Lack of Enzyme-Inducing Effect of Rifampicin on the Pharmacokinetics of Enfuvirtide

Clinical considerations and pharmacokinetic interactions between HIV and tuberculosis therapeutics

INTRODUCTION

Tuberculosis (TB) is a leading infectious disease cause of mortality worldwide, especially for people living with human immunodeficiency virus (PLWH). Treating TB in PLWH can be challenging due to numerous drug interactions.

AREAS COVERED

This review discusses drug interactions between antitubercular and antiretroviral drugs. Due to its clinical importance, initiation of antiretroviral therapy in patients requiring TB treatment is discussed. Special focus is placed on the rifamycin class, as it accounts for the majority of interactions. Clinically relevant guidance is provided on how to manage these interactions. An additional section on utilizing therapeutic drug monitoring (TDM) to optimize drug exposure and minimize toxicities is included.

EXPERT OPINION

Antitubercular and antiretroviral coadministration can be successfully managed. TDM can be used to optimize drug exposure and minimize toxicity risk. As new TB and HIV drugs are discovered, additional research will be needed to assess for clinically relevant drug interactions.

The effect of itraconazole and rifampicin on the pharmacokinetics of osimertinib

AIMS

We investigated the effects of a strong CYP3A4 inhibitor (itraconazole) or inducer (rifampicin) on the pharmacokinetics of the epidermal growth factor receptor-tyrosine kinase inhibitor osimertinib, in patients with advanced non-small cell lung cancer in two Phase I, open-label, two-part clinical studies. Part one of both studies is reported.

METHODS

In the itraconazole study (NCT02157883), patients received single-dose osimertinib 80 mg on Days 1 and 10 and itraconazole (200 mg twice daily) on Days 6-18 orally. In the rifampicin study (NCT02197247), patients received osimertinib 80 mg once daily on Days 1-77 and rifampicin 600 mg once daily on Days 29-49.

RESULTS

In the itraconazole study (n = 36), the geometric least squares mean (GMLSM) ratios (osimertinib plus itraconazole/osimertinib alone) for Cmax and AUC were 80% (90% CI 73, 87) and 124% (90% CI 115, 135), respectively, below the predefined no-effect upper limit of 200%. In the rifampicin study (n = 40), the GMLSM ratios (osimertinib plus rifampicin/osimertinib alone) for Css,max and AUCτ were 27% (90% CI 24, 30) and 22% (90% CI 20, 24), respectively, below the predefined no-effect lower limit of 50%. The induction effect of rifampicin was apparent within 7 days of initiation; osimertinib Css,max and AUCτ values returned to pre-rifampicin levels within 3 weeks of rifampicin discontinuation. No new osimertinib safety findings were observed.

CONCLUSIONS

Osimertinib can be co-administered with CYP3A4 inhibitors, but strong CYP3A inducers should be avoided if possible.

Pharmacological interactions between rifampicin and antiretroviral drugs: challenges and research priorities for resource-limited settings

Coadministration of antituberculosis and antiretroviral therapy is often inevitable in high-burden countries where tuberculosis (TB) is the most common opportunistic infection associated with HIV/AIDS. Concurrent use of rifampicin and many antiretroviral drugs is complicated by pharmacokinetic drug-drug interactions. Rifampicin is a very potent enzyme inducer, which can result in subtherapeutic antiretroviral drug concentrations. In addition, TB drugs and antiretroviral drugs have additive (pharmacodynamic) interactions as reflected in overlapping adverse effect profiles. This review provides an overview of the pharmacological interactions between rifampicin-based TB treatment and antiretroviral drugs in adults living in resource-limited settings. Major progress has been made to evaluate the interactions between TB drugs and antiretroviral therapy; however, burning questions remain concerning nevirapine and efavirenz effectiveness during rifampicin-based TB treatment, treatment options for TB-HIV-coinfected patients with nonnucleoside reverse transcriptase inhibitor resistance or intolerance, and exact treatment or dosing schedules for vulnerable patients including children and pregnant women. The current research priorities can be addressed by maximizing the use of already existing data, creating new data by conducting clinical trials and prospective observational studies and to engage a lobby to make currently unavailable drugs available to those most in need.

