Clinical pharmacokinetics of antiplatelet agents used in the secondary prevention of stroke

Genotype-guided dual antiplatelet therapy in cerebrovascular disease: assessing the risk and benefits for ethnic populations

INTRODUCTION

Cerebrovascular disease is a leading cause of morbidity and mortality in the world and antiplatelet therapy is a main pharmacologic means of secondary prevention. Clinical information has accumulated about benefit of dual antiplatelet therapy in certain clinical scenarios, genetic causes of antiplatelet resistance and its effect on clinical outcomes, and ethnic and geographic distributions of genetic polymorphisms.

AREAS COVERED

This review covers literature related to the pharmacogenomics of antiplatelet agents with a focus on ethnic variability, antiplatelet resistance, and dual antiplatelet therapy in cerebrovascular disease.

EXPERT OPINION

Selecting patients for dual antiplatelet therapy and specific agents require consideration of multiple factors. Ethnic factors should be considered in certain circumstances, but additional research is needed to determine the generalizability of the findings.

Cladribine as a Potential Object of Nucleoside Transporter-Based Drug Interactions

Cladribine is a nucleoside analog that is phosphorylated in its target cells (B and T-lymphocytes) to its active triphosphate form (2-chlorodeoxyadenosine triphosphate). Cladribine tablets 10 mg (Mavenclad®), administered for up to 10 days per year in 2 consecutive years (3.5-mg/kg cumulative dose over 2 years), are used to treat patients with relapsing multiple sclerosis. Cladribine has been shown to be a substrate of various nucleoside transporters (NTs). Intestinal absorption and distribution of cladribine throughout the body appear to be essentially mediated by equilibrative NTs (ENTs) and concentrative NTs (CNTs), specifically by ENT1, ENT2, ENT4, CNT2 (low affinity), and CNT3. Other efficient transporters of cladribine are the ABC efflux transporters, specifically breast cancer resistance protein, which likely modulates the oral absorption and renal excretion of cladribine. A key transporter for the intracellular uptake of cladribine into B and T-lymphocytes is ENT1 with ancillary contributions of ENT2 and CNT2. Transporter-based drug interactions affecting absorption and target cellular uptake of a prodrug such as cladribine are likely to reduce systemic bioavailability and target cell exposure, thereby possibly hampering clinical efficacy. In order to manage optimized therapy, i.e., to ensure uncompromised target cell uptake to preserve the full therapeutic potential of cladribine, it is important that clinicians are aware of the existence of NT-inhibiting medicinal products, various lifestyle drugs, and food components. This article reviews the existing knowledge on inhibitors of NT, which may alter cladribine absorption, distribution, and uptake into target cells, thereby summarizing the existing knowledge on optimized methods of administration and concomitant drugs that should be avoided during cladribine treatment.

Antiplatelet Therapy for Atherothrombotic Disease in 2022—From Population to Patient-Centered Approaches

Antiplatelet agents, with aspirin and P2Y₁₂ receptor antagonists as major key molecules, are currently the cornerstone of pharmacological treatment of atherothrombotic events including a variety of cardio- and cerebro-vascular as well as peripheral artery diseases. Over the last decades, significant changes have been made to antiplatelet therapeutic and prophylactic strategies. The shift from a population-based approach to patient-centered precision medicine requires greater awareness of individual risks and benefits associated with the different antiplatelet strategies, so that the right patient gets the right therapy at the right time. In this review, we present the currently available antiplatelet agents, outline different management strategies, particularly in case of bleeding or in perioperative setting, and develop the concept of high on-treatment platelet reactivity and the steps toward person-centered precision medicine aiming to optimize patient care.

Population pharmacokinetic analysis of clopidogrel in healthy Jordanian subjects with emphasis optimal sampling strategy

AIM

Clopidogrel is metabolized primarily into an inactive carboxyl metabolite (clopidogrel-IM) or to a lesser extent an active thiol metabolite. A population pharmacokinetic (PK) model was developed using NONMEM(®) to describe the time course of clopidogrel-IM in plasma and to design a sparse-sampling strategy to predict clopidogrel-IM exposures for use in characterizing anti-platelet activity.

