title: Radioreceptor assay for sirolimus.
abstract: OBJECTIVE
  To develop a radioreceptor assay (RRA) for sirolimus (rapamycin, RAPA).
  
  
  METHODS
  A direct methanol extraction was used to prepare 45 patient samples for the RRA. Results were compared to the results obtained previously using high-performance liquid chromatography (HPLC). Between-run precision, recovery, and drug interference studies were also performed.
  
  
  RESULTS
  The RRA is sensitive to 1.0 microgram/L RAPA equivalents in whole blood. Comparison with HPLC yielded a correlation coefficient for 45 patient samples of 0.977. Between-run precision at 2.5, 7.5, 12.5, and 20 micrograms/L showed coefficients of variation (CVs) of 12.9, 9.2, 8.5, and 5.9%, respectively. Recoveries from the extraction procedure were 93% at 7.5 micrograms/L and 103% at 12.5 micrograms/L. Drug interference studies showed no interference in the RRA by cyclosporine (CsA), dexamethasone, prednisone, or methotrexate.
  
  
  CONCLUSIONS
  We have demonstrated that the RRA for RAPA correlates well with HPLC, and has excellent precision and recovery. The procedure is far less time-consuming and complex than HPLC and has potential for automation.
authors.affiliation: Department of Laboratory Medicine, Children's National Medical Center, Washington, DC 20010, USA.
authors.forename: N
authors.initials: N
authors.lastname: Goodyear
authors.forename: K L
authors.initials: KL
authors.lastname: Napoli
authors.forename: J N
authors.initials: JN
authors.lastname: Murthy
authors.forename: B D
authors.initials: BD
authors.lastname: Kahan
authors.forename: S J
authors.initials: SJ
authors.lastname: Soldin
mesh_terms: D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D016572:Cyclosporine / Q000008:administration & dosage / Q000097:blood; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000097:blood* / Q000378:metabolism; D000432:Methanol; D008727:Methotrexate / Q000008:administration & dosage / Q000097:blood; D011090:Polyenes / Q000097:blood* / Q000378:metabolism; D011869:Radioligand Assay / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020123:Sirolimus; D022021:Tacrolimus Binding Proteins
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D007166:Immunosuppressive Agents; D011090:Polyenes; D016572:Cyclosporine; D022021:Tacrolimus Binding Proteins; D020123:Sirolimus; D000432:Methanol; D008727:Methotrexate