Dose-related reduction in bupropion plasma concentrations by ritonavir

A genetic algorithm-based approach for the prediction of metabolic drug-drug interactions involving CYP2C8 or CYP2B6

BACKGROUND AND OBJECTIVES

A genetic algorithm (GA) approach was developed to predict drug-drug interactions (DDIs) caused by cytochrome P450 2C8 (CYP2C8) inhibition or cytochrome P450 2B6 (CYP2B6) inhibition or induction. Nighty-eight DDIs, obtained from published in vivo studies in healthy volunteers, have been considered using the area under the plasma drug concentration-time curve (AUC) ratios (i.e., ratios of AUC of the drug substrate administered in combination with a DDI perpetrator to AUC of the drug substrate administered alone) to describe the extent of DDI.

METHODS

The following parameters were estimated in this approach: the contribution ratios (CRCYP2B6 and CRCYP2C8, i.e., the fraction of the dose metabolized via CYP2B6 or CYP2C8, respectively) and the inhibitory or inducing potency of the perpetrator drug (IRCYP2B6, IRCYP2C8 and ICCYP2B6, for inhibition of CYP2B6 and CYP2C8, and induction of CYP2B6, respectively). The workflow consisted of three main phases. First, the initial estimates of the parameters were estimated through GA. Then, the model was validated using an external validation. Finally, the parameter values were refined via a Bayesian orthogonal regression using all data.

RESULTS

The AUC ratios of 5 substrates, 11 inhibitors and 19 inducers of CYP2B6, and the AUC ratios of 19 substrates and 23 inhibitors of CYP2C8 were successfully predicted by the developed methodology within 50-200% of observed values.

CONCLUSIONS

The approach proposed in this work may represent a useful tool for evaluating the suitable doses of a CYP2C8 or CYP2B6 substrates co-administered with perpetrators.

Quantitative Prediction of Drug Interactions Caused by Cytochrome P450 2B6 Inhibition or Induction

BACKGROUND

Numerous drugs have the potential to be affected by cytochrome P450 (CYP) 2B6-mediated drug-drug interactions (DDIs).

OBJECTIVES

In this work, we extend a static approach to the prediction of the extent of pharmacokinetics DDIs between substrates and inhibitors or inducers of CYP2B6.

METHODS

This approach is based on the calculation of two parameters (the contribution ratio [CR], representing the fraction of dose of the substrate metabolized via this pathway and the inhibitory or inducing potency of the perpetrator [IR or IC, respectively]) calculated from the area under the concentration-time curve (AUC) ratios obtained in in-vivo DDI studies.

RESULTS

Forty-eight studies involving 5 substrates, 11 inhibitors and 18 inducers of CYP2B6 (overall 15 inhibition and 33 induction studies) were divided into test and validation sets and considered for estimation of the parameters. The proposed approach demonstrated a fair accuracy for predicting the extent of DDI related to CYP2B6 inhibition and induction, all predictions related to the validation test (N = 18) being 50-200% of the observed ratios.

CONCLUSIONS

This methodology can be used for proposing initial dose adaptations to be adopted, for example in clinical use or for designing DDI studies involving this enzyme.

A Literature Review of Liver Function Test Elevations in Rifampin Drug-Drug Interaction Studies

Although rifampin drug–drug interaction (DDI) studies are routinely conducted, there have been instances of liver function test (LFT) elevations, warranting further evaluation. A literature review was conducted to identify studies in which combination with rifampin resulted in hepatic events and evaluate any similarities. Over 600 abstracts and manuscripts describing rifampin DDI studies were first evaluated, of which 30 clinical studies reported LFT elevations. Out of these, 11 studies included ritonavir in combination with other drug(s) in the rifampin DDI study. The number of subjects that were discontinued from treatment on these studies ranged from 0 to 71 (0–100% of subjects in each study). The number of subjects hospitalized for adverse events in these studies ranged from 0 to 41 (0–83.67% of subjects in each study). LFT elevations in greater than 50% of subjects were noted during the concomitant administration of rifampin with ritonavir‐boosted protease inhibitors and with lorlatinib; with labeled contraindication due to observed hepatotoxicity related safety findings only for saquinavir/ritonavir and lorlatinib. In the lorlatinib and ritonavir DDI studies, considerable LFT elevations were observed rapidly, typically within 24–72 h following co‐administration. A possible sequence effect has been speculated, where rifampin induction prior to administration of the combination may be associated with increased severity of the LFT elevations. The potential role of rifampin in the metabolic activation of certain drugs into metabolites with hepatic effects needs to be taken into consideration when conducting rifampin DDI studies, particularly those for which the metabolic profiles are not fully elucidated.

