Retrospective analysis of transient elevations in alanine aminotransferase during long-term treatment with acetaminophen in osteoarthritis clinical trials.

Background: In two recent osteoarthritis trials, alanine aminotransferase (ALT) elevations were observed more frequently in patients receiving acetaminophen 3.9 g daily than in patients receiving placebo, and the rates were higher than aminotransferase values observed in some previous osteoarthritis studies with acetaminophen.

Objective: To retrospectively analyze ALT data from McNeil osteoarthritis clinical studies involving acetaminophen in order to assess the frequency and magnitude of ALT elevations and rate of ALT resolution while patients remained on acetaminophen treatment. A review of the literature revealed a few reports of isolated aminotransferase elevations occurring during acetaminophen therapy, but these reports were not included in the analysis because they did not include enough information to evaluate the frequency, magnitude, and rate of ALT elevations while patients remained on acetaminophen treatment.

Research Design And Methods: Nine controlled clinical trials were identified in which at least one of the treatments was acetaminophen alone. Studies were included if patients had ALT and aspartate aminotransferase (AST) values obtained at baseline and an ALT value at an additional visit after initiating therapy. Seven studies met these criteria and were included in this analysis. In these studies, patients received acetaminophen 1950-4000 mg/day for 4 weeks up to 12 months. Laboratory testing was performed at weeks 0 and 4 in the three 4-week studies; at weeks 0, 2, 4, 8, and 12 in the two 12-week studies; at weeks 0, 1, 2, 4, 6, 8, and 13 in the 13-week study; and at months 0, 1, 3, 6, 9, and 12 in the 12-month study. The pooled data set consisted of patient demographics, dosing records, aminotransferase and bilirubin laboratory values, and adverse events.

Results: There were no reports of hepatotoxicity or hepatic failure in any acetaminophen-treated patient (n = 1530). In the seven studies, 1039 patients had both baseline AST and ALT activity < or = upper limit of the reference range and an on-treatment ALT measurement. While on long-term acetaminophen treatment, 181 of 1039 (17.4%) patients had an ALT value that exceeded the upper limit of the reference range. None of the 1039 patients had an on-treatment ALT level > 3 times upper limit of the reference range in conjunction with a serum bilirubin > upper limit of the reference range, and no patient had an ALT level > 10 times upper limit of the reference range. Of the 1039 patients, 44 (4.2%) had an on-treatment ALT level > 1.5 times upper limit of the reference range, and 31 of the 44 patients had a subsequent measurement of ALT. Of these 31 patients, 29 (93.5%) had documented resolution or decreasing ALT while on treatment. An ALT level > 1.5 times upper limit of the reference range was not associated with a higher frequency of symptoms potentially related to hepatic origin.

Limitations: The studies included in this analysis were limited to McNeil studies, none of which were designed to specifically evaluate the patterns of ALT activity. Thus, the incidence of ALT elevations after any specific duration of dosing, and the temporal pattern of ALT elevations, cannot be accurately determined. In addition, methodological differences existed across the studies.

Conclusion: This analysis involving > 1000 acetaminophen-treated patients shows that low-level, transient ALT elevations usually resolve or decrease with continued acetaminophen treatment, are unaccompanied by signs or symptoms of liver injury, and, as such, appear to be clinically insignificant. Maximum recommended daily doses of acetaminophen did not cause liver failure or dysfunction.