Phototoxicity of tin protoporphyrin, tin mesoporphyrin, and tin diiododeuteroporphyrin under neonatal phototherapy conditions.

Tin metalloporphyrins are being considered as therapeutic agents for neonatal hyperbilirubinemia, and it is possible that concurrent exposure to phototherapy will occur during their use. Euthymic hairless guinea pigs, Crl:IAF(HA)BR, were given daily intraperitoneal injections of tin protoporphyrin (SnPP), tin mesoporphyrin (SnMP), or tin diiododeuteroporphyrin (SnI2DP) for 3 successive days. They were concurrently exposed to ambient light or two different kinds of phototherapy light under conditions similar to that found in neonatal intensive care units. Phototherapy light exposure was for a continuous period of approximately 72 hours following the first injection of metalloporphyrin. The presence or absence of phototoxicity under these conditions was determined by observations for an erythematous response on the back and ears of the guinea pigs. The dosages used were 0.75, 3.75, and 7.5 mg/kg per day of SnPP, 0.075, 0.375, and 0.75 mg/kg per day of SnMP, and 0.9, 4.5, and 9.0 mg/kg per day of SnI2DP. These dosages for each drug were approximately 1 times, 5 times, and 10 times, respectively, the maximum anticipated clinical dosage. At equal multiples of the clinical dosages, SnI2DP was less phototoxic than SnPP, and SnMP was the least phototoxic of the three compounds. SnPP was marginally phototoxic at the lowest dosage. SnMP was phototoxic only at the highest dosage under phototherapy light emitting ultraviolet A irradiation, but when phototherapy light not emitting ultraviolet A irradiation was used, SnMP was not phototoxic. In all cases, the phototoxic response was reversible when the drug and phototherapy treatment were discontinued.