Suppositories and Pessaries

What are suppositories and pessaries?

A suppository is a solid medicine shaped to be inserted into the rectum. A pessary is a similar solid medicine shaped to be inserted into the vagina. In both cases the base holds the drug while the product is stored. Once inserted, the warmth of the body makes the base melt or dissolve, and the drug is released.

The shape is chosen so the product is easy to insert and stays in place once it is inside.

Why use a suppository?

Most medicines are swallowed, but that does not always work. A suppository is chosen when:

• the patient is vomiting, unconscious, or unable to swallow;
• the patient is a small child who refuses or cannot take tablets or liquids;
• the drug irritates the stomach or is damaged by stomach acid and enzymes;
• the drug tastes very bad;
• a local effect is wanted at the site, for example glycerin suppositories for constipation or preparations for haemorrhoids.

In some places, rectal artesunate is used as a first dose for a child with severe malaria who cannot take medicine by mouth, before the child reaches a hospital.

Advantages and disadvantages

Advantages

• Can be used when the oral route is not possible
• Avoids the taste of the drug and irritation of the stomach
• Part of the drug can bypass the liver on its first pass through the body
• Useful for children and unconscious patients

Disadvantages

• Some patients find them embarrassing or unpleasant to use
• Absorption can be slower and less predictable than with oral medicines
• They cannot be used reliably in patients with severe diarrhoea, because the product may be expelled
• They soften in hot weather and need careful storage
• Leakage after insertion can be messy

Suppository bases

The base is the carrier that holds the drug. A good base carries the drug safely and then releases it at the right place.

An ideal base:

• is solid at room temperature but melts or dissolves at body temperature (about 37°C);
• is non-toxic and does not irritate the tissues;
• is compatible with the drug and does not react with it;
• releases the drug readily;
• is stable and easy to mould, and contracts slightly on cooling so the product comes out of the mould easily.

Types of base

Two points are worth remembering:

1. Cocoa butter must be melted gently. If it is overheated it changes form and may not set properly afterwards.
2. Polyethylene glycol bases do not melt at body temperature; they dissolve. They also draw water from the tissues, so the product may need to be moistened before insertion to avoid irritation.

How suppositories are prepared

1. Moulding (fusion) is the most common method.

1. Melt the base gently.
2. Dissolve or mix in the drug.
3. Pour the mixture into a mould.
4. Cool until it sets, trim any excess, and remove the suppositories.

The mould is lightly lubricated first so the product releases cleanly. Use a lubricant that does not mix with the base: a water-based lubricant for fatty bases, and an oily one such as liquid paraffin for glycerol-gelatin.

2. Compression. The base and drug are mixed cold and pressed into shape using a machine. This suits drugs that are damaged by heat.

3. Hand rolling. The mixture is rolled by hand into a cylinder and shaped. This is used for very small quantities and is the least precise.

Worked example: displacement value

Drug particles take up space in the mould, so they push out some of the base. Ignoring this gives the wrong amount of drug in each suppository. The displacement value is the number of grams of drug that displace 1 g of base.

Make 10 suppositories, each containing 200 mg of drug X. The mould holds 2 g of pure base per suppository. The displacement value of drug X is 1.5.

1. Total drug needed: 10 × 0.2 g = 2 g
2. Base displaced by the drug: 2 g ÷ 1.5 = 1.33 g
3. Total base if no drug were added: 10 × 2 g = 20 g
4. Base needed: 20 g − 1.33 g = 18.67 g

In practice a little extra is prepared to allow for losses.

Packaging and storage

• Wrap suppositories and pessaries individually in foil, or pack them in plastic strips, so they do not stick together.
• Store in a cool, dry place away from heat and direct sunlight. Fatty bases soften easily, and some products are best kept in a refrigerator; follow the label.
• Keep glycerol-gelatin products well closed so they do not dry out or take up moisture.

Labelling. The label should state the route clearly: "For rectal use only" or "For vaginal use only". Useful auxiliary labels include "Remove wrapper before use" and "Store in a cool place".

Using them correctly (patient counselling)

Suppositories (rectal)

1. Wash your hands and remove the wrapper.
2. Lie on your side and insert the narrow end first, gently, past the muscle ring at the entrance.
3. Stay lying down for a few minutes so it does not slip out.
4. Wash your hands afterwards.

Pessaries (vaginal)

1. Wash your hands and remove the wrapper.
2. Lie on your back with your knees bent, and insert the pessary high into the vagina, using the applicator if one is supplied.
3. Use it at bedtime if possible, since it is less likely to leak while you are lying down.
4. A pad can be worn if there is leakage. Complete the full course even if symptoms improve.

Common uses of pessaries include treating vaginal infections (for example, antifungal pessaries for candidiasis) and delivering hormones.