Pharmacokinetic interaction between prasugrel and ritonavir in healthy volunteers

Clinically Relevant Interactions Between Ritonavir-Boosted Nirmatrelvir and Concomitant Antiseizure Medications: Implications for the Management of COVID-19 in Patients with Epilepsy

Ritonavir-boosted nirmatrelvir (RBN) has been authorized recently in several countries as an orally active anti-SARS-CoV-2 treatment for patients at high risk of progressing to severe COVID-19 disease. Nirmatrelvir is the active component against the SARS-CoV-2 virus, whereas ritonavir, a potent CYP3A inhibitor, is intended to boost the activity of nirmatrelvir by increasing its concentration in plasma to ensure persistence of antiviral concentrations during the 12-hour dosing interval. RBN is involved in many clinically important drug–drug interactions both as perpetrator and as victim, which can complicate its use in patients treated with antiseizure medications (ASMs). Interactions between RBN and ASMs are bidirectional. As perpetrator, RBN may increase the plasma concentration of a number of ASMs that are CYP3A4 substrates, possibly leading to toxicity. As victims, both nirmatrelvir and ritonavir are subject to metabolic induction by concomitant treatment with potent enzyme-inducing ASMs (carbamazepine, phenytoin, phenobarbital and primidone). According to US and European prescribing information, treatment with these ASMs is a contraindication to the use of RBN. Although remdesivir is a valuable alternative to RBN, it may not be readily accessible in some settings due to cost and/or need for intravenous administration. If remdesivir is not an appropriate option, either bebtelovimab or molnupiravir may be considered. However, evidence about the clinical efficacy of bebtelovimab is still limited, and molnupiravir, the only orally active alternative, is deemed to have appreciably lower efficacy than RBN and remdesivir.

A Mechanistic Absorption and Disposition Model of Ritonavir to Predict Exposure and Drug-Drug Interaction Potential of CYP3A4/5 and CYP2D6 Substrates

BACKGROUND AND OBJECTIVES

Due to health authority warnings and the recommended limited use of ketoconazole as a model inhibitor of cytochrome P450 (CYP) 3A4 in clinical drug-drug interaction (DDI) studies, there is a need to search for alternatives. Ritonavir is a strong inhibitor for CYP3A4/5-mediated DDIs and has been proposed as a suitable alternative to ketoconazole. It can also be used as a weak inhibitor for CYP2D6-mediated DDIs. Most of the currently available physiologically based pharmacokinetic (PBPK) inhibitor models developed for predicting DDIs use first-order absorption models, which do not mechanistically capture the effect of formulations on the systemic exposure of the inhibitor. Thus, the main purpose of the current study was to verify the predictive performance of a mechanistic absorption and disposition model of ritonavir when it was applied to the inhibition of CYP2D6 and CYP3A4/5 by ritonavir.

METHODS

A PBPK model that incorporates formulation characteristics and enzyme kinetic parameters for post-absorptive pharmacokinetic processes of ritonavir was constructed. Key absorption-related parameters in the model were determined using mechanistic modelling of in vitro biopharmaceutics experiments. The model was verified for systemic exposure and DDI risk assessment using clinical observations from 13 and 18 studies, respectively.

RESULTS

Maximal inhibition of hepatic (3.53% of the activity remaining) and gut (5.16% of the activity remaining) CYP3A4 activity was observed when ritonavir was orally administered in doses of 100 mg or higher. The PBPK model accurately described the concentrations of ritonavir in the different simulated studies. The prediction accuracy for maximum concentration (C_max) and area under the plasma concentration versus time curve (AUC) were assessed. The bias (average fold error, AFE) for the prediction of C_max and AUC was 0.92 and 1.06, respectively, and the precision (absolute average fold error, AAFE) was 1.29 and 1.23, respectively. The PBPK model predictions for all C_max and AUC ratios when ritonavir was used as an inhibitor of CYP metabolism fell within twofold of the clinical observations. The prediction accuracy for C_max and AUC ratios had a bias (AFE) of 0.85 and 0.99, respectively, and a precision (AAFE) of 1.21 and 1.33, respectively.

CONCLUSIONS

The current model, which incorporates formulation characteristics and mechanistic disposition parameters, can be used to assess the DDI potential of CYP3A4/5 and CYP2D6 substrates administered with a twice-daily dose of 100 mg of ritonavir for 14 days.

