Oral cyclosporine but not tacrolimus reduces renal transplant blood flow

Background. Calcineurin inhibitors are important immunosuppressive agents, but cause nephrotoxicity. Methods. Instantaneous intra-renal transplant hemodynamics were assessed in 22 patients using quantitative cineloop color Doppler imaging after dosing with microemulsion cyclosporine (CSA) or tacrolimus (TAC). Results. CSA dosing resulted in renal hypoperfusion, with a mean relative reduction of 43% +/- 20% (range 22-76%) in maximal fractional area (MFA) of color pixels to nadir, compared to baseline. The mean effect occurred 1.1 +/- 0.9 hr (median 1 hr) after CSA dosing and was abrogated by calcium channel blockers (P<0.05). The main renal artery velocities, resistive index and small vessel perfusion were unchanged, suggestive of medium-sized arteries mediated vasoconstriction. In contrast, TAC did not alter renal vascularity (2.3 ± 4.0% absolute reduction of MIFA color pixels vs. 10.7 ± 6.5% with CSA, P < 0.01). Conclusion. CSA, but not TAC, induces phasic hypoperfusion of variable severity within small to medium sized intra-renal arteries soon after dosing, mitigated by calcium channel blockade.