Bleeding Complications in a Patient After the Unexpected Interaction between Valproic Acid and Phenprocoumon

BACKGROUND

Phenprocoumon is a vitamin K antagonist that is widely prescribed in Europe and Latin America for the prophylaxis and treatment of thromboembolic events.

CASE PRESENTATION

A 90-year-old female was admitted to our hospital with tonic-clonic seizures, possibly due to dementia syndrome. Valproic acid (VPA) was prescribed for the treatment of seizures. VPA is an inhibitor of cytochrome P450 (CYP) 2C9 enzymes. A pharmacokinetic interaction with phenprocoumon occurred, which is a substrate for CYP2C9 enzymes. The interaction resulted in a strong INR increase and subsequent clinically relevant bleeding in our patient. Valproic acid is not specifically mentioned in the phenprocoumon drug label as a CYP2C9 inhibitor, and in the Dutch medication surveillance database, no medication alert is shown when prescribing this combination, and no interaction with phenprocoumon has been reported so far.

CONCLUSION

When prescribing this combination, the prescriber should be warned and advised to intensify INR monitoring if the combination is to be continued.

Meropenem to Treat Valproic Acid Intoxication

ABSTRACT

This therapeutic drug monitoring (TDM) grand round describes a patient with serious valproic acid intoxication. A total valproic acid level of 844 mg/L and an unbound valproic acid level of 604 mg/L were observed. Meropenem was administered to enhance the clearance of valproic acid. This off-label usage of meropenem is based on the drug-drug interaction between carbapenems and valproic acid, which reduced the level of valproic acid within 24 hours after administration.

SARS-CoV-2 and HIV protease inhibitors: why lopinavir/ritonavir will not work for COVID-19 infection

Since the beginning of the outbreak of severe acute respiratory syndrome (SARS) coronavirus (CoV) 2, lopinavir/ritonavir was selected for treatment. The recent publication of Cao et al. in the New England Journal of Medicine showed that lopinavir/ritonavir treatment did not accelerate clinical improvement compared with standard of care. This raised the question of whether in retrospect we could have known this. The aim of this paper is to gather all the available evidence and to comprehensively discuss this issue.

Recommendations for Dosing of Repurposed COVID-19 Medications in Patients with Renal and Hepatic Impairment

INTRODUCTION

In December 2019, an outbreak of a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) began, resulting in a number of antivirals and immune modulators being repurposed to treat the associated coronavirus disease 2019 (COVID-19). Many patients requiring treatment for COVID-19 may have either pre-existing renal or hepatic disease or experience acute renal/hepatic injury as a result of the acute infection. Altered renal or hepatic function can significantly affect drug concentrations of medications due to impaired drug metabolism and excretion, resulting in toxicity or reduced efficacy. The aim of this paper is to review the pharmacokinetics and available study data for the experimental COVID-19 therapies in patients with any degree of renal or hepatic impairment to make recommendations for dosing.

METHODS

COVID-19 agents included in these recommendations were listed as primaries on the University of Liverpool COVID-19 drug interaction website ( www.covid19-druginteractions.org ), initially identified from Clinicialtrials.gov and ChicCTR.org.cn. A literature search was performed using PubMed and EMBASE as well as product licences and pharmacokinetic databases.

FINDINGS

Remdesivir, dexamethasone, azithromycin, favipiravir, lopinavir/ritonavir, atazanavir, hydroxychloroquine, interferon beta, ribavirin, tocilizumab, anakinra and sarilumab were identified as experimental drugs being used in COVID-19 trials as of November 2020. Limited study data was found for these drugs in patients with renal or hepatic impairment for COVID-19 or other indications. Recommendations were made based on available data, consideration of pharmacokinetic properties (including variability), the dosing and anticipated treatment duration of each regimen in COVID-19 and known toxicities.

CONCLUSION

Dosing of drugs used to treat COVID-19 in patients with renal or hepatic impairment is complex. These recommendations were produced to provide guidance to clinicians worldwide who are treating patients with COVID-19, many of whom will have some degree of acute or chronic renal or hepatic impairment.

