6. Creatinine clearance ≥70ml/min directly measured with 24hr urine collection or calculated according to the modified formula of Cockcroft and Gault (for men: GFR ≈ ((140 - age) x bodyweight) / (72 x creatinine), for women x 0, 85). Dehydrated patients with an estimated creatinine clearance less than 70 ml/min may be eligible if a repeat estimate after adequate hydration is > 70 ml/min