Quality Control of Tablets
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Direct answer
Tablet quality control divides into in-process checks during compression and finished-product tests against pharmacopoeial limits. In-process, every half hour or so, operators verify weight, hardness, thickness and friability so a drifting press is caught mid-batch. On the finished batch the official battery runs: uniformity of weight with IP tolerances that tighten as tablets shrink (broadly 5 per cent above 250 mg to 10 per cent below 80 mg); hardness of roughly 4 to 8 kg; friability by Roche friabilator — 100 revolutions in 4 minutes, loss not more than 1 per cent; disintegration in water at 37 °C within 15 minutes for uncoated and 30 minutes for film-coated tablets; and dissolution in basket or paddle apparatus with 900 mL medium, where a Q point such as not less than 70 per cent at the stated time decides bioavailability-relevant acceptance. For potent low-dose tablets, weight variation is replaced by content uniformity, the per-unit assay weight can never guarantee.
What you must remember
- In-process rhythm: weight, hardness, thickness and friability at defined intervals, with adjustments and segregated output logged — the data trail inspectors read.
- Weight variation (IP style): about 5 per cent above 250 mg, 7.5 per cent for 80-250 mg, 10 per cent below 80 mg; only isolated tablets may exceed the band.
- Friability: Roche friabilator, 100 revolutions in 4 minutes, acceptance below 1 per cent weight loss.
- Disintegration: uncoated 15 minutes, film-coated 30 minutes; enteric resists 0.1 N hydrochloric acid 2 hours, then breaks up in pH 6.8 buffer within about 60 minutes — breakup, not drug in solution.
- Dissolution: basket (commonly 100 rpm) or paddle (50 or 75 rpm) in 900 mL at 37 ± 0.5 °C against the monograph's Q point, frequently NLT 70 per cent at a stated time for immediate release.
- Content uniformity replaces weight variation when the active is about 25 mg or less, or 25 per cent or less of tablet weight — the quotable rule of thumb.
- Hardness: about 4 to 8 kg by Monsanto or Pfizer tester; the examinable inversion — excessive hardness delays disintegration and dissolution.
- Other finished tests: identification, assay, water content where specified, and visual defect inspection.
A batch drifting, caught the QC way
Halfway through a paracetamol run, the half-hourly check finds weights creeping high — a lower punch retracting slowly means dies are overfilling. The chart catches the drift ten minutes of production deep; the interval is segregated and the press reset. Finished, the batch faces the official tests: twenty tablets weighed individually, none beyond the 5 per cent band — pass; ten tablets dedusted, tumbled 100 revolutions, 0.6 per cent loss — pass; six tablets disintegrated within 8 minutes at 37 °C — pass; six units in the paddle at 50 rpm in 900 mL phosphate buffer pH 6.8 all above the 70 per cent Q point at 30 minutes — the drug is not only released from the press but released in the gut. Only the HPLC assay against a working standard seals label claim. The sequence is the teaching: physical tests look for manufacture errors, dissolution looks for the patient, and assay looks for the molecule.
The confusions that decide marks
Disintegration versus dissolution remains the separator: a tablet can disintegrate into fragments whose drug never dissolves, so "passed disintegration therefore bioavailable" is the sentence examiners fish for. The second is hardness versus friability — opposite directions of one mechanical story — plus the deliberate inversion that the hardest tablet may be pharmacologically the worst, since over-compression slows disintegration and dissolution for poorly soluble drugs. Third, know when weight variation is invalid: a 500 microgram drug in a 300 mg tablet cannot be dosed by weighing, hence content uniformity with its own acceptance tables. Finally, remember friability's arithmetic is a weight-loss percentage, not a force, and that weight-variation tolerances scale inversely with tablet mass — a fact routinely recited backwards.
Frequently asked questions
What does the Roche friabilator measure and what is its limit?
It tumbles dedusted tablets 100 revolutions in 4 minutes and measures percentage weight loss from chipping and abrasion; not more than 1 per cent is the conventional acceptance.
When is content uniformity performed instead of weight variation?
When the active is low — commonly 25 mg or less, or 25 per cent or less of tablet weight — because tablet weight then cannot predict the dose each unit delivers.
Why is dissolution more meaningful than disintegration?
Disintegration confirms only breakup into fragments, while dissolution measures drug actually entering solution at body temperature and hydrodynamics — the step that precedes absorption.
State the IP-style weight variation limits.
About 5 per cent for tablets above 250 mg, 7.5 per cent for 80-250 mg and 10 per cent below 80 mg, with only isolated tablets beyond the band.
Which parameters are checked in-process during compression?
Weight, hardness, thickness and friability at regular intervals, so a drifting press is corrected mid-batch and affected output segregated.