Radioimmunological determination of fenoterol. Part II: Antiserum and tracer for the determination of fenoterol.

A radioimmunological method for the determination of the concentration of fenoterol in biological samples is described. The mixture of antibodies against the enantiomers of fenoterol obtained with the selected hapten shows a high affinity for racemic fenoterol and for the monoiodo125-fenoterol used as a tracer, which is also present as a racemate. The limit of detection of the radioimmunoassay for fenoterol (racemate) in biological samples (plasma, urine) is 10-20 pg/ml. The precision and accuracy of the radioimmunoassay, in the presence of racemic fenoterol, are sufficient for an analysis and meaningful interpretation of samples from human pharmacokinetic studies. A relationship between the cross-reactivity of the antibodies against fenoterol and a preferred conformation of the fenoterol molecule in aqueous solution is discussed.