Pharmacokinetics of oral tenofovir disoproxil fumarate in pregnancy and lactation: a systematic review

BACKGROUND

Tenofovir disoproxil fumarate (TDF), the oral prodrug of tenofovir (TFV), is advocated in pregnancy for prevention of mother-to-child transmission (PMCT) with failure of hepatitis B immunoglobulin and vaccination. The pharmacokinetics of TDF monotherapy for PMCT-HBV is important if deployment is to emulate the success of multiple antiretrovirals (ARVs) for PMCT-HIV in resource-constrained settings.

METHODS

This systematic review followed a protocol and is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA) guidelines. We included studies that enrolled pregnant women who received oral TDF therapy as monotherapy or in combination with other ARVs: irrespective of the reason for receiving the drug (for example, HIV, HBV or pre-exposure prophylaxis); and reported pharmacokinetics.

RESULTS

The area under the concentration-time curve (AUC), maximum plasma concentrations (C_max) and last measurable plasma concentration (C_last) of TFV were decreased in the second and third trimester compared with first trimester or post-partum. In none of the manuscripts was the non-pregnant HBV threshold of C_max of 300 ng/ml reached, but the 50% effective concentration (EC₅₀) of TFV is lower for treatment of HBV compared with HIV. The TFV concentration in breastfed infants was 0.03% of the recommended infant dose.

CONCLUSIONS

Most knowledge of pharmacokinetics of TFV in pregnancy results from studies on HIV involving multiple ARVs. Increased TFV clearance occurred in the second and third trimester when optimal TFV concentrations are required to maximize suppression of HBV in the window before birth. Dose or duration adjustments will be better conceptualized with concurrent analysis of the pharmacokinetics of TFV monotherapy and hepatitis B pharmacodynamics in pregnancy.

Effect of Pregnancy and Concomitant Antiretrovirals on the Pharmacokinetics of Tenofovir in Women With HIV Receiving Tenofovir Disoproxil Fumarate-Based Antiretroviral Therapy Versus Women With HBV Receiving Tenofovir Disoproxil Fumarate Monotherapy

Tenofovir disoproxil fumarate (TDF) is recommended as part of antiretroviral therapy (ART) for pregnant women with HIV and as monotherapy for pregnant women with hepatitis B virus (HBV) monoinfection at high risk of transmitting infection to their infants. Tenofovir (TFV) plasma exposures are reduced during pregnancy; however, concomitant antiretrovirals and the viral infection itself can also influence TFV pharmacokinetics. Our aim was to compare TFV pharmacokinetics in pregnant women receiving TDF‐based ART, with or without a ritonavir‐boosted protease inhibitor (r/PI), to pregnant women with HBV receiving TDF monotherapy. Non‐r/PI regimens were primarily integrase strand transfer inhibitors or nonnucleoside reverse transcriptase inhibitor–based regimens. Data were combined from a pharmacokinetic study of pregnant women with HIV on ART (PANNA), and a study assessing TFV pharmacokinetics in pregnant women with HBV (iTAP). A total of 196 pregnant women, 59 with HIV (32 receiving r/PIs) and 137 with HBV monoinfection were included. Intraindividual TFV area under the plasma concentration–time curve from time 0 to 24 hours was 25%, 26%, and 21% lower during the third trimester compared to 1 month postpartum in women with HIV using TDF and an r/PI or TDF and non‐r/PI and women with HBV receiving TDF monotherapy, respectively. TFV area under the plasma concentration–time curve from time 0 to 24 hours was similar in pregnant women receiving non‐r/PI to pregnant women with HBV receiving TDF monotherapy (1.84 vs 1.86 µg • h/mL); however, pregnant women receiving TDF with an r/PI had higher exposures (2.41 µg • h/mL; P < .01). Pregnancy reduces TFV exposure and the relative size was not impacted by concomitant antiretroviral drugs or viral infection, but a drug‐drug interaction between TDF and r/PI remains during pregnancy, leading to higher exposures than those on TDF and non‐r/PI or TDF monotherapy.

