Drug interactions in the management of HIV infection

Antiretroviral Therapy Management in Adults With HIV During ICU Admission

The extended lifespan of people living with human immunodeficiency (HIV) and acquired immune deficiency syndrome (AIDS) (PLWHA) has increased the potential for ICU admissions unrelated to HIV infection. The objective of this review is to guide continued management of antiretroviral therapy (ART) recommended by the United States Department of Health and Human Services Antiretroviral Guidelines in critically ill adult PLWHA admitted to the intensive care unit (ICU). Pharmacists are uniquely positioned to mitigate these concerns, including whether to continue ART in the ICU, drug interactions with common ICU drugs, renal and hepatic dosing considerations, and alternative methods of administration. Despite these concerns, the original ART regimen should be continued or modified in conjunction with an HIV specialist. Discontinuation greater than 2 weeks should be avoided due to potential resistance and future HIV treatment failure. Use of ART in critically ill patients presents challenges that pharmacists are best equipped to address to prevent adverse events, administration errors, and treatment failure.

Calculated initial parenteral treatment of bacterial infections: Pharmacokinetics and pharmacodynamics

This is the third chapter of the guideline "Calculated initial parenteral treatment of bacterial infections in adults - update 2018" in the 2nd updated version. The German guideline by the Paul-Ehrlich-Gesellschaft für Chemotherapie e.V. (PEG) has been translated to address an international audience. The chapter features the pharmacokinetic and pharmacodynamics properties of the most frequently used antiinfective agents.

Patient counseling about herbal-drug interactions

Many people have the mistaken notion that, being natural, all herbs and foods are safe; this is not so. Very often, herbs and food may interact with medications you normally take, result in serious reactions. During the latter part of this century the practice of herbalism has become mainstream throughout the world. This is due remove to the recognition of the value of traditional medical systems in the world. Herbal medicines are mixtures of more than one active ingredient. The multitude of pharmacologically active compounds obviously increases the likelihood of interactions taking place. Hence, the likelihood of herb-drug interactions is theoretically higher than drug-drug interactions because synthetic drugs usually contain single chemical entity. Case reports and clinical studies have highlighted the existence of a number of clinically important interactions, although cause-and-effect relationships have not always been established. Herbs and drugs may interact either pharmacokinetically or pharmacodynamically. The predominant mechanism for this interaction is the inhibition of cytochrome P-450 3A4 in the small intestine; result in a significant reduction of drug presystemic metabolism. An additional mechanism is the inhibition of Pglycoprotein, a transporter that carries drug from the enterocyte back to the gut lumen, result in a further increase in the fraction of drug absorbed. Some herbal products (e.g. St. John's wort) have been shown to lower the plasma concentration (and/or the pharmacological effect) of a number of conventional drugs including cyclosporine, indinavir, irinotecan, nevirapine, oral contraceptives and digoxin. The data available so far, concerning this interaction and its clinical implications are reviewed in this article. It is likely that more information regarding such interaction would crop up in the future, awareness of which is necessary for achieving optimal drug therapy.

Maraviroc modelling strategy: use of early phase 1 data to support a semi-mechanistic population pharmacokinetic model

AIMS

To model the basic pharmacokinetic (PK) characteristics of maraviroc to construct an integrated semi-mechanistic PK model for use in later population PK analyses.

METHODS

Three analyses were performed utilizing intravenous, oral and radiolabel data. Firstly, a PK disposition model was developed from data from 20 healthy males who received 3, 10 or 30 mg of intravenous maraviroc. Secondly, a sigmoid E(max)vs dose model of dose-normalized non-compartmental AUC from oral dosing in 134 healthy young males and females across five phase 1 studies was constructed. This described absorption dose non-linearities and tested for the influence of food, formulation and dose frequency on model parameters. The third analysis developed a mass balance model for both absorption and disposition of maraviroc with 300 mg solution and predicted the mass balance after administration of 100 mg tablet formulation.

RESULTS

A four-compartment PK model best described the intravenous data and no influence of dose was found on clearance. Total clearance was 48 l h(-1) (2.2% SE). The main covariate effect in the non-compartmental analysis reproduced the dose-dependency of food through a five-fold increase in the ED(50) of the sigmoid E(max) model. The mass balance models calculated that 33.3% and 22.9% of 300 mg solution and 100 mg tablet doses, respectively, are systemically available, and first-pass metabolism extracts 62% of an absorbed dose, estimating a hepatic blood flow of 101 l h(-1).

CONCLUSIONS

The analysis demonstrates a novel integration approach to build a maraviroc semi-mechanistic population PK model for further use in volunteers and patients.

