A sensitive enzyme immunoassay for OPC-7251, a novel pyridone carboxylic acid antimicrobial agent, was developed and applied for the determination of human plasma levels. OPC-7251 was coupled to bovine serum albumin through a formation of N-hydroxysuccinimide ester. By immunization of rabbits, highly specific antiserum was raised. Using the antiserum and #xDF;-D-galactosidase-labeled hapten, the homologous assay system allowed the detection of 2 pg of this compound. Plasma samples were precisely analyzed down to the minimum value of 200 pg/ml after heat treatment. The system was further validated by the recovery test and correlation with the HPLC analyses. Percutaneous application of 10 g of 1 OPC-7251 cream to healthy volunteers resulted in the peak plasma value of 1.6 ng/ml about 8 hours after dosing, indicating extremely low absorption efficiency through a transdermal system.
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