What is Ointment?

Pharmaceutical semi-solid formulations are mainly available in the form of cream, ointment, gel, paste, and suppository. In semisolid formulation, active pharmaceutical ingredient (API) is dispersed in semi-solid base, which mainly applies topically. Topical semisolid products enable the administration of active pharmaceutical ingredients (APIs) in a less invasive approach than the intravenous route and avoid the first-pass effect encountered by oral products, where drug molecules degrade to their inactive metabolites.

Define ointment

Ointments are semisolid dosage forms that, under shear stress, often behave like visco-elastic materials. They are often used topically to the body for therapeutic purposes and include medicinal substances. They act as both protective and therapeutic agents which help to transport the medicines to the infected area. Due to its occlusive qualities, oleaginous ointments are recommended for dried chapped skin in low humid environments. Physical tests such as absorption rate, non-irritancy, penetration, drug release, rheological property, and material uniformity, along with microbiological tests such as microbial content and preservative effectiveness, are used to assess ointments. Apart from the base oil or fat, very few ingredients are present in ointments thus posing a low chance of sensitization and discomfort.

Types of ointments

Based on medicinal value, ointments can be classified into medicated and non-medicated ointments. Drugs with local or systemic effects are used in medicated ointments.

Type of ointments. (APM, H. P., 2023)

Dermatological ointments

Dermatological ointments are usually applied on the surface of the skin to moisturize or prevent dryness or itchy scalps. These are of three types-epidermic, endodermic and diadermic. Epidermic ointments are used to treat infection from fungus or yeast on the surface of the skin. skin's deeper layers. Diadermic ointments penetrate to the deeper layers (hypodermis) of the skin and has a systemic effect (eg: nitroglycerine).

Ophthalmic ointments

Ophthalmic ointments are used to treat eye infections, dry eyes and inflammation of eyelid. Depending upon the ailment, specific types of ophthalmic ointment is used: (a) antibiotic ointment helps to kill the bacteria which cause infection. (b) lubricating ointment helps to keep the eye moist in case of dryness. Some commonly recommended ophthalmic ointments include ciprofloxacin ophthalmic which is used to treat corneal ulcers and inflammation. Bacitracin, polymyxin B, neomycin, tobramycin and erythromycin are antibiotics used to treat eye and eyelid infections.

Nasal ointments

The nasal ointments are used to cure breathing related problems, nasal congestion etc. The ingredients in the nasal ointments get absorbed into the bloodstream through the nasal lining. For example, ipratropium bromide ointment is used to treat wheezing and shortness of breath.

Vaginal ointments

These ointments are used to treat against infections in the vaginal area caused due to fungal infection which results in irritation and intense itching.

Rectal ointments

These ointments are used to treat the perianal area or the anal canal. A combination of white paraffin, PEG 300, cetyl esters, cetyl alcohols are used as bases. Sulfacetamide sodium ointment is used to treat seborrhea dermatitis; Sarjarasamalahara and ArshoharaMalahara are used to cure haemorrhoids.

Types of ointment bases

Ointment base can be referred to as the drug carrier part. The Quality of the medicine, the stability and the area of the application can be determined by the ointment base . There are mainly three classes of ointments and they are differentiated based on the physical composition.

Oleaginous ointment bases

Also known as lipophilic bases, which are primarily made up of hydrocarbons derived from plant, animal, or petroleum sources. These bases have a distinctive feature of being able to incorporate a small amount of aqueous components, which makes them effective emollients that can soften and soothe the skin. Due to their hydrophobic nature, oleaginous bases are difficult to wash off the skin, ensuring that the medication stays in contact with the skin for a longer duration. This property makes them particularly suitable for use in dry, chapped skin conditions in low humidity environments as they provide a protective occlusive layer that helps to retain moisture. Common examples of oleaginous bases include white petrolatum, yellow ointment, and white ointment. They are also used as air and water-tight dressings in first aid settings due to their impermeable characteristics.

