Dipyrone metabolism in liver disease

Metamizole-Associated Risks in Decompensated Hepatic Cirrhosis

BACKGROUND

Because of the increased risk of acute renal failure (ARF), the use of cyclooxygenase (COX) inhibitors is not recommended in patients with decompensated hepatic cirrhosis. Metamizole is not a classic COX inhibitor, but there are insufficient data to support its safe use. In this study, we investigate the effect of metamizole on the risk of ARF in these patients.

METHODS

Metamizole use, ARF incidence, and patient mortality were examined in a large, retrospective, exploratory cohort and validated with data from a prospective registry.

RESULTS

523 patients were evaluated in the exploratory cohort. Metamizole use at baseline was documented in 110 cases (21%) and was independently associated with the development of ARF, severe (grade 3) ARF, and lower survival without liver transplantation at follow-up on day 28 (HR: 2.2, p < 0.001; HR: 2.8, p < 0.001; and HR: 2.6, p < 0.001, respectively). Interestingly, the risk of ARF depended on the dose of metamizole administered (HR: 1.038, p < 0.001). Compared to patients who were treated with opioids, the rate of ARF was higher in the metamizole group (49% vs. 79%, p = 0.014). An increased risk of ARF with metamizole use was also demonstrated in the independent validation cohort (p < 0.001).

CONCLUSION

Metamizole therapy, especially at high doses, should only be used with a high level of caution in patients with decompensated cirrhosis.

Pharmacokinetics of dipyrone in horses: A multi-dose, dose escalation study

Dipyrone is a non-opioid, nonsteroidal anti-inflammatory drug with antipyretic and analgesic properties commonly used in horses. Dipyrone is rapidly hydrolyzed to the primary active metabolite 4-methylaminoantipyrine (4-MAA). The purpose of this study was to determine the pharmacokinetic profile of 4-MAA following repeated and escalating doses of intravenously administered dipyrone. Twenty-six horses were randomly allocated to five treatment groups (one placebo group and four dipyrone groups [30 mg/kg q8h, 30 mg/kg q12h, 60 mg/kg q8h, and 90 mg/kg q12h]) and treated for nine consecutive days. Blood was collected at predetermined timepoints, and plasma was analyzed for 4-MAA concentrations with a validated LC/MS/MS method. Following a single dose, there was a linear correlation to the maximum concentration (Cmax ) achieved. There was a disproportionate increase in the minimum concentration (Cmin ) of 4-MAA with accumulation occurring at higher doses or more frequent dosing intervals. Significant differences were noted in 4-MAA Cmax , half-life, and area under the curve during the dosing interval (AUCtau ) when dipyrone was administered at 30 mg/kg q12h versus q8h. Adverse effects attributed to drug administration were not noted.

Cytochrome P450 1A2 is the most important enzyme for hepatic metabolism of the metamizole metabolite 4-methylaminoantipyrine

Aims

Metamizole (dipyrone) is a prodrug not detectable in serum or urine after oral ingestion. The primary metabolite, 4‐methylaminoantipyrine (4‐MAA), can be N‐demethylated to 4‐aminoantipyrine (4‐AA) or oxidized to 4‐formylaminoantipyrine (4‐FAA) by cytochrome P450 (CYP)‐dependent reactions. We aimed to identify the CYPs involved in 4‐MAA metabolism and to quantify the effect of CYP inhibition on 4‐MAA metabolism.

Methods

We investigated the metabolism of 4‐MAA in vitro using CYP expressing supersomes and the pharmacokinetics of metamizole in the presence of CYP inhibitors in male subjects.

Results

The experiments in supersomes revealed CYP1A2 as the major CYP for 4‐MAA N‐demethylation and 4‐FAA formation with CYP2C19 and CYP2D6 contributing to N‐demethylation. In the clinical study, we investigated the influence of ciprofloxacin (CYP1A2 inhibitor), fluconazole (CYP2C19 inhibitor) and the combination ciprofloxacin/fluconazole on the pharmacokinetics of metamizole in n = 12 male subjects in a randomized, placebo‐controlled, double‐blind study. The geometric mean ratios for the area under the concentration–time curve of 4‐MAA after/before treatment were 1.17 (90% CI 1.09–1.25) for fluconazole, 1.51 (90% CI 1.42–1.60) for ciprofloxacin and 1.92 (90% CI 1.81–2.03) for ciprofloxacin/fluconazole. Fluconazole increased the half‐life of 4‐MAA from 3.22 hours by 0.47 hours (95% CI 0.13–0.81, P < .05), ciprofloxacin by 0.69 hours (95% CI 0.44–0.94, P < .001) and fluconazole/ciprofloxacin by 2.85 hours (95% CI 2.48–3.22, P < .001).

Conclusion

CYP1A2 is the major CYP for the conversion of 4‐MAA to 4‐AA and 4‐FAA. The increase in 4‐MAA exposure by the inhibition of CYP1A2 and by the combination CYP1A2/CYP2C19 may be relevant for dose‐dependent adverse reactions of 4‐MAA.