Molecular Insights of SARS-CoV-2 Antivirals Administration: A Balance between Safety Profiles and Impact on Cardiovascular Phenotypes

The COVID-19 pandemic has resulted in a complex clinical challenge, caused by a novel coronavirus, partially similar to previously known coronaviruses but with a different pattern of contagiousness, complications, and mortality. Since its global spread, several therapeutic agents have been developed to address the heterogeneous disease treatment, in terms of severity, hospital or outpatient management, and pre-existing clinical conditions. To better understand the rationale of new or old repurposed medications, the structure and host–virus interaction molecular bases are presented. The recommended agents by EDSA guidelines comprise of corticosteroids, JAK-targeting monoclonal antibodies, IL-6 inhibitors, and antivirals, some of them showing narrow indications due to the lack of large population trials and statistical power. The aim of this review is to present FDA-approved or authorized for emergency use antivirals, namely remdesivir, molnupinavir, and the combination nirmatrelvir-ritonavir and their impact on the cardiovascular system. We reviewed the literature for metanalyses, randomized clinical trials, and case reports and found positive associations between remdesivir and ritonavir administration at therapeutic doses and changes in cardiac conduction, relatable to their previously known pro-arrhythmogenic effects and important ritonavir interactions with cardioactive medications including antiplatelets, anti-arrhythmic agents, and lipid-lowering drugs, possibly interfering with pre-existing therapeutic regimens. Nonetheless, safety profiles of antivirals are largely questioned and addressed by health agencies, in consideration of COVID-19 cardiac and pro-thrombotic complications generally experienced by predisposed subjects. Our advice is to continuously adhere to the strict indications of FDA documents, monitor the possible side effects of antivirals, and increase physicians’ awareness on the co-administration of antivirals and cardiovascular-relevant medications. This review dissects the global and local tendency to structure patient-based treatment plans, for a glance towards practical application of precision medicine.

Dried blood spots analysis of 6β-hydroxycortisol and cortisol using liquid chromatography/tandem mass spectrometry for calculating 6β-hydroxycortisol to cortisol ratio

Dried blood spot (DBS) sampling is a minimally invasive method used to collect blood samples of any population for personalized medicine. We aimed to develop a sensitive and reliable analytical method for measuring 6β-hydroxycortisol (6β-OHF) and cortisol concentrations in DBS by liquid chromatography/tandem mass spectrometry so as to utilize DBS as a less invasive blood sampling method for calculating the ratio of 6β-OHF/cortisol. The lower limits of quantification obtained using four DBS were 1.08 pg/50 μl for 6β-OHF and 1.01 pg/50 μl for cortisol. The 6β-OHF and cortisol in DBS were stable for 28 days at room temperature. The intraday and interday accuracy and precision of the method was <12%. Additionally, the 6β-OHF and cortisol in DBS were measured before, during, and after 3 days of clarithromycin administration to two of the subjects. Then, their concentration was compared in the plasma and whole blood collected simultaneously. The concentrations of 6β-OHF and cortisol in four DBS ranged from 0.007 to 0.079 ng/50 μl and from 1.15 to 6.66 ng/50 μl, respectively. The 6β-OHF/cortisol ratio in DBS decreased by approximately 50% on administering clarithromycin compared with that before the administration of clarithromycin. The 6β-OHF/cortisol ratio in DBS also showed a strong correlation with that in whole blood (r = 0.9694) and plasma (r = 0.9383). This method provides high accuracy and precision for measuring 6β-OHF and cortisol in DBS. It also allows the use of DBS instead of plasma for calculating the 6β-OHF/cortisol ratio. The 6β-OHF/cortisol ratio could be an index of CYP3A activity in clinical setting.

Pharmacokinetics and Pharmacodynamics of Approved and Investigational P2Y12 Receptor Antagonists

Coronary artery disease remains the major cause of mortality worldwide. Antiplatelet drugs such as acetylsalicylic acid and P2Y12 receptor antagonists are cornerstone treatments for the prevention of thrombotic events in patients with coronary artery disease. Clopidogrel has long been the gold standard but has major pharmacological limitations such as a slow onset and long duration of effect, as well as weak platelet inhibition with high inter-individual pharmacokinetic and pharmacodynamic variability. There has been a strong need to develop potent P2Y12 receptor antagonists with more favorable pharmacological properties. Prasugrel and ticagrelor are more potent and have a faster onset of action; however, they have shown an increased bleeding risk compared with clopidogrel. Cangrelor is highly potent and has a very rapid onset and offset of effect; however, its indication is limited to P2Y12 antagonist-naïve patients undergoing percutaneous coronary intervention. Two novel P2Y12 receptor antagonists are currently in clinical development, namely vicagrel and selatogrel. Vicagrel is an analog of clopidogrel with enhanced and more efficient formation of its active metabolite. Selatogrel is characterized by a rapid onset of action following subcutaneous administration and developed for early treatment of a suspected acute myocardial infarction. This review article describes the clinical pharmacology profile of marketed P2Y12 receptor antagonists and those under development focusing on pharmacokinetic, pharmacodynamic, and drug-drug interaction liability.

