 Most of the decline in renal function after LTx occurs in the first few months. This is in part because patients are exposed to the highest levels of calcineurin inhibitors in the early post-LTx period, when the risk of acute cellular rejection is the greatest. Calcineurin inhibitors produce intense renal vasoconstriction, which may be reversible early on. Over time, however, irreversible changes, such as vascular angiopathy, tubular atrophy and eventually interstitial fibrosis, contribute to permanent reduction in renal perfusion and glomerular filtration. Thus, interventions to preserve renal function after LTx would be most effective in the early post-LTx period, when most reduction in renal function occurs and when renal vascular changes are potentially reversible. 