Clinical management of treatment-experienced, HIV/AIDS patients in the combination antiretroviral therapy era

Despite the success of combination antiretroviral therapy (ART) in improving clinical outcomes, treatment failure remains a significant challenge, particularly for highly treatment-experienced patients. This review evaluates current issues in the management of HIV-infected, treatment-experienced patients. It may provide guidance in selecting active, tolerable drug combinations that promote a reasonable quality of life, full adherence and a durable treatment response. Current treatment guidelines and clinical trial data were reviewed to identify reasons for treatment failure and to summarize therapy options for treatment-experienced and highly treatment-experienced patients. Current treatment options include nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), and inhibitors of viral fusion, entry and integration. The use of NRTIs may be limited by resistance and short- and long-term toxicities. Resistance has restricted the NNRTI class with cross-resistance preventing their sequential use. Etravirine, a next-generation NNRTI, however, demonstrates effective virological suppression in patients with baseline NNRTI resistance. Boosted PIs are key components of ART for treatment-experienced patients. The newer boosted PIs tipranavir and darunavir have demonstrated impressive activity in patients with resistance to NRTIs, NNRTIs and PIs, as well as in less treatment-experienced patients for darunavir. The fusion inhibitor enfuvirtide has demonstrated efficacy in heavily treatment-experienced patients, although injection-site reactions can be problematical. The recently approved integrase inhibitor raltegravir has also shown impressive potency and tolerability in highly treatment-experienced patients. Finally, the entry inhibitor maraviroc has also been approved recently, although its use is somewhat limited by the need for HIV tropism testing. The availability of potent next-generation PIs, NNRTIs, integrase and entry-inhibitors may offer improved therapy for treatment-experienced patients, including those with multiresistant virus. These new drugs may reduce HIV immunological and clinical progression and in doing so may also reduce treatment costs.

The challenge of managing drug interactions in elderly people

Drug therapy is essential when caring for elderly patients, but clearly it is a double-edged sword. Elderly patients are at high risk of having drug interactions, but the prevalence of these interactions is not well documented. Several types of interactions exist: drug-drug, drug-disease, drug-food, drug-alcohol, drug-herbal products, and drug-nutritional status. Factors such as age-related changes in pharmacokinetics and pharmacodynamics, frailty, interindividual variability, reduced homoeostatic mechanisms, and psychosocial issues need to be considered when drug interactions are assessed. Software can help clinicians to detect drug interactions, but many programmes have not been updated with the evolving knowledge of these interactions, and do not take into consideration important factors needed to optimise drug treatment in elderly patients. Any generated recommendations have to be tempered by a holistic, geriatric, multiprofessional approach that is team-based. This second paper in a series of two on prescribing in elderly people proposes an approach to categorise drug interactions, along with strategies to assist in their detection, management, and prevention.

Treatment of dyslipidaemia in HIV-infected persons

Accumulating evidence suggests that HIV-infected individuals have an increased risk of cardiovascular events. This risk seems to be at least partially mediated by dyslipidaemia, which is related to the use of highly active antiretroviral therapy (HAART). As HIV-infected individuals live longer due to HAART, their cardiovascular risk will invariably increase. Because HAART is likely to be used indefinitely, HAART-related dyslipidaemia has emerged as a major cardiovascular concern. This article summarises the evaluation of dyslipidaemia and cardiovascular risk in HIV-infected individuals, the potential pathophysiological and genetic mechanisms involved in HAART-related dyslipidaemia and the current treatment approaches. In general, dyslipidaemia is evaluated and treated as in HIV-negative persons. The first step is cardiovascular risk assessment and the determination of target lipid levels. A healthier lifestyle and, in particular, smoking cessation should be promoted. Lowering levels of low-density lipoprotein cholesterol (or, in the setting of significant hypertriglyceridaemia, non-high-density lipoprotein cholesterol) is the primary target of intervention. Switching HAART to a more lipid-favourable regimen should be considered if this does not jeopardise virological control. Many patients will need lipid-lowering drug therapy. Appropriate low-density lipoprotein cholesterol target levels may be more difficult to reach than in the HIV-negative population, and the potential for drug interactions when using lipid-lowering agents together with HAART needs to be considered. The identification of HAART strategies with no or minimal metabolic toxicity, and the identification of the safest and most efficacious lipid-lowering therapies for HIV-infected individuals with dyslipidaemia are important research goals.

Pharmacotherapy, vaccines and malaria advice for HIV-infected travellers

Since the introduction of effective antiretroviral therapy (ART), HIV-infected individuals are travelling more frequently and international travel has become much safer. Specific concerns include the safety of ART during travel, drug adherence and interaction considerations, and effects of immunosuppression. This review describes potentially important infections, vaccine effectiveness, safety and special approaches for their use, and HIV-related issues regarding predeparture counselling. With advanced immunosuppression (CD4+ T-cell count < 200/microl or < 14%), the immunogenicity of several vaccines is reduced, complications could occur after live attenuated vaccines and certain infections acquired during travel may be more frequent or severe. Challenges include the best options for malaria chemoprophylaxis, standby treatment and medical follow-up of the increasing number of HIV-infected long-term travellers.