The quantitative determination of serum fentanyl (FT), urinary FT and its main metabolite, Nor-FT was examined to ascertain the individual variation in the elimination process of FT among 17 patients. The pharmacokinetics of FT was solved from the obtained data using 2-compartment model including the metabolic process. Furthermore, we compared Nor-FT excretion with CYP3A4 activity based on urinary 6β-hydroxycortisol (6β-OHF) and cortisol (F) excretion ratio.
FT and Nor-FT were determined by isotope dilution analysis using deuterium labeled FT (FT-²H₁₉) or Nor-FT (Nor-FT-²H₁₀) as internal standards. The isotopic fractionation was achieved by a capillary gas chromatograph equipped with a surface ionization detector. The pharmacokinetic parameters were calculated from serum FT concentration time profiles and excreted amount of FT and Nor-FT in urine, using the pharmacokinetic data analysis software, WinNonlin standard Ver. 1.5 (Scientific Consulting). Urinary F and 6β-OHF concentrations were determined by HPLC using fludrocortisone as an internal standard after conversion to fluorescence derivative using 1, 2-diamino-4, 5-methylenedioxybenzene.
The obtained pharmacokinetic parameters showed considerable difference between individuals. The predicted time course for FT and Nor-FT was adapted to FT kinetics. The predicted final excretion rates of FT and Nor-FT were 0.14-15.77% (mean 4.30%) and 7.36-99.38% (mean 55.12%), respectively. The CYP3A4 activity obtained from steroid excretion was not reflected by FT elimination in this study for a low dose of FT (5μg/kg).

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The validation study on the uniformity in β-ray sensitivity of radioluminography (RLG) has been performed. Imaging plates (IP) were irradiated with a ¹⁴⁷Pm planar radiation source and then analyzed by two bio-imaging analyzer systems (BAS). The PSL values observed (PSL_OB) on the irradiated IPs were statistically analyzed by a split method. An area dependency of appreciable extent in β-ray sensitivity was observed, which could be mainly attributed to the mechanics in BAS. The area dependency in β-ray sensitivity could be corrected using imaging plates that were irradiated with a ¹⁴⁷Pm planar radiation source.

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A ¹⁴C test radiation source was prepared for the validation of radioluminography. Each five small polypropylene resin pieces, on which a few hundreds Bq ¹⁴C had been spotted accurately and air-dried, were fixed at equal intervals on the lengthwise and widthwise center lines and the two diagonal lines on a sheet of cardboard of IP size. Simple methods for daily examining the uniformities in sensitivity of BAS and IP were proposed.

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