The influence of various aminoglycoside preparations on bilirubin/albumin binding

The effect of antibiotics of aminoglycoside structure on the albumin binding of bilirubin has been tested in homozygous (jaundiced) Gunn rats aged 3-5 days. The following drugs were investigated: different preparations of gentamycin, kanamycin, tobramycin and sisomicin. The animals received 50-75% of the LD50 of heterozygous (non-jaundiced) Gunn rats. Mortality, weight gain and changes in the plasma bilirubin concentration were recorded. It was found that the displacement of bilirubin from albumin is caused by the different stabilizers used and not by the antibiotic itself. With the exception of lyophilized preparations of gentamycin for intrathecal application all vials contain different amounts of these preservatives. Special preparations used during the newborn period contain relatively more of these stabilizers. The toxicity of the additives has already a negative influence on the LD50 for heterozygous Gunn rats when the low dosed Refobacin and Sulmicin vials are given. For Refobacin (production 1973/74) the tolerance is reduced by nearly 50%. The toxicity caused by the stabilizer alone is even more marked when given to homozygous (jaundiced) Gunn rats. It becomes evident that benzylalcohol is the substance responsible for the displacement of bilirubin from albumin. The serum concentration of bilirubin decreases for 3-24 hrs depending on the doses given to the animal. This offers the opportunity to measure the competitive displacement of bilirubin easily and exactly. The free unbound, unconjugated bilirubin tends to diffuse into the lipid of the brain with resultant kernicterus. This was shown in histochemical preparations of the cerebellum of young homozygous Gunn rats. Using enzyme reactions for lactic acid dehydrogenase and NADH2-tetrazolium reductase the cytotoxic effect of bilirubin on PURKINJE cells could be demonstrated. The effect of the stabilizers used in the other antibiotic drugs tested can be neglected under clinical conditions. Finally the steepness and duration of the decrease of plasma bilirubin after injection of the dangerous stabilizers was studied in animals of different age (3-5 days; 3-4 weeks). Different results observed can be explained by the more rapid metabolism of benzoates in older animals. However, it remains an open question at what age Gunn rats reflect most precisely the human situation in premature and newborn babies.