Napabucasin Drug-Drug Interaction Potential, Safety, Tolerability, and Pharmacokinetics Following Oral Dosing in Healthy Adult Volunteers

Napabucasin is an orally administered reactive oxygen species generator that is bioactivated by the intracellular antioxidant nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1. Napabucasin induces cell death in cancer cells, including cancer stem cells. This phase 1 study (NCT03411122) evaluated napabucasin drug‐drug interaction potential for 7 cytochrome P450 (CYP) enzymes and the breast cancer resistance protein transporter/organic anion transporter 3. Healthy volunteers who tolerated napabucasin during period 1 received probe drugs during period 2, and in period 3 received napabucasin (240 mg twice daily; days 1‐11) plus a phenotyping cocktail containing omeprazole (CYP2C19), caffeine (CYP1A2), flurbiprofen (CYP2C9), bupropion (CYP2B6), dextromethorphan (CYP2D6), midazolam (CYP3A) (all oral; day 6), intravenous midazolam (day 7), repaglinide (CYP2C8; day 8), and rosuvastatin (breast cancer resistance protein/organic anion transporter 3; day 9). Drug‐drug interaction potential was evaluated in 17 of 30 enrolled volunteers. Napabucasin coadministration increased the area under the plasma concentration–time curve from time 0 extrapolated to infinity (geometric mean ratio [90% confidence interval]) of caffeine (124% [109.0%‐141.4%]), intravenous midazolam (118% [94.4%‐147.3%]), repaglinide (127% [104.7%‐153.3%]), and rosuvastatin (213% [42.5%‐1068.3%]) and decreased the area under the plasma concentration–time curve from time 0 extrapolated to infinity of dextromethorphan (71% [47.1%‐108.3%]), bupropion (79% [64.6%‐97.0%]), and hydroxybupropion (45% [15.7%‐129.6%]). No serious adverse events/deaths were reported. Generally, napabucasin is not expected to induce/inhibit drug clearance to a clinically meaningful degree.

Drug interactions: a review of the unseen danger of experimental COVID-19 therapies

As global health services respond to the coronavirus pandemic, many prescribers are turning to experimental drugs. This review aims to assess the risk of drug-drug interactions in the severely ill COVID-19 patient. Experimental therapies were identified by searching ClinicalTrials.gov for 'COVID-19', '2019-nCoV', '2019 novel coronavirus' and 'SARS-CoV-2'. The last search was performed on 30 June 2020. Herbal medicines, blood-derived products and in vitro studies were excluded. We identified comorbidities by searching PubMed for the MeSH terms 'COVID-19', 'Comorbidity' and 'Epidemiological Factors'. Potential drug-drug interactions were evaluated according to known pharmacokinetics, overlapping toxicities and QT risk. Drug-drug interactions were graded GREEN and YELLOW: no clinically significant interaction; AMBER: caution; RED: serious risk. A total of 2378 records were retrieved from ClinicalTrials.gov, which yielded 249 drugs that met inclusion criteria. Thirteen primary compounds were screened against 512 comedications. A full database of these interactions is available at www.covid19-druginteractions.org. Experimental therapies for COVID-19 present a risk of drug-drug interactions, with lopinavir/ritonavir (10% RED, 41% AMBER; mainly a perpetrator of pharmacokinetic interactions but also risk of QT prolongation particularly when given with concomitant drugs that can prolong QT), chloroquine and hydroxychloroquine (both 7% RED and 27% AMBER, victims of some interactions due to metabolic profile but also perpetrators of QT prolongation) posing the greatest risk. With management, these risks can be mitigated. We have published a drug-drug interaction resource to facilitate medication review for the critically ill patient.

Lopinavir-Ritonavir in SARS-CoV-2 Infection and Drug-Drug Interactions with Cardioactive Medications

Lopinavir-ritonavir combination is being used for the treatment of SARS-CoV-2 infection. A low dose of ritonavir is added to other protease inhibitors to take advantage of potent inhibition of cytochrome (CYP) P450 3A4, thereby significantly increasing the plasma concentration of coadministered lopinavir. Ritonavir also inhibits CYP2D6 and induces CYP2B6, CYP2C19, CYP2C9, and CYP1A2. This potent, time-dependent interference of major hepatic drug-metabolizing enzymes by ritonavir leads to several clinically important drug-drug interactions. A number of patients presenting with acute coronary syndrome and acute heart failure may have SARS-CoV-2 infection simultaneously. Lopinavir-ritonavir is added to their prescription of multiple cardiac medications leading to potential drug-drug interactions. Many cardiology, pulmonology, and intensivist physicians have never been exposed to clinical scenarios requiring co-prescription of cardiac and antiviral therapies. Therefore, it is essential to enumerate these drug-drug interactions, to avoid any serious drug toxicity, to consider alternate and safer drugs, and to ensure better patient care.

