Lipophilic ointment

Lipophilic ointment (oil ointment) consists of a lipophilic base (paraffin oil, petroleum jelly, wool fat [lanolin]) and may contain up to 10 % powder materials, such as zinc oxide, titanium oxide, starch, or a mixture of these. Emulsifying ointments are made of paraffins and an emulsifying wax, and are miscible with water. 

The aqueous active substance solution is emulsified in the lipophilic ointment base (resulting in an eye cream). 

The active substance is dispersed in the ointment base. The first ointment t3q>e is applicable for only a few active substances dissolved in the non-aqueous ointment bases. To date, almost only paraffin-based lipophilic ointments are used for semisolid ophthalmic products. An example of this type of preparation is eye ointment with 0.5 % erythromycin (Table 10.13). Suitable triglyceride-based vehicles may lead to more solution-type eye ointments (see Sect. 10.7.3). 

The base must be non-irritant to the conjunctiva. Non-aqueous lipophilic ointment bases consist of a mixture of white or yellow soft paraffin, liquid paraffin and lipophilic surfactants, such as cholesterol or wool fat. 

Wool fat (Adeps lanae this is a wax and not a fat) is used in ointments and in eye ointments and increases the penetration ability of lipophilic ointments. A drawback is the chance of contact allergy. Due to the presence of free surface active lanolin alcohols Wool fat has a greater power to absorb water than flie other waxes. Lanolin (Adeps lanae cum aqua) is an emulsion of 25 %water in 75 % Wool fat. 

Lipophilic (oily) cream is an emulsion of water in oil, easier to spread than oil paste or oil ointments. 

Only solutions of lipophilic antibiotics are able to cross the external barrier of the cornea (drops) and the internal blood-retina barrier (systemic administration) to yield sufficient concentrations in the internal eye (vitreous). Keratitis and ulceration of the cornea can be treated by frequent administration of highly concentrated (fortified) antibiotic drops. In endophtalmitis, emergency vitreous aspirate and in-travitreal and subconjunctival injection of antibiotic solutions with a long half-life is the cornerstone of treatment. These solutions should be prepared by the hospital pharmacy. Empiric topical treatment of minor external eye infections consists of antibiotic containing gels or ointments. 

Formulation additives used in topical drug or pesticide formulations can alter the stratum comeum barrier. Surfactants are least likely to be absorbed, but they can alter the lipid pathway by fluidization and delipidization of lipids, and proteins within the keratinocytes can become denatured. This is mostly likely associated with formulations containing anionic surfactants than non-ionic surfactants. Similar effects can be observed with solvents. Solvents can partition into the intercellular lipids, thereby changing membrane lipophilicity and barrier properties in the following order ether/acetone > DMSO > ethanol > water. Higher alcohols and oils do not damage the skin, but they can act as a depot for lipophilic drugs on the skin surface. The presence of water in several of these formulations can hydrate the skin. Skin occlusion with fabric or transdermal patches, creams, and ointments can increase epidermal hydration, which can increase permeability. 

Fromder, A. and Lippold, B.C., Water vapour transmission and occlusivity in vivo of lipophilic excipients used in ointments, Int. J. Cosmet. Sci., 15, 113, 1993. 

Ointments are greasy and are thicker than creams. Some are both lipophilic and hydrophilic, i.e. by occlusion they promote dermal hydration, but are also water miscible. Other ointment bases are composed largely of lipid by preventing water loss... 

Many pharmaceutical preparations containing oil-water systems (creams, ointments, or suspensions) are subject to microbial contamination. Bacteria in these heterogenous systems are usually grown in the aqueous phase and at the oil-water interface. To preserve the shelf-life of these preparations, benzoic acid or other organic acids are added as preservatives. Because the microbial cell membrane is lipophilic in nature, the bacteriostatic actions of the acidic preservative are attributable almost entirely to the undissociated acid and not to the ionized form. A good understanding of the partition coefficient and the degree of ionization allows accurate calculation of the free un-ionized acid in the aqueous phase, which provides the bacteriostatic concentration. 

Waxes have been used by the pharmaceutical industry for many years. Their applications in semisolid preparations, including ointments, creams, or lotions, and in suppositories are well known and numerous publications exist on this topic. Because of their lipophilic properties, waxes have been used in sustained-release single or multiple unit solid dosage forms. This article reviews the different uses of waxes as sustained-release carrier or coating materials. 

Polyoxyethylene stearates are particularly useful as emulsifying agents when astringent salts or other strong electrolytes are present. They can also be blended with other surfactants to obtain any hydrophilic-lipophilic balance for lotions or ointment formulations. See Table III. 

Sorbitan esters are widely used in cosmetics, food products, and pharmaceutical formulations as lipophilic nonionic surfactants. They are mainly used in pharmaceutical formulations as emulsifying agents in the preparation of creams, emulsions, and ointments for topical application. When used alone, sorbitan esters produce stable water-in-oil emulsions and microemulsions but are frequently used in combination with varying... 

The results of incorporating pilocarpine (V) (a relatively water-soluble dmg) and fluoro-metholone (a lipophilic dmg) into a water-inoil ointment base can be compared in Fig. 9.36. Pilocarpine is thought to be released only when in contact with aqueous tear fluid, whereas the steroid, being soluble in the base, can diffuse through the base to replenish the surface concentrations and thus produce a sustained effect. 

Topical corticosteroids are available in ointments, creams, lotions, gels, sprays, shampoos, and mousses. An ointment is considered the most clinically effective dosage form in psoriasis treatment because it consists of an oily phase that is occlusive and conveys a hydrating effect. Due to the lipophilicity of ointments, penetration of corticosteroid into dermis is enhanced, resulting in increased vasoconstriction. 

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