Formulations topical preparations

Topical preparations, like all other dosage forms, must be formulated, manufactured, and packaged in a manner that assures that they meet general standards of bioavailability, physical (physical system) stability, chemical (ingredient) stability, freedom from contamination, and elegance. Like all other pharmaceuticals, these factors must remain essentially invariant over the stated shelf life of the product and they must be reproducible from batch to batch. 

Evaluation of the cosmetic elegance of topical preparations can be accomplished scientifically, but it is questionable whether physical experiments on system rheology and the like offer appreciable advantage over the subjective evaluations of the pharmacist, the formulator, or other experienced people. Persons who use cosmetics are particularly adept and helpful as evaluators. 

Naproxen is a naphthylpropionic acid derivative. It is the only NSAID presently marketed as a single enantiomer. Naproxen s free fraction is significantly higher in women than in men, but half-life is similar in both sexes (Table 36-1). Naproxen is effective for the usual rheumatologic indications and is available in a slow-release formulation, as an oral suspension, and over the counter. A topical preparation and an ophthalmic solution are also available. 

Containers used for topical administration include plastics, glass, and metals. Most topical preparations are packaged in plastic jars, metal tubes, glass jars or, in some cases, a combination of these materials. Suitable tests are performed to ensure that drug products do not leach or react with the proposed containers. The various types of topical formulations are discussed in Pharmaceutical Dosage Forms (1151) of the USP/NFP ... 

Ascorbyl palmitate is primarily used either alone or in combination with alpha tocopherol as a stabilizer for oils in oral pharmaceutical formulations and food products generally 0.05% w/v is used. It may also be used in oral and topical preparations as an antioxidant for drugs unstable to oxygen. The combination of ascorbyl palmitate with alpha tocopherol shows marked synergism, which increases the effect of the components and allows the amount used to be reduced. 

Canola oil is a refined rapeseed oil obtained from particular species of rapeseed that have been genetically selected for their low erucic acid content. In pharmaceutical formulations, canola oil is used mainly in topical preparations such as soft soaps and liniments. It is also used in cosmetics. 

Although widely used in topical preparations, including ophthalmic formulations, castor oil has been associated with some reports of allergic contact dermatitis, mainly to cosmetics such as lipsticks. 

Corn oil is used primarily in pharmaceutical formulations as a solvent for intramuscular injections or as a vehicle for topical preparations. Emulsions containing up to 67% corn oil are also used as oral nutritional supplements see also Section 18. When combined with surfactants and gel-forming polymers, it is used to formulate veterinary vaccines. 

Dimethicone is generally regarded as a relatively nontoxic and nonirritant material although it can cause temporary irritation to the eyes. In pharmaceutical formulations it may be used in oral and topical preparations. Dimethicones are also used extensively in cosmetic formulations and in certain food applications. 

Included in the FDA Inactive Ingredients Guide (IV infusions, SC implants, and topical preparations). Available in the USA as a 50% solution for irrigation in the treatment of interstitial cystitis. Also available in Canada as a 70% solution for use as a topical antifibrotic and in Germany as a topical gel containing 10% dimethyl sulfoxide for the treatment of musculoskeletal and joint disorders. Included in topical formulations of idoxuridine and diclofenac licensed in the UK. 

Glycerin is used in a wide variety of pharmaceutical formulations including oral, ophthalmic, parenteral, and topical preparations. Adverse effects are mainly due to the dehydrating properties of glycerin. ... 

In oral medicines, kaolin has been used as a diluent in tablet and capsule formulations it has also been used as a suspending vehicle. In topical preparations, sterilized kaolin has been used in poultices and as a dusting powder. Therapeutically, kaolin has been used in oral antidiarrheal preparations. ... 

Peanut oil is used as an excipient in pharmaceutical formulations primarily as a solvent for sustained-release intramuscular injections. It is also used as a vehicle for topical preparations and as a solvent for vitamins and hormones. In addition, it has been part of sustained-release bead formulations, nasal drug delivery systems, and controlled-release injectables. ... 

Adverse reactions to peanut oil in foods and pharmaceutical formulations have been reported extensively. These include severe allergic skin rashes and anaphylactic shock following consumption of peanut butter. Some workers have suggested that the use in infancy of preparations containing peanut oil, including infant formula and topical preparations, is associated with sensitization to peanut, with a subsequent risk of hypersensitivity reactions, and that such products should therefore be avoided or banned. However, the role of pharmaceutical preparations in later development of hypersensitivity is disputed since such preparations contain highly refined peanut oil that should not contain the proteins associated with allergic reactions in susceptible indivi-... 

Phenylethyl alcohol is used as an antimicrobial preservative in nasal, ophthalmic, and otic formulations at 0.25-0.5% v/v concentration it is generally used in combination with other preservatives.Phenylethyl alcohol has also been used on its own as an antimicrobial preservative at concentrations up to 1% v/v in topical preparations. At this concentration, mycoplasmas are inactivated within 20 minutes, although enveloped viruses are resistant. " Phenylethyl alcohol is also used in flavors and as a perfumery component, especially in rose perfumes. 

Sodium sulfite is used as an antioxidant in applications similar to those for sodium metabisulfite It is also an effective antimicrobial preservative, particularly against fungi at low pH (0.1% w/v of sodium sulfite is used). Sodium sulfite is used in cosmetics, food products, and pharmaceutical applications such as parenteral formulations, inhalations, oral formulations, and topical preparations. 

In liquid preparations sorbitol is used as a vehicle in sugar-free formulations and as a stabilizer for drug, vitamin, and antacid suspensions. It has also been shown to be a suitable carrier to enhance the in vitro dissolution rate of indometa-cin. In syrups it is effective in preventing crystallization around the cap of bottles. Sorbitol is additionally used in injectable and topical preparations and therapeutically as an osmotic laxative. 

Starch is also used in topical preparations for example, it is widely used in dusting powders for its absorbency, and is used as a protective covering in ointment formulations applied to the skin. Starch mucilage has also been applied to the skin as an emollient, has formed the base of some enemas, and has been used in the treatment of iodine poisoning. 

A comprehensive account of the pharmaceutics and biopharmaceutics of topical preparations is not possible here. This section has therefore been deliberately restricted in scope to deal with the physicochemical principles involved in the process of treating the skin or in systemic medication by the transdermal or percutaneous route. Formulation of topical vehicles for the potent dmgs applied to the skin is now an exact art. It is readily demonstrated that the... 

Key parameters are different for different routes of delivery and different formulations particle size is a key factor in inhalation products and in topical preparations where the dmg is dispersed rather than dissolved in the vehicle. 

The rheological properties of topical preparations and formulations for nasal delivery are important, and a key factor is the syringeability of injectables. 

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