Ointments are viscous semi solid preparations used for application to the skin or mucous membrane. These are one of the commonly used dosage forms. They are oily in nature and contain more than 50% oily contents. There are different types of ointments. Ointments are used as protectants, antiseptics, emollients, astringents etc. Some ointments are also used for systemic delivery of drugs.
Read more: What is dosage form
Advantages of ointments
- Ointments help application of medicines to its site of action directly. It avoids exposing other body parts to the effects of drugs, that is in the case of oral delivery.
- Ointments also provide a soothing and protective effect to the applied area.
- Some medicines which are destroyed by the effects of gastric acid or by hepatic first pass effect can be given in ointment form.
- Fast onset of action
- Treatment can be terminated any time when needed.
- Easy to administer medication and increased patient compliance.
- There is a large area for absorption of drugs
Disadvantages of ointments
- Only selected medicines can be administered in ointment form. Most of the medicines, especially antimicrobial drugs have a large molecular weight and they are not properly absorbed through skin.
- There is a chance for forming contact dermatitis.
- Absorption through skin can be varied depending on the physical and physiological nature of the skin area. So a uniform effect cannot be predicted for all patients.
How ointments are prepared
Ointments are prepared by incorporating medicines or other active agents to an ointment base using different methods. Ointment bases used depend on the types of ointments.
Following methods are used for preparation of ointments
- Fusion method:
Here the ingredients for the preparation of ointments are heated above their melting point and mixed together. Other ingredients and medicines are added and cooled slowly by continuous stirring.
- Trituration method:
Here finely powdered ingredients are mixed with ointment base using trituration. First powders are mixed with a small amount of bases to form a homogenous mass then added more and more quantities of base and triturated.
- Chemical reaction method:
It is not a common method. Here a chemical reaction between ingredients is undergone during preparation. Example is Strong mercuric nitrate ointment.
- Emulsification method:
In this method an aqueous phase is emulsified in an oily phase with the help of an emulsifying agent. One example is Cold cream.
Different types of ointments
We can classify ointments in different ways. In the first method we can divide ointments on the basis of whether they are medicated or unmedicated.
- Unmedicated ointments:
These types of ointments will not contain any drugs inside it. They are used for their protective, emollient or soothing effect.
Example: petroleum jelly, soft paraffin etc.
- Medicated ointments:
These ointments contain medicines in the form of fine particles. They may be either dissolved, dispersed or emulsified in an ointment base.
Example: Betamethasone ointment, Gentamicin ointment.
In another method we can discuss different types of ointments on the basis of their action on different layers of skin. Here we can classify ointments in to following categories,
- Epidermic ointments:
These types of ointments exert their action on the outer layer of the skin. They are usually not absorbed. They are used for their topical antimicrobial, protective, or soothing action.
Example: povidone iodine ointments, salicylic acid ointments etc
- Endodermic ointments:
These types of ointments contain medicaments which are absorbed into subcutaneous tissues and produce action on these tissues.
Example: Crotamiton ointment, Permethrin ointment etc
- Diadermic ointments:
These types of ointments contain drugs which are absorbed into the systemic circulation and produce systemic effect.
Example: Nitroglycerine ointments.
Another one important method of classification of ointments is on the basis of the type of ointment bases used in the formulation. There are mainly four types of ointment bases used. The type of base used plays an important role in the characteristics of the final product.
- Ointments made with Hydrocarbon bases
Hydrocarbon bases are oily, anhydrous and water insoluble materials derived from petroleum. They cannot absorb or contain water. They are mainly used as an occlusive protective layer to water labile drugs. Their disadvantage is they are greasy in nature and stain the dresses
Examples of hydrocarbon bases include cetyl alcohol, stearyl alcohol, petrolatum etc.
- Ointments made with Absorption bases:
This type of ointment is water insoluble. They are made with absorption bases which contain an oily phase and a water in oil emulsifier. They can absorb water and form water in oil emulsion. Examples for this type base are Wool fat and aqueous wool fat.
These preparations are mainly used as emollients and moisturizers.
- Ointments made with emulsion bases
Here the base used is a water in oil emulsion base. It contains an oily inner phase and an aqueous continuous phase stabilized with an oil in water emulsifying agent. Major importance of this type of ointment is it is water washable and non greasy. Also many kinds of water soluble and oil soluble drugs can be incorporated into this base. It is more customer accepted and is used in most of the cosmetic preparations.
Example: vanishing cream, hydrophilic ointments.
- Ointments made with water soluble bases
These types of ointments are made with some water soluble materials like Polyethylene glycol ( PEG ). They are also water washable and do not stain clothes. There are are wide range of these types of ointment bases available. Their only disadvantages are they absorb water from skin and prevent absorption of some drugs.
Conclusion
Ointments are viscous semi solid preparations used for application to the skin or mucous membrane. Ointments are prepared by incorporating active ingredients to an ointment base. There are different types of ointments. Ointments are used as protectants, antiseptics, emollients, astringents etc. Some ointments are also used for systemic delivery of drugs.
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