A population pharmacokinetic analysis of zanamivir in subjects with experimental and naturally occurring influenza: effects of formulation and route of administration

A Systematic Review of Clinical Pharmacokinetics of Inhaled Antiviral

Background and Objectives: The study of clinical pharmacokinetics of inhaled antivirals is particularly important as it helps one to understand the therapeutic efficacy of these drugs and how best to use them in the treatment of respiratory viral infections such as influenza and the current COVID-19 pandemic. The article presents a systematic review of the available pharmacokinetic data of inhaled antivirals in humans, which could be beneficial for clinicians in adjusting doses for diseased populations. Materials and Methods: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. A comprehensive literature search was conducted using multiple databases, and studies were screened by two independent reviewers to assess their eligibility. Data were extracted from the eligible studies and assessed for quality using appropriate tools. Results: This systematic review evaluated the pharmacokinetic parameters of inhaled antiviral drugs. The review analyzed 17 studies, which included Zanamivir, Laninamivir, and Ribavirin with 901 participants, and found that the non-compartmental approach was used in most studies for the pharmacokinetic analysis. The outcomes of most studies were to assess clinical pharmacokinetic parameters such as the Cmax, AUC, and t1/2 of inhaled antivirals. Conclusions: Overall, the studies found that the inhaled antiviral drugs were well tolerated and exhibited favorable pharmacokinetic profiles. The review provides valuable information on the use of these drugs for the treatment of influenza and other viral respiratory infections.

Clinical pharmacokinetics of inhaled antimicrobials

Administration of inhaled antimicrobials affords the ability to achieve targeted drug delivery into the respiratory tract, rapid entry into the systemic circulation, high bioavailability and minimal metabolism. These unique pharmacokinetic characteristics make inhaled antimicrobial delivery attractive for the treatment of many pulmonary diseases. This review examines recent pharmacokinetic trials with inhaled antibacterials, antivirals and antifungals, with an emphasis on the clinical implications of these studies. The majority of these studies revealed evidence of high antimicrobial concentrations in the airway with limited systemic exposure, thereby reducing the risk of toxicity. Sputum pharmacokinetics varied widely, which makes it challenging to interpret the result of sputum pharmacokinetic studies. Many no vel inhaled antimicrobial therapies are currently under investigation that will require detailed pharmacokinetic studies, including combination inhaled antimicrobial therapies, inhaled nanoparticle formulations of several antibacterials, inhaled non-antimicrobial adjuvants, inhaled antiviral recombinant protein therapies and semi-synthetic inhaled antifungal agents. Additionally, the development of new inhaled delivery devices, particularly for mechanically ventilated patients, will result in a pressing need for additional pharmacokinetic studies to identify optimal dosing regimens.

Pharmacometric Models for Characterizing the Pharmacokinetics of Orally Inhaled Drugs

During the last decades, the importance of modeling and simulation in clinical drug development, with the goal to qualitatively and quantitatively assess and understand mechanisms of pharmacokinetic processes, has strongly increased. However, this increase could not equally be observed for orally inhaled drugs. The objectives of this review are to understand the reasons for this gap and to demonstrate the opportunities that mathematical modeling of pharmacokinetics of orally inhaled drugs offers. To achieve these objectives, this review (i) discusses pulmonary physiological processes and their impact on the pharmacokinetics after drug inhalation, (ii) provides a comprehensive overview of published pharmacokinetic models, (iii) categorizes these models into physiologically based pharmacokinetic (PBPK) and (clinical data-derived) empirical models, (iv) explores both their (mechanistic) plausibility, and (v) addresses critical aspects of different pharmacometric approaches pertinent for drug inhalation. In summary, pulmonary deposition, dissolution, and absorption are highly complex processes and may represent the major challenge for modeling and simulation of PK after oral drug inhalation. Challenges in relating systemic pharmacokinetics with pulmonary efficacy may be another factor contributing to the limited number of existing pharmacokinetic models for orally inhaled drugs. Investigations comprising in vitro experiments, clinical studies, and more sophisticated mathematical approaches are considered to be necessary for elucidating these highly complex pulmonary processes. With this additional knowledge, the PBPK approach might gain additional attractiveness. Currently, (semi-)mechanistic modeling offers an alternative to generate and investigate hypotheses and to more mechanistically understand the pulmonary and systemic pharmacokinetics after oral drug inhalation including the impact of pulmonary diseases.