Thromboembolic events and Covid-19

The novel Corona virus infection (Covid-19) first identified in China in December 2019 has rapidly progressed in pandemic leading to significant mortality and unprecedented challenge for healthcare systems. Although the clinical spectrum of Covid-19 is variable, acute respiratory failure and systemic coagulopathy are common in severe Covid-19 patients. Lung is an important target of the SARS-CoV-2 virus causing eventually acute respiratory distress syndrome associated to a thromboinflammatory state. The cytokinic storm, thromboinflammation and pulmonary tropism are the bedrock of tissue lesions responsible for acute respiratory failure and for prolonged infection that may lead to multiple organ failure and death. The thrombogenicity of this infectious disease is illustrated by the high frequency of thromboembolic events observed even in Covid-19 patients treated with anticoagulation. Increased D-Dimers, a biomarker reflecting activation of hemostasis and fibrinolysis, and low platelet count (thrombocytopenia) are associated with higher mortality in Covid-19 patients. In this review, we will summarize our current knowledge on the thromboembolic manifestations, the disturbed hemostatic parameters, and the thromboinflammatory conditions associated to Covid-19 and we will discuss the modalities of anticoagulant treatment or other potential antithrombotic options.

Impact of Boosted Antiretroviral Therapy on the Pharmacokinetics and Efficacy of Clopidogrel and Prasugrel Active Metabolites

BACKGROUND AND OBJECTIVES

Prasugrel and clopidogrel are inhibitors of the ADP-P₂Y₁₂ platelet receptor used in acute coronary syndrome patients. They require bioactivation via isoenzymes such as cytochrome P450 (CYP) 3A4, CYP2C19 and CYP2B6. Ritonavir and cobicistat are potent CYP3A inhibitors, prescribed as pharmacokinetic (PK) enhancers in the treatment of human immunodeficiency virus (HIV) infection.

METHODS

In this study, the impact of boosted antiretroviral therapies (ARTs) on the PK of clopidogrel and prasugrel active metabolites (AMs), and on the efficacy of prasugrel and clopidogrel, were evaluated in a randomized crossover clinical trial.

RESULTS

A significantly lower exposure to clopidogrel AM [3.2-fold lower area under the concentration-time curve (AUC) and maximum plasma concentration (C_max)] and prasugrel AM (2.1-fold and 1.7-fold lower AUC and C_max) were demonstrated in HIV-infected patients treated with boosted ARTs compared with healthy controls; however, a differential impact was observed on platelet inhibition between clopidogrel and prasugrel. Clopidogrel 300 mg induced adequate (although modest) platelet inhibition in all healthy subjects, while platelet inhibition was insufficient in 44% of HIV patients. On the contrary, prasugrel 60 mg induced a potent platelet inhibition in both healthy and HIV-infected subjects.

CONCLUSION

Prasugrel appears to remain an adequate antiplatelet agent in HIV-infected patients and could be preferred to clopidogrel in this context, regardless of the metabolic interaction and inhibition of its bioactivation pathways.

Evaluation of cytochrome P450 3A4‑mediated drug‑drug interaction potential between P2Y12 inhibitors and statins

Ticagrelor and prasugrel are widely used in the treatment of acute coronary syndrome. The co‑administration of ticagrelor or prasugrel with statins in the clinic has already drawn a great deal of attention. The aims of the present study were to evaluate the safety and effectiveness, and guide the rational clinical use of, co‑administration of ticagrelor or prasugrel with statins by exploring potential drug interactions. The activity of cytochrome P450 family 3 subfamily A member 4 (CYP3A4) was detected, and its protein and mRNA expression levels were measured in a rat model and liver microsomes to evaluate the effect of the drug combinations on CYP3A4. High performance liquid chromatography, western blotting and reverse transcription‑quantitative PCR were used to perform these investigations. The in vitro experiments suggested that ticagrelor inhibited CYP3A4 activity, with IC50 and inhibitor constant (Ki) values of 68.74 and 26.47 µM, respectively; prasugrel also inhibited CYP3A4, activity with IC50 and Ki values of 16.24 and 10.84 µM, respectively. When different dosages of the antagonists were combined with simvastatin or atorvastatin, the metabolic rate was reduced more effectively at higher dosages when compared with lower dosages. An in vivo pharmacokinetic study demonstrated that the co‑administration of ticagrelor or prasugrel with simvastatin caused an increase in the principal pharmacokinetic parameters of the probe drug dapsone [area under the concentration/time curve (AUC)0‑t, AUC0‑∞ and t1/2] and a decrease in clearance compared with ticagrelor, prasugrel or simvastatin alone. Additional studies confirmed that the two investigated P2Y12 inhibitors were able to decrease the protein level of CYP3A4 by promoting protein degradation through the proteasomal pathway, and combination with statins such as simvastatin had a synergistic inhibitory effect on CYP3A4 activity. These results demonstrated that the co‑administration of P2Y12 inhibitors with simvastatin could markedly inhibit the activity of CYP3A4, and these findings will further influence the assessment of the clinical effectiveness (reduced or enhanced efficacy) and safety (bleeding and rhabdomyolysis) in the clinic.

