Effect of the catechol-O-methyltransferase inhibitor entacapone on the steady-state pharmacokinetics and pharmacodynamics of warfarin

Drug Interactions Affecting Oral Anticoagulant Use

Oral anticoagulants (OACs) are medications commonly used in patients with atrial fibrillation and other cardiovascular conditions. Both warfarin and direct oral anticoagulants are susceptible to drug-drug interactions (DDIs). DDIs are an important cause of adverse drug reactions and exact a large toll on the health care system. DDI for warfarin mainly involve moderate to strong inhibitors/inducers of cytochrome P450 (CYP) 2C9, which is responsible for the elimination of the more potent S-isomer of warfarin. However, inhibitor/inducers of CYP3A4 and CYP1A2 may also cause DDI with warfarin. Recognition of these precipitating agents along with increased frequency of monitoring when these agents are initiated or discontinued will minimize the impact of warfarin DDI. Direct oral anticoagulants are mainly affected by medications strongly affecting the permeability glycoprotein (P-gp), and to a lesser extent, strong CYP3A4 inhibitors/inducers. Dabigatran and edoxaban are affected by P-gp modulation. Strong inducers of CYP3A4 or P-gp should be avoided in all patients taking direct oral anticoagulant unless previously proven to be otherwise safe. Simultaneous strong CYP3A4 and P-gp inhibitors should be avoided in patients taking apixaban and rivaroxaban. Concomitant antiplatelet/anticoagulant use confers additive risk for bleeding, but their combination is unavoidable in many cases. Minimizing duration of concomitant anticoagulant/antiplatelet therapy as indicated by evidence-based clinical guidelines is the best way to reduce the risk of bleeding.

Edoxaban and the Issue of Drug-Drug Interactions: From Pharmacology to Clinical Practice

Edoxaban, a direct factor Xa inhibitor, is the latest of the non-vitamin K antagonist oral anticoagulants (NOACs). Despite being marketed later than other NOACs, its use is now spreading in current clinical practice, being indicated for both thromboprophylaxis in patients with non-valvular atrial fibrillation (NVAF) and for the treatment and prevention of venous thromboembolism (VTE). In patients with multiple conditions, the contemporary administration of several drugs can cause relevant drug-drug interactions (DDIs), which can affect drugs' pharmacokinetics and pharmacodynamics. Usually, all the NOACs are considered to have significantly fewer DDIs than vitamin K antagonists; notwithstanding, this is actually not true, all of them are affected by DDIs with drugs that can influence the activity (induction or inhibition) of P-glycoprotein (P-gp) and cytochrome P450 3A4, both responsible for the disposition and metabolism of NOACs to a different extent. In this review/expert opinion, we focused on an extensive report of edoxaban DDIs. All the relevant drugs categories have been examined to report on significant DDIs, discussing the impact on edoxaban pharmacokinetics and pharmacodynamics, and the evidence for dose adjustment. Our analysis found that, despite a restrained number of interactions, some strong inhibitors/inducers of P-gp and drug-metabolising enzymes can affect edoxaban concentration, just as it happens with other NOACs, implying the need for a dose adjustment. However, our analysis of edoxaban DDIs suggests that given the small propensity for interactions of this agent, its use represents an acceptable clinical decision. Still, DDIs can be significant in certain clinical situations and a careful evaluation is always needed when prescribing NOACs.

Drug Safety Analysis in a Real-Life Cohort of Parkinson's Disease Patients with Polypharmacy

BACKGROUND

Polypharmacy is common in geriatric Parkinson's disease (PD) patients in advanced disease stages with multiple comorbidities, bearing multiple risks for drug safety in theory.

OBJECTIVE

The aim of this study was to empirically identify the most frequent and relevant contraindications and drug interactions actually occurring and compromising drug safety in PD in real life.

METHODS

We conducted a prospective observational study in a multimorbid cohort of PD patients with polypharmacy admitted to a specialized hospital. Inclusion criteria were the presence of at least one comorbidity requiring pharmacotherapy and at least five different drugs in the discharge prescription. Hoehn and Yahr stage during the 'on' state, therapeutic problems related to motor and non-motor PD symptoms, comorbidities, and drug regimens on admission and discharge were analyzed for contraindications and interactions.