Cardiovascular Risk Management and Hepatitis C: Combining Drugs

Direct-acting antivirals (DAAs) are known victims (substrate) and perpetrators (cause) of drug–drug interactions (DDIs). These DAAs are used for the treatment of hepatitis C virus (HCV) infections and are highly effective drugs. Drugs used for cardiovascular risk management are frequently used by HCV-infected patients, whom also are treated with DAAs. Therefore, the aim of this review was to describe DDIs between cardiovascular drugs (CVDs) and DAAs. An extensive literature search was performed containing search terms for the marketed DAAs and CVDs (β-blocking agents, ACE inhibitors, angiotensin II antagonists, renin inhibitors, diuretics, calcium channel blockers, statins/ezetimibe, fibrates, platelet aggregation inhibitors, vitamin K antagonists, heparins, direct Xa inhibitors, nitrates, amiodarone, and digoxin). In particular, the drug labels from the European Medicines Agency and the US Food and Drug Administration were used. A main finding of this review is that CVDs are mostly victims of DDIs with DAAs. Therefore, when possible, monitoring of pharmacodynamics is recommended when coadministering these drugs with DAAs. Nevertheless, it is sometimes better to discontinue a drug on a temporary basis (statins, ezetimide). The DAAs are victims of DDIs in combination with bisoprolol, carvedilol, labetalol, verapamil, and gemfibrozil. Despite there are many DDIs predicted in this review, most of these DDIs can be managed by monitoring the efficacy and toxicity of the victim drug or by switching to another CVD/DAA.

Prospective validation of a model-informed precision dosing tool for vancomycin in intensive care patients

AIMS

Vancomycin is an important antibiotic for critically ill patients with Gram-positive bacterial infections. Critically ill patients typically have severely altered pathophysiology, which leads to inefficacy or toxicity. Model-informed precision dosing may aid in optimizing the dose, but prospectively validated tools are not available for this drug in these patients. We aimed to prospectively validate a population pharmacokinetic model for purpose model-informed precision dosing of vancomycin in critically ill patients.

METHODS

We first performed a systematic evaluation of various models on retrospectively collected pharmacokinetic data in critically ill patients and then selected the best performing model. This model was implemented in the Insight Rx clinical decision support tool and prospectively validated in a multicentre study in critically ill patients. The predictive performance was obtained as mean prediction error and relative root mean squared error.

RESULTS

We identified 5 suitable population pharmacokinetic models. The most suitable model was carried forward to a prospective validation. We found in a prospective multicentre study that the selected model could accurately and precisely predict the vancomycin pharmacokinetics based on a previous measurement, with a mean prediction error and relative root mean squared error of respectively 8.84% (95% confidence interval 5.72-11.96%) and 19.8% (95% confidence interval 17.47-22.13%).

CONCLUSION

Using a systematic approach, with a retrospective evaluation and prospective verification we showed the suitability of a model to predict vancomycin pharmacokinetics for purposes of model-informed precision dosing in clinical practice. The presented methodology may serve a generic approach for evaluation of pharmacometric models for the use of model-informed precision dosing in the clinic.

Mercaptopurine and Metabolites in Breast Milk

A 35-year-old pregnant woman visited our outpatient clinical questioning the safety of once daily 50 mg mercaptopurine (MP) during pregnancy and lactation, which was successfully treating her Crohn's disease. We measured MP and its metabolites in plasma and breast milk and found after 4 hours of intake of MP, no MP or its metabolites in breast milk. We concluded that 4 hours after intake of MP, no exposure of the suckling infant to MP and its metabolites was found while being breastfed.

Metformin Alters Human Host Responses to Mycobacterium tuberculosis in Healthy Subjects

BACKGROUND

Metformin, the most widely administered diabetes drug, has been proposed as a candidate adjunctive host-directed therapy for tuberculosis, but little is known about its effects on human host responses to Mycobacterium tuberculosis.

METHODS

We investigated in vitro and in vivo effects of metformin in humans.

