Diluents. These add bulk to make the tablet easier to handle. Examples include lactose, mannitol, sorbitol and calcium carbonate

 Binders. These enable granules to be prepared which improves the flow properties of the mixture during manufacture. Examples include polyvinylpyrrolidone and microcrystalline cellulose

 Disintegrants. These encourage the tablet to break into smaller particles after ingestion. Examples include modified cellulose and modified starch

 Lubricants, glidants, antiadherents. These are essential for the flow of the tablet material into the tablet dies and preventing sticking of the compressed tablet in the punch and die. Examples of lubricants are magnesium and calcium stearate, sodium lauryl sulphate and sodium stearyl fumarate. Colloidal silica is usually the glidant of choice. Talc and magnesium stearate are effective antiadherents

 Miscellaneous agents may be added, such as colours and flavours in chewable tablets.

Dispensing of tablets

Many tablets in the UK and other countries are packaged by the manufacturer into patient packs suitable for issue to the patient without repacking by the pharmacist. Patient information leaflets are also contained in these patient packs. When dispensing these packs to patients, the pharmacist must ensure that they are labelled correctly, according to the prescriber’s instructions (see Ch. 31), and that the patient is counselled on the use of the medication (see Ch. 25).

For some controlled-release tablets, variations in bioavailability may occur with different brands. It is important that patients are given the brand that they are stabilized on in order to maintain therapeutic outcome. Examples where this is important include theophylline, lithium and phenytoin.

Tablets may also be supplied in a bulk container. The required number of tablets needs to be counted out (see Ch. 30) and placed in a suitable container for dispensing to the patient (see Ch. 32). It is important to minimize errors by ensuring that the correct bulk container has been selected and the correct drug dispensed. The pharmacist should verify this by checking the label of the bulk container and by examining the shape, size and markings on the dispensed tablets where appropriate, with the prescription. A copy of the patient information leaflet should be included.

Some tablets are supplied in a strip-packed form where each tablet has its own blister. A development of this is the calendar pack where the day or date on which the tablet is to be taken is indicated on the pack.

Shelf-life and storage of tablets

Most tablets should be stored in airtight packaging, protected from light and extremes of temperature. When stored properly, they generally have a long shelf-life. The expiry date will be printed on the package or the individual strip packs. Some tablets need to be stored in a cool place, e.g. Ketovite® and Leukeran® (chlorambucil) (both stored between 2 and 8°C). Some tablets contain volatile drugs, e.g. glyceryl trinitrate, and must be packed in glass containers with tightly fitting metal screw caps (see Ch. 32).