process

Capsule defects and remedies during the filling process are listed below, with the cause and remedy for each of 13 defects. A capsule filling defect is a fault in the capsule shell, fill or closure that arises during filling and must be corrected so that each capsule holds one correct dose.

Capsules are solid dosage forms. A shell encloses one drug or a combination of drugs, with or without excipients. The shell can be hard gelatin or soft soluble gelatin. It can also be a hard or soft shell of any other acceptable material. Capsules come in a variety of shapes and capacities. Normally, they are meant for oral consumption and contain a single dose of active ingredient(s).

Capsules must be free from manufacturing defects. They can develop several types of defects during manufacturing, and several defects can appear together, so each one must be identified separately.

Types of capsule defects and remedies during the filling process

The list below names the 13 capsule defects that can occur during filling, and each defect is described in its own section with its causes and remedies.

1. Loss of cap during transfer / Misalignment of cap and body bush
2. Dents and pinholes (on tips)
3. Cracks in Capsules
4. Telescopic Capsules
5. Dusty Capsules
6. Empty Capsules
7. Damaged band
8. The capsule does not enter the rectifier block
9. Capsule getting damaged during loading
10. Capsule non-separation
11. Target weight not achieved
12. Weight variation
13. Capsule lock length variation

The sections below give the causes and remedies for each capsule filling problem.

1. Loss of cap during transfer / Misalignment of cap and body bush

Causes: High vacuum

Remedies: Reduce the vacuum, but keep it high enough for the capsules to separate.

Check the alignment of the cap and body bush visually to correct misalignment.

2. Dents and pinholes (on tips)

Causes:

• Excess closing/lock length setting during the encapsulation process
• Excessive lock length
• Excessive closing pressure
• Over-filling of capsules
• Incorrect pin size or pin configuration
• Improper storage conditions (moisture)

Remedies: The correct size disc must be used, and the correct amount of dose must be filled in the capsule.

3. Cracks in Capsules

Causes

1. Improper (storage) conditions favor the transfer of moisture from the capsule shell to encapsulated components.

2. Misalignment of the upper and lower capsule segments. Incorrect setting of the cap hold-down pin in the joining station.

Remedies

1. Store the capsules properly.

2. Make a proper setting of the station.

4. Telescopic Capsules

Causes

1. Misalignment of cap and body bush

2. Closing pin not in the center of body bushes

3. Damage to the rubber sheet of the closing plate

Remedies

1. Align the cap/body bush to the bush gauge.

2. Check pin straightness using a gauge pin. If the pin is bent, replace it with a new one.

3. Wear of the capsule closing unit rubber sheet, specifically at the point where the capsule strikes the sheet, can lead to telescopic capsules. The rubber sheet should be replaced if required.

5. Dusty Capsules

Causes

1. Filling dusty fill.

Remedies

Use a capsule polisher.

6. Empty Capsules

Causes

1. Malfunction in the capsule filling machine, which allows empty capsules to reach the exit chute (e.g. load cells, capacitive sensors, etc.).

Remedies

1. Make sure the capsule filling machine has safeguards that stop empty or under-filled capsules from reaching the exit chute (e.g. load cells, capacitive sensors, etc.).

Schedule M requires in-process controls and calibrated, qualified equipment during filling. Qualification of the automatic capsule filling machine is described in the posts on Installation Qualification, Operational Qualification and Performance Qualification.

7. Damaged band

Causes

1. Badly tuned banding process, such as improper wheel height and speed, improper processing temperature, improper band thickness, and poor/bad band wheel.

Remedies

1. Set all the parameters accurately.

8. Capsule does not enter the rectifier block

Causes

1. Capsule stored overnight and without climatic control.

2. Magazine non-alignment with rectifier block

Remedies

1. Improper room or storage conditions can make capsules stick to each other. Stuck capsules cannot transfer to the magazine slots. Rooms and storage should be kept under climatic control.

2. The magazine alignment with the rectifier block could have shifted or not been set right. The magazine should be aligned to the rectifier block using a gauge.

