Among the 2446 patients who received tacrine in clinical trials , ALT levels greater than the upper limit of normal ( ULN ) occurred on at least one occasion in 1203 patients ( 49 % ) , ALT levels greater than three times the ULN occurred in 621 patients ( 25 % ) , and ALT levels greater than 20 times the ULN occurred in 40 patients ( 2 % ) .
