Semi-solid ointments

Ointments are semi-solid greasy preparation for local application to the skin, rectum and mucous membrane also. The ointment base is usually anhydrous and contain the medicaments in solution or suspension. Ointments are used for its soothing, astringent, antiseptic and other selected actions e.g. Chloromycetin eye ointment. 

Pastes are semi-solid preparation for external application that differ from similar products (i.e. ointment) in containing a high proportion of finely powdered medicaments. 

Davis, S.S. Viscoelastic properties of pharmaceutical semi-solids. I Ointment bases. J. Pharm. Sci. 1969, 58, 412-417. 

White soft paraffin and yellow soft paraffin are mixtures of semi-solid hydrocarbons. They are used as bases for ointments, as emollients in skin diseases, and as lubricants in treating dry eyes. Soft paraffin is also known as petroleum jelly, petrolatum, and Vaseline. 

Eye ointments are prepared in a semi-solid base (e.g. Simple Eye Ointment BP, which consists of yellow soft paraffin [8 parts], liquid paraffin [1 part] and wool fat [1 part]). The base is filtered when molten to remove particles and sterilized at 160°C for 2 hours. The drug is incorporated prior to sterilization if heat-stable, or added aseptically to the sterile base. Finally the product is aseptically packed in clear sterile aluminium or plastic tubes. As the product contains virtually no water the danger of bacteria proliferating in the ointment is negligible. 

Percentage weight in weight (% w/w) is the number of grams of drug in 100 g of final product. This term is encountered most often in solid dosage preparations such as powders, and semi-solid preparations such as creams and ointments, e.g. 1 % salicylic acid ointment. 

Semi-solid gel type preparations have also been developed for ophthalmic delivery as an alternative to traditional ointments, based on the effect of increasing the viscosity to prolong the retention of drug in the eye (for example, Pilopine HS gel, Alcon Laboratories, Inc.). Several types of gelling agents have been used, such as polyacrylic acid derivatives, carbomer and hypromellose. 

Eye ointments are sterile semi-solid preparations intended for application to the conjunctiva. They are attractive because of their increased contact time and better bioavailability compared to solutions. They can be very useful for night-time application, However, they are not always well accepted by patients because upon application they often cause blurred vision. A wide variety of ointments are available commercially. 

The choice of packaging for ophthalmic products will depend on the type of dosage form, such as whether it is a liquid solution/suspension or semi-solid gel or ointment. Also, choice will depend on how the product is to be used by the patient, such as whether it is intended to... 

The exact product optimisation studies to be conducted will depend on the type of ophthalmic dosage form to be developed (liquid drops, semi-solid gel/ointment or solid device). However, the dosage form type should be clearly defined from the product design evaluation and supporting preformulation studies, to enable the formulator to focus on the most relevant product optimisation studies. 

In general, the preparation of such formulations as poultices and pastes is extemporaneous, and it is unlikely that the industrial pharmaceutical formulator will be required to develop stable, safe and efficacious products of this type. Solutions and powders lack staying power (retention time) on the skin and can only afford transient relief. In modern-day pharmaceutical practice, semi-solid formulations are preferred vehicles for dermatological therapy because they remain in situ and deliver their drug payload over extended periods. In the majority of cases, therefore, the developed formulation will be an ointment, emulsion or a gel. Typical constituents for these types of formulations are shown in Table 14.5. 

In its strictest definitive form, an ointment is classified as any semi-solid containing fatty material and intended for external application (U.S. Pharmocopeia, USP). In this discussion, ointments will be defined as semisolid anhydrous external preparations. In the nineteenth century, ointments were based on lard, a compounding material, the usefulness of which was severely limited by its tendency to turn rancid. Early in the twentieth century, lard was replaced by petrolatum (white or yellow soft paraffin or petroleum jelly). In present practice, nonmedicated ointments (ointment bases) are used alone, for emollient or lubricating purposes, or in combination with a drug for therapeutic purposes. 

Herbal therapies also come in the form of salves. Salves are semi-solid fatty preparations such as balms, creams, and ointments. They are prepared in a way similar to herbal oils except once the dried herb is soaked in oil, melted wax is mixed with the oil. It is left to cool and harden to form the therapeutic balm, cream, or ointment. 

Because the activity of the drug in various formulations, especially those in semi-solid bases such as creams, ointments and gels, can be improved by penetration enhancers, it is important to understand thermally induced changes in the skin, in order to understand its molecular structure and the mechanism of action of penetration enhancers. 

Ophthalmic ointments are sterile, homogeneons, semi-solid preparations intended for application to the conjunctiva or the eyelids. 

From semi-solid to the higher molecular weight hard waxy white solids, this group of polyethylene glycols finds use as mold lubricants and mold release agents in the rubber industry. Used in preparation of ointments, cosmetic creams and lotions, metal polishes, shoe polishes, abrasives and adhesives. 

A three roll mill (or ointment miU) is used to disperse solid substances in a semi solid or thick fluid base. The constituents themselves should be mixed homogeneously in advance. 

Topical formulations that are applied externally can be ointments, creams, pastes and gels. Ointments are semi-solid drug formulations that are intended for application to healthy, diseased or injured skin. Ointments for injuries and corticosteroid ointments, which penetrate the upper layers of the skin, have a local curative effect. Some ointments are designed for deeper penetration into the skin [51]. 

Semi-solids and gels have tan 3 i (usually in the region of 0.2 or even lower for ointments and 0.2-0.4 for creams and gels). 

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