Management of Antiretroviral Therapy with Boosted Protease Inhibitors-Darunavir/Ritonavir or Darunavir/Cobicistat

A major challenge in the management of antiretroviral therapy (ART) is to improve the patient's adherence, reducing the burden caused by the high number of drugs that compose the treatment regimens for human immunodeficiency virus positive (HIV+) patients. Selection of the most appropriate treatment regimen is responsible for therapeutic success and aims to reduce viremia, increase the immune system response capacity, and reduce the incidence rate and intensity of adverse reactions. In general, protease inhibitor (PI) is one of the pillars of regimens, and darunavir (DRV), in particular, is frequently recommended, along with low doses of enzyme inhibitors as cobicistat (COBI) or ritonavir (RTV), by the international guidelines. The potential of clinically significant drug interactions in patients taking COBI or RTV is high due to the potent inhibitory effect on cytochrome CYP 450, which attracts significant changes in the pharmacokinetics of PIs. Regardless of the patient or type of virus, the combined regimens of DRV/COBI or DRV/RTV are available to clinicians, proving their effectiveness, with a major impact on HIV mortality/morbidity. This study presents current information on the pharmacokinetics, pharmacology, drug interactions, and adverse reactions of DRV; it not only compares the bioavailability, pharmacokinetic parameters, immunological and virological responses, but also the efficacy, advantages, and therapeutic disadvantages of DRV/COBI or DRV/RTV combinations.

HIV Infection and Related Mental Disorders

Over the more than thirty-year period of the human immunodeficiency virus type 1 (HIV-1) epidemic, many data have been accumulated indicating that HIV infection predisposes one to the development of mental pathologies. It has been proven that cognitive disorders in HIV-positive individuals are the result of the direct exposure of the virus to central nervous system (CNS) cells. The use of antiretroviral therapy has significantly reduced the number of cases of mental disorders among people infected with HIV. However, the incidence of moderate to mild cognitive impairment at all stages of HIV infection is still quite high. This review describes the most common forms of mental pathology that occur in people living with HIV and presents the current concepts on the possible pathogenetic mechanisms of the influence of human immunodeficiency virus (HIV-1) and its viral proteins on the cells of the CNS and the CNS’s functions. This review also provides the current state of knowledge on the impact of the antiretroviral therapy on the development of mental pathologies in people living with HIV, as well as current knowledge on the interactions between antiretroviral and psychotropic drugs that occur under their simultaneous administration.

Clinically Significant Drug Interactions Between Psychotropic Agents and Repurposed COVID-19 Therapies

As many patients with underlying psychiatric disorders may be infected with COVID-19, and COVID-19-affected subjects may frequently experience a new onset of psychiatric manifestations, concomitant use of psychotropic medications and COVID-19 therapies is expected to be highly likely and raises concerns of clinically relevant drug interactions. In this setting, four major mechanisms responsible for drug interactions involving psychotropic agents and COVID-19 therapies may be identified: (1) pharmacokinetic drug-drug interactions mainly acting on cytochrome P450; (2) pharmacodynamic drug-drug interactions resulting in additive or synergistic toxicity; (3) drug-disease interactions according to stage and severity of the disease; and (4) pharmacogenetic issues associated with polymorphisms of cytochrome P450 isoenzymes. In this review, we summarise the available literature on relevant drug interactions between psychotropic agents and COVID-19 therapies, providing practical clinical recommendations and potential management strategies according to severity of illness and clinical scenario.

Drug Interactions of Psychiatric and COVID-19 Medications

INTRODUCTION

Coronavirus disease 2019 (COVID-19) has become a pandemic with 1771514 cases identified in the world and 70029 cases in Iran until April 12, 2020. The co-prescription of psychotropics with COVID-19 medication is not uncommon. Healthcare providers should be familiar with many Potential Drug-Drug Interactions (DDIs) between COVID-19 therapeutic agents and psychotropic drugs based on cytochrome P450 metabolism. This review comprehensively summarizes the current literature on DDIs between antiretroviral drugs and chloroquine/hydroxychloroquine, and psychotropics, including antidepressants, antipsychotics, mood stabilizers, and anxiolytics.

METHODS

Medical databases, including Google Scholar, PubMed, Web of Science, and Scopus were searched to identify studies in English with keywords related to psychiatric disorders, medications used in the treatment of psychiatric disorders and COVID-19 medications.

RESULTS

There is a great potential for DDIs between psychiatric and COVID-19 medications ranging from interactions that are not clinically apparent (minor) to those that produce life-threatening adverse drug reactions, or loss of treatment efficacy. The majority of interactions are pharmacokinetic interactions via the cytochrome P450 enzyme system.

CONCLUSION

DDIs are a major concern in the comorbidity of psychiatric disorders and COVID-19 infection resulting in the alteration of expected therapeutic outcomes. The risk of toxicity or lack of efficacy may occur due to a higher or lower plasma concentration of medications. However, psychiatric medication can be safely used in combination with COVID-19 pharmacotherapy with either a wise selection of medication with the least possibility of interaction or careful patient monitoring and management.

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.

Population Pharmacokinetics, Safety and Tolerability of Extended-Release Bupropion and Its Three Metabolites in Chinese Healthy Volunteers

BACKGROUND AND OBJECTIVE

Bupropion is used for the treatment of major depressive disorder. We determined the pharmacokinetics, safety, and tolerability of extended-release bupropion XL in healthy Chinese volunteers.