WHO GMP expects equipment to be qualified. EU GMP Annex 15 also covers equipment qualification. International Council for Harmonisation (ICH) Q9 supports risk-based control of room and storage conditions that affect capsule moisture.

Read Also: Tablets Manufacturing Defects and remedies

9. Capsule getting damaged during loading

Cause

1. Misalignment of rectifier block with bushes

Remedies

1. Verify visually if the rectifier block is in alignment with the cap/body bush. Use an alignment gauge if there is any doubt.

10. Capsule non-separation

Causes

1. Insufficient vacuum or incorrect vacuum pump

2. Leakage through filters

3. Cap body bush misalignment

4. Worn out bushes

5. Loss of spring tension at the top slide

Remedies

1. A pump of proper capacity should be used.

2. If the vacuum drops, check the filters on the vacuum pump. Clean or replace the filters if required.

3. A misalignment of cap and body bush can cause non-separation.

4. If non-separation occurs in specific bushes and cleaning does not help, replace these bushes with new ones.

5. Poor spring tension at the top side, or sluggish movement of the top slide, can stop the cap/body bush holder plate from closing properly. A pin can cause the sluggish movement. Replace the spring or the pin.

11. Target weight not achieved

Causes

1. Incorrect target weight with respect to selected capsule size

2. Improper slug formation due to incorrect setting parameters

3. Insufficient binding if a proper slug is not formed

4. Poor flow of product

Remedies

1. Check for the variation in physical parameters (tapped density, moisture content, particle size distribution and flow properties of the formulation).

2. Check for correct parameters setting.

3. If a proper slug is not formed, part of the powder could be lost before delivery to the capsule.

4. Poor flow of the powder in the dosing disc will result in insufficient powder flowing in the disc cavity.

In-process controls during filling are described in the post on In Process Quality check during Manufacturing.

12. Weight variation

Causes

• Wrong selection of dosing disc thickness
• Incorrect gap between

1. dosing disc and supporting pad
2. Tamping pin and body bush
3. Dosing disc and wiper block
4. Dosing disc and body bush

Remedies:

• Select the dosing disc that fills the powder fully into the capsule shell.
• Correct the Gap Between:

1. dosing disc and supporting pad: NMT 0.1 mm
2. Tamping pin and body bush: maintained at 0.2 to 0.4 mm
3. Dosing disc and wiper block: NMT 0.1 mm
4. Dosing disc and body bush: maintained at 0.8 to 1.0 mm

United States Pharmacopeia (USP) <2091> Weight Variation of Dietary Supplements and the pharmacopoeial uniformity of dosage units chapters (USP <905>, Ph. Eur. 2.9.40) set the limits that capsule fill weight must meet. Under 21 CFR Part 211, written in-process controls are required, such as checks of capsule weight variation.

13. Capsule lock length variation

Causes

Remedies

1. Excess joined length

2. Improper setting of the closing plate

3. Damage to the rubber sheet of the closing plate

4. Incorrect setting of the closing plate

Remedies:

1. Check for the standard locking length.

2. Check for the gap between the closing unit rubber sheet and capsules. The distance between the two points should be between 0.5 and 0.8 mm.

3. Wear off of the capsule closing unit rubber sheet, especially at the point where the capsule strikes the sheet, can lead to this problem. Replace it with a new one.

4. The flap should be visually parallel to the cap bush lock plate. Check to ensure that capsules are hitting the center of the rubber sheet and not the edge. If a capsule hits the edge of the rubber sheet, it falls off the edge and fails to lock properly.

Other Common Capsule Defects and Remedies

Deliquescent / Hygroscopic powders- Adsorbent [magnesium carbonate, heavy / light magnesium oxide]
A small dose of drug Remedy-Addition of inert powder.
Incompatibilities of materials -Use of two capsules – small in large
Lack of adhesiveness difficult to fill by punch method-Moistened with alcohol, granules reduced to powders.

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Frequently Asked Questions

References

• 21 CFR 211.110