Effects of nutritional status on acetaminophen measurement and exposure.

INTRODUCTION: Fasting, as well as a high-fat diet, might increase the risk on acetaminophen-induced toxicity after an acute overdose. Therefore, it has been suggested to lower the threshold for acetylcysteine treatment to prevent liver injury in case of fasting. This study aims to investigate the effects of 36 hours of fasting and three days of a hypercaloric high-fat diet on acetaminophen measurement and exposure. METHODS: Nine healthy male subjects were enrolled in a randomized crossover intervention study. Subjects received 1000mg oral acetaminophen after an overnight fast following: (1) regular diet,(2) 36h of fasting and (3) three days of a hypercaloric high-fat diet consisting of 500ml of cream (1715 kcal) supplemented to their regular diet. Pharmacokinetic parameters were determined by non-compartmental analysis. Samples were analyzed by an enzymatic colorimetric method used in routine practice and by LC-MS/MS being the gold standard. Agreement between these methods was assessed by the Bland-Altman method. RESULTS: Short-term fasting increased acetaminophen exposure by 20% (ΔAUC0-8 hours, p = .04) in comparison with the control diet. Three days of hypercaloric high-fat diet did not affect acetaminophen exposure (ΔAUC0-8 hours= 9%, p = .67). The intraclass correlation coefficient between the enzymatic assay and LC-MS/MS methods of the fasting samples was 0.46 (0.28-0.61), compared to 0.87 (0.81-0.92) and 0.87 (0.79-0.91) in the control and high-fat samples respectively. CONCLUSIONS: Short-term fasting increases acetaminophen exposure in healthy subjects, whereas no effect is observed after a high-fat diet. Furthermore, short-term fasting decreases the accuracy of the enzymatic colorimetric method when measuring relatively low acetaminophen concentrations. This suggests considering nutritional status when assessing the risk of acetaminophen-induced toxicity, although further research at toxic doses is needed.

Metabolic acidosis caused by concomitant use of paracetamol (acetaminophen) and flucloxacillin? A case report and a retrospective study.

PURPOSE: A patient was identified with severe metabolic acidosis, a high anion gap and 5-oxoproline accumulation, probably caused by the simultaneous use of paracetamol (acetaminophen) and flucloxacillin. We wanted to investigate the necessity to control the interaction between both drugs with an automatic alert system. METHODS: To investigate the relevance of the interaction of paracetamol and flucloxacillin, a retrospective study was conducted. Data on paracetamol and flucloxacillin prescriptions and laboratory data (pH, Na+, HCO3-, Cl-, albumin and 5-oxoproline levels) were combined to assess the prevalence of acidosis, calculate the anion gap and analyse 5-oxoproline levels in clinically admitted patients using both drugs simultaneously. RESULTS: In the 2-year study period, approximately 53,000 admissions took place in our hospital. One thousand and fifty-seven patients used paracetamol and flucloxacillin simultaneously, of which 51 patients (4.8%) had a serum pH ≤ 7.35. One patient, the same patient as presented in the case report, had a high anion gap and a toxic level of 5-oxoproline. CONCLUSION: The prevalence of metabolic acidosis is very low and the only patient identified with the interaction was recognised during normal clinical care. We conclude that automatic alerts based on simultaneous use of paracetamol and flucloxacillin will generate too many signals. To recognise patients earlier and prevent severe outcomes, a warning system (clinical rule) based on paracetamol, flucloxacillin and pH measurement may be helpful. Early calculation of the anion gap can narrow the differential diagnosis of patients with metabolic acidosis and measurement of 5-oxoproline can explain acidosis due the interaction of paracetamol and flucloxacillin.

Fasting-Induced Changes in Hepatic P450 Mediated Drug Metabolism Are Largely Independent of the Constitutive Androstane Receptor CAR.