Treatment optimization in patients co-infected with HIV and Mycobacterium tuberculosis infections: focus on drug-drug interactions with rifamycins

Tuberculosis (TB) and HIV continue to be two of the major causes of morbidity and mortality in the world, and together are responsible for the death of millions of people every year. There is overwhelming evidence to recommend that patients with TB and HIV co-infection should receive concomitant therapy of both conditions regardless of the CD4 cell count level. The principles for treatment of active TB disease in HIV-infected patients are the same as in HIV-uninfected patients. However, concomitant treatment of both conditions is complex, mainly due to significant drug-drug interactions between TB and HIV drugs. Rifamycins are potent inducers of the cytochrome P450 (CYP) pathway, leading to reduced (frequently sub-therapeutic) plasma concentrations of some classes of antiretrovirals. Rifampicin is also an inducer of the uridine diphosphate glucuronosyltransferase (UGT) 1A1 enzymes and interferes with drugs, such as integrase inhibitors, that are metabolized by this metabolic pathway. Rifampicin is also an inducer of the adenosine triphosphate (ATP) binding cassette transporter P-glycoprotein, which may also lead to decreased bioavailability of concomitantly administered antiretrovirals. On the other side, rifabutin concentrations are affected by the antiretrovirals that induce or inhibit CYP enzymes. In this review, the pharmacokinetic interactions, and the relevant clinical consequences, of the rifamycins-rifampicin, rifabutin, and rifapentine-with antiretroviral drugs are reviewed and discussed. A rifampicin-based antitubercular regimen and an efavirenz-based antiretroviral regimen is the first choice for treatment of TB/HIV co-infected patients. Rifabutin is the preferred rifamycin to use in HIV-infected patients on a protease inhibitor-based regimen; however, the dose of rifabutin needs to be reduced to 150 mg daily. More information is required to select optimal treatment regimens for TB/HIV co-infected patients whenever efavirenz cannot be used and rifabutin is not available. Despite significant pharmacokinetic interactions between antiretrovirals and antitubercular drugs, adequate clinical response of both infections can be achieved with an acceptable safety profile when the pharmacological characteristics of drugs are known, and appropriate combination regimens, dosing, and timing of initiation are used. However, more clinical research is needed for newer drugs, such as rifapentine and the recently introduced integrase inhibitor antiretrovirals, and for specific population groups, such as children, pregnant women, and patients affected by multidrug-resistant TB.

Alcohol use disorders negatively influence antiretroviral medication adherence among men who have sex with men in Peru

As international guidelines increase access to antiretroviral therapy (ART) globally, ART adherence becomes increasingly important to achieve HIV treatment as prevention (TasP) goals. In the concentrated HIV epidemic among men who have sex with men (MSM) and transgendered women (TGW) in Lima, Peru, the independent correlates of ART nonadherence were examined to inform treatment intervention priorities. Cross sectional survey of HIV-infected MSM and TGW who are engaged in clinical care in Lima, Peru. From June to August 2012, 302 HIV-infected Peruvian MSM/TGW from three clinical care sites were recruited using convenience sampling to participate in a cross-sectional computer-assisted adherence survey. Several standardized screening measures associated with ART nonadherence were examined in order to determine the independent correlates of optimal (≥90%) and perfect (100%) adherence, which were assessed using logistic regression. Of the 302 participants recruited, 263 (87.1%) were prescribed ART. Among those prescribed ART, 229 (87.1%) reported optimal and 146 (55.5%) reported perfect adherence. The prevalence of alcohol use disorders (AUD; 43.2%), alcohol dependence (5.3%), recent drug use (6.0%), and depression (44.5%) was high, and most participants had some evidence of neurocognitive impairment. Meeting criteria for having an AUD and depression were collinear (p < 0.001). On multivariate analysis, having an AUD was inversely related and the only independent correlate of optimal (AOR = 0.427; 95% CI = 0.187-0.976) and perfect (AOR = 0.552; 95% CI = 0.327-0.930) ART adherence. AUDs are highly prevalent among Peruvian HIV-infected MSM and contribute significantly to ART nonadherence. These findings support the need for screening and treating underlying AUDs. In order to meet HIV TasP goals, evidence-based strategies targeting AUDs are likely to directly improve ART adherence and indirectly improve overall individual health, HIV treatment engagement, and reduce transmission to sexual partners among this vulnerable and disproportionally affected population.

Therapy and prophylaxis of opportunistic infections in HIV-infected patients: a guideline by the German and Austrian AIDS societies (DAIG/ÖAG) (AWMF 055/066)

INTRODUCTION

There was a growing need for practical guidelines for the most common OIs in Germany and Austria under consideration of the local epidemiological conditions.