RESULTS

Metformin added to peripheral blood mononuclear cells from healthy volunteers enhanced in vitro cellular metabolism while inhibiting the mammalian target of rapamycin targets p70S6K and 4EBP1, with decreased cytokine production and cellular proliferation and increased phagocytosis activity. Metformin administered to healthy human volunteers led to significant downregulation of genes involved in oxidative phosphorylation, mammalian target of rapamycin signaling, and type I interferon response pathways, particularly following stimulation with M. tuberculosis, and upregulation of genes involved in phagocytosis and reactive oxygen species production was increased. These in vivo effects were accompanied by a metformin-induced shift in myeloid cells from classical to nonclassical monocytes. At a functional level, metformin lowered ex vivo production of tumor necrosis factor α, interferon γ, and interleukin 1β but increased phagocytosis activity and reactive oxygen species production.

CONCLUSION

Metformin has a range of potentially beneficial effects on cellular metabolism, immune function, and gene transcription involved in innate host responses to M. tuberculosis.

Review article: clinical pharmacology of current and investigational hepatitis B virus therapies

BACKGROUND

Treatment of hepatitis B virus (HBV) infection with current therapy suppresses HBV DNA, but loss of hepatitis B surface antigen (HBsAg; functional cure), is rare. Multiple compounds are under investigation.

AIMS

To describe the pharmacology, including drug interactions, efficacy, safety and mechanisms of action of investigational compounds for HBV infection.

METHODS

Descriptive review using PubMed and Google to identify literature/conference papers on investigational compounds (≥Phase 2) with data on efficacy and safety in HBV-infected patients.

RESULTS

Bulevirtide, JNJ-56136379, ABI-H0731, REP-2139, and inarigivir decrease HBV DNA/RNA, with greater potency than current nucleos(t)ide analogues. REP-2139 (25%-75% of patients, 20-48 weeks treatment) and inarigivir (26% of patients, 12-24 weeks treatment) induce HBsAg loss. ARO-HBV reduced (>1.5 log₁₀ UI/mL) HBsAg in 85% of patients (12 weeks treatment). There are some safety concerns with investigational agents (e.g., increased bile acids with bulevirtide, and liver enzyme flares with REP-2139) which will require a risk benefit assessment compared with current therapies. Single and multidose pharmacokinetic data are available for bulevirtide, JNJ-56136379, ABI-H0731; no such data are available for REP-2139, ARO-HBV, inarigivir. Initial drug interaction assessments have been performed with bulevirtide and inarigivir (only in vitro).

CONCLUSIONS

There are promising investigational therapies for HBV infection. Increasing the potential for HBsAg loss may result in more patients achieving functional cure. However, many knowledge gaps remain such as pharmacokinetics in those with HBV, cirrhosis and renal impairment but also the interaction potential between investigational therapies, risk-benefit profiles, and potential for drug interactions with medications used to treat comorbidities associated with aging.

Viral Hepatitis C Therapy: Pharmacokinetic and Pharmacodynamic Considerations: A 2019 Update

It has been estimated by the World Health Organization (WHO) that over 71 million people were infected with the hepatitis C virus (HCV) in 2015. Since then, a number of highly effective direct-acting antiviral (DAA) regimens have been licensed for the treatment of chronic HCV infection: sofosbuvir/daclatasvir, sofosbuvir/ledipasvir, elbasvir/grazoprevir, sofosbuvir/velpatasvir, glecaprevir/pibrentasvir, and sofosbuvir/velpatasvir/voxilaprevir. With these treatment regimens, almost all chronic HCV-infected patients, even including prior DAA failures, can be treated effectively and safely. It is therefore likely that further development of DAAs will be limited. In this descriptive review we provide an overview of the clinical pharmacokinetic characteristics of currently available DAAs by describing their absorption, distribution, metabolism, and excretion. Potential drug-drug interactions with the DAAs are briefly discussed. Furthermore, we summarize what is known about the pharmacodynamics of the DAAs in terms of efficacy and safety. We briefly discuss the relationship between the pharmacokinetics of the DAAs and efficacy or toxicity in special populations, such as hard to cure patients and patients with liver cirrhosis, liver transplantation, renal impairment, hepatitis B virus or HIV co-infection, bleeding disorders, and children. The aim of this overview is to educate/update prescribers and pharmacists so that they are able to safely and effectively treat HCV-infected patients even in the presence of underlying co-infections or co-morbidities.