Postoperative bleeding after dental extraction in liver pretransplant patients

PURPOSE

The aim of this prospective observational study was to evaluate the incidence of postoperative bleeding after dental extraction in candidates for liver transplantation and the efficacy of the association of tranexamic acid and absorbable hemostatic sponges.

PATIENTS AND METHODS

All individuals referred for oral health evaluation requiring extraction were considered in this study. Patients were included in the analysis when the blood examinations showed a platelet count of 30,000/mm(3) or greater and an international normalized ratio (INR) of 3.0 or less. In group 1 local pressure was applied by use of gauze soaked with tranexamic acid, and in group 2 gauze without tranexamic acid was used. Absorbable hemostatic sponges and cross sutures were used as a standard hemostatic measure.

RESULTS

In the 23 patients included in this study, 84 simple extractions were performed during 35 dental surgical procedures. The main preoperative blood tests found the following: a mean hematocrit level of 34.54% (SD, 5.84%; range, 21.7%-44.4%), platelet counts from 31,000/mm(3) to 160,000/mm(3), and a mean INR of 1.50 (SD, 0.39; range, 0.98-2.59). Postoperative bleeding occurred during only 1 procedure (2.9%), and local pressure with gauze was effective for achieving hemostasis. No statistically significant difference in the time to hemostasis was found between the 2 groups.

CONCLUSIONS

This study found a low risk of bleeding for tooth extractions in patients with liver cirrhosis, INRs of 2.50 or less, and platelet counts of 30,000/mm(3) or greater. Blood transfusions were not needed, and in the case of postoperative bleeding, the use of local hemostatic measures was satisfactory.

Stripping Voltammetric Determination of Analgesics in Their Pharmaceuticals Using Nano-Riboflavin-Modified Glassy Carbon Electrode

Cyclic voltammetric behaviors of three analgesics, acetaminophen (AAP), acetylsalicylic acid (ASA), and dipyrone (DP), were studied using nano-riboflavin-modified glassy carbon electrode. One well-defined oxidation peak each for AAP and ASA and three oxidation peaks for DP were observed. The influence of pH, scan rate, and concentration reveals irreversible diffusion controlled reaction. The SEM analysis confirmed good accumulation of the drugs on the electrode surface. Calibration was made under the maximum peak current conditions. The concentration range studied for the determination of drugs was 0.02 to 0.4 μg mL−1for AAP and ASA and 0.025 to 0.4 μg mL−1for DP. The lower limit of detection observed for AAP, ASA, and DP was 0.016, 0.007 μg mL−1, and 0.013 μg mL−1, respectively. The suitability of the method for the determination of these analgesics in pharmaceutical preparations and urine samples was also ascertained.

Arylamine N-acetyltransferases and drug response

Arylamine N-acetyltransferases (NATs) play an important role in the interaction of competing metabolic pathways determining the fate of and response to xenobiotics as therapeutic drugs, occupational chemicals and carcinogenic substances. Individual susceptibility for drug response and possible adverse drug reactions are modulated by the genetic predisposition (manifested for example, by polymorphisms) and the phenotype of these enzymes. For all drugs metabolized by NATs, the impact of different in vivo enzyme activities is reviewed with regard to therapeutic use, prevention of side effects and possible indications for risk assessment by phenotyping and/or genotyping. As genes of NATs are susceptibility genes for multifactorial adverse effects and xenobiotic-related diseases, risk prediction can only be made possible by taking the complexity of events into consideration.

Comparison of acetylation phenotype with genotype coding for N-acetyltransferase (NAT2) in children

The present study focused on evaluation of the extent to which genotype coding for N-acetyltransferase agrees with acetylation phenotype in children at various ages. In 82 Caucasian children aged from 1 mo to 17 y (57 boys and 25 girls) and including 37 infants, the acetylation phenotype was evaluated from the urinary metabolic ratio of 5-acetylamino-6-formylamino-3-methyluracil (AFMU) to 1-methylxanthine (1X) after oral administration of caffeine. At the same time, by use of PCR and restriction analysis of amplified fragments of the N-acetyltransferase gene, four nucleotide transitions were identified: 481C-->T (KpnI), 590 G-->A (TaqI), 803 A-->G (DdeI), and 857 G-->A (BamHI). The wild-type allele was detected in 27 (33%) children, and the slow acetylation genotype was found in 55 (67%) children. The results of the study show that the metabolic ratio AFMU/1X could be calculated only in 72 children, because in 10 (14%) infants <20 wk of age, AFMU was not detected. Determination of the relation between the acetylation phenotype and genotype revealed that 18 children (23%) containing at least one wild-type allele had AFMU/1X <0.4 (slow acetylation activity) and 7 (8%) of genotypically slow acetylators presented high metabolic ratio (high acetylation activity). We concluded that the disagreement between the acetylation phenotype and genotype is more often found in the group of children characterized by low AFMU/1X and that in small children only N-acetyltransferase genotype studies enable the detection of genetic acetylation defect.