MATERIALS AND METHODS

The German and Austrian AIDS societies developed these guidelines between March 2010 and November 2011. A structured Medline research was performed for 12 diseases, namely Immune reconstitution inflammatory syndrome, Pneumocystis jiroveci pneumonia, cerebral toxoplasmosis, cytomegalovirus manifestations, candidiasis, herpes simplex virus infections, varizella zoster virus infections, progressive multifocal leucencephalopathy, cryptosporidiosis, cryptococcosis, nontuberculosis mycobacteria infections and tuberculosis. Due to the lack of evidence by randomized controlled trials, part of the guidelines reflects expert opinions. The German version was accepted by the German and Austrian AIDS Societies and was previously published by the Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF; German Association of the Scientific Medical Societies).

CONCLUSION

The review presented here is a translation of a short version of the German-Austrian Guidelines of opportunistic infections in HIV patients. These guidelines are well-accepted in a clinical setting in both Germany and Austria. They lead to a similar treatment of a heterogeneous group of patients in these countries.

Lack of Interaction between Enfuvirtide and Ritonavir or Ritonavir-Boosted Saquinavir in HIV-1-Infected Patients

Enfuvirtide (Fuzeon) is an HIV fusion inhibitor, the first drug in a new class of antiretrovirals. The HIV protease inhibitors ritonavir and saquinavir both inhibit cytochrome P450 (CYP450) isoenzymes, and low-dose ritonavir is often used to boost pharmacokinetic exposure to full-dose protease inhibitors. These two studies were designed to assess whether ritonavir and ritonavir-boosted saquinavir influence the steady-state pharmacokinetics of enfuvirtide. Both studies were single-center, open-label, one-sequence crossover clinical pharmacology studies in 12 HIV-1-infected patients each. Patients received enfuvirtide (90 mg twice daily [bid], subcutaneous injection) for 7 days and either ritonavir (200 mg bid, ritonavir study, orally) or saquinavir/ritonavir (1000/100 mg bid, saquinavir/ritonavir study, orally) for 4 days on days 4 to 7. Serial blood samples were collected up to 24 hours after the morning dose of enfuvirtide on days 3 and 7. Plasma concentrations for enfuvirtide, enfuvirtide metabolite, saquinavir, and ritonavir were measured using validated liquid chromatography tandem mass spectrometry methods. Efficacy and safety were also monitored. Bioequivalence criteria require the 90% confidence interval (CI) for the least squares means (LSM) of C(max) and AUC(12h) to be between 80% and 125%. In the present studies, analysis of variance showed that when coadministered with ritonavir, the ratio of LSM for enfuvirtide was 124% for C(max) (90% confidence interval [CI]: 109%-141%), 122% for AUC(12h) (90% CI: 108%-137%), and 114% for C(trough) (90% CI: 102%-128%). Although the bioequivalence criteria were not met, the increase in enfuvirtide exposure was small (< 25%) and not clinically relevant. When administered with ritonavir-boosted saquinavir, the ratio of LSM for enfuvirtide was 107% for C(max) (90% CI: 94.3%-121%) and 114% for AUC(12h) (90% CI: 105%-124%), which therefore met bioequivalence criteria, and 126% for C(trough) (90% CI: 117%-135%). The pharmacokinetics of enfuvirtide are affected to a small extent when coadministered with ritonavir at a dose of 200 mg bid but not when coadministered with a saquinavir-ritonavir combination (1000/100 mg bid). However, previous clinical studies have shown that such increases in enfuvirtide exposure are not clinically relevant. Thus, no dosage adjustments are warranted when enfuvirtide is coadministered with low-dose ritonavir or saquinavir boosted with a low dose of ritonavir.

AtriplaR/anti-TB combination in TB/HIV patients. Drug in focus

Background

Co-administration of anti-tuberculosis and antiretroviral therapy is often inevitable in high-burden countries where tuberculosis is the most common opportunistic infection associated with HIV/AIDS. Concurrent use of rifampicin and several antiretroviral drugs is complicated by pharmacokinetic drug-drug interaction.

Method

Pubmed and Google search following the key words tuberculosis, HIV, emtricitabine, tenofovir efavirenz, interaction were used to find relevant information on each drug of the fixed dose combination Atripla^R

Results

Information on generic name, trade name, pharmacokinetic parameter, metabolism and the pharmacokinetic interaction with Anti-TB drugs of emtricitabine, tenofovir, and efavirenz was obtained.