The Observed Effect of Gastric Bypass Surgery on Direct-acting Antiviral Treatment: a Case Report

Chronic hepatitis C virus (HCV) infection can be cured with treatment using direct-acting antivirals (DAAs). Although these drugs have been widely studied, information about certain special populations is missing. In this case report we describe a treatment-experienced patient with chronic HCV infection genotype 1b, treated with 150 mg/day simeprevir, 400 mg/day sofosbuvir, and 1,000 mg/ day ribavirin for 24 weeks, after a Roux-and-Y gastric bypass. At steady-state a pharmacokinetic curve was recorded of sofosbuvir, GS-331007, and simeprevir. Ribavirin trough plasma concentration (Ctrough) was determined. The simeprevir area under the-concentration time curve (AUClast) and Ctrough were 9.42 h.mg/L and 0.046 mg/L, respectively. Compared to what was described in the literature, simeprevir exposure was low and therefore the simeprevir dose was increased to 300 mg/day. The increased dose of simeprevir was well tolerated and Ctrough was 0.532 mg/L. Sofosbuvir AUClast and Ctrough were 0.63 h.mg/L and 0.0013 mg/L. GS-331007 AUClast and Ctrough were 21.02 h.mg/L and 0.35 mg/L. Ribavirin Ctrough was 2.5 mg/L. Sofosbuvir, GS-331007, and ribavirin exposure were comparable with levels described in literature. The patient achieved a sustained virological response twelve weeks after the completion of treatment.

Peg-interferon and ribavirin treatment in HIV/HCV co-infected patients in Thailand: efficacy, safety and pharmacokinetics

OBJECTIVE

In Thailand, 7.2% of HIV patients are co-infected with hepatitis C virus (HCV), and these patients are treated with peg-interferon + ribavirin (PR) for their HCV infection. This study evaluates efficacy and safety of PR treatment and pharmacokinetics of ribavirin in this population.

METHODS

HIV/HCV co-infected Thai patients were treated with PR for 24 or 48 weeks. Sustained virological response 24 weeks after the end of treatment (SVR24) was used to describe efficacy. (laboratory) safety parameters and ribavirin plasma concentrations were evaluated during study visits. Ribavirin concentrations were compared with t-tests for patients with and without anaemia (haemoglobin <10 g/dl) and SVR24.

RESULTS

A total of 101 HIV/HCV co-infected patients were included; 88% were male (n = 88), and 46% were infected with genotype 3. The median (IQR) start dose was 14.28 mg/kg/day. SVR24 rate was 56%. All patients reported at least one (serious) adverse event, of which 28% of patients developed anaemia. Seven patients discontinued treatment due to toxicity issues. Geometric mean (IQR) ribavirin concentration was 1.81 (1.42-2.32) mg/l at week 8 of treatment. At week 8, patients with and without anaemia and SVR had ribavirin concentrations of 2.29 and 1.63 mg/l and 1.91 and 1.74 mg/l, respectively.

CONCLUSIONS

PR treatment has comparable response rates and toxicity profile in Thai HIV/HCV co-infected patients as in Western HIV/HCV patients. However, ribavirin plasma concentrations were comparable with previously published studies in HIV/HCV co-infected patients, but both, just as SVR rate, were lower than in mono-infected patients.

Ribavirin steady-state plasma level is a predictor of sustained virological response in hepatitis C-infected patients treated with direct-acting antivirals

BACKGROUND

In the era of highly effective direct-acting antivirals (DAAs) for treatment of patients with chronic hepatitis C virus (HCV) infection, ribavirin (RBV) is still considered beneficial in certain patients.

AIM

To assess the association between RBV steady-state plasma levels and sustained virological response (SVR).

METHODS

Consecutive HCV-infected patients treated with DAAs plus RBV from four Dutch academic medical centres were enrolled. RBV steady-state plasma levels were prospectively measured at treatment week 8 using validated assays. Logistic regression analyses were performed to assess the influence of RBV steady-state plasma level on SVR, and RBV therapeutic range was explored using area under the ROC curve analyses.

