The effect of anastrozole on the single-dose pharmacokinetics and anticoagulant activity of warfarin in healthy volunteers

Degradation Mechanisms of 4,7-Dihydroxycoumarin Derivatives in Advanced Oxidation Processes: Experimental and Kinetic DFT Study

Coumarins represent a broad class of compounds with pronounced pharmacological properties and therapeutic potential. The pursuit of the commercialization of these compounds requires the establishment of controlled and highly efficient degradation processes, such as advanced oxidation processes (AOPs). Application of this methodology necessitates a comprehensive understanding of the degradation mechanisms of these compounds. For this reason, possible reaction routes between HO^• and recently synthesized aminophenol 4,7-dihydroxycoumarin derivatives, as model systems, were examined using electron paramagnetic resonance (EPR) spectroscopy and a quantum mechanical approach (a QM-ORSA methodology) based on density functional theory (DFT). The EPR results indicated that all compounds had significantly reduced amounts of HO^• radicals present in the reaction system under physiological conditions. The kinetic DFT study showed that all investigated compounds reacted with HO^• via HAT/PCET and SPLET mechanisms. The estimated overall rate constants (k_overall) correlated with the EPR results satisfactorily. Unlike HO^• radicals, the newly formed radicals did not show (or showed negligible) activity towards biomolecule models representing biological targets. Inactivation of the formed radical species through the synergistic action of O₂/NO_x or the subsequent reaction with HO^• was thermodynamically favored. The ecotoxicity assessment of the starting compounds and oxidation products, formed in multistage reactions with O₂/NO_x and HO^•, indicated that the formed products showed lower acute and chronic toxicity effects on aquatic organisms than the starting compounds, which is a prerequisite for the application of AOPs procedures in the degradation of compounds.

Pharmacokinetic drug interactions of the non-vitamin K antagonist oral anticoagulants (NOACs)

The use of warfarin, the most commonly prescribed oral anticoagulant, is being questioned by clinicians worldwide due to warfarin several limitations (a limited therapeutic window and significant variability in dose-response among individuals, in addition to a potential for drug-drug interactions). Therefore, the need for non-vitamin K antagonist oral anticoagulants (NOACs) with a rapid onset of antithrombotic effects and a predictable pharmacokinetic (PK) and pharmacodynamic (PD) profile led to the approval of five new drugs: the direct factor Xa (F-Xa) inhibitors rivaroxaban, apixaban, edoxaban and betrixaban (newly approved by FDA) and the direct thrombin (factor-IIa) inhibitor dabigatran etexilate. The advantages of NOACs over warfarin are a fixed-dosage, the absence of the need for drug monitoring for changes in anti-coagulation and fewer clinically significant PK and PD drug-drug interactions. NOACs exposure will likely be increased by the administration of strong P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4-inhibitors and may increase the risk of bleeds. On the contrary, P-gp inducers could significantly decrease the NOACs plasma concentration with an associated reduction in their anticoagulant effects. This manuscript gives an overview of NOACs PK profiles and their drug-drug interactions potential. This is meant to be of help to physicians in choosing the best therapeutic approach for their patients.

The use of aromatase inhibitors in boys with short stature: what to know before prescribing?

Aromatase is a cytochrome P450 enzyme (CYP19A1 isoform) able to catalyze the conversion of androgens to estrogens. The aromatase gene mutations highlighted the action of estrogen as one of the main regulators of bone maturation and closure of bone plate. The use of aromatase inhibitors (AI) in boys with short stature has showed its capability to improve the predicted final height. Anastrozole (ANZ) and letrozole (LTZ) are nonsteroidal inhibitors able to bind reversibly to the heme group of cytochrome P450. In this review, we describe the pharmacokinetic profile of both drugs, discussing possible drug interactions between ANZ and LTZ with other drugs. AIs are triazolic compounds that can induce or suppress cytochrome P450 enzymes, interfering with metabolism of other compounds. Hydroxilation, N-dealkylation and glucoronidation are involved in the metabolism of AIs. Drug interactions can occur with azole antifungals, such as ketoconazole, by inhibiting CYP3A4 and by reducing the clearance of AIs. Antiepileptic drugs (lamotrigine, phenobarbital, and phenytoin) also inhibit aromatase. Concomitant use of phenobarbital or valproate has a synergistic effect on aromatase inhibition. Therefore, it is important to understand the pharmacokinetics of AIs, recognizing and avoiding possible drug interactions and offering a safer prescription profile of this class of aromatase inhibitors. Arch Endocrinol Metab. 2017;61(3):391-7.

