Primary sensitization potentials of some halogenated salicylanilides and their cross-sensitivity in guinea-pigs

Spectroscopic studies of cutaneous photosensitizing agents--XIV. The spin trapping of free radicals formed during the photolysis of halogenated salicylanilide antibacterial agents

Several antibacterial halogenated salicylanilides, including 3,3',4',5-tetrachlorosalicylanilide (TCSA) and 3,4',5-tribromosalicylanilide (TBSA) are known to cause photoallergy. We have carried out photochemical and spin trapping studies to determine whether free radicals may be involved in the photoallergic response. Irradiation (lambda greater than 300 nm) of TCSA in buffered (pH 7.4) 50% ethanol resulted in the rapid loss of the 3-chloro atom, followed by the much slower release of 5- and then the 4'-chloro atoms to give 3'-chlorosalicylanilide as a stable photoproduct. Under the same conditions TBSA successively lost the 3-, 5- and 4'-bromine atoms to give salicylanilide. When TCSA or TBSA were irradiated (lambda = 356 nm) in buffered (pH 7.4) 50% ethanol containing 2-methyl-2-nitrosopropane (MNP) only solvent-derived free radicals were detected. However, irradiation (lambda = 356 nm) of TCSA and MNP in 0.1 N NaOH generated an ESR spectrum consisting of a broad triplet (aN = 15.6 G). This spectrum was attributed to the adduct formed by the reaction of MNP with the aryl radical generated by the loss of a chlorine atom from the sterically hindered 3-(or 4'-)-position. Under the same conditions TBSA initially generated a broad triplet (aN = 15.5 G) similar to that observed for TCSA. However, upon further irradiation a 21-line spectrum (aN = 14.4 G, a2H = 2.0 G and a2H = 0.9 G) appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictive animal testing for photocontact allergenicity

The purpose of this investigation was to establish a standardized animal model to predict the photoallergenic potential of new chemical compounds. In a first series of experiments the main factors influencing the induction of photoallergenicity were evaluated (induction concentration, pH of the test solution, pretreatment of the irradiation site with sodium lauryl sulphate, additional use of adjuvant injections and routes of administration). Osram Ultravitalux lamps were utilized for these studies. In a second series of experiments a Xenon 6000 W radiation source was used. Positive results were obtained with well known photosensitizers, as, for instance, the halogenated salicylanilides, as well as with so-called weak photoallergens (e.g. bithionol, sulphanilamide) by stimulating the animals' immune system with Freund's complete adjuvant. The photoallergenic compounds were at the same time tested for their contact allergenic potential in the optimization test. A standard procedure for the predictive photoallergenicity assay in guinea-pigs is proposed.