CYP3A4*22 Impairs the Elimination of Ticagrelor, But Has No Significant Effect on the Bioactivation of Clopidogrel or Prasugrel

CYP3A enzymes participate in the elimination of ticagrelor and the bioactivation of clopidogrel and prasugrel. We studied the effects of functional CYP3A genetic variants (CYP3A4*22; rs35599367 and CYP3A5*3; rs776746) on the pharmacokinetics and pharmacodynamics of ticagrelor, clopidogrel, and prasugrel. Six healthy volunteers with the CYP3A4*1/*22 and CYP3A5*3/*3 genotype (CYP3A4*22 carriers), eight with the CYP3A4*1/*1 and CYP3A5*1/*3 genotype (CYP3A5 expressors), and 11-13 with the CYP3A4*1/*1 and CYP3A5*3/*3 genotypes (controls) ingested single doses of ticagrelor, clopidogrel, and prasugrel on separate occasions. Ticagrelor area under the plasma concentration-time curve (AUC) was 89% (P = 0.004) higher in CYP3A4*22 carriers than in controls. CYP3A4*22 carriers also showed more pronounced platelet inhibition at 24 hours after ticagrelor ingestion than the controls (43% vs. 21%; P = 0.029). The CYP3A5 genotype did not affect ticagrelor pharmacokinetics. Neither CYP3A5 nor CYP3A4 genotypes significantly affected prasugrel or clopidogrel. In conclusion, the CYP3A4*22 allele markedly impairs ticagrelor elimination enhancing its antiplatelet effect.

Cytochrome P450 2B6 and 2C9 genotype polymorphism – a possible cause of prasugrel low responsiveness

The cytochrome P450 (CYP) isoenzymes are essential for the metabolic activation of the prodrug prasugrel. Little is known about the impact of polymorphism of these isoenzymes on the prevalence of prasugrel low responsiveness (PLR) in patients with coronary artery disease. We investigated the frequency of PLR and the question whether PLR is associated with decreased/non-function polymorphisms of the CYP isoenzymes (2C9*2, 2C9*3, 2C19*2, 2C19*3, and 2B6*6). Our study included 355 patients who underwent percutaneous coronary stenting. The patients were initially treated with either prasugrel (n=90; 60/10 mg: loading/daily maintenance dose) or 600/75 mg clopidogrel hydrogensulfate (n=265) in combination with 500/100 mg acetylsalicylic acid (ASA). Platelet function was tested by impedance aggregometry 48 hours after taking the loading dose. Prasugrel achieved on the average significantly higher levels of platelet inhibition as compared to clopidogrel (mean 27.3 U vs 41.2 U). The frequencies of low response for prasugrel, clopidogrel and ASA were 9.8%, 35.1% and 14.9%, respectively. We identified only body mass index to be associated with PLR. PLR was not caused by a loss of ADP P2Y12-receptor function. Half of the patients with PLR were carriers of the reducedfunction allele CYP2B6*6, and 41.7% had the genetic variant CYP2C9*2. The allele CYP2C9*3 was detected in three patients with PLR (25%) and two patients with PLR (16.7%) carried the gene variant CYP2C19*2. In conclusion, the rate of low responders was significantly lower among patients treated with prasugrel than with clopidogrel. PLR are more often carriers of CYP2C9*2 (50% in PLR) than when compared to the prevalence described in literature. Also, there is a trend to an increased frequency of CYP2B6*6 in PLR. In conclusion, CYP2B6 and CYP2C9 polymorphisms seem to be associated with prasugrel low-response.

The challenge of polypharmacy in an aging population and implications for future antiretroviral therapy development

: It is estimated that by 2030 nearly three-quarters of persons living with HIV will be 50 years and older. The aging HIV population presents a new clinical concern for HIV providers: adverse effects from polypharmacy. An aging population means more comorbidities and potentially more drug-drug interactions for providers to manage. This review discusses major comorbidities including cardiovascular disease, anticoagulation, hypertension, diabetes mellitus and malignancy and considerations for drug-interactions with antiretrovirals.

Coadministration of ticagrelor and ritonavir: Toward prospective dose adjustment to maintain an optimal platelet inhibition using the PBPK approach

Ticagrelor is a potent antiplatelet drug metabolized by cytochrome (CYP)3A. It is contraindicated in patients with human immunodeficiency virus (HIV) because of the expected CYP3A inhibition by most protease inhibitors, such as ritonavir and an increased bleeding risk. In this study, a physiologically based pharmacokinetic (PBPK) model was created for ticagrelor and its active metabolite (AM). Based on the simulated interaction between ticagrelor 180 mg and ritonavir 100 mg, a lower dose of ticagrelor was calculated to obtain, when coadministered with ritonavir, the same pharmacokinetic (PK) and platelet inhibition as ticagrelor administered alone. A clinical study was thereafter conducted in healthy volunteers. Observed PK profiles of ticagrelor and its AM were successfully predicted with the model. Platelet inhibition was nearly complete in both sessions despite administration of a fourfold lower dose of ticagrelor in the second session. This PBPK model could be prospectively used to broaden the usage of ticagrelor in patients with ritonavir-treated HIV regardless of the CYP3A inhibition.