METHODS

This open-label, single-center pharmacokinetic study was conducted between May 2016 and June 2016. Eligible volunteers received bupropion XL 150 mg once daily for 5 days, then 300 mg once daily from days 6 to 14. Pharmacokinetic parameters were evaluated after first and repeated doses by non-compartmental and population pharmacokinetic analyses.

RESULTS

Fifteen out of 16 enrolled volunteers completed the study. The geometric mean of the bupropion area under the concentration-time curve from 0 to 24 h (AUC_0-24) was 498.2 and 1,165.7 h·ng/mL on days 1 and 14, respectively; maximum plasma concentration (C_max) was 49.9 ng/mL on day 1 and steady-state maximum observed plasma concentration (C_{ss_max}) was 111.9 ng/mL on day 14. Among the three metabolites, hydroxybupropion showed the highest AUC_0-24 and C_max. The population pharmacokinetic model findings indicated an apparent oral clearance of 221 L/h for bupropion in a typical healthy 60.9-kg Chinese volunteer.

CONCLUSIONS

This was the first pharmacokinetic study for bupropion XL and its active metabolites in the Chinese population. The AUC and C_max of bupropion XL and its three metabolites increased approximately in a dose-proportional manner with an increase from 150 mg to 300 mg. Adverse events were similar to those reported in studies outside China. A population pharmacokinetic model was developed for bupropion XL, with pharmacokinetics of bupropion adequately described by a two-compartment model with first-order absorption and linear elimination plus lag time.

TRIAL REGISTRATION NUMBER

NCT02698553.

Safety and Efficacy of Weight-Loss Pharmacotherapy in Persons Living with HIV: A Review of the Literature and Potential Drug-Drug Interactions with Antiretroviral Therapy

The prevalence of obesity among persons living with human immunodeficiency virus (HIV) has increased significantly and may be linked to the use of antiretroviral therapy. Although weight-loss medications approved by the U.S. Food and Drug Administration are recommended as an adjunct to diet and exercise to treat obesity in the general population, little is known about the safety and efficacy of these drugs specifically in persons living with HIV. We review the available evidence regarding the effective use of weight-loss pharmacotherapy in persons living with HIV and its potential to interact with antiretroviral therapy. Persons living with HIV are frequently not reported or included in clinical trials for weight-loss medications; however, treatment efficacy is likely similar to the general population. Several important reported or theoretical drug-drug interactions exist between antiobesity pharmacotherapy and antiretroviral therapy. Orlistat is a weight-loss drug available in the United States without a prescription and was linked to HIV viral rebound in several case reports. Clinicians should be aware of the potential for loss of HIV viremia control when certain weight-loss pharmacotherapies are used in combination with antiretrovirals.

Drug-drug interactions and clinical considerations with co-administration of antiretrovirals and psychotropic drugs

Psychotropic medications are frequently co-prescribed with antiretroviral therapy (ART), owing to a high prevalence of psychiatric illness within the population living with HIV, as well as a 7-fold increased risk of HIV infection among patients with psychiatric illness. While ART has been notoriously associated with a multitude of pharmacokinetic drug interactions involving the cytochrome P450 enzyme system, the magnitude and clinical impact of these interactions with psychotropics may range from negligible effects on plasma concentrations to life-threatening torsades de pointes or respiratory depression. This comprehensive review summarizes the currently available information regarding drug-drug interactions between antiretrovirals and pharmacologic agents utilized in the treatment of psychiatric disorders-antidepressants, stimulants, antipsychotics, anxiolytics, mood stabilizers, and treatments for opioid use disorder and alcohol use disorder-and provides recommendations for their management. Additionally, overlapping toxicities between antiretrovirals and the psychotropic classes are highlighted. Knowledge of the interaction and adverse effect potential of specific antiretrovirals and psychotropics will allow clinicians to make informed prescribing decisions to better promote the health and wellness of this high-risk population.

Probable interaction between levothyroxine and ritonavir: Case report and literature review

PURPOSE

A case of probable interaction of levothyroxine and ritonavir is presented along with a review of the relevant literature and recommendations on clinical management.

SUMMARY

A 37-year-old woman with human immunodeficiency virus infection who had recently undergone thyroidectomy for a benign multinodular goiter presented to a clinic with hypothyroidism (she was also found to be pregnant), and treatment with levothyroxine 75 μg daily was initiated. While receiving antiretroviral therapy (abacavir-lamivudine and lopinavir-ritonavir) during pregnancy, the patient had persistently elevated serum thyroid-stimulating hormone (TSH) concentrations (up to 125.89 μIU/mL) despite gradual escalation of the levothyroxine dosage to 175 μg daily. An interaction between ritonavir and levothyroxine was suspected, and dolutegravir was substituted for lopinavir-ritonavir. Within 4 months, the TSH concentration had normalized. The daily levothyroxine dose was tapered over a 5-month period and stabilized at 125 μg, and TSH concentrations remained within the normal range over an 18-month follow-up period. Scoring of the case using the Drug Interaction Probability Scale yielded a score of 6 out of 11, indicating a probable interaction between levothyroxine and ritonavir. A literature search identified 4 reported cases of interactions involving levothyroxine and ritonavir.

