PHAR2911 · Pharmaceutics And Professional Practice
Solid Dosage Forms: Tablets & Quality Control
This chapter covers the compressed tablet as a dosage form: what it is made of (a small percentage of active drug surrounded by excipients), how powder becomes a hard compact by compression, and the pharmacopoeial (BP/Ph.Eur.) quality-control battery that releases a batch. It is high-yield because exams reward you for naming the method, the sample size, the limit and the pass rule of each test — not for memorising a dataset — and for never confusing disintegration (break-up) with dissolution (the release-rate test that predicts absorption).
What this chapter covers
- 01The five excipient jobs: diluent/filler, binder, disintegrant, lubricant, glidant
- 02Compression in a die: direct compression vs wet granulation
- 03Uniformity of mass: 20 tablets, 10/7.5/5% deviation bands by size
- 04Uniformity of content: 10 tablets, 85-115% inner / 75-125% outer
- 05Disintegration: 6 tablets, 37 C, the break-up step
- 06Dissolution: >=75% in 45 min, the four BP apparatus
- 07Hardness (Newtons) and friability (drum, 100 rotations, <=1.0%)
- 08Immediate vs modified release and coating (sugar / film / enteric)
Uniformity of mass: build the acceptance window and judge the batch
- +1Pick the band from the average mass. 480 mg is >=250 mg, so the allowed deviation is 5% of the average.
- +1Build the inner window: 5% of 480 = 24 mg, so each tablet should sit within 480 +/- 24 = 456-504 mg.
- +1State the outer limit: no tablet may deviate by more than twice the band (2 x 5% = 10% = 48 mg), giving an absolute outer window of 432-528 mg.
- +1Apply the pass rule: the batch PASSES if not more than 2 tablets fall outside 456-504 mg AND no single tablet falls outside 432-528 mg.
Key terms
- Excipient
- Any non-active ingredient in a tablet with a defined functional job: diluent/filler (bulk), binder (cohesion), disintegrant (break-up), lubricant (anti-stick at ejection) or glidant (powder flow).
- Direct compression vs wet granulation
- Two ways to make a tablet. Direct compression simply blends the powders and presses them (no water or heat); wet granulation wets the blend with a binder, forms and dries granules, then compresses, improving flow and content uniformity for poorly-flowing or low-dose drugs.
- Uniformity of mass
- BP release test: weigh 20 tablets, find the average, and check each against a size-dependent deviation band (10% if <=80 mg, 7.5% if >80 and <250 mg, 5% if >=250 mg). Not more than 2 tablets may exceed the band, and none may exceed twice it.
- Uniformity of content
- Assay of the drug content of 10 individual tablets, used for low-dose/potent drugs where weight alone is insufficient. Pass if each unit is 85-115% of the average content; fail if more than one unit is outside that band or any unit is outside 75-125%.
- Disintegration vs dissolution
- Disintegration is the coarse break-up of the tablet (6 tablets, 37 C basket-rack); dissolution is the quantitative measure of how fast the drug goes into solution (typically >=75% released in 45 min). Disintegration must happen before dissolution, but a tablet can disintegrate fast yet dissolve slowly.
- Friability
- Mechanical-strength test: tumble a dedusted, pre-weighed sample of 10 tablets in a drum for 100 rotations, reweigh, and compute the percentage mass lost. Acceptable loss for uncoated tablets is <=1.0%; high friability shows as chipping or capping.
Solid Dosage Forms: Tablets & Quality Control FAQ
What is the difference between disintegration and dissolution testing?
Disintegration only proves the tablet breaks up into smaller pieces (6 tablets, raised and lowered in 37 C water until all fully break apart). Dissolution measures how fast and how much drug actually goes into solution over time, against a spec such as >=75% released in 45 min. Dissolution is the step that limits absorption for a poorly-soluble drug, so it is the test that correlates with how the medicine works in the body; disintegration is just a prerequisite to it.
How do I know which deviation band to use in the uniformity of mass test?
The band is chosen from the AVERAGE mass of the 20 tablets, not the label dose: <=80 mg uses 10%, more than 80 and less than 250 mg uses 7.5%, and 250 mg or more uses 5%. Apply the band to build the inner window, then double it for the outer limit that no single tablet may exceed.
Why do tablets need a uniformity-of-content test if there is already a mass test?
Uniformity of mass only assumes the drug is evenly distributed, which is fine when a high-dose active dominates the weight. For a low-dose, potent drug a tablet can weigh exactly right yet carry the wrong amount of active, so the pharmacopoeia adds a separate assay of the drug content of 10 individual tablets (each must be 85-115% of average).
Why can too much lubricant cause a tablet to fail?
Magnesium stearate, the common lubricant, is hydrophobic and coats the granules. A little eases ejection from the die, but too much waterproofs the compact, slowing disintegration and dissolution and softening the tablet. That is why lubricant is added last and blended only briefly.
What is the point of an enteric coat compared with a film coat?
A film coat (HPMC is the usual polymer, 2-3% weight gain) mainly protects, masks taste and improves appearance, with little effect on release. An enteric coat is acid-resistant (polymers such as CAP, HPMCP, PVAP or acrylates) so the tablet releases little to nothing at gastric pH and only releases once past the stomach, protecting an acid-labile drug or a sensitive stomach.
Exam move
Treat each QC test as a four-part flashcard and learn the parts, not a dataset: the sample size (20 / 10 / 6 / 10 / 10), the limit (10-7.5-5% by size; 85-115%; 37 C; >=75% in 45 min; Newtons; <=1.0%), the pass rule, and the one trap. In a calculation question, always pick the band first, then build the inner and outer windows before touching the individual values; in a written question, quote the n, the limit and the pass rule because the marks are on the method. Lock in the two classic confusions that examiners probe: disintegration is not dissolution, and uniformity of mass (weight of each tablet) is not uniformity of content (assayed drug in each tablet). Note that PHAR2911 assessment weightings are not officially confirmed, so check your unit outline for how the exam is split rather than assuming a percentage.