Conclusion

Fixed dose combination of emtricitabine/tenofovir/efavirenz (ATRIPLA^R) which has been approved by Food and Drug Administration shows promising results as far as safety and efficacy is concerned in TB/HIV co-infection patients, hence can be considered effective and safe antiretroviral drug in TB/HIV management for adult and children above 3 years of age.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

Reassessment of enfuvirtide's role in the management of HIV-1 infection

BACKGROUND

The development of new protease inhibitors, new non-nucleoside reverse transcriptase inhibitors and novel therapeutic drug classes has dramatically changed the approach to managing HIV-1 patients with multidrug resistant virus. This has led many clinicians to reevaluate the clinical utility of enfuvirtide.

OBJECTIVES

To summarize recent literature on enfuvirtide and to reassess enfuvirtide's role in the management of HIV-1 infection.

METHODS

MEDLINE (1990 to February Week 2 2008) and EMBASE (1990 to 2008 week 8) databases were searched using the following terms: 'enfuvirtide', 'Fuzeon', 'T20', 'HIV fusion inhibitors', and 'HIV entry inhibitor'; limits: English language. Reference lists of articles deemed relevant were hand searched for additional publications. Significant abstracts from recent international HIV conferences were also identified.

CONCLUSION

Enfuvirtide can optimize the response to new combinations of HIV-1 drug regimens in multiresistant patients. Its inclusion as an active agent is effective but use is impacted by its high cost, inconvenient route of administration and cosmetic side-effect profile.

Modeling, prediction, and in vitro in vivo correlation of CYP3A4 induction

CYP3A4 induction is not generally considered to be a concern for safety; however, serious therapeutic failures can occur with drugs whose exposure is lower as a result of more rapid metabolic clearance due to induction. Despite the potential therapeutic consequences of induction, little progress has been made in quantitative predictions of CYP3A4 induction-mediated drug-drug interactions (DDIs) from in vitro data. In the present study, predictive models have been developed to facilitate extrapolation of CYP3A4 induction measured in vitro to human clinical DDIs. The following parameters were incorporated into the DDI predictions: 1) EC(50) and E(max) of CYP3A4 induction in primary hepatocytes; 2) fractions unbound of the inducers in human plasma (f(u, p)) and hepatocytes (f(u, hept)); 3) relevant clinical in vivo concentrations of the inducers ([Ind](max, ss)); and 4) fractions of the victim drugs cleared by CYP3A4 (f(m, CYP3A4)). The values for [Ind](max, ss) and f(m, CYP3A4) were obtained from clinical reports of CYP3A4 induction and inhibition, respectively. Exposure differences of the affected drugs in the presence and absence of the six individual inducers (bosentan, carbamazepine, dexamethasone, efavirenz, phenobarbital, and rifampicin) were predicted from the in vitro data and then correlated with those reported clinically (n = 103). The best correlation was observed (R(2) = 0.624 and 0.578 from two hepatocyte donors) when f(u, p) and f(u, hept) were included in the predictions. Factors that could cause over- or underpredictions (potential outliers) of the DDIs were also analyzed. Collectively, these predictive models could add value to the assessment of risks associated with CYP3A4 induction-based DDIs by enabling their determination in the early stages of drug development.

Recombinant protein of heptad-repeat HR212, a stable fusion inhibitor with potent anti-HIV action in vitro

HR212, a recombinant protein expressed in Escherichia coli, has been previously reported to inhibit HIV-1 membrane fusion at low nanomolar level. Here we report that HR212 is effective in blocking laboratory strain HIV-1(IIIB) entry and replication with EC(50) values of 3.92+/-0.62 and 6.59+/-1.74 nM, respectively, and inhibiting infection by clinic isolate HIV-1(KM018) with EC(50) values of 44.44+/-10.20 nM, as well as suppressing HIV-1-induced cytopathic effect with an EC(50) value of 3.04+/-1.20 nM. It also inhibited HIV-2(ROD) and HIV-2(CBL-20) entry and replication in the microM range. Notably, HR212 was highly effective against T20-resistant strains with EC(50) values ranging from 5.09 to 7.75 nM. Unlike T20, HR212 showed stability sufficient to inhibit syncytia formation in a time-of-addition assay, and was insensitive to proteinase K digestion. These results suggest that HR212 has great potential to be further developed as novel HIV-1 fusion inhibitor for treatment of HIV/AIDS patients, particularly for those infected by T20-resistant variants.