CONCLUSION

A potentially serious and underrecognized drug interaction between ritonavir and levothyroxine was observed in a pregnant woman with postthyroidectomy-related hypothyroidism. This case and a review of other cases reported in the literature indicate that higher-than-usual doses of levothyroxine may be required in patients who are taking ritonavir concurrently.

Differential effects of psychoactive substances on human wildtype and polymorphic T356M dopamine transporters (DAT)

Many psychoactive substances affect the human dopamine (DA) reuptake transporter (hDAT). Polymorphisms in the encoding gene could affect the functionality of the transporter and consequently alter effects of psychotropic and recreational drugs. Recently, a T356 M single nucleotide polymorphism in the human SLC6A3 gene was described, which resulted in functional impairments of DA uptake. Therefore, we investigated the effects of 10 psychoactive substances (0.01-1000 μM)) on DA uptake in human embryonic kidney (HEK) 293 cells transiently overexpressing wildtype (WT) or T356 M hDAT. Our data shows that T356 M hDAT has a 3 times lower V_max and a 3 times higher K_m compared to WT hDAT. Additionally, all psychoactive substances inhibited DA uptake by T356 M and WT hDAT. The DA reuptake inhibitors (methylphenidate, cocaine, and bupropion) inhibited DA uptake by WT hDAT most potently, followed by amphetamine-type stimulants [4-fluoroamphetamine (4-FA), amphetamine and MDMA], selective serotonin reuptake inhibitors (SSRI; fluoxetine and citalopram) and arylcyclohexylamines [methoxetamine (MXE) and ketamine]. Compared to DA uptake by WT hDAT, bupropion, methylphenidate, cocaine, and MXE less potently inhibited DA uptake by T356 M hDAT, while citalopram more potently inhibited uptake. The differences in IC₅₀ values between T356 M and WT hDAT were considerable (3-45 fold). As such, the presence of this polymorphism could affect treatment efficiency with these substances as well as susceptibly for toxicity and addiction for individuals carrying this polymorphism.

Drug-Drug Interaction Studies of Methadone and Antiviral Drugs: Lessons Learned

Different views appear in the literature on the extent of specific cytochrome P450 (CYP) involvement in methadone metabolism. The aim of this work is to leverage knowledge from drug-drug interaction (DDI) studies in new drug applications between methadone and antiviral medications to better understand methadone disposition and to inform design of future DDI studies with methadone. A database of DDI studies between all FDA-approved human immunodeficiency virus and hepatitis C virus medications and methadone was constructed. The database contains data from 29 DDI studies. Sixteen of the 29 studies had statistically significant changes in methadone area under the concentration-time curve. Methadone exposure was either decreased or unchanged when it was coadministered with weak to strong CYP3A inhibitors or a moderate CYP3A4 inducer. Methadone exposure was reduced when it was coadministered with CYP2B6 inducers. The role of other enzymes (CYP2C9, CYP2C19, and CYP2D6) cannot be fully elucidated from these studies. In conclusion, CYP2B6 plays a prominent role in methadone metabolism, although methadone exposure is not sensitive to CYP3A perturbation. In designing methadone DDI studies, (1) measuring R- and S-methadone is more informative than measuring total methadone, and (2) CYP2B6 genotyping of subjects enrolled in methadone DDI studies should be considered. Finally, there is a need for the development of predictive models to determine the influence of medications on methadone disposition.

Amenamevir: Studies of Potential CYP3A-Mediated Pharmacokinetic Interactions With Midazolam, Cyclosporine, and Ritonavir in Healthy Volunteers

Amenamevir (formerly ASP2151) is a helicase‐primase inhibitor being developed for the treatment of herpesvirus infection. Amenamevir is both a substrate and inducer of cytochrome P450 (CYP) 3A4. Three studies were done in healthy volunteers to investigate potential CYP3A pharmacokinetic interactions with the following drugs: (1) Midazolam (probe substrate for CYP3A): After 10 days’ pretreatment with amenamevir 400 mg daily, geometric mean maximum concentration of drug in blood plasma (C_max) and area under the plasma drug concentration‐time curve from time zero to infinity (AUC_0‐∞) of midazolam 7.5 mg were about 68% and 51%, respectively, of those after midazolam alone. (2) Cyclosporine (substrate and inhibitor of CYP3A): After 5 days’ pretreatment with cyclosporine 100 mg twice daily, geometric mean C_max of amenamevir after 400‐mg and 1200‐mg single doses was, respectively, about 66% and 69%, and AUC_0‐∞ about 82% and 79%, of those after amenamevir alone. (3) Ritonavir (inhibitor of CYP3A): When given with single doses of ritonavir 600 mg, geometric mean C_max of amenamevir after 400‐mg and 1200‐mg single doses was, respectively, about 1.4 and 1.6 times higher, and geometric mean AUC_0‐∞ about 2.6 and 3.3 times higher, than after amenamevir alone. Amenamevir has the potential to be involved in CYP3A‐mediated pharmacokinetic interactions in clinical practice.