Absorption bases

The emulsifying property of an ointment is referred to by the term 'absorption base'. They are generally insoluble in water and anhydrous lanolin. Water in oil emulsion or oleaginous bases allows the incorporation of aqueous solution.They cannot be easily washed off with water. Anhydrous lanolin and hydrophilic petrolatum are used for emollient applications.

Water removable bases

Also known as emulsifying bases or oil-in-water emulsion bases, which can be diluted with water. Some medications are more effective in these bases. Hydrophilic ointment and vanishing cream are water removable base ointments.

Water soluble bases

Water-soluble bases are completely water-washable and are greaseless in nature, which could serve as a vehicle for water-soluble drugs. Polyethylene glycol ointment, is an example of water-soluble base. Polyethylene glycol (PEG) is a polymer which exists in liquid, semisolid or solid form based on its average molecular weights the greater the molecular weight, the greater the viscosity.

Preparation of ointment

Choice of ointment base: The choice of substrate depends on the intended use of the ointment.

When choosing an ointment base, consider:

Desired drug release rate.

Topical or percutaneous absorption preference.

Moisture occlusion requirements.

Drug stability in the base.

Potential interaction between drug and base consistency.

Ease of base removal by water.

Surface characteristics to which the ointment is applied.

Incorporation of active ingredients: The API is incorporated into the substrate using techniques such as grinding (grinding the drug with a small amount of substrate to form a smooth dispersion) or melting (melting the substrate and API together).

Homogenization: Ensure that APIs are evenly distributed within the matrix. This can be done using a mechanical agitator or a homogenizer.

Cooling and packaging: The ointment is cooled and solidified, then packed into a suitable container to prevent contamination and spoilage.

Related ointment development services at BOC Sciences

Method of preparation of ointment

Incorporation method

This method is typically used for small-scale preparation of ointments where the components are finely ground and mixed using a spatula on a glass slab or porcelain plate. If the ingredients react with metal, a rubber spatula can be used instead. A small portion of the finely powdered component is blended with a portion of the base to create a uniform mixture. The levigating agent (such as mineral oil or glycerine) must be compatible with both the drug and the base to avoid grittiness in the final product.

Preparation of ointment using homogeniser. (APM, H. P., 2023)

Fusion method

Ingredients are melted together and then cooled while continuously stirring. This method ensures homogeneity and prevents separation. Heat-sensitive ingredients are added towards the end to avoid decomposition or volatilization. The bases used in this method often include stearyl alcohol, high molecular weight PEG, and beeswax.

Emulsification method

This method involves mixing two or more incompatible liquids into a semi-stable emulsion. A thermally stable aqueous solution is heated to the same temperature as the melted base, then gently combined with continuous stirring until the mixture cools down. This technique is particularly useful for creating water-in-oil emulsions.

Each of these methods is selected based on the physical and chemical characteristics of the ingredients, such as their melting points, solubility, and compatibility with other components. The choice of method is critical for achieving an ointment with the desired consistency, stability, and effectiveness.

Ointment evaluation test

Ointment evaluation tests are critical for ensuring the quality and safety of topical formulations. Physical tests, such as the rate of absorption, assess how effectively the medication penetrates the skin to reach systemic circulation. The non-irritancy test evaluates the potential for allergic reactions by monitoring for any visible reactions, erythema, or intense inflammation on human volunteers. The penetration rate test measures how quickly the drug is absorbed through the skin, impacting its onset and duration of action. Drug release rate tests determine the speed at which the active ingredient is released from the ointment into a saline or serum solution. Rheological properties, including viscosity, are tested to ensure the product's spreadability and ease of application. Content uniformity tests verify that the drug concentration is consistent across multiple samples. Microbiological tests, such as microbial content analysis and preservative efficacy checks, ensure the ointment is free from contaminants and that any preservatives used are effective. These tests collectively guarantee that ointments meet necessary standards for patient safety and efficacy.