Assessment of Pharmacokinetic Interactions Between Obeticholic Acid and Caffeine, Midazolam, Warfarin, Dextromethorphan, Omeprazole, Rosuvastatin, and Digoxin in Phase 1 Studies in Healthy Subjects

Introduction

Obeticholic acid (OCA), a potent and selective farnesoid X receptor agonist, is indicated for the treatment of primary biliary cholangitis (PBC). We investigated the potential drug–drug interaction effect of OCA on metabolic CYP450 enzymes and drug transporters.

Methods

Five phase 1 single-center, open-label, fixed-sequence, inpatient studies were conducted in healthy adult subjects to evaluate the effect of oral daily doses of 10 or 25 mg OCA on single-dose plasma pharmacokinetics of specific probe substrates for enzymes CYP1A2 (caffeine, R-warfarin), CYP3A (midazolam, R-warfarin), CYP2C9 (S-warfarin), CYP2D6 (dextromethorphan), CYP2C19 (omeprazole), and drug transporters, BCRP/OATP1B1/OATP1B3 (rosuvastatin), and P-gp (digoxin).

Results

OCA showed no substantial suppression/inhibition of S-warfarin, digoxin, and dextromethorphan and weak interactions with caffeine, omeprazole, rosuvastatin, and midazolam. The maximal pharmacodynamic responses (E_max) to warfarin-based INR, PT, and aPTT were reduced by 11%, 11%, and 1%, respectively, for the 10-mg dose group and by 7%, 7% and 0%, respectively, for the 25-mg dose group. Overall, drugs dosed in combination with OCA were well tolerated, and most adverse events were mild in severity. No clinically important trends were noted in laboratory evaluations, vital signs, or 12-lead ECGs.

Conclusion

In these studies, OCA showed weak to no suppression/inhibition of metabolic enzymes and drug transporters at the highest recommended therapeutic dose in patients with PBC. On the basis on these analyses, monitoring and maintenance of target INR range are required during coadministration of OCA with drugs that are metabolized by CYP1A2 (R-warfarin).

Funding

Intercept Pharmaceuticals, Inc.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-017-0601-0) contains supplementary material, which is available to authorized users.

A guide to clinically relevant drug interactions in oncology

This paper presents an overview of new information on clinically relevant drug-drug interactions, particular focuses on negative drug interactions in oncology. We have generated a concise table of drug-drug interactions that provides a synopsis of the clinical outcome of the interaction along with a recommendation for management. We have also generated other tables that describe specific interactions with methotrexate and dosing guidelines for cytotoxic drugs in the presence of renal or hepatic dysfunction. Since warfarin is one of the non-anticancer drugs that is commonly used in cancer patients for the treatment and prevention of venous thromboembolism, its interactions with other anticancer drugs that have been reported in literatures were also reviewed in this paper. In general, drug interactions observed in cancer patients may be categorized into pharmacokinetic, pharmacodynamic and pharmaceutic interactions. Pharmacokinetic interactions involve one drug altering the absorption, distribution, metabolism, or excretion of another drug. Interpatient variability in the pharmacokinetic profile of many anticancer agents often complicates the predictability of the antitumor response and toxicities. Among four pharmacokinetic characteristics, drug interactions involving hepatic metabolism is probably the most common and important mechanism responsible for oncologic drug interactions. For example, several anticancer drugs including taxanes, vinca alkaloids, and irinotecan are known to be metabolized by cytochrome CYP3A4. Enzyme-inducing anticonvulsants have been shown to significantly decrease the plasma levels of these anticancer drugs, thereby compromising the anti-tumor effects. N ephrotoxicity or changes in hepatic function caused by some anticancer drugs (e.g., cisplatin, asparaginase) may also have an impact on the pharmacokinetics of the interacting agents. Pharmacodynamic interactions may occur when two or more drugs acting at a common receptor-binding site impact on the pharmacologic action of the object drug, without influencing the pharmacokinetics of each interacting agent. In clinical setting, a decrease of antitumor efficacy was observed in breast cell lines when gemcitabine or vinorelbine were used in combination with paclitaxel. On the other hand, a decreased incidence of thrombocytopenia was seen in patients receiving combination of carboplatin and palcitaxel compared to those receiving carboplatin alone. The third type of drug-drug interaction is known as pharmaceutic interaction. When one drug may alter the physical or chemical compatibility of another drug that utlimately leads to a change in appearance of the solution or a decrease of effectiveness of the drug due to drug inactivation or degradation.