Update on rifampin and rifabutin drug interactions

Rifampin is a potent inducer of cytochrome P-450 oxidative enzymes as well as the P-glycoprotein transport system. Several examples of well-documented clinically significant interactions include warfarin, oral contraceptives, cyclosporine, itraconazole, digoxin, verapamil, nifedipine, simvastatin, midazolam, and human immunodeficiency virus-related protease inhibitors. Rifabutin reduces serum concentrations of antiretroviral agents, but less so than rifampin. Examples of clinically relevant interactions demonstrated by recent reports include everolimus, atorvastatin, rosiglitazone/pioglitazone, celecoxib, clarithromycin, caspofungin, and lorazepam. To avoid a decreased therapeutic response, therapeutic failure, or toxic reactions when rifampin is added to or discontinued from medication regimens, clinicians need to be cognizant of these interactions. Studies and cases of rifampin drug interactions continue to increase rapidly. This review is a timely reminder to clinicians to be vigilant.

Complications of Antiretroviral Therapy in Patients with Tuberculosis: Drug Interactions, Toxicity, and Immune Reconstitution Inflammatory Syndrome

Access to antiretroviral therapy is rapidly expanding in resource-limited settings, where tuberculosis is the most common opportunistic infection. Coadministration of antitubercular and antiretroviral agents is, therefore, occurring commonly, and it is associated with 3 major complications. First, induction of cytochrome P-450 enzymes and P-glycoprotein by rifampin results in reduced concentrations of nonnucleoside reverse-transcriptase inhibitors and, particularly, protease inhibitors. This potentially results in the loss of antiviral efficacy and the development of viral resistance. Replacing rifampin with rifabutin, which does not significantly affect the concentrations of antiretroviral agents, is advocated but is currently unaffordable in resource-limited settings. Second, overlapping toxicities of antitubercular and antiretroviral agents occur frequently, necessitating discontinuation of therapy and increasing the risk of nonadherence. Third, immunopathological reactions, termed "the immune reconstitution inflammatory syndrome," occur frequently when antiretroviral therapy is initiated in patients with tuberculosis. These complexities of coadministration of antitubercular and antiretroviral agents are reviewed, and research priorities are highlighted.

Tuberculosis and HIV co-infection: a practical therapeutic approach

HIV and tuberculosis (TB) are leading global causes of mortality and morbidity, and yet effective treatment exists for both conditions. Rifamycin-based antituberculosis therapy can cure HIV-related TB and, where available, the introduction of highly active antiretroviral therapy (HAART) has markedly reduced the incidence of AIDS and death. Optimal treatment regimens for HIV/TB co-infection are not yet clearly defined. Combinations are limited by alterations in the activity of the hepatic cytochrome P450 (CYP) enzyme system, which in particular may produce subtherapeutic plasma concentrations of antiretroviral drugs. For example, protease inhibitors often must be avoided if the potent CYP inducer rifampicin is co-administered. However, an alternative rifamycin, rifabutin, which has similar efficacy to rifampicin, can be used with appropriate dose reduction. Available clinical data suggest that, for the majority of individuals, rifampicin-based regimens can be successfully combined with the non-nucleoside reverse transcriptase inhibitors nevirapine and efavirenz. Most available HAART regimens in areas that have a high burden of TB contain one or the other of these drugs as a backbone. However, significant questions remain as to the optimal dose of either agent required to ensure therapeutic plasma concentrations, especially in relation to particular ethnic groups. The timing of HAART initiation after starting antituberculosis therapy continues to be controversial. Debate centres upon whether early initiation of HAART increases the risk of paradoxical reactions (immune reconstitution-related events) and other adverse events, or whether delay greatly elevates the risk of disease progression. Further prospective clinical data are needed to help inform practice in this area.

Recomendaciones españolas sobre el uso adecuado de enfuvirtida

Enfuvirtide is a high-cost, parenterally administered drug commonly used in late phases of HIV infection, when its efficacy may be compromised. To optimize enfuvirtide use, consensus recommendations for this purpose have been formulated by 247 physicians attending patients with HIV infection in Spain. A literature review was performed in which grades of evidence and recommendations were defined according to the origin of the data (randomized clinical trials, non-randomized studies, expert opinion). Twenty-eight local consensus meetings were held between May and September 2005 to discuss the most important aspects related to the use of enfuvirtide, following a pre-established system used in all the meetings. The main conclusions were as follows: a) enfuvirtide use is often excessively delayed and is given to patients with little chance of treatment success; b) enfuvirtide is indicated in patients who require antiretroviral treatment and for whom an optimum treatment with three other fully effective drugs cannot be designed; c) the most important prognostic factor is the availability of at least one other completely active drug; d) there is no infallible method to avoid the development of local reactions, but measures are available to decrease their incidence and severity; and e) patient counseling and training for correct administration of the drug are essential to improve adherence, the repercussions of local reactions and, of course, the efficacy of the treatment.