Cobicistat Versus Ritonavir: Similar Pharmacokinetic Enhancers But Some Important Differences

OBJECTIVE

To describe properties of cobicistat and ritonavir; compare boosting data with atazanavir, darunavir, and elvitegravir; and summarize antiretroviral and comedication interaction studies, with a focus on similarities and differences between ritonavir and cobicistat. Considerations when switching from one booster to another are discussed.

DATA SOURCES

A literature search of MEDLINE was performed (1985 to April 2017) using the following search terms: cobicistat, ritonavir, pharmacokinetic, drug interactions, booster, pharmacokinetic enhancer, HIV, antiretrovirals. Abstracts from conferences, article bibliographies, and product monographs were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Relevant English-language studies or those conducted in humans were considered.

DATA SYNTHESIS

Similar exposures of elvitegravir, darunavir, and atazanavir are achieved when combined with cobicistat or ritonavir. Cobicistat may not be as potent a CYP3A4 inhibitor as ritonavir in the presence of a concomitant inducer. Ritonavir induces CYP1A2, 2B6, 2C9, 2C19, and uridine 5'-diphospho-glucuronosyltransferase, whereas cobicistat does not. Therefore, recommendations for cobicistat with comedications that are extrapolated from studies using ritonavir may not be valid. Pharmacokinetic properties of the boosted antiretroviral can also affect interaction outcome with comedications. Problems can arise when switching patients from ritonavir to cobicistat regimens, particularly with medications that have a narrow therapeutic index such as warfarin.

CONCLUSIONS

When assessing and managing potential interactions with ritonavir- or cobicistat-based regimens, clinicians need to be aware of important differences and distinctions between these agents. This is especially important for patients with multiple comorbidities and concomitant medications. Additional monitoring or medication dose adjustments may be needed when switching from one booster to another.

A review of drug-drug interactions in older HIV-infected patients

INTRODUCTION

The number of older HIV-infected people is growing due to increasing life expectancies resulting from the use of antiretroviral therapy (ART). Both HIV and aging increase the risk of other comorbidities, such as cardiovascular disease, osteoporosis, and some malignancies, leading to greater challenges in managing HIV with other conditions. This results in complex medication regimens with the potential for significant drug-drug interactions and increased morbidity and mortality. Area covered: We review the metabolic pathways of ART and other medications used to treat medical co-morbidities, highlight potential areas of concern for drug-drug interactions, and where feasible, suggest alternative approaches for treating these conditions as suggested from national guidelines or articles published in the English language. Expert commentary: There is limited evidence-based data on ART drug interactions, pharmacokinetics and pharmacodynamics in the older HIV-infected population. Choosing and maintaining effective ART regimens for older adults requires consideration of side effect profile, individual comorbidities, interactions with concurrent prescriptions and non-prescription medications and supplements, dietary patterns with respect to dosing, pill burden and ease of dosing, cost and affordability, patient preferences, social situation, and ART resistance history. Practitioners must remain vigilant for potential drug interactions and intervene when there is a potential for harm.

Evaluation of CYP2B6 Induction and Prediction of Clinical Drug-Drug Interactions: Considerations from the IQ Consortium Induction Working Group-An Industry Perspective

Drug-drug interactions (DDIs) due to CYP2B6 induction have recently gained prominence and clinical induction risk assessment is recommended by regulatory agencies. This work aimed to evaluate the potency of CYP2B6 versus CYP3A4 induction in vitro and from clinical studies and to assess the predictability of efavirenz versus bupropion as clinical probe substrates of CYP2B6 induction. The analysis indicates that the magnitude of CYP3A4 induction was higher than CYP2B6 both in vitro and in vivo. The magnitude of DDIs caused by induction could not be predicted for bupropion with static or dynamic models. On the other hand, the relative induction score, net effect, and physiologically based pharmacokinetics SimCYP models using efavirenz resulted in improved DDI predictions. Although bupropion and efavirenz have been used and are recommended by regulatory agencies as clinical CYP2B6 probe substrates for DDI studies, CYP3A4 contributes to the metabolism of both probes and is induced by all reference CYP2B6 inducers. Therefore, caution must be taken when interpreting clinical induction results because of the lack of selectivity of these probes. Although in vitro-in vivo extrapolation for efavirenz performed better than bupropion, interpretation of the clinical change in exposure is confounded by the coinduction of CYP2B6 and CYP3A4, as well as the increased contribution of CYP3A4 to efavirenz metabolism under induced conditions. Current methods and probe substrates preclude accurate prediction of CYP2B6 induction. Identification of a sensitive and selective clinical substrate for CYP2B6 (fraction metabolized > 0.9) is needed to improve in vitro-in vivo extrapolation for characterizing the potential for CYP2B6-mediated DDIs. Alternative strategies and a framework for evaluating the CYP2B6 induction risk are proposed.