Lack of clinical pharmacodynamic and pharmacokinetic drug-drug interactions between warfarin and the antisense oligonucleotide mipomersen

Mipomersen is a second-generation antisense oligonucleotide indicated as an adjunct therapy for homozygous familial hypercholesterolemia (HoFH). Warfarin is commonly prescribed for a variety of cardiac disorders in homozygous familial hypercholesterolemia population, and concurrent use of warfarin and mipomersen is likely. This open-label, single-sequence 2-period phase 1 study in healthy subjects evaluated the potential drug-drug interactions between mipomersen and warfarin. The subjects received a single oral 25 mg dose of warfarin alone on day 1, and after a 7-day washout period, received 200 mg mipomersen alone subcutaneously every other day on days 8-12, and received both concurrently on day 14. Coadministration of mipomersen did not change the pharmacodynamics (international normalized ratio, prothrombin time, and activated partial thromboplastin time) and pharmacokinetics (PK) of warfarin. There were no clinically significant changes in the PK of mipomersen with concurrent administration of warfarin. There were no events indicative of an increase in bleeding tendency when warfarin was coadministered with mipomersen, and the adverse event profile of mipomersen did not appear to be altered in combination with warfarin, as compared with that of the respective reference treatment. The combination of these 2 medications appeared to be safe and well tolerated. These results suggest that the dosage adjustment of warfarin or mipomersen is not expected to be necessary with coadministration.

Interactions between oral antineoplastic agents and concomitant medication: a systematic review

INTRODUCTION

In recent years, the number of oral antitumoral agents has considerably increased. Oral administration increases the risk of interactions, because most oral anticancer drugs are taken on a daily basis. Interactions can increase exposure to antitumoral agents or cause treatment failure. Many antitumoral drugs undergo enzymatic metabolism by cytochrome P450. As some act as inducers or inhibitors of one or more isoenzymes, they can lead to decreases or increases in plasma concentrations of concomitant drugs. Hence, cytostatic drugs can act not only as victims but also as perpetrators. P-glycoprotein, an efflux transporter, can also be involved in pharmacokinetic interactions.

AREAS COVERED

A Medline search was performed to summarize the available evidence of the most clinically relevant interactions between oral chemotherapy agents and other drugs. The search covered the period from 1966 until August 2012 for each antitumoral drug using the medical subject headings 'Drug Interactions' OR 'Pharmacokinetics'. While the present review is not exhaustive, it aims to increase clinicians' awareness of potential drug-drug interactions.

EXPERT OPINION

As cancer patients are often polymedicated and treated by different physicians, the risk of drug interactions between antitumoral agents and other medications is high. More clinical interaction studies are encouraged to ensure appropriate antineoplastic pharmacokinetics 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.

Anastrozole: a new gold standard of hormonal treatment for breast cancer?

