Sensitivity of the Limulus test and inhibitory factors in the radiopharmaceuticals

The basic sensitivity of the Limulus test and the inhibitory factors were examined in 21 radiopharmaceuticals commonly used in Japan. The sensitivity of the Limulus test using pre-gel was found to be 1 mug/ml for Escherichia coli endotoxin. This sensitivity is about ten times that of the rabbit test adopted by USP and JP. The Limulus test was applicable, with full sensitivity and without inhibitory reaction, for the evaluation of 99mTcO4-, 99mTc-albumin, 99mTc-MAA, 99,Tc-Sn-colloid, 131I-Hippuran, Na131I, Na251CrO49, 67Ga citrate, and 57Co-bleomycin as commercially supplied. On the other hand, with 111In-DTPA, 99mTc-phytate, 99mTc-pyrophosphate, 99mTc-DTPA, 131I-polyvinylpyrrolidone (PVP), 59FeCl3, Na232PO4, 198Au colloid, and selenomethionine (Se-75), the pH required adjustment to avoid inhibition of the gelation reaction. Benzyl alcohol showed an inhibitory effect on the gelation reaction at concentrations of more than 1%. Iodine-131-Bromsulphalein (BSP) and 131I-rose bengal showed intense inhibition of the gelation reaction.