RESULTS

A total of 183 patients were included, of whom 85% had one or more difficult-to-cure characteristics (ie treatment experienced, HCV genotype 3, cirrhosis). The majority was treated with a sofosbuvir-based regimen and 163 (89%) patients achieved SVR. Median RBV dose was 12.9 (interquartile range 11.2-14.7) mg/kg/d, and median RBV steady-state plasma level was 2.66 (1.95-3.60) mg/L. In multivariable analyses, higher RBV steady-state plasma level (adjusted odds ratio 1.79 [95% CI 1.09-2.93]) was an independent predictor of SVR. With regard to the optimal RBV therapeutic range, 2.28 mg/L was the optimal lower cut-off for achieving SVR and 3.61 mg/L was the upper cut-off for preventing significant anaemia (Haemoglobin < 10 g/dL).

CONCLUSION

In this cohort of mainly difficult-to-cure patients treated with DAAs plus RBV, higher RBV steady-state plasma level was an independent predictor of SVR.

Drug-Drug Interactions Between Direct-Acting Antivirals and Psychoactive Medications

Treatment options for chronic hepatitis C virus (HCV) infection have drastically changed since the development and licensing of new potent direct-acting antivirals (DAAs). The majority of DAAs are extensively metabolized by liver enzymes and have the ability to influence cytochrome P450 (CYP) enzymes. Additionally, these DAAs are both substrates and inhibitors of drug transporters, which makes the DAAs both possible victims or perpetrators of drug–drug interactions (DDIs). There is a high prevalence of mental illnesses such as depression or psychosis in HCV-infected patients; therefore, psychoactive medications are frequently co-administered with DAAs. The majority of these psychoactive medications are also metabolized by CYP enzymes but remarkably little information is available on DDIs between psychoactive medications and DAAs. Hence, the aim of this review is to provide an overview of the interaction mechanisms between DAAs and psychoactive agents. In addition, we describe evidenced-based interactions between DAAs and psychoactive drugs and identify safe options for the simultaneous treatment of mental illnesses and chronic HCV infection.

Metformin and daclatasvir: absence of a pharmacokinetic-pharmacodynamic drug interaction in healthy volunteers

AIM

The aim of the present study was to evaluate the effect of the proposed organic cation transporter (OCT) inhibitor daclatasvir on the pharmacokinetics and pharmacodynamics of the OCT substrate metformin.

METHODS

This was an open-label, two-period, randomized, crossover trial in 20 healthy subjects. Treatment A consisted of metformin and treatment B consisted of metformin + daclatasvir. Pharmacokinetic curves were recorded at steady-state. Geometric mean ratios (GMRs) with 90% confidence intervals (CIs) were calculated for metformin area under the concentration-time curve from 0 h to 12 h (AUC_0-12 ), maximum plasma concentration (C_max ) and final plasma concentration (C_last ). An oral glucose tolerance test was performed, measuring insulin, glucose and lactate levels.

RESULTS

The GMRs (90% CI) of metformin AUC_0-12 , C_max and C_last (B vs. A) were 109% (102-116%), 108% (101-116%) and 112% (103-122%). The geometric mean AUC_0-2 for insulin, glucose and lactate during treatments A and B were 84 h^. mEl^-1 and 90 h^. mEl^-1 , 13.6 h^. mmol l^-1 and 13.4 h^. mmol l^-1 , and 3.4 h^. mmol l^-1 and 3.5 h^. mmol l^-1 , respectively.

CONCLUSIONS

Bioequivalence analysis showed that daclatasvir does not influence the pharmacokinetics of metformin in healthy subjects. Pharmacodynamic parameters were also comparable between treatments.

Decreased tacrolimus plasma concentrations during HCV therapy: a drug-drug interaction or is there an alternative explanation?

Chronic hepatitis C virus (HCV) infection can cause severe liver cirrhosis, for which liver transplantation is the only therapy. To prevent organ rejection, transplanted patients are treated with immunosuppressive agents. We describe two transplanted patients treated with tacrolimus who were simultaneously treated with direct-acting antivirals (DAAs) for their chronic HCV infection. No pharmacokinetic drug-drug interactions (DDIs) were expected between tacrolimus and the selected DAAs. However, in both patients, tacrolimus plasma concentrations decreased during HCV treatment. We hypothesise that decreased plasma concentrations were not caused by a DDI but were an indirect result of the clearance of the HCV infection. During chronic HCV infection, pro-inflammatory cytokines may inhibit cytochrome P450 (CYP) enzymes, which are primarily responsible for tacrolimus metabolism. If this is true, then with clearance of the virus the activity of these enzymes will normalise and tacrolimus metabolism will increase. These changes were clinically relevant because the tacrolimus dosage needed to be adjusted. Therefore, physicians should be aware that CYP substrates with narrow therapeutic ranges might require dose adaption during HCV therapy with DAAs.

