Pharmacokinetics of roxithromycin in kidney grafted patients under cyclosporin A or azathioprine immunosuppression and in healthy volunteers.

The pharmacokinetics of roxithromycin was studied in 9 kidney grafted patients under cyclosporin A immunosuppression, in 10 transplanted patients with azathioprine, and in 6 healthy volunteers. The biological half-life (beta-phase) of roxithromycin in cyclosporin patients was 34.4 (+/- 12.25) h (mean +/- SD), in azathioprine patients 23.4 (+/- 8.18) h and in healthy volunteers 17.0 (+/- 3.8) h. The total elimination constant (k10) was 0.046 (+/- 0.014), 0.068 (+/- 0.019) and 0.084 (+/- 0.036) h, respectively. The total clearance was 0.79 (+/- 0.21), 1.45 (+/- 0.66) and 1.84 (+/- 0.56) l/h, respectively. The areas under the serum level curves were 407.6 (+/- 118.3), 251.0 (+/- 106.6) and 180.7 (+/- 73.2) mg.h/l, respectively. The differences in these parameters between healthy volunteers and cyclosporin patients were statistically significant, as well as those between cyclosporin and azathioprine patients. The differences between healthy volunteers and azathioprine patients were not statistically significant. The results cannot be interpreted unambiguously as an interaction between roxithromycin and cyclosporin; the effect of cyclosporin on the function of eliminating organs which causes the slowed-down elimination of roxithromycin could be taken into account.