Dosing Recommendations for Concomitant Medications During 3D Anti-HCV Therapy

The development of direct-acting antiviral (DAA) agents has reinvigorated the treatment of hepatitis C virus infection. The availability of multiple DAA agents and drug combinations has enabled the transition to interferon-free therapy that is applicable to a broad range of patients. However, these DAA combinations are not without drug-drug interactions (DDIs). As every possible DDI permutation cannot be evaluated in a clinical study, guidance is needed for healthcare providers to avoid or minimize drug interaction risk. In this review, we evaluated the DDI potential of the novel three-DAA combination of ombitasvir, paritaprevir, ritonavir, and dasabuvir (the 3D regimen) with more than 200 drugs representing 19 therapeutic drug classes. Outcomes of these DDI studies were compared with the metabolism and elimination routes of prospective concomitant medications to develop mechanism-based and drug-specific guidance on interaction potential. This analysis revealed that the 3D regimen is compatible with many of the drugs that are commonly prescribed to patients with hepatitis C virus infection. Where interaction is possible, risk can be mitigated by paying careful attention to concomitant medications, adjusting drug dosage as needed, and monitoring patient response and/or clinical parameters.

Ritonavir is the best alternative to ketoconazole as an index inhibitor of cytochrome P450-3A in drug-drug interaction studies

AIMS

The regulatory prohibition of ketoconazole as a CYP3A index inhibitor in drug-drug interaction (DDI) studies has compelled consideration of alternative inhibitors.

METHODS

The biomedical literature was searched to identify DDI studies in which oral midazolam (MDZ) was the victim, and the inhibitory perpetrator was either ketoconazole, itraconazole, clarithromycin, or ritonavir. The ratios (RAUC ) of total area under the curve (AUC) for MDZ with inhibitor divided by MDZ AUC in the control condition were aggregated across individual studies for each inhibitor.

RESULTS

Mean (± SE) RAUC values were: ketoconazole (15 studies, 131 subjects), 11.5 (±1.2); itraconazole (five studies, 48 subjects), 7.3 (±1.0); clarithromycin (five studies, 73 subjects), 6.5 (±10.9); and ritonavir (13 studies, 159 subjects), 14.5 (±2.0). Differences among inhibitors were significant (F = 5.31, P < 0.005). RAUC values were not significantly related to inhibitor dosage or to duration of inhibitor pre-exposure prior to administration of MDZ.

CONCLUSIONS

Ritonavir produces CYP3A inhibition equivalent to or greater than ketoconazole, and is the best index CYP3A inhibitor alternative to ketoconazole. Cobicistat closely resembles ritonavir in structure and function, and can also be considered. Itraconazole and clarithromycin are not suitable alternatives since they do not produce inhibition comparable with ketoconazole or ritonavir, and have other significant disadvantages as well.

Effect of grapefruit juice on the bioactivation of prasugrel

AIMS

The P2Y12 inhibitor prasugrel is a prodrug, which is activated after its initial hydrolysis partly by cytochrome P450 (CYP) 3A4. Grapefruit juice, a strong inactivator of intestinal CYP3A4, greatly reduces the activation and antiplatelet effects of clopidogrel. The aim of this study was to investigate the effects of grapefruit juice on prasugrel.

METHODS

In a randomized crossover study, seven healthy volunteers ingested 200 ml of grapefruit juice or water three times daily for 4 days. On day 3, they ingested a single 10 mg dose of prasugrel with an additional 200 ml of grapefruit juice or water. Plasma concentrations of prasugrel metabolites and the antiplatelet effect were measured.

RESULTS

Grapefruit juice increased the geometric mean area under the plasma concentration-time curve (AUC(0-∞)) of the primary, inactive metabolite of prasugrel to 164% of the control value (95% confidence interval 122-220%, P = 0.008), without a significant effect on its peak plasma concentration (C(max)). The C(max) and AUC(0-∞) of the secondary, active metabolite were decreased to 51% (95% confidence interval 32-84%, P = 0.017) and 74% of the control value (95% confidence interval 60-91%, P = 0.014) by grapefruit juice (P < 0.05). The average platelet inhibition, assessed with the VerifyNow® method at 0-24 h after prasugrel intake, was 5 percentage points (95% confidence interval 1-10 percentage points) lower in the grapefruit juice phase than in the water phase (P = 0.034).

CONCLUSIONS

Grapefruit juice reduces the bioactivation of prasugrel, but this has only a limited effect on the antiplatelet effect of prasugrel.

