PHENYLMERCURIC BORATE

Chemical properties

Phenylmercuric borate occurs as colorless, shiny flakes or as a white or slightly yellow, odorless, crystalline powder.

Production Methods

Phenylmercuric borate may be prepared by heating mercuric borate with benzene or by evaporating to dryness, under vacuum, an alcoholic solution containing equimolar proportions of phenylmercuric hydroxide and boric acid.

Pharmaceutical Applications

Phenylmercuric borate is used as an alternative antimicrobial preservative to phenylmercuric acetate or phenylmercuric nitrate. It is more soluble than phenylmercuric nitrate and has also been reported to be less irritant than either phenylmercuric acetate or phenylmercuric nitrate.

Safety

Phenylmercuric borate is mainly used as an antimicrobial preservative in topical pharmaceutical formulations. A number of adverse reactions to mercury-containing preservatives have been reported; see Phenylmercuric Nitrate.
Although phenylmercuric borate is an irritant, it has been reported to be less so than either phenylmercuric acetate or phenylmercuric nitrate.(1) There is, however, some cross-sensitization potential with other mercurial preservatives. Systemic absorption has been reported following regular use of a hand disinfectant soap containing 0.04% phenylmercuric borate, resulting in an increase in the estimated total daily body load of mercury from 30–100 mg per 24 hours.

storage

As for other phenylmercuric salts; see Phenylmercuric Nitrate. Solutions may be sterilized by autoclaving.
Phenylmercuric borate should be stored in a well-closed container, protected from light, in a cool, dry place.

Incompatibilities

Incompatible with: halides; anionic emulsifying agents and suspending agents; tragacanth; starch; talc; sodium metabisulfite; sodium thiosulfate; disodium edetate; silicates; aluminum and other metals; amino acids; ammonia and ammonium salts; sulfur compounds; rubber; and some plastics.
Phenylmercuric acetate is reported to be incompatible with cefuroxime and ceftazidime.

Regulatory Status

Included in nonparenteral medicines licensed in Europe. Included in the Canadian List of Acceptable Non-medicinal Ingredients (ophthalmic, nasal and otic preparations up to 0.004%; there must be no other suitable alternative preservative).
In Europe, use is limited to eye makeup and eye makeup remover at not more than 0.007% mercury alone or in combination with other permitted mercurial substances.In France, a maximum concentration of up to 0.01% is permitted for use in pharmaceutical formulations. Prohibited from use in cosmetic products in Canada. Prohibited in antimicrobial diaper rash drug products in the USA. Limited use in Japan (see Phenylmercuric Nitrate).