The majority of hepatitis C patients treated with direct acting antivirals are at risk for relevant drug-drug interactions

BACKGROUND

Direct-acting antivirals have improved treatment of chronic hepatitis C virus infection significantly. Direct-acting antivirals inhibit/induce and can also be substrates of drug-metabolising enzymes and transporters. This increases the risk for drug-drug interactions.

OBJECTIVE

The purpose of this study was to predict drug-drug interactions with co-medication used by hepatitis C virus-infected patients.

METHODS

We assembled a nationwide cohort of hepatitis C patients and collected cross-sectional data on co-medication use. We compiled a list of currently available direct-acting antiviral regimens and cross-checked for potential drug-drug interactions with used co-medication.

RESULTS

The cohort included 461 patients of which 77% used co-medication. We identified 260 drugs used as co-medication. Antidepressants (7.4%), proton pump inhibitors (7.1%) and benzodiazepines (7.1%) were most frequently used. Of the patients, 60% were at risk for a clinically relevant drug-drug interaction with at least one of the direct-acting antiviral regimens. Interactions were most common with paritaprevir/ritonavir/ombitasvir/dasabuvir and least interactions were predicted with grazoprevir/elbasvir.

CONCLUSION

Co-medication use is rich in frequency and diversity in chronic hepatitis C patients. The majority of patients are at risk for drug-drug interactions which may affect efficacy or toxicity of direct-acting antivirals or co-medication. The most recently introduced direct-acting antivirals are associated with a lower risk of drug-drug interactions.

Daclatasvir 30 mg/day is the correct dose for patients taking atazanavir/cobicistat

BACKGROUND

Atazanavir is boosted with the cytochrome P450 (CYP) 3A4 inhibitor ritonavir. When combined with the CYP3A4 substrate daclatasvir, the daclatasvir dosage should be reduced from 60 to 30 mg once daily. Recently, cobicistat was licensed as a CYP3A booster and used with atazanavir.

OBJECTIVES

To determine whether the fixed-dose combination of atazanavir/cobicistat has an influence on daclatasvir pharmacokinetics comparable to that of the separate agents atazanavir and ritonavir.

METHODS

A prospective, open-label, two-period, randomized, cross-over trial was performed in 16 healthy subjects (NCT02565888). Treatment consisted of 300/100 mg of atazanavir/ritonavir plus 30 mg of daclatasvir once daily (reference) and a second period of 300/150 mg of atazanavir/cobicistat plus 30 mg of daclatasvir once daily (test). A 24 h pharmacokinetic, steady-state curve was recorded for all drugs. Geometric mean ratios (GMRs) with 90% CI were calculated for daclatasvir and atazanavir AUC_τ and C_max to compare the effect of both treatments (test versus reference). Laboratory safety and adverse events were evaluated throughout the trial.

RESULTS

All 16 healthy subjects completed the study. Median (range) age and BMI were 48.5 (21-55) years and 24.5 (19.0-29.2) kg/m², respectively. Pharmacokinetic parameters of ritonavir and cobicistat were comparable to those in the literature. The GMRs (90% CI) of daclatasvir AUC_τ and C_max (test versus reference) were 101% (92%-111%) and 97% (89%-106%), respectively. Atazanavir GMRs (90% CI) of AUC_τ and C_max were 82% (75%-79%) and 74% (68%-81%), respectively. No serious adverse events were reported.

CONCLUSIONS

Atazanavir/cobicistat and atazanavir/ritonavir had a similar influence on daclatasvir pharmacokinetics in healthy volunteers. Daclatasvir at 30 mg once daily is the correct dose when combined with atazanavir/cobicistat.