Unexpected drug-drug interaction between tipranavir/ritonavir and enfuvirtide

Fifty-five patients placed on tipranavir/ritonavir 500/200 mg twice a day (27 with enfuvirtide and 28 without) underwent tipranavir and ritonavir plasma concentration measurements by high-pressure liquid chromatography. Markedly higher tipranavir and ritonavir trough concentrations were observed in enfuvirtide recipients. The modelling of sparse plasma samples using a first order absorption and elimination monocompartmental model without time lag predicted higher tipranavir elimination half-life and volume of distribution in enfuvirtide takers. This unexpected drug-drug interaction warrants further investigation.

Pharmacokinetics of enfuvirtide in patients treated in typical routine clinical settings

Therapeutic drug monitoring (TDM) is gaining importance for improving the success of antiretroviral treatment in human immunodeficiency virus-infected patients. However, enfuvirtide (ENF) concentrations are not regularly determined. The objective of this work was to study the pharmacokinetics (PK) of ENF in patients treated in routine clinical settings, to develop a population PK model describing the concentration-time profile, and to establish PK reference values. A liquid chromatography-tandem mass spectrometry method was developed and applied to serum samples submitted for TDM. A two-compartment model with linear absorption and elimination was fitted to 329 concentrations from 131 patients. The PK model was used for simulations resulting in percentile curves for ENF levels for the full dosing interval. The model predicted that a median concentration of 1,968 ng/ml would be reached 12 h after administration of 90 mg of ENF, and 23% and 58% of patients are expected to have concentrations below 1,000 ng/ml and 2,200 ng/ml, respectively. Both values have been proposed as cutoffs for virological efficacy. The median maximum concentration of drug in serum (Cmax) of 3,943 ng/ml, predicted for 3 h after drug administration, is lower than the Cmax reported previously. We found an enormous interpatient variability at every time point, with concentration spectrums covering >1 log and 52% and 123% interindividual variabilities in the typical clearance and volume of distribution, respectively, in contrast to preexisting PK data. In summary, ENF levels are lower and more variable than expected. Many patients may achieve insufficient concentrations. Further covariate analysis in the population PK model might help to identify factors influencing the variability in ENF concentrations.

Enfuvirtide for nurses: answering patient questions on activity, safety, and lifestyle impact

The introduction of enfuvirtide, the first self-administered parenteral antiretroviral, has reinforced the HIV nurse's role in patient education, support, and motivation. Detailed background knowledge of the drug will assist nurses to provide answers to common questions and concerns raised during patient training. Three particular concerns often raised are curiosity about how enfuvirtide works, what side effects can be expected, and how these and the process of daily injection will affect the patient's daily routine. This brief review is designed to provide nurse-educators with clinical information on these three issues to help them better provide the answers patients will need to help them feel confident self-administering this new drug.

Fosamprenavir

Fosamprenavir is one of the most recently approved HIV-1 protease inhibitors (PIs) and offers reductions in pill number and pill size, and omits the need for food and fluid requirements associated with the earlier-approved HIV-1 PIs. Three fosamprenavir dosage regimens are approved by the US FDA for the treatment of HIV-1 PI-naive patients, including fosamprenavir 1,400 mg twice daily, fosamprenavir 1,400 mg once daily plus ritonavir 200mg once daily, and fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily. Coadministration of fosamprenavir with ritonavir significantly increases plasma amprenavir exposure. The fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily regimen maintains the highest plasma amprenavir concentrations throughout the dosing interval; this is the only approved regimen for the treatment of HIV-1 PI-experienced patients and is the only regimen approved in the European Union. Fosamprenavir is the phosphate ester prodrug of the HIV-1 PI amprenavir, and is rapidly and extensively converted to amprenavir after oral administration. Plasma amprenavir concentrations are quantifiable within 15 minutes of dosing and peak at 1.5-2 hours after fosamprenavir dosing. Food does not affect the absorption of amprenavir following administration of the fosamprenavir tablet formulation; therefore, fosamprenavir tablets may be administered without regard to food intake. Amprenavir has a large volume of distribution, is 90% bound to plasma proteins and is a substrate of P-glycoprotein. With <1% of a dose excreted in urine, the renal route is not an important elimination pathway, while the principal route of amprenavir elimination is hepatic metabolism by cytochrome P450 (CYP) 3A4. Amprenavir is also an inhibitor and inducer of CYP3A4. Furthermore, fosamprenavir is commonly administered in combination with low-dose ritonavir, which is also extensively metabolised by CYP3A4, and is a more potent CYP3A4 inhibitor than amprenavir. This potent CYP3A4 inhibition contraindicates the coadministration of certain CYP3A4 substrates and requires others to be co-administered with caution. However, fosamprenavir can be co-administered with many other antiretroviral agents, including drugs of the nucleoside/nucleotide reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor and HIV entry inhibitor classes. Coadministration with other HIV-1 PIs continues to be studied.The extensive fosamprenavir and amprenavir clinical drug interaction information provides guidance on how to co-administer fosamprenavir and fosamprenavir plus ritonavir with many other commonly co-prescribed medications, such as gastric acid suppressants, HMG-CoA reductase inhibitors, antibacterials and antifungal agents.