Population pharmacokinetics of inhaled tobramycin powder in cystic fibrosis patients

Tobramycin powder for inhalation (TOBI Podhaler or TIP) is approved for the treatment of Pseudomonas aeruginosa airway infection in patients with cystic fibrosis (CF). A population pharmacokinetic model for tobramycin inhalation powder (TIP) in CF patients was developed to characterize the effect of covariates including body mass index (BMI) and lung function (forced expiratory volume in 1 s as percent of the predicted value (FEV₁% predicted) at baseline) on the serum exposure parameters.

A two-compartment model with first-order elimination and first-order absorption was developed. Across a range of baseline demographic values in the study population, the predicted mean values for the maximum (C_max) and trough (C_trough) plasma concentrations at steady state were at least 7.5 and 5-fold lower, respectively, than the recommended thresholds for tobramycin toxicity (12 µg/ml for C_max and 2 µg/ml for C_trough). This model adequately described the tobramycin serum concentration–time course in CF patients following inhalation of TIP. The results indicate that no BMI- or FEV₁-based dose adjustment is needed for use of TIP in CF patients.

Pharmacokinetic properties of anti-influenza neuraminidase inhibitors

Neuraminidase inhibitors are the mainstay of anti-influenza treatment. Oseltamivir is the most widely used drug but is currently available only as an oral formulation. Resistance spreads rapidly in seasonal H1N1 influenza A viruses, which were universally resistant in 2008, because of the H275Y mutation in the neuraminidase (NA) gene. Oseltamivir is a prodrug for the active carboxylate metabolite. Ex vivo conversion in blood samples may have confounded early pharmacokinetic studies. Oseltamivir shows dose linear kinetics, and oseltamivir carboxylate has an elimination half-life (t(1/2) β) after oral administration in healthy individuals of approximately 7.7 hours. Oseltamivir carboxylate is eliminated primarily by tubular secretion, and both clearance and tissue distribution are reduced by probenecid. The H275Y mutation in NA confers high-level oseltamivir resistance and intermediate peramivir resistance but does not alter zanamivir susceptibility. Zanamivir is available as a powder for inhalation, and a parenteral form is under development. Zanamivir distributes in an apparent volume of distribution approximating that of extracellular water and is rapidly eliminated (t(1/2) β of approximately 3.0 hours). Peramivir is slowly eliminated (t(1/2) β of 7.7-20.8 hours) and is prescribed as either a once-daily injection or as a single infusion. Laninamivir is a recently developed slowly eliminated compound for administration by inhalation.

Neuraminidase inhibitor resistance in influenza viruses

Zanamivir and oseltamivir, the currently marketed influenza virus neuraminidase inhibitors (NAIs), are prescribed for the treatment and prophylaxis of influenza and are being stockpiled for pandemic influenza. Oseltamivir resistance has been reported in up to 2% of patients in clinical trials of oseltamivir and in up to 18% of treated children. There are also reports in at least three patients treated with oseltamivir for influenza A (H5N1) infections. At this stage, there are no reports of resistance occurring to zanamivir in immunocompetent patients. Zanamivir and oseltamivir bind differently at the neuraminidase catalytic site and this contributes to different drug resistance profiles. The magnitude and duration of NAI concentrations at the site of infection are also expected to be important factors and are determined by route and timing of drug administration, dose, and pharmacokinetic differences between patients. In addition, the type, strain, and virulence of the influenza strain and the nature of the immune response all appear to play a role in determining the likelihood of drug resistance arising. The clinical significance of a particular NAI-resistant isolate from a patient is often not clear but virus viability and transmissibility are clearly important characteristics. Early initiation of NAI treatment in suspected cases of influenza is important for maximizing efficacy and minimizing the risk of drug resistance. Higher NAI doses and longer periods of treatment may be required for patients with influenza A (H5N1) infections but further work is needed in this area.