Cardiovascular disease in HIV patients: from bench to bedside and backwards

HIV patients are exposed to a higher risk of adverse cardiovascular events, due to complex interactions between traditional risk factors and HIV infection itself in terms of ongoing endothelial dysfunctional immune activation/inflammation and increased risk of thrombosis. On the other hand, long-span antiretroviral therapy administration still raises questions on its long-term safety in an era in which life expectancy is becoming longer and longer while treatment of non-HIV-related serious events is increasingly raising concern. In this article, we will critically analyse the current knowledge of pathological and clinical aspects pertaining to the increased risk of cardiovascular events associated with HIV.

Pharmacokinetic drug interactions with clopidogrel: updated review and risk management in combination therapy

Background

Coprescribing of clopidogrel and other drugs is common. Available reviews have addressed the drug–drug interactions (DDIs) when clopidogrel is as an object drug, or focused on combination use of clopidogrel and a special class of drugs. Clinicians may still be ignorant of those DDIs when clopidogrel is a precipitant drug, the factors determining the degree of DDIs, and corresponding risk management.

Methods

A literature search was performed using PubMed, MEDLINE, Web of Science, and the Cochrane Library to analyze the pharmacokinetic DDIs of clopidogrel and new P2Y₁₂ receptor inhibitors.

Results

Clopidogrel affects the pharmacokinetics of cerivastatin, repaglinide, ferulic acid, sibutramine, efavirenz, and omeprazole. Low efficacy of clopidogrel is anticipated in the presence of omeprazole, esomeprazole, morphine, grapefruit juice, scutellarin, fluoxetine, azole antifungals, calcium channel blockers, sulfonylureas, and ritonavir. Augmented antiplatelet effects are anticipated when clopidogrel is coprescribed with aspirin, curcumin, cyclosporin, St John’s wort, rifampicin, and angiotensin-converting enzyme inhibitors. The factors determining the degree of DDIs with clopidogrel include genetic status (eg, cytochrome P540 [CYP]2B6*6, CYP2C19 polymorphism, CYP3A5*3, CYP3A4*1G, and CYP1A2-163C.A), species differences, and dose strength. The DDI risk does not exhibit a class effect, eg, the effects of clopidogrel on cerivastatin versus other statins, the effects of proton pump inhibitors on clopidogrel (omeprazole, esomeprazole versus pantoprazole, rabeprazole), the effects of rifampicin on clopidogrel versus ticagrelor and prasugrel, and the effects of calcium channel blockers on clopidogrel (amlodipine versus P-glycoprotein-inhibiting calcium channel blockers). The mechanism of the DDIs with clopidogrel involves modulating CYP enzymes (eg, CYP2B6, CYP2C8, CYP2C19, and CYP3A4), paraoxonase-1, hepatic carboxylesterase 1, P-glycoprotein, and organic anion transporter family member 1B1.

Conclusion

Effective and safe clopidogrel combination therapy can be achieved by increasing the awareness of potential changes in efficacy and toxicity, rationally selecting alternatives, tailoring drug therapy based on genotype, checking the appropriateness of physician orders, and performing therapeutic monitoring.

Drug interactions and antiretroviral drug monitoring

Owing to the improved longevity afforded by combination antiretroviral therapy (cART), HIV-infected individuals are developing several non-AIDS-related comorbid conditions. Consequently, medical management of the HIV-infected population is increasingly complex, with a growing list of potential drug-drug interactions (DDIs). This article reviews some of the most relevant and emerging potential interactions between antiretroviral medications and other agents. The most common DDIs are those involving protease inhibitors or non-nucleoside reverse transcriptase inhibitors, which alter the cytochrome P450 enzyme system and/or drug transporters such as p-glycoprotein. Of note are the new agents for the treatment of chronic hepatitis C virus infection. These new classes of drugs and others drugs that are increasingly used in this patient population represent a significant challenge with regard to achieving the goals of effective HIV suppression and minimization of drug-related toxicities. Awareness of DDIs and a multidisciplinary approach are imperative in reaching these goals.

Automated direct extraction and analysis of dried blood spots employing on-line SPE high-resolution accurate mass bioanalysis

Background: Online automated extraction of dried blood spots (DBS) via direct extraction to a solid-phase extraction (SPE) cartridge and bioanalysis by high-resolution accurate mass spectrometry was examined. The methodology was validated and used to investigate the effect of hematocrit on assay bias using partial and whole spot extractions from accurately dispensed blood samples. Results: The completed analysis of a DBS sample was accomplished within 2 to 3 min using the online DBS-SPE platform. Hematocrit related bias was observed (>15%) for the partial DBS extractions, but not when the whole DBS was eluted. Conclusion: Results demonstrate successful implementation of automated online DBS-SPE high-resolution accurate mass spectrometry analysis and the remediation of hematocrit bias using a capillary micro dispenser for accurate spotting of blood samples.