Tamoxifen has long been the standard endocrine therapy for postmenopausal women with hormone-sensitive breast cancer. However, data now suggest that the third-generation aromatase inhibitors have emerged as superior alternatives for advanced disease. In early disease evaluation of initial adjuvant therapy, data from the Arimidex((R)), Tamoxifen, Alone and in Combination trial has shown that anastrozole is more effective than tamoxifen with a better risk-benefit profile. This trial provides the most mature data of any aromatase inhibitor study and suggests that anastrozole should be considered the preferred initial adjuvant therapy for postmenopausal women with hormone-responsive early breast cancer. The emergence of aromatase inhibitors as an alternative to tamoxifen for the treatment of breast cancer is challenging the management of the disease and influencing the change of regulatory guidelines.

Effect of aliskiren, an oral direct renin inhibitor, on the pharmacokinetics and pharmacodynamics of a single dose of acenocoumarol in healthy volunteers

OBJECTIVE

Aliskiren is a direct renin inhibitor approved for the treatment of hypertension. This study investigated the effects of aliskiren on the pharmacokinetics and pharmacodynamics of a single dose of acenocoumarol in healthy volunteers.

METHODS

This two-sequence, two-period, randomized, double-blind crossover study recruited 18 healthy subjects (ages 18-45) to receive either aliskiren 300 mg or placebo once daily on days 1-10 of each treatment period and a single dose of acenocoumarol 10 mg on day 8. Treatment periods were separated by a 10-day washout. Blood samples were taken frequently for determination of steady-state plasma concentrations of aliskiren (LC-MS/MS) and of R(+)- and S(-)-acenocoumarol (HPLC-UV), prothrombin time (PT) and international normalized ratio (INR).

RESULTS

Co-administration with aliskiren had no effect on exposure to R(+)-acenocoumarol. Geometric mean ratios (GMR; aliskiren:placebo co-administration) for R(+)-acenocoumarol AUC(0-t) and C(max) were 1.08 and 1.04, respectively, with 90% CI within the range 0.80-1.25. Co-administration of aliskiren resulted in a 19% increase in S(-)-acenocoumarol AUC(0-t) (GMR 1.19; 90% CI 0.92, 1.54) and a 9% increase in C(max) (GMR 1.09; 90% CI 0.88, 1.34). The anticoagulant effect of acenocoumarol was not affected by co-administration of aliskiren. Geometric mean ratios were 1.01 for all pharmacodynamic parameters (AUC(PT), PT(max), AUC(INR) and INR(max)), with 90% CI within the range 0.97-1.05.

CONCLUSION

Aliskiren has no clinically relevant effect on the pharmacokinetics or pharmacodynamic effects of a single dose of acenocoumarol in healthy volunteers, hence no dosage adjustment of acenocoumarol is likely to be required during co-administration with aliskiren.

Multiple doses of the antimuscarinic agent solifenacin do not affect the pharmacodynamics or pharmacokinetics of warfarin or the steady-state pharmacokinetics of digoxin in healthy subjects

AIMS

Solifenacin succinate is used for the treatment of overactive bladder (OAB). The potential for pharmacokinetic and/or pharmacodynamic interactions between solifenacin and warfarin or digoxin was investigated.

METHODS

The solifenacin-warfarin study was a two-period crossover trial conducted in healthy males. Subjects received warfarin on the 10th day of 16 days of dosing with either solifenacin or placebo. The solifenacin-digoxin study was an one-sequence crossover trial conducted in healthy males and females. Following a phase-in period for digoxin, solifenacin was administered concomitantly with the drug on days 9-18.

RESULTS

The AUC(PT; 0-168 h) following a single dose of warfarin was unchanged in the presence of solifenacin [point estimate = 1.005; 90% confidence interval (CI) 0.98, 1.02)]. The AUC(0-infinity) values for both warfarin enantiomers were also unchanged. A small increase in the C(max) of digoxin was observed during treatment with solifenacin, but for AUC(ss,tau) and C(max) the 90% CI fell within the prespecified interval of 0.80-1.25. Combined administration of solifenacin and warfarin or digoxin was well tolerated.