Zanamivir: an influenza virus neuraminidase inhibitor

Zanamivir is the first of two registered neuraminidase inhibitors for the treatment and prophylaxis of influenza. Relenza, an orally inhaled powder form of zanamivir, is currently approved in 19 countries for treatment, and in two for prophylaxis. Relenza reduces the time to alleviation of symptoms by 1 to 2 days in the influenza-positive population, if taken within 48 h of symptom onset, and in prophylaxis in family settings, it confers an 80% reduction in the odds of contracting influenza. The resistance profile of zanamivir is encouraging in the sense that there are still no reports of patients on acute therapy shedding drug-resistant virus. However, patient uptake of the inhaled drug has been insufficient to conclude that drug resistance will not be an issue in the future. All zanamivir-resistant variants selected in the laboratory so far have diminished viability.

THEINTEGRATION OFPHARMACOKINETICS ANDPHARMACODYNAMICS: Understanding Dose-Response

Pharmacokinetic (PK) and pharmacodynamic (PD) studies have proven to be powerful and instructive tools, particularly in elucidating important aspects of human pharmacology. Nevertheless, they remain imperfect tools in that they only allow researchers to indirectly extrapolate, through computational modeling, the dynamic processes of drug action. Furthermore, neither tool alone provides a complete nor necessarily relevant picture of drug action. This review explores the utility and applications of PK and PD in the study of drugs, provides examples of lessons learned from their application to studies of human pharmacology, points out some of their limitations, and advances the thesis that these tools ideally should be employed together in an integrated approach. As we continue to apply these tools across the continuum of age and disease, they provide a powerful means to enhance our understanding of drug action, drug interactions, and intrinsic host factors that influence pharmacologic response.

Fatores de risco e medidas profiláticas nas pneumonias adquiridas na comunidade

Este artigo revisa os efeitos do envelhecimento, tabagismo, DPOC, insuficiência cardíaca, colonização da orofaringe, aspiração (micro e macro), alcoolismo, cirrose hepática, deficiência nutricional, imunossupressão e fatores ambientais sobre o risco de adquirir pneumonia na comunidade e sua gravidade. Na segunda parte, é feita revisão sobre a ação profilática das vacinas antiinfluenza e antipneumococo, assim como a ação das drogas antivirais, na profilaxia e tratamento das pneumonias adquiridas na comunidade.

Zanamivir and oseltamivir: two new options for the treatment and prevention of influenza

BACKGROUND

Influenza infection is responsible for thousands of hospitalizations and deaths in the United States each year. Until recently, management options were limited to vaccination or use of the antiviral agents amantadine and rimantadine. Two antiviral drugs, zanamivir and oseltamivir, have recently been approved by the US Food and Drug Administration for the treatment of influenza A and influenza B.

OBJECTIVE

This article reviews the published data on the pharmacology and clinical utility of zanamivir and oseltamivir in the treatment and prevention of influenza A and influenza B illness.

METHODS

To identify relevant literature, a search of MEDLINE, International Pharmaceutical Abstracts, and the Iowa Drug Information Service was conducted for the period from 1969 to 2000. The search terms used were influenza, neuraminidase, zanamivir, oseltamivir; amantadine, and rimantadine. The reference lists of the articles so obtained were used to identify additional publications.

RESULTS

Zanamivir and oseltamivir inactivate viral neuraminidase, an enzyme responsible for cleaving sialic acid residues on newly formed virions as they bud off from the host cell. This inhibition results in aggregation of virions on the surface of the host cell, which limits the extent of infection and speeds recovery from illness. Clinical studies have shown that neuraminidase inhibitors can decrease the median duration of influenza-related symptoms by approximately 1 day if initiated within 48 hours of the onset of symptoms of influenza.

CONCLUSIONS

Evidence supports the use of zanamivir and oseltamivir in the treatment of influenza; however, additional studies are needed to clarify their utility and tolerability in pediatric and high-risk patients, as well as their utility in the prevention of influenza.