Radioimmunoassay of salivary cyclosporine with use of 125I-labeled cyclosporine.
We prepared 125I-labeled cyclosporine (125I-CS) by modifying the procedure of Mahoney and Orf (Clin Chem 1985;31:459) and characterized it with regards to maximal immunoreactivity (greater than 90%), trichloroacetic acid precipitability (greater than 90%), and stability (90% immunoreactive after five half-lives of 125I). For a particular preparation of 125I-CS, we estimated its immunoreaction concentration (50 pmol/L) and the equilibrium constant for its reaction with Sandoz polyclonal antiserum (K = 3.9 X 10(9) L/mol). By substituting 125I-CS as tracer in the Sandoz radioimmunoassay and by modifying other aspects of the assay, we developed a procedure that is sufficiently sensitive (0.34 micrograms/L) to allow measurement of "trough" (lowest inter-dose) cyclosporine concentrations in parotid saliva. Of 38 kidney-transplant patients, 35 had measurable concentrations in saliva (mean 8.3, SD 5.2 micrograms/L), and these correlated moderately with paired serum concentrations (r = 0.68, P less than 0.001). We believe that measurement of salivary cyclosporine may offer a simple way of estimating the free fraction of the drug in serum or plasma.
Coates
J E
JE
Department of Laboratory Medicine, University of Alberta Hospitals, Edmonton, Canada.
Lam
S F
SF
McGaw
W T
WT
D003524:Cyclosporins / Q000032:analysis*; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D011863:Radioimmunoassay / Q000379:methods; D012463:Saliva / Q000032:analysis*
D003524:Cyclosporins; D007457:Iodine Radioisotopes