The use of bivalirudin in patients with renal impairment

The majority of patients with acute coronary syndromes have renal impairment from either the aging process or from underlying disease, such as nephrosclerosis or diabetes. For example, in the phase 3 studies of bivalirudin use in PTCA, only 25% of patients had normal renal function: 46% had mild renal impairment, 28% had moderate renal impairment and about 1% had severe renal impairment. In patients with normal renal function, the intravenous pharmacokinetics of bivalirudin are dose proportional (linear) and are characterized by rapid plasma clearance (4.58 ml/minute/kg), a small volume of distribution (0.2 L/kg), and an elimination half-life of about 30 minutes. Renal clearance is the primary route of elimination of bivalirudin. As for other small polypeptides, bivalirudin is filtered at the glomerulus, secreted in the proximal convoluted tubule, reabsorbed in the distal convoluted tubule and degraded within intracellular lysosomes to constituent amino acids. There is a direct positive relationship between the dose of bivalirudin, plasma concentrations and the activated partial thromboplastin time (aPTT) or activated clotting time (ACT). A study comparing the pharmacokinetics and pharmacodynamics of bivalirudin with normal renal function (GFR greater than or = 90 ml/minute; n = 8), mild (GFR 60-89 ml/minute; n = 8), moderate (GFR 30-59 ml/minute; n = 7), or severe (GFR < 30 ml/minute; n = 10) renal impairment showed that while clearance was similar in the normal (4.58 ml/minute/kg) and mildly impaired (4.94 ml/minute/kg) groups, the clearance rate was reduced 45% in the moderate impairment (2.50 ml/minute/kg) group and about 68% in the severe impairment (1.46 ml/minute/kg) group. Clearance was further reduced (77%) in a group of 12 dialysis dependent patients (1.04 ml/minute/kg). There was a strong positive correlation between plasma bivalirudin concentrations and aPTT. The derived maximal effect (Emax) was similar for the normal (58.3 seconds), mildly impaired (44.7 seconds) and moderately impaired (56.8 seconds) groups, but prolonged in the severely renally impaired (79.4 seconds) and dialysis dependent (84.4 seconds) patients. These kinetic and dynamic results have recently been substantially confirmed in patients undergoing percutaneous transluminal coronary angioplasty (PTCA), where reduced plasma clearance (20%) and elevated ACTs were observed in patients with moderate renal impairment. The bleeding results of the phase 3 PTCA clinical trial (involving 4,312 patients) in which patients were classified as having normal renal function, or mild, moderate or severe renal impairment (using the above criteria), is consistent with the pharmacokinetic data. The incidence of major bleeding was directly correlated with renal function for both bivalirudin (normal, 1.2%; mild, 1.9%; moderate, 6%; severe, 0%) and heparin (normal, 3.1%; mild, 8.5%; moderate, 12.7%; severe, 26.7%). Importantly, the incidence of major bleeding was significantly less on bivalirudin than heparin in patients with any degree of renal impairment. The mean 45-minute ACT values were similar (350-400 seconds) in the normal, mild and moderately impaired groups, but elevated in the severely impaired group (450 seconds). A multivariate analysis of bleeding covariates in this database indicated that GFR is an important risk factor for bleeding (r(2) = 0.054), and accounted for twice the variability in bleeding as either sex or age.