The effect of 1g of acetaminophen twice daily for 12 weeks on alanine transaminase levels--A randomized placebo-controlled trial.

Acetaminophen is often used on a regular, daily basis for the treatment of chronic pain; however, the safety of regular acetaminophen is still debated. This study determined whether 12 weeks of treatment with acetaminophen at half the maximum recommended daily dose causes an increase in alanine transaminase (ALT) in healthy adults participating in a clinical trial of the effect of acetaminophen on asthma control and severity. 94 healthy adults aged 18-65 years with mild to moderate asthma and with no history of previous liver dysfunction and an ALT within 1.5 times the upper limit of normal at baseline participated in a randomized, double-blind, placebo-controlled, parallel-group, clinical trial of 1g of acetaminophen twice daily or placebo twice daily for 12 weeks. Liver function monitoring was undertaken at baseline, weeks 2, 4, 6 and 12. The primary outcome variable was mean ALT levels at week 12 compared to baseline in the acetaminophen group versus placebo group. 94 participants were randomized and commenced study treatment. One participant in each treatment group was withdrawn due to an increase in ALT to greater than three times the upper limit of normal. Mean ALT at week 12 was 25.4I U/L (SD 9.7) in the acetaminophen group (N=31) and 19.0 IU/L (SD 6.0) in the placebo group (N=54). After controlling for baseline this represented a statistically significant difference of 3.6 IU/L (95% CI 1.3 to 6.0, P=0.003). There was no progressive increase in ALT demonstrated throughout the trial. Regular, daily use of acetaminophen at half the maximum recommended daily dose for 12 weeks in a healthy adult population is associated with a small elevation in mean ALT of no probable clinical significance. Further assessment of the effects on liver function of the maximum recommended dose of acetaminophen is required.