Dangerous effects of tin-protoporphyrin plus photoirradiation on neonatal rats.

In vivo and in vitro effects of porphyrins (tin-protoporphyrin [SnPP], cobalt-mesoporphyrin, haemin and protoporphyrin) on neonatal rats were investigated. Under photoirradiation a high mortality rate was recognized in SnPP injected rats. None died from the application of SnPP without photoirradiation. In photoirradiated rats the median lethal dose (LD50) value of SnPP was calculated to be about 7.4 mumol/kg body weight. Haemolysis and malonaldehyde formation of red blood cells were induced by SnPP together with photoirradiation. SnPP may be useful in reducing bilirubin levels in severely jaundiced infants under non-photoirradiated conditions or dim light, but prophylactic administration of SnPP to the majority of infants is not recommended.