Selective effect of liver disease on the activities of specific metabolizing enzymes: investigation of cytochromes P450 2C19 and 2D6

BACKGROUND AND OBJECTIVES

Drug metabolism is influenced by liver disease because of the central role that the liver plays in metabolic activities in the body. However, it is still unclear how activities of specific drug-metabolizing enzymes are influenced by the presence and severity of liver disease. As a consequence, alteration in metabolism of specific drugs cannot be easily predicted or appropriate dosage adjustment recommendations made.

METHODS

The activities of cytochromes P450 (CYP) 2C19 and 2D6 were investigated in a group of patients with mild or moderate liver disease (n = 18) and a group of healthy control subjects (n = 10). The disposition of racemic mephenytoin for CYP2C19 and debrisoquin for CYP2D6 were characterized in plasma and urine samples collected over 192 hours.

RESULTS

The elimination of S-mephenytoin was severely reduced among patients with liver disease, resulting in a 79% decrease in plasma clearance for all patients combined. This reduction was related to the severity of disease, patients with moderate disease being affected more severely than patients with mild disease. Similar differences were observed in the urinary excretion of 4'-hydroxymephenytoin metabolite. By contrast, there was no effect on the disposition of R-mephenytoin or debrisoquin.

CONCLUSION

These results show selectivity in the effect of liver disease on activities of specific metabolizing enzymes, CYP2C19 being more sensitive than CYP2D6. They suggest that recommendations for modification in drug dosage in the presence of liver disease should be based on knowledge of the particular enzyme involved in metabolism of the drug. The results emphasize the need for further studies of each specific drug-metabolizing enzyme in the presence of liver disease.

Drug acetylation in liver disease

N-Acetylation is a phase II conjugation reaction mediated in humans by the polymorphic N-acetyltransferase 2 (NAT2) and N-acetyltransferase 1 (NAT1). Acetylation of some drugs may be modestly decreased in patients with chronic liver disease, whereas acute liver injury has no effect on drug acetylation. For NAT2 substrates, the impairment in acetylation capacity seems to be phenotype-specific, with a more prominent effect being exerted in rapid than slow acetylators. Thus, in the presence of significant hepatic dysfunction, the activity of NAT2 may not exhibit its usual bimodal distribution, and hence phenotypic assignment may not be reliable. Furthermore, it remains to be evaluated whether the precautions advised for slow acetylators when treated with drugs metabolised by NAT2 apply to all patients (regardless of phenotype) with liver cirrhosis.

Impairment of the metabolism of dipyrone in asymptomatic carriers of the hepatitis B virus

BACKGROUND

The pharmacokinetics of a number of drugs has been shown to be impaired in patients with acute or chronic viral liver disease.

OBJECTIVE

To examine the effect of the asymptomatic hepatitis B virus carrier state on the metabolism of dipyrone (INN, metamizole) as a model drug.

METHODS

The pharmacokinetics of the metabolites of dipyrone-4-methylaminoantipyrine, 4-aminoantipyrine, 4-formylaminoantipyrine, and 4-acetylaminoantipyrine-after a 1.0 gm oral dose of dipyrone were evaluated in nine asymptomatic carriers of hepatitis B virus with normal liver function tests and nine healthy subjects. All subjects displayed the slow acetylator phenotype.

RESULTS

The nonrenal (metabolic) clearance of 4-methylaminoantipyrine was significantly reduced (mean +/- SEM) (123.3 +/- 15.8 versus 182.9 +/- 15.1 ml.min-1, respectively; p < 0.02) in the carriers of hepatitis B virus compared with the healthy subjects, and the elimination half-life of this metabolite was significantly longer (3.69 +/- 0.35 versus 2.64 +/- 0.28 hours, respectively; p < 0.03). The formation clearances of 4-aminoantipyrine and 4-formylaminoantipyrine were significantly smaller in the carriers of hepatitis B virus compared with healthy subjects (33.8 +/- 6.2 versus 55.2 +/- 6.4 ml.min-1; p < 0.03, and 16.7 +/- 2.2 versus 34.2 +/- 4.2 ml.min-1; p < 0.002; respectively). However, the elimination half-life of 4-formylaminoantipyrine was found to be slightly shorter in the carriers of hepatitis B virus. No significant differences were noted between the groups in the pharmacokinetics of 4-acetylaminoantipyrine.

CONCLUSION

The metabolism of dipyrone is impaired in asymptomatic carriers of hepatitis B virus. Clinically latent infection with hepatitis B virus seems to exert a differential effect on metabolism of the drug. Oxidative pathways to produce 4-aminoantipyrine and 4-formylaminoantipyrine were significantly affected, whereas acetylation remained intact. This study provided an additional example of the effect of a virus on the disposition of a drug.