- Renal: Age equal to or older than 12: The estimated creatinine clearance (CrCl) must be equal or greater than 60 mL/min/1.73 m2 as calculated by the Cockcroft-Gault Formula. Age younger than 12: Either estimated or measured CrCl should be greater than 90 ml/min/1.73m2. For estimation, Schwartz formula will be used.