Topical formulations, solvents glycols

In 11 patients allergic to topical minoxidil lotion, patch tests showed that four were positive to minoxidil itself (11). Propylene and butylene glycol are used as solvents for minoxidil in topical formulations. Nine of the 11 patients appeared to have positive patch tests to propylene glycol and one of the 11 reacted to its alternative butylene glycol. 

Propylene glycol is extensively used in numerous topical formulations as illustrated in Table 3, abstracted from the FDA Inactive Ingredient Guide (1996). Over 230 drug products at that time contained the solvent, and at levels up to 99.99% of the formulation. 

Formulators can use the tendency of creams, gels, and other systems to evaporatively concentrate to advantage. Solvents are chosen and blended so that the drug remains soluble in the formed film long after application is made. This can be accomplished by replacing a fraction of the water or other highly volatile solvent found in these systems with solvents of far lower volatility. As previously pointed out, 5-15% propylene glycol is found in many topical corticosteroid creams and lotions just for this reason. 

Although its systemically administered medical uses have been limited to the treatment of methanol and ethylene glycol poisoning, alcohol is an excellent solvent and is used as a vehicle in many pharmaceutical formulations. It is also used topically as a disinfectant and to reduce fever through evaporation. Medieval alchemists considered it to be the elixir of life, a title that has survived in certain European fruit brandies called collectively eau de vie. 

Light mineral oil is used in applications similar to those of mineral oil. It is used primarily as an excipient in topical pharmaceutical formulations where its emollient properties are exploited in ointment bases see Table I. It is also used in ophthalmic formulations. Light mineral oil is additionally used in oil-in-water and polyethlylene glycol/gylcerol emulsions as a solvent and lubricant in capsules and tablets as a solvent and penetration enhancer in transdermal preparations and as the oily medium used in the microencapsulation of many drugs. ... 

Formulations containing an absorption promoting substance, such as propylene glycol or sodium lauryl sulphate, may increase the permeability of the stratum comeum to water-soluble drugs. Propylene glycol is a commonly used vehicle in topical corticosteroid preparations for veterinary use. Various aprotic solvents, which include dimethylacetamide, dimethylformamide, dimethylsulphoxide, tetrahydrofurfuryl alcohol, and 2-pyrrolidone, serve as penetration enhancers of polar drugs (Barry, 1983). Dimethylsulphoxide... 

Propylene glycol is used as solvents in many formulations (e.g., oral, topical, and parenteral routes) for poorly soluble compounds such as phenobarbital, phenytoin, diazepam, and multivitamin concentrates. Because of the limited metabolic pathways in children younger than four years, number of adverse events has been described (laxative effects per os, contact dermatitis) but mainly serious systemic CNS depression. Seven of... 

---