Drug Interactions Between Antiplatelet or Novel Oral Anticoagulant Medications and Antiretroviral Medications

Objective: To review potential drug interactions between antiretroviral (ARV) medications and antiplatelets or novel oral anticoagulants (NOACs). Data Sources: A literature search of MEDLINE, PubMed, EMBASE, International Pharmaceutical Abstracts, and Google Scholar was performed using the search terms (1) clopidogrel or ticagrelor or prasugrel, (2) dabigatran or rivaroxaban or apixaban, and (3) antiretrovirals. Study Selection and Data Extraction: Any English language study or case report describing a drug interaction between an ARV and an antiplatelet or NOAC was included. Additional information was taken from pharmacokinetic studies of individual agents alone or information from similar drug interactions. Results: Two studies were identified through the literature search: one reporting an in vivo interaction between ritonavir and prasugrel and the other an in vitro interaction between efavirenz and clopidogrel. A case report describing a drug interaction between nevirapine and rivaroxaban was also located. Information from pharmacokinetic studies and from similar drug interactions allowed for a comprehensive review of potential drug interactions. Conclusions: There are potential drug interactions between ARVs, antiplatelet agents or NOACs. Management of these interactions may include selecting ARVs with a lower potential for drug interactions or choosing antiplatelet agents or NOACs least likely to interact with ARVs. With protease inhibitors or cobicistat, clopidogrel and dabigatran do not appear to have clinically significant interactions. Nonnucleoside reverse transcriptase inhibitors have a low potential for interactions with prasugrel and dabigatran. Clinically significant drug interactions are unlikely to occur between antiplatelet agents or NOACs and nucleoside reverse transcriptase inhibitors raltegravir, dolutegravir, or maraviroc.

How to manage prasugrel and ticagrelor in daily practice

Prasugrel and ticagrelor are next-generation antiplatelet agents that provide a rapider and more potent inhibition of platelet P2Y12 receptor than clopidogrel. In combination with aspirin, these new P2Y12 inhibitors are now the first line treatments for patients with acute coronary syndrome. However, these potent antiplatelet agents introduce a new paradigm in the daily management of antithrombotic drugs, particularly when an invasive procedure is planned. The pharmacology of these antiplatelet agents, and the results of the main clinical trials, are reviewed with a special focus on good prescription practices (indications, contra-indications, drug interactions), and on peri-operative management. Strategies are proposed for safely reducing the bleeding risk in elderly patients, in patients requiring concomitant oral anticoagulant therapy, or in patients with an increased haemorrhagic risk.

Clinical implications of drug-drug interactions with P2Y12 receptor inhibitors

Polypharmacy in patients undergoing coronary artery stenting or in those presenting with an acute coronary syndrome is common. Nevertheless, the risk of drug-drug interactions in patients treated simultaneously with P2Y12 receptor inhibitors is less well considered in routine clinical practice. Whereas the irreversible P2Y12 receptor inhibitors clopidogrel and prasugrel are prodrugs requiring cytochrome P450 (CYP) enzymes for metabolic activation, such activation is not necessary for the direct-acting reversible P2Y12 receptor inhibitor ticagrelor. Several drugs frequently used in cardiology have been shown to interact with the metabolism of P2Y12 receptor inhibitors in pharmacodynamic studies. Whereas several drug-drug interactions have been described for clopidogrel and ticagrelor, prasugrel seems to have a low potential for drug-drug interactions. The clinical implications of these interactions have raised concern. In general, concomitant administration of P2Y12 receptor antagonists and strong inhibitors or inducers of CYP3A/CYP2C19 should be performed with caution in patients treated with clopidogrel/ticagrelor. Under most circumstances, clinicians have the option of prescribing alternative drugs with less risk of drug-drug interactions when used concomitantly with P2Y12 receptor inhibitors.

Simultaneous LC–MS/MS quantification of P-glycoprotein and cytochrome P450 probe substrates and their metabolites in DBS and plasma

Background: An LC–MS/MS method has been developed for the simultaneous quantification of P-glycoprotein (P-gp) and cytochrome P450 (CYP) probe substrates and their Phase I metabolites in DBS and plasma. P-gp (fexofenadine) and CYP-specific substrates (caffeine for CYP1A2, bupropion for CYP2B6, flurbiprofen for CYP2C9, omeprazole for CYP2C19, dextromethorphan for CYP2D6 and midazolam for CYP3A4) and their metabolites were extracted from DBS (10 µl) using methanol. Analytes were separated on a reversed-phase LC column followed by SRM detection within a 6 min run time. Results: The method was fully validated over the expected clinical concentration range for all substances tested, in both DBS and plasma. The method has been successfully applied to a PK study where healthy male volunteers received a low dose cocktail of the here described P-gp and CYP probes. Good correlation was observed between capillary DBS and venous plasma drug concentrations. Conclusion: Due to its low-invasiveness, simple sample collection and minimal sample preparation, DBS represents a suitable method to simultaneously monitor in vivo activities of P-gp and CYP.