Small-Scale Production of Semi-Solids: Creams, Ointments, Pastes, Gels, Jellies and Suppositories

Creams, ointments and pastes in batches

The small-scale methods are in BDP 331. In a batch:

• Jacketed mixing vessels (steam or hot water in the jacket) melt the bases and mix with a stirrer or paddle.
• For ointments, the base is melted, the drug is added, and the mixture is stirred while it cools.
• For creams, the oil phase and water phase are heated to the same temperature and mixed, and then stirred as they cool.
• For pastes, the powders are mixed into the softened base in a mixer that can handle stiff material.
• An ointment mill (roller mill) passes the product between rollers to make it smooth and free from grit.
• The product is filled into jars or tubes by a filling machine, which weighs or measures each one.

Quality checks include appearance, smoothness, consistency, fill weight, type of emulsion for creams, and preservative content for creams.

Gels

A gel is a semi-solid in which a gelling agent forms a network that holds a liquid. Gels are often clear and not greasy, and they are used on the skin and in the mouth, eyes and nose.

Method (general): the gelling agent is sprinkled slowly on the water, stirred and left to swell, so it does not form lumps. Other ingredients and a preservative are added. Gels are water-based, so germs can grow, and they need a preservative.

Jellies

A jelly is a gel, usually water-based and clear, that is used for lubrication (for example for catheters or examinations) or to apply drugs. It is made with a gelling agent, glycerol and a preservative. A jelly used for medical procedures may need to be sterile.

Suppositories

The theory is in BDT 152. This lesson covers moulding.

Bases

Making suppositories by moulding

1. Calculate the base needed (see below).
2. Prepare the moulds: clean, dry and, if needed, lightly lubricated. Cocoa butter usually needs none.
3. Melt the base gently on a water bath. For cocoa butter, melt only part and let the rest dissolve in the heat, so it does not overheat.
4. Add the drug, and mix. A powder is first made fine, and is mixed in smoothly.
5. Pour into the moulds, slightly overfilling, while stirring to keep the drug evenly spread.
6. Cool until set. Do not freeze.
7. Trim the extra from the top, remove and inspect them.
8. Wrap or pack and label. Store in a cool place.

Displacement value

The drug takes up space in the mould, and therefore displaces some base. The displacement value (DV) is the weight of drug that displaces 1 g of base.

base displaced = total weight of drug ÷ DV
base needed = (number × mould capacity) − base displaced

Worked example

Make 12 suppositories, each with 200 mg of a drug. The mould holds 2 g of base. The DV is 1.5.

1. Total drug = 12 × 0.2 = 2.4 g
2. Base displaced = 2.4 ÷ 1.5 = 1.6 g
3. Base needed = (12 × 2) − 1.6 = 24 − 1.6 = 22.4 g

In practice, extra is made to allow for loss (for example, enough for 14 suppositories).

Precautions

• Hygiene and clean equipment, especially for water-based gels and creams.
• Gentle heat, because high heat can damage the base and the drug.
• Even mixing, so each unit has the right dose.
• Correct moulds and careful pouring.
• Cool storage, because suppositories and ointments soften in heat.
• Labelling: "For external use only" or "Insert into the rectum or vagina as directed", with the date and the discard date.