Smoking Cessation for People Living With HIV/AIDS: A Literature Review and Synthesis

INTRODUCTION

People living with HIV/AIDS (PLWHA) are more likely to smoke cigarettes than are individuals in the general population. The health implications of tobacco use are substantially more dire among PLWHA than among otherwise healthy smokers, including higher rates of various cancers, cardiovascular disease, inflammation, and lung infections. Efficacious behavioral and medication treatments for treating nicotine dependence have rarely been investigated in PLWHA.

METHODS

We present a review of studies examining the efficacy of smoking cessation interventions.

RESULTS AND CONCLUSIONS

The literature reveals some limited evidence for the efficacy of behavioral interventions. However, the research literature on these interventions is sparse and the efficacy findings are mixed. Studies exploring the use of mobile technologies for reducing treatment barriers are becoming more prevalent. Few published trials have directly examined the efficacy of pharmacological smoking cessation interventions among PLWHA. Specific gaps in the treatment literature are discussed in detail, and a strategy is presented for developing a greater understanding of factors that contribute to the efficacy of smoking cessation among PLWHA.

IMPLICATIONS

This paper provides the most comprehensive review to date on smoking cessation intervention research conducted with PLWHA. It also discusses specific gaps in the literature that should be a priority for future research.

Cobicistat versus ritonavir boosting and differences in the drug-drug interaction profiles with co-medications

Nearly all HIV PIs and the integrase inhibitor elvitegravir require a pharmacokinetic enhancer in order to achieve therapeutic plasma concentrations at the desired dose and frequency. Whereas ritonavir has been the only available pharmacokinetic enhancer for more than a decade, cobicistat has recently emerged as an alternative boosting agent. Cobicistat and ritonavir are equally strong inhibitors of cytochrome P450 (CYP) 3A4 and consequently were shown to be equivalent pharmacokinetic enhancers for elvitegravir and for the PIs atazanavir and darunavir. Since cobicistat is a more selective CYP inhibitor than ritonavir and is devoid of enzyme-inducing properties, differences are expected in their interaction profiles with some co-medications. Drugs whose exposure might be altered by ritonavir but unaltered by cobicistat are drugs primarily metabolized by CYP1A2, CYP2B6, CYP2C8, CYP2C9 and CYP2C19 or drugs undergoing mainly glucuronidation. Thus, co-medications should be systematically reviewed when switching the pharmacokinetic enhancer to anticipate potential dosage adjustments.

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.

Prevalence of non-HIV cancer risk factors in persons living with HIV/AIDS: a meta-analysis

OBJECTIVE

The burden of cancer among persons living with HIV/AIDS (PLWHA) is substantial and increasing. We assessed the prevalence of modifiable cancer risk factors among adult PLWHA in Western high-income countries since 2000.

DESIGN

Meta-analysis.

METHODS

We searched PubMed to identify articles published in 2011-2013 reporting prevalence of smoking, alcohol consumption, overweight/obesity, and infection with human papillomavirus (HPV), hepatitis C virus (HCV) and hepatitis B virus (HBV) among PLWHA. We conducted random effects meta-analyses of prevalence for each risk factor, including estimation of overall, sex-specific, and HIV-transmission-group-specific prevalence. We compared prevalence in PLWHA with published prevalence estimates in US adults.

RESULTS

The meta-analysis included 113 publications. Overall summary prevalence estimates were current smoking, 54% [95% confidence interval (CI) 49-59%] versus 20-23% in US adults; cervical high-risk HPV infection, 46% (95% CI 34-58%) versus 29% in US females; oral high-risk HPV infection, 16% (95% CI 10-23%) versus 4% in US adults; anal high-risk HPV infection (men who have sex with men), 68% (95% CI 57-79%), with no comparison estimate available; chronic HCV infection, 26% (95% CI 21-30%) versus 0.9% in US adults; and HBV infection, 5% (95% CI 4-5%) versus 0.3% in US adults. Overweight/obesity prevalence (53%; 95% CI 46-59%) was below that of US adults (68%). Meta-analysis of alcohol consumption prevalence was impeded by varying assessment methods. Overall, we observed considerable study heterogeneity in prevalence estimates.

CONCLUSION

Prevalence of smoking and oncogenic virus infections continues to be extraordinarily high among PLWHA, indicating a vital need for risk factor reduction efforts.

Prediction of drug-drug interactions between various antidepressants and efavirenz or boosted protease inhibitors using a physiologically based pharmacokinetic modelling approach

BACKGROUND AND OBJECTIVE

The rate of depression in patients with HIV is higher than in the general population. The use of antidepressants can have a beneficial effect, improving antiretroviral therapy adherence and consequently their efficacy and safety. Efavirenz and protease inhibitor boosted with ritonavir are major components of the antiretroviral therapy and are inducers and/or inhibitors of several cytochrome P450 (CYP) isoforms. Although antidepressants are prescribed to a significant proportion of patients treated with antiretrovirals, there are limited clinical data on drug-drug interactions. The aim of this study was to predict the magnitude of drug-drug interactions among efavirenz, boosted protease inhibitors and the most commonly prescribed antidepressants using an in vitro-in vivo extrapolation (IVIVE) model simulating virtual clinical trials.