RESULTS

Overall, 127 patients were included (medium Hoehn and Yahr stage = IV, range II-V). Interactions with the anti-PD medication were mainly caused by other central nervous system (CNS)-active substances, cytochrome P450-metabolized substances, and QT-time prolonging substances. Contraindications against the anti-PD medication mainly occurred from internal, haematopoietic, neurologic and psychiatric diseases, and QT-time prolonging drugs. The highest frequency of interactions and contraindications were identified with levodopa (n = 119 at admission/n = 126 at discharge), entacapone (n = 46/42), pramipexole (n = 44/24), and amantadine (n = 32/30).

CONCLUSIONS

Several medically relevant risk factors (interactions and contraindications) frequently occurred in advanced PD patients. These findings provide a basis for developing programmes for awareness, education, monitoring, and preventive interventions to avoid adverse incidents. Future studies will need to evaluate preventive efficacy of structured drug safety programmes.

Absence of an effect of T89 on the steady-state pharmacokinetics and pharmacodynamics of warfarin in healthy volunteers

This open-label, multi-dose, single-center, sequential, inpatient study evaluated the effects of a two herb combination drug (T89, Danshen plus Sanqi) on the steady-state pharmacodynamics (PD) and pharmacokinetics (PK) of warfarin in 24 healthy volunteers. Twenty-three subjects attained a stable international normalized ratio (INR) by taking warfarin alone prior to 1-week of added-on use of T89. INR was not increased after the addition of T89 for 7 days (P > .05). The 90% confidence interval (CI) of the geometric mean ratio for maximum plasma concentrations (Cmax) and area under curve (AUClast ) of both R- and S-warfarin when warfarin was administered with or without T89 was within the 0.80 to 1.25 equivalence ratio. These results indicate that T89 has no effect on the steady-state PD and PK of warfarin. Warfarin and T89 dose adjustments are not required when these two drugs are co-administrated in clinical practice.

Pharmacokinetics and Pharmacodynamics of Warfarin When Coadministered With Pentosan Polysulfate Sodium

The effect of pentosan polysulfate sodium on warfarin pharmacokinetics and pharmacodynamics was investigated in healthy subjects. Warfarin was titrated to an international normalized ratio between 1.4 and 1.8. Subjects continued their titrated dose of warfarin and received pentosan polysulfate sodium 100 mg or placebo every 8 hours for 7 days. The Cmax of R- and S-warfarin was approximately 840 to 890 ng/mL and 680 to 730 ng/mL, respectively, and was similar in the absence and presence of pentosan polysulfate sodium. The half-life for R- and S-warfarin was 52 to 56 hours and 36 to 40 hours, respectively. Prothrombin time, partial thromboplastin time, and the international normalized ratio for warfarin + placebo and warfarin + pentosan polysulfate sodium were comparable. The AUC(INR) indicated no treatment effect (P = .772); however, there was a period effect. Analysis of variance for the treatments by period indicated no treatment effect (P > .1). Adverse events were mild and included headache, epistaxis, and rash. Most adverse events were unrelated to treatment and were seen during warfarin titration. Pentosan polysulfate sodium did not affect warfarin pharmacokinetics or pharmacodynamics.

Effects of duloxetine on the pharmacodynamics and pharmacokinetics of warfarin at steady state in healthy subjects

This study evaluated the pharmacodynamics and pharmacokinetics of once-daily dosing of warfarin at steady state when taken concomitantly with once-daily doses of duloxetine. Healthy subjects with a stable international normalized ratio (INR) of 1.5 to 2.0 on an individualized fixed dose of warfarin (2-9 mg) in period 1 received daily warfarin and duloxetine (60 mg for 14 days [n = 15] or 60 mg for 4 days, then 120 mg for 10 days [n = 15]) in period 2. Across the 14-day period when warfarin was coadministered with duloxetine, the least squares mean INR changes from baseline (warfarin alone) ranged from -0.05 to +0.07, and the 90% confidence intervals ranged from -0.12 to +0.14. Following coadministration of warfarin with 60 mg duloxetine, but not with 120 mg duloxetine, there was a statistically significant prolongation in bleeding time compared to warfarin alone. For both R- and S-warfarin, the 90% confidence interval for the geometric mean ratios of area under the curve (AUC(tau,ss)) and maximum plasma concentrations (C(max,ss)) between warfarin administered alone and with 60 or 120 mg duloxetine were contained within the bioequivalence limits of 0.8 to 1.25. In conclusion, duloxetine had no clinically or statistically significant effect on the pharmacodynamics or pharmacokinetics of warfarin at steady state.