METHODS

Serial blood samples from 76 healthy Jordanian subjects administered a single 75 mg oral dose of clopidogrel were collected and assayed for clopidogrel-IM using reverse phase high performance liquid chromatography. A two-compartment (2-CMT) PK model with first-order absorption and elimination plus an absorption lag-time was evaluated, as well as a variation of this model designed to mimic enterohepatic recycling (EHC). Optimal PK sampling strategies (OSS) were determined using WinPOPT based upon collection of 3-12 post-dose samples.

RESULTS

A two-compartment model with EHC provided the best fit and reduced bias in C(max) (median prediction error (PE%) of 9.58% versus 12.2%) relative to the basic two-compartment model, AUC(0-24) was similar for both models (median PE% = 1.39%). The OSS for fitting the two-compartment model with EHC required the collection of seven samples (0.25, 1, 2, 4, 5, 6 and 12 h). Reasonably unbiased and precise exposures were obtained when re-fitting this model to a reduced dataset considering only these sampling times.

CONCLUSIONS

A two-compartment model considering EHC best characterized the time course of clopidogrel-IM in plasma. Use of the suggested OSS will allow for the collection of fewer PK samples when assessing clopidogrel-IM exposures.

Metabolism and disposition of the thienopyridine antiplatelet drugs ticlopidine, clopidogrel, and prasugrel in humans

Ticlopidine, clopidogrel, and prasugrel are thienopyridine prodrugs that inhibit adenosine-5'-diphosphate (ADP)-mediated platelet aggregation in vivo. These compounds are converted to thiol-containing active metabolites through a corresponding thiolactone. The 3 compounds differ in their metabolic pathways to their active metabolites in humans. Whereas ticlopidine and clopidogrel are metabolized to their thiolactones in the liver by cytochromes P450, prasugrel proceeds to its thiolactone following hydrolysis by carboxylesterase 2 during absorption, and a portion of prasugrel's active metabolite is also formed by intestinal CYP3A. Both ticlopidine and clopidogrel are subject to major competing metabolic pathways to inactive metabolites. Thus, varying efficiencies in the formation of active metabolites affect observed effects on the onset of action and extent of inhibition of platelet aggregation (IPA). Knowledge of the CYP-dependent formation of ticlopidine and clopidogrel thiolactones helps explain some of the observed drug-drug interactions with these molecules and, more important, the role of CYP2C19 genetic polymorphism on the pharmacokinetics of and pharmacodynamic response to clopidogrel. The lack of drug interaction potential and the absence of CYP2C19 genetic effect result in a predictable response to thienopyridine antiplatelet therapy with prasugrel. Current literature shows that greater ADP-mediated IPA is associated with significantly better clinical outcomes for patients with acute coronary syndrome.

Simultaneous determination of dipyridamole and salicylic acid in human plasma by high performance liquid chromatography-mass spectrometry

A sensitive, rapid and simple high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) method for simultaneous determination of dipyridamole and salicylic acid in human plasma has been developed and validated. After the addition of diazepam and rosiglitazone as internal standard (IS), plasma samples were prepared by liquid-liquid extraction followed by an isocratic elution with methanol:2 mM ammonium acetate buffer (pH 4.25; 70/30, v/v) on a Shimadzu VP-ODS C(18) column (5 microm, 150 x 2.0 mm I.D.). Detection was performed on a quadrupole mass spectrometer with ESI interface operating in the positive-ion mode for dipyridamole and negative-ion mode for salicylic acid. Calibration curves were linear (r(2) > 0.99) over the concentration range 10-2500 ng/mL for dipyridamole and 30-4000 ng/mL for salicylic acid with acceptable accuracy and precision, respectively. The intra- and inter-batch precisions were less than 15% of the relative standard deviation. The limits of detection of dipyridamole and salicylic acid were 1 and 15 ng/mL, respectively. The validated HPLC-ESI-MS method was successfully applied to a preliminary pharmacokinetic study of fixed-dose combination of sustained-release dipyridamole/aspirin in Chinese healthy male volunteers.

Aspirin Plus Dipyridamole Versus Aspirin for Prevention of Vascular Events After Stroke or TIA

Background and Purpose— This meta-analysis systematically reviewed randomized controlled trials comparing aspirin plus dipyridamole with aspirin alone in patients with stroke and TIA to determine the efficacy of these agents in preventing recurrent cerebral and systemic vascular events.

