Effect of omeprazole on the anticoagulant activity and the pharmacokinetics of warfarin enantiomers in rats

A Study of Proton Pump Inhibitors and Other Risk Factors in Warfarin-Associated Gastrointestinal Bleeding

Background

Warfarin users are at increased risk for gastrointestinal bleeding (GIB). History of GIB, stroke, cardiovascular or chronic kidney disease, age greater than 65 years, and drug interaction with proton pump inhibitors (PPI) have previously been identified as risk factors for GIB in warfarin users. We hypothesized that concomitant use of warfarin and PPI would increase the incidence of GIB relative to warfarin use alone.

Methods

We did a retrospective review of medical records of 626 patients taking warfarin for at least two weeks. Parameters including age, concomitant medication use (non-steroidal anti-inflammatory drugs (NSAID), aspirin, selective serotonin reuptake inhibitors (SSRIs), PPI, and anti-platelet drug), history of GIB, chronic renal failure (CRF), and peptic ulcer disease (PUD) prior to warfarin use were analyzed.

Results

Variables that increase the likelihood of bleeding in warfarin users included aspirin, PPI, history of PUD, history of previous GIB, CRF, and elevated prothrombin time (PT)/international normalized ratio (INR) values. Concomitant antiplatelet use showed a slight increase in GIB but this was not statistically significant (p=0.082). NSAID use and SSRI use were not associated with a higher risk of GIB among warfarin users. Patients who are on PPI and warfarin simultaneously are more likely to be on acetylsalicylic acid (ASA) or have a history of PUD, GIB, or CRF, all of which are associated with increased incidences of GIB.

Conclusions

Although concomitant use of warfarin and PPI appears to be associated with an increased incidence of GIB, these patients are more likely to have other risk factors that also increase the risk of a GIB outcome. Therefore, the interaction between PPI and warfarin is clinically insignificant.

Validation and Application of a Simple UHPLC-MS-MS Method for the Enantiospecific Determination of Warfarin in Human Urine

A simple and rapid liquid chromatographic-tandem mass spectrometric method has been developed and validated for the enantiospecific determination of R- and S-warfarin in human urine. Warfarin enantiomers were extracted from urine using methyl tert-butyl ether. Chromatographic separation of warfarin enantiomers and the internal standard d5-warfarin was achieved using a Astec Chirobiotic V column with gradient mobile phase at a flow rate of 400 µL/min over 10 min. Detection was performed on a TSQ Quantum Ultra triple quadrupole mass spectrometer equipped with a heated electrospray ionization source. Analytes were detected in negative ionization mode using selected reaction monitoring. Calibration curves were linear with a correlation coefficient of ≥0.996 for both enantiomers over a concentration range of 5-500 ng/mL. The intra- and interday accuracy and precision for both analytes were within ±9.0%. Excellent extraction efficiency and negligible matrix effects were observed. The applicability of the method was demonstrated by successful measurement of warfarin enantiomers in urine of patients with kidney disease. The method is simple, accurate and reproducible and is currently being used to support warfarin pharmacokinetic studies.

Effects of etravirine on the pharmacokinetics and pharmacodynamics of warfarin in rats

BACKGROUND AND PURPOSE

Warfarin is often used with etravirine (ETV) to prevent HIV-related thromboembolic events. As both warfarin and ETV bind to plasma proteins and are metabolized by hepatic cytochrome P450s, they are likely to interact. Hence, we evaluated the effect of ETV on the pharmacokinetics and blood clotting time of racemic warfarin in rats.

EXPERIMENTAL APPROACH

Two groups of male Sprague-Dawley rats, in which the jugular vein had been cannulated, were studied. The control group (n = 10) received 1 mg·kg(-1) racemic warfarin i.v., and the test group (n = 13) 1 mg·kg(-1) of racemic warfarin followed by 25 mg·kg(-1) ETV i.v. Serial blood samples were collected for up to 144 h and the blood clotting time (calculated as international normalized ratio [INR]) measured in blood plasma at each sample point. Plasma concentrations of R-warfarin, S-warfarin, R-7-hydroxywarfarin and S-7-hydroxywarfarin were measured by a LC/MS/MS method using a chiral lux cellulose-1 column. Pharmacokinetic parameters were analysed using non-compartmental methods.

KEY RESULTS

ETV significantly increased, by threefold, the systemic clearance and volume of distribution of S-warfarin, but not those of R-warfarin. ETV decreased the total AUC of warfarin, but had no effect on its elimination half-life. ETV also increased the systemic clearance of both R-7-hydroxywarfarin and S-7-hydroxywarfarin but only increased the volume of distribution of R-7-hydroxywarfarin. Interestingly, the effect of warfarin on blood clotting time (INR) was significantly increased in the presence of etravirine.

CONCLUSION AND IMPLICATIONS

Our data suggest that etravirine may potentiate the anticoagulant effect of warfarin and this could have clinical significance.

Effect of rutin on warfarin anticoagulation and pharmacokinetics of warfarin enantiomers in rats

Objectives

The effects of the flavonoid rutin on the anticoagulant activity of oral warfarin and the protein binding and pharmacokinetics of its enantiomers were investigated in rats.

Methods

A single dose of racemic warfarin, 1.5 mg/kg, was administered orally to rats either alone or on day 5 of an 8-day oral regimen of rutin, 1 g/kg daily.

Results

Rutin reduced the anticoagulant effect of racemic warfarin, evident as a 31% reduction in the area under the prothrombin complex activty–time curve (P < 0.05).

Key findings

Rutin had no apparent effect on pre-treatment baseline blood coagulation. It enhanced the in-vitro serum protein binding of S- and R-warfarin (reflected by 40% and 26% reductions in unbound fraction, respectively), and thus restricted distribution by 33 and 21%, respectively. Treatment with rutin significantly decreased the elimination half-life of S-warfarin by 37% as a result of the 69% increase in unbound clearance of the S-enantiomer. This effect was attributed to a significant 77% increase in the unbound formation clearance of the overall oxidative and reductive metabolites, and an increase in the unbound renal clearance of the more potent S-enantiomer of warfarin.

Conclusions

Concurrent rutin administration is likely to reduce the anticoagulant effect of racemic warfarin, reflecting a significant decrease in the elimination half-life of the more potent S-enantiomer.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.