Drug interaction studies with dexlansoprazole modified release (TAK-390MR), a proton pump inhibitor with a dual delayed-release formulation: results of four randomized, double-blind, crossover, placebo-controlled, single-centre studies

BACKGROUND AND OBJECTIVE

Most proton pump inhibitors are extensively metabolized by cytochrome P450 (CYP) isoenzymes, as are many other drugs, giving rise to potential drug-drug interactions. Dexlansoprazole modified release (MR) [TAK-390MR] is a modified-release formulation of dexlansoprazole (TAK-390), an enantiomer of lansoprazole, which employs an innovative Dual Delayed Release technology designed to prolong the plasma dexlansoprazole concentration-time profile following once-daily oral administration. As with lansoprazole, dexlansoprazole is metabolized mainly by CYP3A and CYP2C19. Based on in vitro studies, dexlansoprazole has the potential to inhibit activity of these isoenzymes and also may induce human hepatic CYP1A and CYP2C9 activity. To determine whether dexlansoprazole has an effect on these isoenzymes in vivo, drug interaction studies with dexlansoprazole MR were conducted.

METHODS

Four separate randomized, double-blind, two-way crossover, placebo-controlled, single-centre studies were conducted in healthy volunteers to evaluate the effect of dexlansoprazole on the pharmacokinetics of four test substrates (diazepam, phenytoin, theophylline [administered as intravenous aminophylline] and warfarin), which were selected based on in vitro and/or in vivo data that suggest a potential drug interaction with CYP isoenzymes or potentially coadministered narrow therapeutic index drugs. In each study, dexlansoprazole MR 90 mg or placebo was administered once daily for 9 or 11 days in each period. Subjects received a single dose of test substrate in each study period. Pharmacokinetic parameters of the test substrates were estimated using noncompartmental methods. A conclusion of no effect of dexlansoprazole MR on the test substrate was made if the 90% confidence intervals (CIs) for the ratios of the central values for the observed maximum plasma drug concentration (C(max)) and the area under the plasma concentration-time curve (AUC) of test substrate administered with dexlansoprazole MR versus placebo were within 0.80-1.25 based on an analysis of variance model. The potential for a pharmacodynamic interaction was also assessed for warfarin using prothrombin time, measured as the international normalized ratio. Routine safety assessments were conducted in these studies.

RESULTS

Mean C(max) and AUC values were generally similar for each test substrate when administered with multiple once-daily doses of dexlansoprazole MR or placebo. The 90% CIs for the bioavailability of these test substrates administered with dexlansoprazole MR relative to that obtained when the substrates were administered with placebo were within the bioequivalency range of 0.80-1.25, indicating that multiple doses of dexlansoprazole MR had no effect on the pharmacokinetics of these drugs. Additionally, dexlansoprazole MR had no effect on the pharmacodynamics of warfarin. Administration of these drugs with dexlansoprazole MR 90 mg or placebo was well tolerated; the only serious adverse event, which led to a subject's discontinuation from the study, was considered unrelated to study drugs.

CONCLUSIONS

Coadministration of dexlansoprazole MR with diazepam, phenytoin or theophylline did not affect the pharmacokinetics of these drugs, and therefore is unlikely to alter the pharmacokinetic profile of other drugs metabolized by CYP2C19, CYP2C9, CYP1A2 and perhaps CYP3A. Additionally, dexlansoprazole MR coadministered with warfarin did not affect the pharmacokinetics of the warfarin enantiomers and had no effect on the anticoagulant activity of warfarin. Dexlansoprazole MR was well tolerated in these trials of healthy subjects.