Enfuvirtide: a review of its use in the management of HIV infection

Enfuvirtide (Fuzeon), a fusion inhibitor, is indicated in combination with other antiretroviral agents in the treatment of HIV infection in treatment-experienced adults and children aged >6 years. The addition of subcutaneous enfuvirtide to an optimised antiretroviral background regimen improved the virological and immunological response in treatment-experienced HIV-infected patients in the two large, well designed TORO (T-20 vs Optimised Regimen Only) trials. Although injection-site reactions occurred almost universally in enfuvirtide recipients, they were rarely treatment-limiting. Enfuvirtide was otherwise generally well tolerated. The challenge for clinicians is in determining the appropriate timing for enfuvirtide initiation, which requires consideration of the likelihood of a better virological response with the construction of an active background regimen versus the potential for a low rate of adherence to therapy in patients in the early stages of treatment and/or disease development. Enfuvirtide is a novel antiretroviral that is effective in HIV-infected patients whose treatment options are limited by multi-class antiretroviral resistance.

The appealing story of HIV entry inhibitors : from discovery of biological mechanisms to drug development

Current therapeutic intervention in HIV infection relies upon 20 different drugs. Despite the impressive efficacy shown by these drugs, we are confronted with an unexpected frequency of adverse effects, such as mitochondrial toxicity and lipodystrophy, and resistance, not only to individual drugs but to entire drug classes.Thus, there is now a great need for new antiretroviral drugs with reduced toxicity, increased activity against drug-resistant viruses and a greater capacity to reach tissue sanctuaries of the virus. Two different HIV molecules have been selected as targets of drug inhibition so far: reverse transcriptase and protease. Drugs that target the interactions between the HIV envelope and the cellular receptor complex are a 'new entry' into the scenario of HIV therapy and have recently raised great interest because of their activity against multidrug-resistant viruses. There are several compounds that are at different developmental stages in the pipeline to counter HIV entry, among them: (i) the attachment inhibitor dextrin-2-sulfate; (ii) the inhibitors of the glycoprotein (gp) 120/CD4 interaction PRO 542, TNX 355 and BMS 488043; (iii) the co-receptor inhibitors subdivided in those targeting CCR5 (SCH 417690 [SCH D], UK 427857 GW 873140, PRO 140, TAK 220, AMD 887) and those targeting CXCR4 (AMD 070, KRH 2731); and (iv) the fusion inhibitors enfuvirtide (T-20) and tifuvirtide (T-1249). The story of the first of these drugs, enfuvirtide, which has successfully completed phase III clinical trials, has been approved by the US FDA and by the European Medicines Agency, and is now commercially available worldwide, is an example of how the knowledge of basic molecular mechanisms can rapidly translate into the development of clinically effective molecules.

Review: mixing new cocktails: drug interactions in antiretroviral regimens

Current highly active antiretroviral therapy (HAART) for the treatment of HIV infection requires the concomitant administration of three or four different agents, often with a high potential for drug-drug interactions. Additionally, some HIV-positive patients still require concomitant treatment with drugs for opportunistic infections, some require medication to treat unrelated medical conditions and/or the metabolic complications of antiretroviral therapy, others may self-medicate with herbal formulations and/or over-the-counter drugs, and still others many take drugs for recreational reasons or to manage addiction. Therefore, the virtually limitless number of drug combinations that may be taken by patients undergoing treatment of HIV infection makes drug-drug interactions almost inevitable. Managing these interactions is one of the major challenges associated with the multidrug regimens used for HIV therapy. This paper provides an overview of the most common interactions between antiretrovirals in the same and different classes-nucleoside analogue reverse transcriptase inhibitors (NRTI), protease inhibitors (PI), and non-nucleoside reverse transcriptase inhibitors (NNRTI)-by focusing on principles rather than specific interactions. The paper also addresses interactions between these antiretrovirals and other commonly used medications that may be prescribed concomitantly.

