RESUMO
BACKGROUND: Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is difficult to administer because of the pharmacokinetic complexity of MPA. Although dosage adjustment according to the 12-h area under the concentration-time curve (AUC0-12) is thought to be desirable, multiple blood samplings for AUC calculation may pose a clinical challenge. A limited sampling strategy (LSS) would provide a solution; however, little is known about MPA pharmacokinetics in lupus nephritis patients, especially in those with Asian backgrounds, or few, if any, LSSs are reported for them. METHODS: Thirty-four adult Japanese patients receiving MMF for lupus nephritis were examined retrospectively. MPA pharmacokinetics were investigated, and a PPK model was developed using Phoenix® NLME™ software. Single and double blood sampling strategies from Bayesian estimation using the PPK model and from multiple linear regression were compared. Tolerability was also evaluated. RESULTS: In the pharmacokinetic analysis, renal function and serum albumin had significant effects on dose-normalized AUC0-12; and serum albumin, concomitant proton pump inhibitor (PPI) and iron/magnesium oxide did on dose-normalized maximum concentration. As a PPK model, a two-compartment model was developed with a transit absorption model and first-order elimination, in which creatinine clearance and serum albumin were covariates for MPA clearance. The double sampling strategy at 1 and 4 h by multiple linear regression showed the best agreement with the observed AUC0-12 (r2 = 0.885). Of the single sampling strategies, the one at 6 h by Bayesian estimation performed best (r2 = 0.769). The tolerability evaluation showed that correlations were suggested for gastrointestinal involvement. CONCLUSIONS: The present study developed the first PPK model of MPA for Japanese lupus nephritis patients. As for LSSs, a double sampling strategy at 1 and 4 h by multiple linear regression would work best; when only a single blood sampling is allowed, a strategy at 6 h by Bayesian estimation using the PPK model developed in this study would be best. The LSSs good enough for clinical use may facilitate safer, more effective, and individualized therapy.
RESUMO
In Japan, transdermal fentanyl (Durotep Patch) was launched in March 2002, and it was regarded as making opioid rotation possible. When changing from morphine to transdermal fentanyl, the efficacy ratio of 1:150 is used in Japan as well as in many other countries. However, the ratio of 1:100 is used in Germany. As a result, a dose increase in transdermal fentanyl is often required to control pain. We studied transdermal fentanyl use in the Aichi Cancer Center (ACC) to investigate the actual conversion ratio and appropriate switching by following up 144 patients (81 men, 63 women) who had received transdermal fentanyl in the ACC from March 19, 2002, to April 30, 2003. Transdermal fentanyl improved pain control in patients who had difficulty in tolerating oral medication or in continuing morphine because of side effects. Regression analysis indicated that the efficacy ratio of oral morphine to transdermal fentanyl was 1:78. As the fentanyl dosage was excessive even in some patients who followed the recommended morphine/fentanyl conversion of 150:1, it is dangerous to use the conversion ratio of 78:1 at first. Morphine side effects were reduced in some patients who changed to transdermal fentanyl, but there was no reduction in those who needed high-dose morphine for rescue analgesia. Therefore it is safe and effective to use low-dose transdermal fentanyl in the beginning and to control pain promptly using rescue morphine based on the present recommended dosage. For opioid rotation, quick-acting opioids other than morphine are expected to be launched in Japan.