INTRODUCTION: Hepatic drug metabolism by cytochrome P450 enzymes is altered by the nutritional status of patients. The expression of P450 enzymes is partly regulated by the constitutive androstane receptor (CAR). Fasting regulates the expression of both P450 enzymes and CAR and affects hepatic drug clearance. We hypothesized that the fasting-induced alterations in P450 mediated drug clearance are mediated by CAR. METHODS: To investigate this we used a drug cocktail validated in humans consisting of five widely prescribed drugs as probes for specific P450 enzymes: caffeine (CYP1A2), metoprolol (CYP2D6), omeprazole (CYP2C19), midazolam (CYP3A4) and s-warfarin (CYP2C9). This cocktail was administered to wild type (WT, C57Bl/6) mice or mice deficient for CAR (CAR-/-) that were either fed ad libitum or fasted for 24 hours. Blood was sampled at predefined intervals and drug concentrations were measured as well as hepatic mRNA expression of homologous/orthologous P450 enzymes (Cyp1a2, Cyp2d22, Cyp3a11, Cyp2c37, Cyp2c38 and Cyp2c65). RESULTS: Fasting decreased Cyp1a2 and Cyp2d22 expression and increased Cyp3a11 and Cyp2c38 expression in both WT and CAR-/- mice. The decrease in Cyp1a2 was diminished in CAR-/- in comparison with WT mice. Basal Cyp2c37 expression was lower in CAR-/- compared to WT mice. Fasting decreased the clearance of all drugs tested in both WT and CAR-/- mice. The absence of CAR was associated with an decrease in the clearance of omeprazole, metoprolol and midazolam in fed mice. The fasting-induced reduction in clearance of s-warfarin was greater in WT than in CAR-/-. The changes in drug clearance correlated with the expression pattern of the specific P450 enzymes in case of Cyp1a2-caffeine and Cyp2c37-omeprazole. CONCLUSION: We conclude that CAR is important for hepatic clearance of several widely prescribed drugs metabolized by P450 enzymes. However the fasting-induced alterations in P450 mediated drug clearance are largely independent of CAR.

The impact of CYP2D6-predicted phenotype on tamoxifen treatment outcome in patients with metastatic breast cancer.

BACKGROUND: Cytochrome P450 2D6 (CYP2D6) has a crucial role in the metabolic conversion of tamoxifen into the active metabolite endoxifen. In this cohort study, the effect of CYP2D6-predicted phenotype, defined as the combined effect of CYP2D6 genetic variation and concomitant use of CYP2D6-inhibiting medication, on time to breast cancer progression (TTP) and overall survival (OS) in women who use tamoxifen for metastatic breast cancer (MBC) was examined. METHODS: We selected patients treated with tamoxifen (40 mg per day) for hormone receptor-positive MBC from whom a blood sample for pharmacogenetic analysis (CYP2D6*3, *4, *5, *6, *10 and *41) was available. Patient charts (n=102) were reviewed to assess TTP and OS, and to determine whether CYP2D6 inhibitors were prescribed during tamoxifen treatment. RESULTS: OS was significantly shorter in patients with a poor CYP2D6 metaboliser phenotype, compared with extensive metabolisers (HR=2.09; P=0.034; 95% CI: 1.06-4.12). Co-administration of CYP2D6 inhibitors alone was also associated with a worse OS (HR=3.55; P=0.002; 95% CI: 1.59-7.96) and TTP (HR=2.97; P=0.008; 95% CI: 1.33-6.67) compared with patients without CYP2D6 inhibitors. CONCLUSION: CYP2D6 phenotype is an important predictor of treatment outcome in women who are receiving tamoxifen for MBC. Co-administration of CYP2D6 inhibitors worsens treatment outcome of tamoxifen and should therefore be handled with care.

Crystallization of the A-domain of the mannitol transport protein enzyme IImtl.

The A-domain of the mannitol transport protein enzyme IImtl from Escherichia coli (relative molecular mass 16,300) was crystallized, both at room temperature and 4 degrees C, from 40% polyethylene glycol 6000 (pH 8.5 to 9.0) using the hanging-drop method of vapour diffusion. The crystals have the monoclinic space group P2(1), with unit cell dimensions a = 54.0 A, b = 67.0 A, c = 80.9 A and beta = 100.8 degrees. They diffract to 2.6 A resolution. A self-rotation function and self-Patterson suggest that there are four molecules in the asymmetric unit showing mmm symmetry.