Chlorhexidine

Chlorhexidine has caused photoallergy in one case (Wahlberg and Wennersten 1971). 

Recently the result of photopatch testing with PABA was shown to be vehicle dependent. A positive reaction in a photoallergic patient could be elicited by 5% PABA in alcohol but not in petrolatum (Mathias et al. 1978 a). A variety of other chemicals have occasionally been described as photoallergens. 

Anaphylaxis to chlorhexidine can occur, and although rare, it is these reactions that have aroused allergists attention to the agent. Many dmgs provoke an occasional anaphylactic or anaphylactoid response but with chlorhexidine there are some features of the cases that were unanticipated, surprising, and, initially at least, obscure. The first reported cases of anaphylaxis 

Instillagel which contains 0.25 % chlorhexidine, 2 % lidocaine, and mixed hydroxybenzoates, demonstrates why its involvement in indncing allergic reactions might in some cases remain unrecognized. A survey in 2005 conclnded that chlorhexidine accounted for 27 % of overlooked perioperative hypersensitivity reactions. 

Incidences of anaphylaxis to chlorhexidine are not necessarily readily found or widespread and, in fact, there are no reports of any cases from many countries. This may reflect the local absence of chlorhexidine preparations, failure to recognize and/or investigate reactions, the different concentrations used in antiseptics in different countries, or absence of sensitivity to the agent. The Danish Anaesthesia Allergy Centre, established in 1998 to investigate patients referred from all over Denmark, found 4 men of 21 patients with positive skin tests to various substances tested positive to chlorhexidine. Three cases of anaphylaxis to chlorhexidine were reported in Finland up to 1999, 11 cases were seen in Australia in the period 1985-1994 and 9 in Japan between 1967 and 1984. 

Skin prick tests on a patient who experienced an anaphylactic reaction to Instillagel produced results that draw attention to a potential pitfall when testing for sensitivity to this preparation. The demonstration of a positive skin test to chlorhexidine after the finding of a negative skin prick test to Instillagel was attributed to the presence of lidocaine in the gel and its effect in ablating the neurogenic wheal response required for a positive prick test. 

2 IgE Antibody Tests for Diagnosis and Drug Aiiergen Studies 

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Ghlorhexidine Gluconate. Chlorhexidine gluconate [18472-51 -0] (l,l -hexamethylene bis[5-(p-chlorophenyl) biguanide] di-D-gluconate) is used as an antimicrobial against both aerobic and anaerobic bacteria ia the oral cavity. It is used as a therapeutic supplement ia the treatment of gingivitis, periodontal disease, and dental caries. A mouth riase form is available as a 0.12 wt% aqueous solution (288). 

Active agents vary according to use. For controlling bad breath, 2iac salts, sodium lauryl sulfate, and flavors are used. To destroy oral microorganisms, chlorhexidine, cetylpyridinium chloride [123-03-5] and ben2alkonium chloride [68391-01-5] are valuable. Essential oils, such as thymol [89-83-8] eucalyptol [470-82-6] menthol, and methyl salicylate [119-36-8] reduce plaque-related gingivitis (see Oils, essential). Sodium fluoride aids ia caries coatrol. 

Chlorhexidine is the most poteat oral antimicrobial agent available. It has side effects and is sold only with a prescription. It is active deflvered from a riase, but a compatible toothpaste vehicle for chlorhexidine has yet to be developed. 

Ethanol and 2-propanol have also found use ia disinfecting clinical thermometers, and as preservatives to prevent microbial deterioration of cosmetics and mediciaals. They are sometimes combiaed with other disiafectants, namely formaldehyde (69), phenoHcs (70), chlorhexidine (71), hypochlorite (72), and phenols (70). 

The optimum pH for chlorhexidine antimicrobial activity is in the range 5.5—7.0 but varies with the buffer used and the organism, having a range of pH 5—8. With S. aureus and E. coli, activity increases with increased pH the reverse occurs with P. aeruginosa. 

After washing with chlorhexidine skin cleanser for 15 seconds, a 99.9% reduction of transient contaminants was achieved (216). Chlorhexidine is sometimes combined with alcohol to achieve the rapid reduction obtained with alcohol and the residual effect of chlorhexidine. It is substantive to the skin, and repeated use results in lower levels of bacteria on the skin. 

Chlorhexidine has found other medical appHcations, eg, in urology in preventing urinary tract infections (217), in obstetrics and gynecology (218), in controlling infection in bums and wounds (219), and in the prevention of oral disease (220). Hypersensitivity to chlorhexidine has been reported in Japan (221) but 0.05% concentration is considered to be safe. 

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