Phenotyping of N-acetyltransferase type 2 and xanthine oxidase with caffeine: when should urine samples be collected?

OBJECTIVES: Individual activities of N-acetyltransferase 2 (NAT2) and of xanthine oxidase (XO) can be assessed using ratios of urinary caffeine metabolites. We investigated how ratios changed over time and which urine collection interval would be the best for NAT2 and XO activity assessments. METHODS: On two occasions separated by 14 days, 16 healthy male Caucasians collected urine before and 0-2, 2-4, 4-6, 6-8, 8-12, 12-16 and 16-24 h after a dose of 150 mg caffeine given in the framework of a phenotyping cocktail study. The metabolites 5-acetylamino-6-formylamino-3-methyluracil (AFMU), 5-acetylamino-6-amino-3-methyluracil (AAMU), 1-methylxanthine (1X), and 1-methylurate (1U) were quantified with LC-MS/MS. The molar ratio (AFMU + AAMU)/(1X + 1U + AFMU + AAMU) was used as a NAT2 metric, while the ratio 1U/(1X + 1U) served as XO metric. RESULTS: The NAT2 ratios were stable in the intervals 4-24 h after caffeine dosing. Mean intra-individual coefficients of variation were 11-23% starting 4 h post-dose, while inter-individual variability reached 37-75%. The XO ratios increased gradually by 14% from the 2-4 to the 16-24 h interval. The mean intra- and inter-individual coefficients of variation of XO activity were 3-18 and 7-10% respectively. No significant differences between study occasions were observed. CONCLUSIONS: Any sampling interval at least 4 h after caffeine dosing is suitable for NAT2 and XO activity assessments. XO activities can only be compared between volunteers and studies if the same urine collection schedule has been respected. The low intraindividual variability allows for sample sizes of 16 and 6 participants in crossover interaction studies of NAT2 and XO activity respectively

Antiviral Therapy Completion and Response Rates Among Hepatitis C Patients With and Without Schizophrenia

Background: Despite disproportionately high rates of hepatitis C (HCV) among patients with severe mental illness, to date, there is scant empirical data available regarding antiviral therapy outcomes within this population. Objective: To compare antiviral therapy completion and response rates between HCV patients with vs those without schizophrenia (SCHZ). Methods: A regional Veterans Healthcare Administration database was used to identify veterans meeting criteria for this retrospective chart review. All patients confirmed to have SCHZ and to have received antiviral therapy between 1998 and 2006 (n = 30) were compared with a control group of demographically matched (HCV genotype, age, race, gender) patients with no history of SCHZ (n = 30). Results: For HCV patients with genotype 1, antiviral completion, end of treatment response (ETR), and sustained viral response (SVR) rates did not significantly differ between groups. For those with genotypes 2 and 3 combined, antiviral therapy completion rates did not significantly differ between groups; however, the SCHZ group was significantly (P < 0.050) more likely to achieve an ETR and an SVR. For all genotypes combined, the SCHZ patients were no more likely than controls to discontinue therapy early for psychiatric symptoms, medical complications, or other adverse events, and groups did not significantly differ in terms of hospitalization rates during antiviral therapy. Conclusion: Our retrospective chart review suggests that patients with SCHZ complete and respond to antiviral therapy for HCV at rates comparable with those without SCHZ. Based on these data, SCHZ should not be considered a contraindication to antiviral therapy for HCV