BDT 152Basic Dispensing Theory I
Tablets
10 minute read
What you will learn
- Define a tablet and list the main types
- State why tablets are the most popular dosage form, and their disadvantages
- Name the tablet excipients and state what each one does
- Describe the steps a tablet machine follows
- Explain why tablets are coated and compare the types of coating
- Describe how tablets are packaged, stored and swallowed correctly
Key points
- A tablet is a solid unit dose made by compressing a drug with excipients.
- Tablets are popular because the dose is accurate, they are cheap to produce in bulk, convenient to carry, and stable.
- Excipients are the non-drug ingredients: diluent, binder, disintegrant, lubricant, glidant, and colours and flavours.
- A tablet machine works in three steps: die filling, tablet formation (compression), ejection.
- Coating hides taste, protects the drug, protects the stomach, controls release and improves appearance.
- Enteric-coated and modified-release tablets must not be crushed or chewed.
- Store in a cool, dry place, in a tightly closed container, away from light.
What is a tablet?
A tablet is a solid dose of medicine made by pressing one or more drugs together with other ingredients (excipients) into a single unit. Tablets are the most widely used dosage form in the world.
Common types of tablet
| Type | How it is used |
|---|---|
| Plain compressed tablet | Swallowed whole with water |
| Coated tablet | Swallowed whole; the coating improves taste, protection or release |
| Enteric-coated tablet | Swallowed whole; releases the drug in the intestine |
| Chewable tablet | Chewed before swallowing (for example, some antacids) |
| Dispersible tablet | Dissolved or dispersed in water before taking |
| Effervescent tablet | Dissolved in water; fizzes as it dissolves |
| Sublingual tablet | Placed under the tongue and allowed to dissolve |
| Modified-release tablet | Releases the drug slowly over many hours |
Why tablets are so popular
- The dose is accurate, because each tablet is made to the same weight and strength.
- They are cheap to produce in large numbers.
- They are convenient: light, compact, easy to carry and to take.
- They are stable, so they last longer than most liquids.
- They are easy to identify by shape, colour and markings.
- They can be coated to hide taste or protect the drug, and made to release the drug slowly.
Disadvantages
- Some drugs cannot be compressed into a tablet.
- Children, elderly patients and unconscious patients may be unable to swallow them.
- A tablet must first break up and dissolve, so the effect is slower than from a liquid.
- Some drugs irritate the stomach.
- The taste can be bitter if the tablet is not coated.
Tablet excipients
A tablet contains much more than the drug. The extra ingredients are called excipients, and each has a job.
| Excipient | What it does | Examples |
|---|---|---|
| Diluent (filler) | Adds bulk so the tablet is big enough to handle | Lactose, starch, microcrystalline cellulose |
| Binder | Holds the particles together | Starch paste, gelatin, acacia, polyvinylpyrrolidone (PVP) |
| Disintegrant | Breaks the tablet apart after swallowing | Starch, sodium starch glycolate |
| Lubricant | Reduces friction so the tablet does not stick in the die | Magnesium stearate, talc |
| Glidant | Helps the powder flow smoothly into the die | Colloidal silica, talc |
| Colours, flavours, sweeteners | Improve appearance and taste | Approved dyes and flavours |
Lubricant vs glidant: a lubricant works at the surface of the tablet and die, so the tablet comes out cleanly. A glidant works on the powder, so it flows evenly. Talc can act as both.
How a tablet is made
Before compression, the powder is usually made into granules, mixed with the lubricant, and checked. The tablet machine then repeats a cycle of three steps:
- Die filling. The granules flow from the hopper into the die (a hole in the machine). The lower punch sits low in the die so the right volume of granules fills the space.
- Tablet formation. The upper punch comes down and presses the granules against the lower punch with great force. The granules are squeezed into a solid tablet.
- Ejection. The upper punch lifts away, and the lower punch rises and pushes the finished tablet out of the die. A scraper pushes it off the machine, and the cycle starts again.
Tablet coating
Coating means putting a thin layer of material over the outside of the tablet.
Why tablets are coated
- To hide a bad taste or smell
- To protect the drug from air, moisture and light
- To protect the stomach from a drug that irritates it
- To protect the drug from stomach acid
- To control where or how fast the drug is released
- To improve appearance, make the tablet easier to swallow, and help with identification
Types of coating
| Type | Description |
|---|---|
| Sugar coating | Several layers of sugar syrup. Looks smooth and tastes sweet, but adds a lot of size and weight and takes a long time to apply. |
| Film coating | A thin layer of polymer, applied faster. The tablet stays close to its original size and weight. This is the most common modern coating. |
| Enteric coating | A coating that does not dissolve in stomach acid but dissolves in the small intestine. |
Packaging and storage
- Blister packs and strips protect each tablet from moisture and make it easy to count doses.
- Bottles (glass or plastic) must be tightly closed. A small bag of drying agent (desiccant) may be placed in the bottle. It should not be swallowed.
- Store in a cool, dry place, away from direct sunlight.
- Always check the expiry date and the storage instruction on the label.
Helping patients take tablets correctly
- Sit or stand upright and take a few sips of water first.
- Place the tablet on the tongue and swallow with a full glass of water.
- Do not lie down straight after, as the tablet can get stuck in the food pipe.
- Do not crush or chew enteric-coated and modified-release tablets, unless told to.
- Chewable, dispersible and effervescent tablets are the exceptions: follow the instructions on the label.
Exam focus
- Matching questions on excipients are very common: binder holds, disintegrant breaks up, lubricant reduces friction, diluent adds bulk.
- Know the three steps in the tablet machine in the correct order.
- Enteric coating questions: the coating resists stomach acid and dissolves in the intestine.
- Sugar coating makes the tablet larger and heavier; film coating adds only a thin layer.
- Common mistake: mixing up a lubricant (reduces friction in the die) with a glidant (improves powder flow).
Quick check
Test yourself before you move on. Pick an answer to see the explanation.
1.Which excipient helps a tablet break up after it is swallowed?
2.Magnesium stearate is added to a tablet formula as a:
3.What is the correct order of steps in a tablet machine?
4.The purpose of an enteric coating is to:
5.Which tablet should NOT be crushed before swallowing?