Small-Scale Production of Tablets and Capsules
9 minute read
What you will learn
- Outline the steps in making a batch of tablets
- Outline the steps in filling a batch of capsules
- Calculate the quantity of drug needed for a batch
- Describe the tests for weight variation, hardness, friability and disintegration
- Calculate friability and the weight limits of a tablet
- State the precautions in solid dosage production
Key points
- A tablet batch is made by weighing, sieving, mixing, granulating (or direct compression), compressing, and then checking, coating and packing.
- Capsules are made by mixing the powder, filling the shells, closing, cleaning and checking.
- Drug needed = tablets in the batch × dose per tablet.
- Weight variation checks that tablets contain the same amount. Allowed limits depend on the average weight.
- Hardness tests strength. Friability tests how well the tablet resists chipping and crumbling.
- Disintegration tests whether the tablet breaks up in a set time in fluid.
- Dust control and mix-up prevention are essential in solid production.
Solid dosage forms in batches
The theory of tablets and capsules, including the types, excipients and coating, is in BDT 152. This lesson looks at making batches and checking their quality.
Making tablets
| Step | What happens |
|---|---|
| 1. Weighing | Each ingredient is weighed by one person and checked by another |
| 2. Milling and sieving | Powders are made fine and even |
| 3. Mixing | The drug and excipients are mixed. Small amounts are mixed first (geometric dilution) |
| 4. Granulation | Wet or dry granulation, or direct compression if the powder flows and compresses well without it |
| 5. Drying and screening | Wet granules are dried and screened |
| 6. Lubrication | A lubricant is added in the last mix |
| 7. Compression | A tablet press compresses the granules in dies, using punches |
| 8. Coating (if needed) | The tablets are coated for taste, protection or release |
| 9. Checking | In-process and final tests |
| 10. Packing and labelling | Tablets are packed with batch number and expiry date |
Batch quantity
Example. 10 000 tablets, each with 500 mg of paracetamol.
- Drug = 10 000 × 500 mg = 5 000 000 mg = 5 000 g = 5 kg
Excipients are added to the formula amounts, and the tablet weight is set so that each tablet has exactly the dose.
Small presses
In a small pharmacy or school, a single-punch tablet press or a hand-operated press may be used. Industrial presses are rotary machines making many thousands of tablets an hour.
Making capsules
- Weigh the ingredients, and sieve and mix them.
- Fill the powder into the lower part (body) of each shell, by hand, with a capsule-filling device or a machine.
- Close the capsules by fitting on the caps.
- Clean the outside to remove dust.
- Check: weight, appearance and closure.
- Pack and label.
The size of the capsule is chosen to fit the dose. See the lesson on capsules in BDT 152.
In-process and final tests
| Test | What it shows | How |
|---|---|---|
| Appearance | Colour, shape, cracks, chips, spots | Looking at a sample |
| Weight variation | That each tablet or capsule has about the same amount of drug | Weigh a sample of units, find the average, and compare each one with it |
| Hardness | The strength of a tablet | A hardness tester measures the force needed to crush a tablet |
| Friability | How well the tablet resists chipping and crumbling | Tumble in a drum, and weigh before and after |
| Disintegration | That the tablet breaks up in fluid in a set time | A basket is raised and lowered in fluid at body temperature |
| Dissolution | How fast and how much drug dissolves | Tablet is stirred in fluid, and samples are tested |
| Content of drug | That the right amount of drug is present | A chemical assay |
Weight variation
The limits depend on the average weight. A commonly quoted set for uncoated tablets is:
| Average weight | Allowed deviation |
|---|---|
| 80 mg or less | ±10% |
| More than 80 mg and less than 250 mg | ±7.5% |
| 250 mg or more | ±5% |
Example. The average weight is 200 mg and the limit is ±7.5%.
- 7.5% of 200 = 15 mg
- Acceptable range = 185 mg to 215 mg
Use the limits in the pharmacopoeia or textbook that your school follows.
Friability
friability (%) = (initial weight − final weight) ÷ initial weight × 100
Example. 6.50 g of tablets weighs 6.45 g after the test.
- Loss = 6.50 − 6.45 = 0.05 g
- Friability = 0.05 ÷ 6.50 × 100 = 0.77%
A loss of not more than about 1% is usually accepted.
Disintegration
Uncoated tablets are generally expected to break up within a short set time, often 15 minutes, and coated tablets longer. Check the limit for each type in your textbook.
Precautions
- Control dust, with masks, extraction and cleaning.
- Prevent mix-ups: one product at a time, line clearance between batches, clear labels.
- Keep dry, because moisture ruins tablets and capsules.
- Record each step, and keep retained samples.
- Check that punches and dies are clean and undamaged.
Exam focus
- List the steps of tablet manufacture in order.
- Calculate the weight of drug for a batch of tablets.
- Calculate friability, and state its limit.
- Common mistake: confusing hardness (strength) with disintegration (breaking up in fluid).
Quick check
Test yourself before you move on. Pick an answer to see the explanation.
1.A batch of 10 000 tablets each contains 500 mg of paracetamol. How much paracetamol is needed?
2.Which test measures how well a tablet resists chipping and crumbling during handling?
3.6.50 g of tablets lose 0.05 g in a friability test. What is the percentage loss?
4.A tablet has an average weight of 200 mg. If the allowed deviation is ±7.5%, what is the acceptable range?
5.The test that shows whether a tablet breaks apart in fluid in a set time is: