Levels of serum ALT in fast acetylators and slow acetylators. There were 47 fast acetylators and seven slow acetylators in the cohort. Levels of serum ALT in patients with systemic lupus erythematosus were measured 14 day after initiation of co-trimoxazole. Serum ALT levels in slow acetylators were significantly higher than in fast acetylators (median: 82.0 ± 45.3 IU/ml versus 30.0 ± 47.0 IU/ml; *P = 0.0096, by Mann-Whitney U-test). ALT, alanine aminotransferase.