Five jobs, five helpers
When the drug is only a few milligrams, you still need a tablet you can pick up. The excipients do the work the drug cannot, and the classic tablet uses five archetypes. Think of them as a small crew, each with one task.
- [[diluent|Diluent]] (filler) — bulk. Lactose, microcrystalline cellulose or dicalcium phosphate make up the volume so the tablet is a sensible size and the press can handle it.
- [[binder|Binder]] — glue. Povidone, starch paste or HPMC hold the granule and the tablet together so it survives handling without crumbling.
- [[disintegrant|Disintegrant]] — the demolition charge. Croscarmellose or sodium starch glycolate swell on contact with water and burst the tablet back into particles so the drug can dissolve.
- [[lubricant|Lubricant]] — non-stick. Magnesium stearate stops the tablet welding itself to the punches and die wall, and lets it eject cleanly.
- [[glidant|Glidant]] — flow aid. Colloidal silicon dioxide coats the granules so they pour smoothly and fill each die evenly, protecting flow and weight.
Why more is not better
Every helper has a dark side at high levels, and the famous example is magnesium stearate. It is hydrophobic: it coats every granule with a water-repelling film. Just enough stops sticking; a little too much, or over-long mixing, waterproofs the tablet so it neither disintegrates nor dissolves on schedule. Lubricant level and mixing time are among the most carefully controlled numbers in the whole formulation.
The helpers also pull against each other. A stronger binder makes a harder tablet — but a harder tablet may resist the disintegrant. More lubricant eases ejection but slows wetting. Formulation is a balancing act, and the disintegration test is the early warning that the balance has tipped.