CONCLUSIONS

Since the pharmacokinetics and pharmacodynamics of a single dose of warfarin and the steady-state pharmacokinetics of digoxin were not affected by coadministration of solifenacin in healthy subjects, the need for dosing adjustments for digoxin and/or warfarin does not seem warranted.

Fulvestrant: pharmacologic profile versus existing endocrine agents for the treatment of breast cancer

OBJECTIVE

To compare the pharmacologic profile of fulvestrant with that of tamoxifen and the aromatase inhibitors with respect to the choice of treatment for advanced breast cancer (ABC).

DATA SOURCES

Principal literature and review articles were obtained from MEDLINE (1991-March 2006). Key search terms included fulvestrant, tamoxifen, aromatase inhibitors, pharmacology, and breast cancer. Further data sources were identified from the bibliographies of selected articles.

STUDY SELECTION AND DATA EXTRACTION

English-language preclinical and clinical research and review articles reporting pharmacologic and safety data for fulvestrant, tamoxifen, and the aromatase inhibitors were evaluated to identify relevant information. Randomized clinical trial data were preferred over preclinical or Phase I and II trial data.

DATA SYNTHESIS

A total of 52 clinical papers (including 10 reviews) and 17 clinical abstracts were evaluated reporting results from controlled Phase I-III studies and pilot studies. Eleven preclinical papers (including 2 reviews) and 6 preclinical abstracts were also included. Fulvestrant has little effect on sex hormone endocrinology, bone metabolism, and lipid biochemistry and appears unlikely to be the subject or cause of CYP3A4-mediated drug interactions. Tamoxifen has a protective effect on bone (due to its partial estrogen agonist activity) and reduces plasma low-density lipoprotein cholesterol but increases triglyceride levels. The aromatase inhibitors have variable effects on lipid profiles and sex hormone endocrinology but have detrimental effects on bone due to inhibition of estrogen synthesis. Drug interactions have been noted between tamoxifen and anticoagulants and tamoxifen and aromatase inhibitors, which may be due to CYP-mediated mechanisms.

CONCLUSIONS

Fulvestrant appears to have little effect on sex hormone endocrinology, bone metabolism, and lipid biochemistry and is unlikely to be subject to or the cause of CYP3A4-mediated drug-drug interactions. As such, fulvestrant represents a valuable new endocrine therapy for the treatment of ABC and broadens the options available to clinicians in the treatment of this disease.

The adjuvant endocrine treatment revolution: focus on anastrozole

Anastrozole is a nonsteroidal, third-generation aromatase inhibitor, which is heralded as an effective alternative endocrine therapy to tamoxifen in postmenopausal women with hormone-responsive breast cancer. Anastrozole has a high affinity for aromatase, a CYP enzyme involved in estrogen synthesis, and provides effective estrogen suppression with little, if any, impact on other CYP enzymes, lipid profiles or steroidogenesis. The use of anastrozole is now widely accepted in advanced breast cancer and its superior efficacy and tolerability to tamoxifen has recently been demonstrated in early breast cancer.

Role of aromatase inhibitors in the treatment of breast cancer

BACKGROUND

Estrogens play a pivotal role in the development of breast cancer. Endocrine therapy based on estrogen blockade is a well-established treatment in hormone-dependent breast cancer. Tamoxifen citrate has long been considered the "gold standard" due to its relative safety and efficacy. Aromatase inhibitors are anti-estrogen agents that target specifically the aromatase enzyme, which is the final step in the estrogen production. The first use of aromatase inhibitors in breast cancer was associated with adverse effects such as rash, drowsiness, and adrenal-gland suppression. Newer third-generation agents are emerging as potential alternatives to tamoxifen, associating clinical efficacy with a more favorable safety profile.

OBJECTIVES

The aim of this article is to review the mechanisms of actions pharmacology, adverse effects, and clinical applications of the aromatase inhibitors available in the United States.

METHODS

The terms breast cancer or neoplasia, aromatase, aromatase inhibitors, third-generation, endocrine therapy, and antiestrogens were used to search MEDLINE for English-language studies published between 1966 and April 2004. A parallel search was performed at the corresponding Web site of each of the aromatase inhibitors available in the United States. Identified publications relevant to the article objectives were selected.

