Ointment water-removable bases

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. 

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. 

Water-soluble bases do not contain any oily or oleaginous phase. Solids can be easily incorporated into these bases. They may be completely removed from the skin due to their water solubility. Polyethylene glycol (PEG) ointment National Formulary (NF) is an example of a water-soluble base. 

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. 

Eye ointments are prepared in a semi-sohd base (e.g. Simple Eye Ointment BP, which consists of yellow soft paraffin, eight parts hqnid paraffin, one part wool fat, one 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 prodnct is aseptically packed in clear sterile alumirtinm or plastic tnbes. Since the prodnct contains virtnally no water, the danger of bacteria proliferating in the ointment is neghgible. Therefore, there is no recommended maximum period during which they can be nsed. 

Hoebus et al. (1993) used silica gel TLC with various mobile phases to identify corticosteroid hormones available on the European market. Detection was by fluorescence after the plates were sprayed with alcoholic sulfuric acid and heated. Datta and Das (1994) identified and quantified corticosteroids and their esters in pharmaceutical preparations of creams and ointments. The preparations were dissolved in chloroform, centrifuged to remove water and insoluble material, and silica gel TLC with hexane mobile phase was used to wash out base ingredients followed by chloroform-ethyl acetate (1 1) for free steroids or (2 1) for esters and spectrodensitometry at 240 nm recoveries were 99 1% and the agreement of results with the official methods used was excellent. 

Many active ingredients of ointments and lotions are not readily dispersible because of their insolubility. Coal-tar products are an example which have been successfully blended into ointment bases by the use of surfactants [227]. A 1 % crude coal-tar ointment in which the tar is dispersed by the addition of 0.5 % polysorbate 20 prior to its incorporation in the base, produces fewer adverse skin reactions than the normal preparations without surfactant [228]. Such preparations are also more readily removed from the skin with water. It has been stated, however, that incorporation of coal-tar into hydrophilic ointment bases allows the penetration of carcinogenic components which may be present in the tar. A clear transparent solution of the US Formulary Coal-Tar Solution can be made, provided that 10% polysorbate 20 remains in the final dilution [229]. 

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