Pharmacokinetics, pharmacodynamics and drug interaction potential of enfuvirtide

Enfuvirtide, the first fusion inhibitor approved for the treatment of HIV-1 infection, is a synthetic peptide that binds to HIV-1 glycoprotein 41, blocking the fusion of viral and cellular membranes. When administered subcutaneously at the recommended dose of 90 mg twice daily with optimised background antiretroviral therapy, enfuvirtide significantly reduces plasma HIV-1 RNA levels up to 48 weeks compared with optimised background therapy alone. Enfuvirtide exhibits a small volume of distribution (5.48 L), low systemic clearance (1.4 L/h) and high plasma protein binding (92%). Less than 17% of enfuvirtide is converted to a minimally active deaminated form of the parent drug. Both enfuvirtide and its metabolite are primarily eliminated via catabolism to amino acid residues. Following subcutaneous administration, enfuvirtide is almost completely absorbed, and exposure increases almost linearly with dose over the range 45-180 mg. When administered at the recommended dose in adults, subcutaneous absorption is slow and protracted, resulting in relatively flat steady-state plasma concentration-time profiles. Bioavailability is high (84.3%) and the elimination half-life (3.8 hours) supports twice-daily administration. Comparable absorption was observed from three different anatomical injection sites. The pharmacokinetic-pharmacodynamic relationship indicates that the recommended dose, in combination with other active antiretrovirals, is optimal. Enfuvirtide clearance is influenced to a small extent by sex and bodyweight but this does not necessitate dosage adjustment. In vitro and in vivo studies indicate that enfuvirtide has a low potential to interact with concomitantly administered drugs. Enfuvirtide did not influence concentrations of drugs metabolised by cytochrome P450 (CYP) 3A4, CYP2D6 or N-acetyltransferase, and had only minimal effects on those metabolised by CYP1A2, CYP2E1 or CYP2C19. Coadministration of ritonavir, ritonavir-boosted saquinavir or rifampicin (rifampin) did not result in clinically significant changes in enfuvirtide pharmacokinetics. In HIV-1-infected paediatric patients, subcutaneous dosages based on bodyweight (2 mg/kg twice daily) produce pharmacokinetics broadly similar to those observed in adults administered 90 mg twice daily.

Enfuvirtida: primer fármaco de una nueva familia de antirretrovirales

Enfuvirtide or T-20 is the first drug approved by the FDA and the EMEA within the group of fusion inhibitors. Its mechanism of action is based on the blockade of the entry of the HIV to the body cells. Enfuvirtide is recommended in combination with other antiretroviral drugs for the treatment of patients infected by HIV that have developed resistance or intolerance to other prior antiretroviral therapies. Clinical trials have shown the effectiveness and safety of the treatment with this drug. Side effects most commonly reported are local reactions in the injection site. Enfuvirtide contributes to increase the therapeutic arsenal available for the management of the HIV infection, providing rescue therapy for patients in which prior treatments have failed.

Peptide inhibitors of virus-cell fusion: enfuvirtide as a case study in clinical discovery and development

The peptidic antiretroviral enfuvirtide (Fuzeon) is the first clinically approved antiviral fusion inhibitor and the first antiretroviral that must routinely be administered parenterally. Its extracellular activity results both in activity against current drug-resistant strains of HIV-1 and a low potential for systemic toxicities. As a peptide, enfuvirtide also exhibits few interactions with other antiretrovirals and concomitant medications used in HIV disease. Enfuvirtide shows potent antiretroviral activity and significantly improves medical outcomes in highly treatment-experienced patients with HIV-1 infection, but like other antiretrovirals must be given as part of a carefully selected combination regimen to minimise the risk of emergent drug resistance. Despite its subcutaneous route of administration, clinical data indicate that most patients can accept long-term enfuvirtide treatment with little difficulty or impact on daily activities. The only common adverse event associated with enfuvirtide use is injection-site reactions of generally mild-to-moderate severity, which are seldom treatment-limiting.