RESULTS

Anastrozole, letrozole, and exemestane are the 3 commercially available aromatase inhibitors approved by the US Food and Drug Administration for the treatment of hormone receptor-positive breast cancer in postmenopausal women. They have been used in several clinical scenarios, including advanced and early disease and chemoprevention, and in the neoadjuvant setting. There is evidence that aromatase inhibitors are more effective and tolerable than tamoxifen in advanced breast cancer and in the neoadjuvant setting. Based on the results of a large, randomized trial, their use in early disease and in chemoprevention is also promising. Aromatase inhibitors appear safe; however, the long-term safety profile is still unknown, especially concerning bone metabolism.

CONCLUSION

Third-generation aromatase inhibitors are a new treatment modality in estrogen and/or progesterone-receptor positive breast cancer. Although they are replacing the "classic" antiestrogen agents used in metastatic breast cancer, their benefit in early disease and as chemopreventive agents is not completely clear. Ongoing clinical studies should become available within the next few years and will provide additional recommendations for their use in patients with breast cancer.

A placebo-controlled pharmacodynamic and pharmacokinetic interaction study between tamsulosin and acenocoumarol

AIM

To evaluate pharmacokinetic and pharmacodynamic interactions between tamsulosin and acenocoumarol.

METHODS

Twelve healthy volunteers received tamsulosin 0.4 mg or placebo once daily for 9 days in a double-blind, cross-over study. On day 5 of each study period, a single 10-mg oral dose of racemic acenocoumarol was administered.

RESULTS

The ratios (point estimates (90% confidence intervals)) of values in the presence and absence of tamsulosin were: AUCPT 1.01 (0.98, 1.03); maximum prothrombin time (Ptmax) 0.99 (0.94, 1.05); AUC (R)-acenocoumarol 1.02 (0.90, 1.16), and AUC (S)-acenocoumarol 1.03 (0.89, 1.20). Both combinations, tamsulosin and placebo with acenocoumarol, were well-tolerated.

CONCLUSIONS

Multiple doses of tamsulosin had no effect on the pharmacokinetics or pharmacodynamics of a single high dose of acenocoumarol.

An overview of the pharmacology and pharmacokinetics of the newer generation aromatase inhibitors anastrozole, letrozole, and exemestane

BACKGROUND

The newer generation, nonsteroidal aromatase inhibitors (AIs) anastrozole and letrozole have shown superior efficacy compared with tamoxifen as first-line treatments and compared with megestrol acetate as second-line therapy in postmenopausal women with advanced breast carcinoma. In an open-label, Phase II trial, it was reported that exemestane showed numerical superiority compared with tamoxifen for objective response and clinical benefit. Because these agents ultimately may be administered for periods of up to 5 years in the adjuvant setting, it is of increasing importance to assess their tolerability and pharmacologic profiles.

METHODS

In the absence of data from direct clinical comparisons, the published literature was reviewed for the clinical pharmacology, pharmacokinetic characteristics, and selectivity profiles of anastrozole, letrozole, and exemestane.

RESULTS

At clinically administered doses, the plasma half-lives of anastrozole (1 mg once daily), letrozole (2.5 mg once daily), and exemestane (25 mg once daily) were 41-48 hours, 2-4 days, and 27 hours, respectively. The time to steady-state plasma levels was 7 days for both anastrozole and exemestane and 60 days for letrozole. Androgenic side effects have been reported only with exemestane. Anastrozole treatment had no impact on plasma lipid levels, whereas both letrozole and exemestane had an unfavorable effect on plasma lipid levels. In indirect comparisons, anastrozole showed the highest degree of selectivity compared with letrozole and exemestane in terms of a lack of effect on adrenosteroidogenesis.

CONCLUSIONS

All three AIs demonstrated clinical efficacy over preexisting treatments. However, there were differences in terms of pharmacokinetics and effects on lipid levels and adrenosteroidogenesis. The long-term clinical significance of these differences remains to be elucidated.