Methods— We performed separate analyses of the incidences of stroke alone and composite outcome of stroke, myocardial infarction, or vascular death. We also performed two subset analyses, planned a priori, to examine effect size based on trials using (1) exclusively immediate-release and (2) predominantly extended-release dipyridamole.

Results— The summary results indicate a significant reduction in the overall risk ratio in favor of aspirin plus dipyridamole for stroke alone with relative risk 0.77 (0.67 to 0.89) and the composite end point with relative risk 0.85 (0.76 to 0.94). Studies using immediate-release dipyridamole showed a nonstatistically significant trend in favor of the combination for stroke alone with relative risk 0.83 (0.59 to 1.15) and for the composite outcome with relative risk 0.95 (0.75 to 1.19). Studies using predominantly extended-release dipyridamole showed a statistically significant difference in favor of the combination for stroke alone with relative risk 0.76 (0.65 to 0.89) and for the composite outcome with relative risk 0.82 (0.73 to 0.92).

Conclusions— The combination of aspirin plus dipyridamole is more effective than aspirin alone in preventing stroke and other serious vascular events in patients with minor stroke and TIAs. The risk reduction was greater and statistically significant for studies using primarily extended release dipyridamole, which may reflect a true pharmacological effect or lack of statistical power in studies using immediate release dipyridamole.

Determination of clopidogrel metabolite (SR26334) in human plasma by LC–MS

A new, sensitive, specific and reproducible method for determination of clopidogrel metabolite (SR26334) in human plasma has been developed. After liquid-liquid extraction on Chem Elut cartridges with dichloromethane, samples were quantified using reversed-phase high performance liquid chromatography with mass detection. The determination was performed on a Luna C18, 3 microm (75 mmx4.6 mm i.d.) column with an acetonitrile-water-formic acid mixture (60:40:0.1, v/v/v) as a mobile phase. The flow rate was set at 0.2 mL/min. Repaglinide was chosen as an internal standard and the time of analysis was 12 min. For SR26334 the limits of detection and quantification were 7.5 ng/mL and 20 ng/mL, respectively, and the calibration curve was linear up to 3000 ng/mL. The extraction recovery of SR26334 from plasma was within the range of 85-90%. The method has been successfully used to study clopidogrel metabolite pharmacokinetics in healthy volunteers.

Dipyridamole bioavailability in subjects with reduced gastric acidity

Dipyridamole (DP) is an antiplatelet agent that shows decreased oral bioavailability with increased gastric pH that occurs with commonly prescribed antacids. An extended-release (ER) formulation of DP that employs tartaric acid to improve bioavailability of DP in the presence of elevated gastric pH was developed as a combination antiplatelet product with immediate-release aspirin. This crossover-designed study examined the relative bioavailability of DP from the composite product compared to conventional DP tablets during reduced gastric acidity. Gastric pH was increased (pH > 4.0) in 20 healthy subjects with lansoprazole (30 mg/d for 5 days). Dipyridamole systemic exposure over 12 hours was compared after oral administration of a single composite ER capsule (200 mg DP + 25 mg aspirin) versus two 100-mg conventional DP tablets given 6 hours apart combined with 81 mg aspirin. DP relative bioavailability was reduced 53% with conventional tablets compared to the composite buffered ER capsule in reduced gastric acid conditions. Peak DP plasma concentrations were 57% lower with immediate-release tablets compared to the composite formulation with high stomach pH. Substituting generic DP plus low-dose aspirin may be less effective than the buffered DP composite product in patients with concomitant antacid therapies.

BCRP transports dipyridamole and is inhibited by calcium channel blockers

PURPOSE

We investigated whether dipyridamole and various calcium channel blockers are inhibitors and/or substrates of breast cancer resistance protein (BCRP).

METHODS

The effect of dipyridamole and the calcium channel blockers on mitoxantrone efflux by BCRP-overexpressing human embryonic kidney (HEK) cells was determined by flow cytometry. The ability of some of these compounds to reverse BCRP-mediated mitoxantrone resistance was measured by cytotoxicity assays. Transport studies were performed using radiolabeled compounds.