METHODS

In vitro data describing the chemical characteristics, and absorption, distribution, metabolism and elimination (ADME) properties of efavirenz, boosted protease inhibitors and the most commonly prescribed antidepressants were obtained from published literature or generated by standard methods. Pharmacokinetics and drug-drug interaction were simulated using the full physiologically based pharmacokinetic model implemented in the Simcyp™ ADME simulator. The robustness of our modeling approach was assessed by comparing the magnitude of simulated drug-drug interactions using probe drugs to that observed in clinical studies.

RESULTS

Simulated pharmacokinetics and drug-drug interactions were in concordance with available clinical data. Although the simulated drug-drug interactions with antidepressants were overall weak to moderate according to the classification of the US FDA, fluoxetine and venlafaxine represent better candidates from a pharmacokinetic standpoint for patients on efavirenz and venlafaxine or citalopram for patients on boosted protease inhibitors.

CONCLUSION

The modest magnitude of interaction could be explained by the fact that antidepressants are substrates of multiple isoforms and thus metabolism can still occur through CYPs that are weakly impacted by efavirenz or boosted protease inhibitors. These findings indicate that IVIVE is a useful tool for predicting drug-drug interactions and designing prospective clinical trials, giving insight into the variability of exposure, sample size and time-dependent induction or inhibition.

Bupropion for the treatment of seasonal affective disorder

INTRODUCTION

Seasonal affective disorder (SAD) is a psychiatric illness with recurring depressive episodes during particular seasons, mostly winter. Bupropion is effective in the preventive treatment of SAD and is probably also effective in the acute treatment of SAD.

AREAS COVERED

This review covers the pharmacokinetics and pharmacodynamics of bupropion. The authors also evaluate bupropion's clinical efficacy as well as its safety and tolerability.

EXPERT OPINION

Bupropion is available in an immediate release formulation, as well as a sustained release formulation and an extended release (XR) formulation. The XR formulation is recommended for SAD due to its ease of use and is the only formulation currently used as a therapy. Due to the predictable nature of SAD, the use of bupropion XR is considered a relevant treatment option. Bupropion's efficacy is shown in three trials that started in autumn at a time when SAD symptoms were not yet present although treatment effects were relatively small compared with a placebo. Bupropion was also shown to have efficacy in an open-label study. That being said, in order to reach definitive conclusions about its efficacy with acute treatment of SAD, more placebo-controlled trials are needed.

Pharmacotherapy considerations in patients with HIV and psychiatric disorders: focus on antidepressants and antipsychotics

OBJECTIVE

To review the evidence for the efficacy and safety of pharmacologic agents for the treatment of depressive and psychotic disorders in patients with HIV infection and to provide clinical considerations for the treatment of depression and psychosis in these patients.

DATA SOURCES

PubMed was searched for articles published between 1966 and August 1, 2012, using the search terms antiretrovirals, HIV, AIDS, depression, psychosis, schizophrenia, antidepressant, antipsychotic, and individual drug names (fluoxetine, sertraline, paroxetine, citalopram, escitalopram, venlafaxine, duloxetine, mirtazapine, bupropion, haloperidol, perphenazine, fluphenazine, aripiprazole, asenapine, clozapine, iloperidone, lurasidone, olanzapine, paliperidone, quetiapine, risperidone, ziprasidone).

STUDY SELECTION AND DATA EXTRACTION

For the purposes of evaluating efficacy data, we limited our selection to randomized placebo-controlled or active comparator-controlled trials for agents that have been used for depression and psychosis in HIV-infected patients.

DATA SYNTHESIS

We found 11 studies for depression treatment and 1 study for psychosis treatment that met our inclusion and exclusion criteria. Selective serotonin reuptake inhibitors (SSRIs; especially fluoxetine) and tricyclic antidepressants appear to be effective in treating depressive symptoms in patients with HIV infection without affecting immune status. Testosterone, stimulants, and dehydroepiandrosterone may also be effective in subsyndromal depression; however, studies on these agents in general were limited by small sample size. There are limited data for antipsychotics, with the only controlled study found for haloperidol and chlorpromazine used for AIDS delirium. Drug-drug interactions and potentiation of metabolic syndrome are concerns for the combined use of antidepressants and antipsychotics with antiretrovirals.

CONCLUSIONS

Larger controlled studies are needed to validate the current findings as well as expand knowledge for non-SSRI antidepressants and second-generation antipsychotics for use in HIV-infected patients.

Age-related changes in antidepressant pharmacokinetics and potential drug-drug interactions: a comparison of evidence-based literature and package insert information

BACKGROUND

Antidepressants are among the most commonly prescribed psychotropic agents for older patients. Little is known about the best source of pharmacotherapy information to consult about key factors necessary to safely prescribe these medications to older patients.

