Ointment absorption bases

Creams are semisolid emulsion systems having a creamy appearance as the result of reflection of light from their emulsified phases. This contrasts them with simple ointments, which are translucent. Little agreement exists among professionals as to what constitutes a cream, and thus the term has been applied both to absorption bases containing emulsified water (w/o emulsions) and to semisolid o/w systems, which are physicochemically totally different, strictly because of their similar creamy appearances. Logically, classification of these systems should be based on their physical natures, in which case absorption bases would be ointments and the term cream could be reserved exclusively for semisolid o/w systems, which in all instances derive their structures from their emulsifiers and internal phases. 

Water-removable bases are basically oil-in-water emulsions. Unlike hydrocarbon and absorption bases, a large proportion of aqueous phase can be incorporated into water-removable bases with the aid of suitable emulsifying agents. It is easy to remove these bases from the skin due to their hydrophilic nature. Hydrophilic ointment USP is an example of a water-removable ointment base. 

Absorption base component Emollient and plasticizer in ointments... 

As outlined when discussing absorption bases, the drug may also be dissolved in water to form a solution to be levigated into an ointment base or cream. Such addition softens creams even to the point of converting them to thick lotions. The chosen vehicle, of course, must have an inherent capacity to emulsify or otherwise take up the solution. Aromatic materials such as essential oils, perfume oils, camphor, and menthol, which volatilize if added when the base is hot, are incorporated into these semisolids while they are stiU being mixed but near the temperature where a particular system starts to congeal. Volatile materials are often introduced into the formulation as hydroalcoholic solutions. 

Chem, Descrip. Wh. petrolatum LISP CAS 8027-32-5 EINECS/ELINCS 232-373-2 Uses Ointment base for ophthalmic and topical ointments carrier for medical materials absorption base in cosmetics food-contact applies. release agent, lubricant, sealant, polishing agent, protective coating, defoamer in foods... 

Uses Absorption base emulsifier for w/o systems, emollient, moisturizer for pharmaceutical ointments and hair prods. 

Ointments are semisolid preparations that are intended for external use. Ointments may contain either finely powdered drugs or their mixtures, liquids, and other drug forms incorporated into appropriate bases. They are applied to the skin for their physical effects as emollients (which make the skin more pliable), protectants, lubricants, and drying agents. Ointment bases are also used as vehicles in which to incorporate topical medications which exert specific effect. There are four types of ointment bases, namely, oleaginous, absorption, water removable, and water soluble bases. 

Experimental studies on the percutaneous absorption of hydrocortisone fail to reveal a significant increase in absorption when applied on a repetitive basis and a single daily application may be effective in most conditions. Ointment bases tend to give better activity to the corticosteroid than do cream or lotion vehicles. Increasing the concentration of a corticosteroid increases the penetration but not proportionately. For example, approximately 1% of a 0.25% hydrocortisone solution is absorbed from the forearm. A 10-fold increase in concentration causes only a fourfold increase in absorption. Solubility of the corticosteroid in the vehicle is a significant determinant of the percutaneous absorption of a topical steroid. Marked increases in efficacy are noted when optimized vehicles are used, as demonstrated by newer formulations of betamethasone dipropionate and diflorasone diacetate. 

Death. Humans exposed occupationally to DNOC for acute- (Steer 1951 van Noort et al. 1960) or intermediate- (Bidstrup and Payne 1951 Bidstrup et al. 1952) durations have died. Occupational exposure usually involves a combination of inhalation and dermal exposure. A blood level of 75 pg/g DNOC was found in one worker who died (Bidstrup et al. 1952). In addition, a worker died after he drank water contaminated with DNOC (Bidstrup and Payne 1951). The dose or the amount of DNOC was not specified in case reports regarding death in humans after occupational or oral exposure to DNOC. However, in one case report, the application of a fat-based ointment containing 12,500 mg of DNOC to a skin rash resulted in death in a 4-year-old boy (Buchinskii 1974). Because DNOC was applied to the rash rather than intact healthy skin, absorption of DNOC was facilitated. 

Selection of an appropriate base for an ointment or cream formulation depends on the type of activity desired (e.g., topical or percutaneous absorption), compatibility with other components, physicochemical and microbial stability of the product, ease of manufacture, pourability and spreadability of the formulation, duration of contact, chances of hypersensitivity reactions, and ease of washing from the site of application. In addition, bases that are used in ophthalmic preparations should be nonirritating and should soften at body temperatures. White petrolatum and liquid petrolatum are generally used in ophthalmic preparations. Table 1 summarizes... 

Increased absorption with occlusive dressing Used for lipid-soluble drugs with low dose and low MW Type of cream or ointment base affects drug release and absorption... 

Ointments utilize certain bases that act as vehicles to deliver the drug and to impart emollient and lubricant properties to the preparation. Usually, but not always, they contain medicinal substances. Properties of ointments may vary from product to product depending on their specific use, ease, and extent of application. In general, ointment bases may be classified into four general groups hydrocarbon, absorption, water-removable, and water-soluble bases. 

In suppositories cetyl alcohol is used to raise the melting point of the base, and in modified-release dosage forms it may be used to form a permeable barrier coating. In lotions, creams, and ointments cetyl alcohol is used because of its emollient, water-absorptive, and emulsifying properties. It enhances stability, improves texture, and increases consistency. The emollient properties are due to absorption and retention of cetyl alcohol in the epidermis, where it lubricates and softens the skin while imparting a characteristic velvety texture. 

Petrolatum has also been tentatively implicated in the formation of spherulosis of the upper respiratory tract following use of a petrolatum-based ointment packing after surgery, and lipoid pneumonia following excessive use in the perinasal area. Other adverse reactions to petrolatum include granulomas (paraffinomas) following injection into soft tissue. Also, when taken orally, petrolatum acts as a mild laxative and may inhibit the absorption of lipids and lipid-soluble nutrients. 

Transdermal Slow absorption, rate may vary. Increased absorption with occlusive dressing. Transdermal delivery system (patch) is easy to use. Used for lipid-soluble drugs with low dose and low MW. Some irritation by patch or drug. Permeability of skin variable with condition, anatomic site, age, and gender. Type of cream or ointment base affects drug release and absorption. 

Fang, W.F., Wu, P.C., Huang, Y.B., Tsai, Y.H., In vivo percutaneous absorption of capsaicin, nonivamide and sodium nonivamide acetate from ointment bases pharmacokinetic analysis in rabbits, J. Pharm., 128, 169-177, 1996. 

It should be mentioned that product formulation can also influence percutaneous absorption. An ointment vehicle with a high proportion of oils and fats is more likely to ensure skin penetration. A hydrophilic cream base is favorable to the absorption of more hydrophilic compounds. Skin hydration, which is achievable by the incorporation of humectants (e.g., glycerol) or by occluding dressings, can also be helpful. Particle size of substances that are not readily solubilized in the vehicle used must also be considered in developing the dermatological product. 

VEHICLE Most topical medications are incorporated into bases or vehicles that are applied directly to the skin. The chosen vehicle can influence drug absorption and provide therapeutic efficacy for example, an ointment is more occlusive and has superior emollient properties than a cream or a lotion base. 

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