RESULTS

Dipyridamole, nicardipine, nitrendipine, and nimodipine effectively inhibited BCRP-mediated mitoxantrone efflux; however, bepridil, diltiazem, and verapamil had no significant effect. Nifedipine is a much weaker BCRP inhibitor compared with other dihydropyridines tested. Nicardipine and dipyridamole were the most potent BCRP inhibitors among the compounds tested with IC50 values of 4.8 +/- 1.3 and 6.4 +/- 0.9 microM, respectively. Nicardipine and dipyridamole also effectively reversed BCRP-mediated mitoxantrone resistance in HEK cells. [3H]Nitrendipine was found not to be transported by BCRP. However, the transport of [3H]dipyridamole by BCRP was observed in both HEK and Madin-Darby canine kidney cells stably expressing the transporter, and this transport was completely abolished by fumitremorgin C, a known BCRP inhibitor.

CONCLUSIONS

Dipyridamole and several dihydropyridines are effective BCRP inhibitors, but bepridil, diltiazem, and verapamil are not. We also identified a new BCRP substrate, dipyridamole.

Secondary Stroke Prevention With Antiplatelet Therapy With Emphasis on the Cardiac Patient

The prevention of secondary vascular events is of paramount importance in patients with a history of stroke or transient ischemic attack (TIA). Most cardiologists are aware of the benefits of clopidogrel plus aspirin versus those of other antiplatelet regimens in patients with acute coronary syndrome. Using a representative post-stroke patient as an example, this article reviews data evaluating the effectiveness of antiplatelet regimens in preventing secondary vascular events in stroke and TIA patients. These results differ from those seen in clinical trials of acute coronary syndrome patients. Clinical studies provide little evidence that clopidogrel, with or without aspirin, is more efficacious in this setting than aspirin alone. Moreover, the increased risk of bleeding episodes with clopidogrel and aspirin in combination probably outweighs any small reductions in secondary event risk. In contrast, extended-release dipyridamole (ER-DP) plus aspirin reduces secondary stroke risk to a significantly greater extent (23% relative risk reduction) than aspirin alone. Currently available clinical trial data support the use of ER-DP plus aspirin, but not clopidogrel plus aspirin, to prevent secondary vascular events after stroke or TIA.

Female-specific aspects in the pharmacotherapy of chronic cardiovascular diseases

Differences in pharmacokinetics, pharmacodynamics, and physiology contribute to the phenomenon that women and men frequently respond differently to cardiovascular drugs. Hormonal influences, in addition, can play an important role: for example, the menstrual cycle, menopause, and pregnancy--as a result of fluctuations in concentrations of sexual steroids, and of changes in total body water--can be associated with gender-specific differences in the plasma levels of cardiovascular drugs. Clinical relevance accordingly results, especially for substances with a narrow therapeutic margin. This review treats the most important pharmacodynamic gender-relevant differences in this context, and surveys available evidence on the benefits of therapy of chronic cardiovascular diseases in women. On the whole, the study situation for women is appreciably less favourable than for men: owing to the fact that women are under-represented in most studies, and that few gender-specific analyses have been conducted.

Emboli rate during and early after carotid endarterectomy after a single preoperative dose of 120 mg acetylsalicylic acid--a prospective double-blind placebo controlled randomised trial

PURPOSE

To investigate whether a single pre-operative dose of 120 mg acetylsalicylic acid (ASA) decreased either (1) emboli rate, as detected by transcranial Doppler (TCD), during and early after carotid endarterectomy (CEA) and (2) clinical intra- and post-operative signs suggestive of embolism or increased bleeding tendency.

DESIGN

Prospective, double-blind placebo controlled trial.

PATIENTS AND METHODS

One-hundred consecutive patients were randomised to receive either 120 mg ASA (n = 48) or placebo (n = 49) by suppository on the night before CEA; three patients were excluded. Emboli were counted and expressed as emboli rate (ER). The incidence of bleeding complications was assessed. Surgeons were asked to indicate which patients had received ASA or placebo.

RESULTS

There were no significant differences between the ASA and placebo groups in ER in the intraoperative and postoperative periods. ER higher than 0.9 min(-1) was associated with a significantly increased risk of complications (26 vs. 0%, P < 0.01). No extra bleeding complications were observed in the ASA group. Surgeon assessment of whether or not ASA had been administered had a sensitivity of 42% and a specificity of 70%.

CONCLUSION

A single pre-operative dose of ASA (120 mg) did not reduce significantly the emboli rate during and after CEA and surgeons could not correctly identify whether or not ASA had been administered.