OBJECTIVE

The objective of this study was to synthesize and contrast information in the package insert (PI) with information found in the scientific literature about age-related changes of antidepressants in systemic clearance and potential pharmacokinetic drug-drug interactions (DDIs).

METHODS

A comprehensive search of two databases (MEDLINE and EMBASE from January 1, 1975 to September 30, 2011) with the use of a combination of search terms (antidepressants, pharmacokinetics, and drug interactions) was conducted to identify relevant English language articles. This information was independently reviewed by two researchers and synthesized into tables. These same two researchers examined the most up-to-date PIs for the 26 agents available at the time of the study to abstract quantitative information about age-related decline in systemic clearance and potential DDIs. The agreement between the two information sources was tested with κ statistics.

RESULTS

The literature reported age-related clearance changes for 13 antidepressants, whereas the PIs only had evidence about 4 antidepressants (κ < 0.4). Similarly, the literature identified 45 medications that could potentially interact with a specific antidepressant, whereas the PIs only provided evidence about 12 potential medication-antidepressant DDIs (κ < 0.4).

CONCLUSION

The evidence-based literature compared with PIs is the most complete pharmacotherapy information source about both age-related clearance changes and pharmacokinetic DDIs with antidepressants. Future rigorously designed observational studies are needed to examine the combined risk of antidepressants with age-related decline in clearance and potential DDIs on important health outcomes such as falls and fractures in older patients.

Clinically significant drug interactions with newer antidepressants

After the introduction of selective serotonin reuptake inhibitors (SSRIs), other newer antidepressants with different mechanisms of action have been introduced in clinical practice. Because antidepressants are commonly prescribed in combination with other medications used to treat co-morbid psychiatric or somatic disorders, they are likely to be involved in clinically significant drug interactions. This review examines the drug interaction profiles of the following newer antidepressants: escitalopram, venlafaxine, desvenlafaxine, duloxetine, milnacipran, mirtazapine, reboxetine, bupropion, agomelatine and vilazodone. In general, by virtue of a more selective mechanism of action and receptor profile, newer antidepressants carry a relatively low risk for pharmacodynamic drug interactions, at least as compared with first-generation antidepressants, i.e. monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants (TCAs). On the other hand, they are susceptible to pharmacokinetic drug interactions. All new antidepressants are extensively metabolized in the liver by cytochrome P450 (CYP) isoenzymes, and therefore may be the target of metabolically based drug interactions. Concomitant administration of inhibitors or inducers of the CYP isoenzymes involved in the biotransformation of specific antidepressants may cause changes in their plasma concentrations. However, due to their relatively wide margin of safety, the consequences of such kinetic modifications are usually not clinically relevant. Conversely, some newer antidepressants may cause pharmacokinetic interactions through their ability to inhibit specific CYPs. With regard to this, duloxetine and bupropion are moderate inhibitors of CYP2D6. Therefore, potentially harmful drug interactions may occur when they are coadministered with substrates of these isoforms, especially compounds with a narrow therapeutic index. The other new antidepressants are only weak inhibitors or are not inhibitors of CYP isoforms at usual therapeutic concentrations and are not expected to affect the disposition of concomitantly administered medications. Although drug interactions with newer antidepressants are potentially, but rarely, clinically significant, the use of antidepressants with a more favourable drug interaction profile is advisable. Knowledge of the interaction potential of individual antidepressants is essential for safe prescribing and may help clinicians to predict and eventually avoid certain drug combinations.

Complex drug interactions of HIV protease inhibitors 2: in vivo induction and in vitro to in vivo correlation of induction of cytochrome P450 1A2, 2B6, and 2C9 by ritonavir or nelfinavir

Drug-drug interactions (DDIs) with the HIV protease inhibitors (PIs) are complex, paradoxical (e.g., ritonavir/alprazolam), and involve multiple mechanisms. As part of a larger study to better understand these DDIs and to devise a framework for in vitro to in vivo prediction of these DDIs, we determined the inductive effect of ∼2 weeks of administration of two prototypic PIs, nelfinavir (NFV), ritonavir (RTV), and rifampin (RIF; induction positive control) on the cytochrome P450 enzymes CYP1A2, CYP2B6, CYP2C9, and CYP2D6 and the inductive or inductive plus inhibitory effect of NFV, RTV, or RIF on CYP3A and P-glycoprotein in healthy human volunteers. Statistically significant induction of CYP1A2 (2.1-, 2.9-, and 2.2-fold), CYP2B6 (1.8-, 2.4-, and 4-fold), and CYP2C9 (1.3-, 1.8-, and 2.6-fold) was observed after NFV, RTV, or RIF treatment, respectively (as expected, CYP2D6 was not induced). Moreover, we accurately predicted the in vivo induction of these enzymes by quantifying their induction by the PIs in human hepatocytes and by using RIF as an in vitro to in vivo scalar. On the basis of the modest in vivo induction of CYP1A2, CYP2B6, or CYP2C9, the in vivo paradoxical DDIs with the PIs are likely explained by mechanisms other than induction of these enzymes such as induction of other metabolic enzymes, transporters, or both.