How does a patient maximally benefit from anti-infective chemotherapy?

Effects of Food and Omeprazole on a Novel Formulation of Super Bioavailability Itraconazole in Healthy Subjects

To address the limited bioavailability and intolerance of the conventional itraconazole (ITZ) formulations, a new formulation labeled super bioavailability (SUBA) itraconazole has been developed; however, the specific effects of food and gastric pH are unknown. This study evaluated the pharmacokinetic profile of SUBA itraconazole under fasting and fed conditions, as well as with the concomitant administration of a proton pump inhibitor. First, the effect of food was assessed in an open-label, randomized, crossover bioavailability study of 65-mg SUBA itraconazole capsules (2 65-mg capsules twice a day) in healthy adults (n = 20) under fasting and fed conditions to steady-state levels. Second, an open-label, two-treatment, fixed-sequence comparative bioavailability study in healthy adults (n = 28) under fasted conditions compared the pharmacokinetics of a single oral dose of SUBA itraconazole capsules (2 65-mg capsules/day) with and without coadministration of daily omeprazole delayed-release capsules (1 40-mg capsule/day) under steady-state conditions. In the fed and fasted states, SUBA itraconazole demonstrated similar concentrations at the end of the dosing interval, with modestly lower total and peak ITZ exposure being shown when it was administered under fed conditions than when it was administered in the fasted state, with fed state/fasted state ratios of 78.09% (90% confidence interval [CI], 74.49 to 81.86%) for the area under the concentration-time curve over the dosing interval (14,183.2 versus 18,479.8 ng · h/ml), 73.05% (90% CI, 69.01 to 77.33%) for the maximum concentration at steady state (1,519.1 versus 2,085.2 ng/ml), and 91.53% (90% CI, 86.41 to 96.96%) for the trough concentration (1,071.5 versus 1,218.5 ng/ml) being found. When dosed concomitantly with omeprazole, there was a 22% increase in the total plasma exposure of ITZ, as measured by the area under the concentration-time curve from time zero to infinity (P = 0.0069), and a 31% increase in the peak plasma exposure of ITZ, as measured by the maximum concentration (P = 0.0083).

Therapeutic drug monitoring for triazoles: A needs assessment review and recommendations from a Canadian perspective

Invasive fungal infections cause significant morbidity and mortality in patients with concomitant underlying immunosuppressive diseases. The recent addition of new triazoles to the antifungal armamentarium has allowed for extended-spectrum activity and flexibility of administration. Over the years, clinical use has raised concerns about the degree of drug exposure following standard approved drug dosing, questioning the need for therapeutic drug monitoring (TDM). Accordingly, the present guidelines focus on TDM of triazole antifungal agents. A review of the rationale for triazole TDM, the targeted patient populations and available laboratory methods, as well as practical recommendations based on current evidence from an extended literature review are provided in the present document.

Voriconazole serum levels measured by high-performance liquid chromatography: a monocentric study in treated patients

In this study we present the results of a therapeutic drug monitoring retrospective analysis involving 14 patients with several underlying diseases who were receiving voriconazole for the treatment of fungal infections. A simple high performance liquid chromatography assay with ultraviolet detection was used in the drug monitoring. We report here that serum concentrations were highly variable and unpredictable in most patients. We also found that lack of response was more frequent in patients with levels persistently lower than 1 mg/l. The number of samples with voriconazole concentrations below 1 mg/l was significantly higher in patients who exhibited therapeutic failures (88% versus 27%; P < 0.001). In addition, the period of time in which voriconazole concentrations were maintained below 1 mg/l was slightly higher in patients in the failure group. We suggest that serum concentration should be individually quantified for patients receiving voriconazole therapy. Further prospective studies are needed to clarify the potential benefit of the individualization of treatment.

Pharmacokinetics and pharmacodynamics: optimal antimicrobial therapy in the intensive care unit

This article reviews the principles of antimicrobial pharmacokinetics and pharmacodynamics in the context of the ICU for the most commonly used antibiotics. For therapy to truly be efficacious, the regimen must be effective against the organism, but not harmful to the patient. We review how optimization of chemotherapy requires a careful balancing of efficacy against toxicity when selecting dose and dose schedules. In addition, we discuss the importance of considering concentrations at the site of infection and how dose optimization can help suppress resistance emergence and preserve our antimicrobial armamentarium for the future. Finally, we examine combination chemotherapy and strategies for optimizing the administration of multiple agents.

Use of pharmacodynamic principles to inform β-lactam dosing: "S" does not always mean success

Dose optimization is one of the key strategies for enhancing antimicrobial stewardship. There have been tremendous strides in our understanding of antibiotic exposure-response relationships over the past 25 years. For many antibiotics, the "pharmacodynamic" or the exposure variable associated with outcome has been identified. With advances in mathematical modeling, it is possible to apply our understanding of antimicrobial pharmacodynamics (PD) into clinical practice and design empirical regimens that have a high probability of achieving the PD target linked to effect. By optimizing antibiotic doses to achieve PD targets predictive of efficacy, clinicians can improve care and minimize drug toxicity. For β-lactams, the PD parameter most predictive of maximal bactericidal activity is the duration of time free drug concentrations remain above the minimum inhibitory concentration (MIC) during the dosing interval (fT > MIC). Unfortunately, the conventional intermittent β-lactam dosing schemes often used in practice have suboptimal PD profiles. Prolonging the infusion time of β-lactams is one method to maximize the probability of achieving concentrations in excess of the MIC for the majority of the dosing interval, especially against pathogens with elevated MIC values. Prolonged infusions of intravenous β-lactams are not only associated with improved probability of target attainment (PTA) profiles but offer possible cost savings and greater potential for reducing emergence of resistance relative to intermittent infusions.

Management of invasive aspergillosis in patients with COPD: rational use of voriconazole

Invasive pulmonary aspergillosis (IPA) is an important cause of mortality in patients with hematologic malignancies. The reported incidence of IPA in the context of chronic obstructive pulmonary disease (COPD) seems to increase. Approximately 1%-2% of overall fatal cases of IPA occur in COPD patients. The combination of factors such as lung immune imbalance, long-term corticosteroid use, increasing rate of bacterial exacerbations over time, and malnutrition are responsible for the emergence of IPA in these patients. The diagnosis of IPA is difficult to establish, which explains the delay in implementing accurate antifungal therapy and the high mortality rate. Persistent pneumonia nonresponsive to appropriate antibiotic treatment raises the concern of an invasive fungal infection. Definite diagnosis is obtained from tissue biopsy evidencing Aspergillus spp. on microscopic examination or in culture. Culture and microscopy of respiratory tract samples have a sensitivity and specificity of around 50%. Other diagnostic tools can be useful in documenting IPA: computed tomography (CT) scan, nonculture-based tests in serum and/or in bronchoalveolar lavage such as antibody/antigen tests for Aspergillus spp. More recent tools such as polymerase chain reaction or [1-->3]-beta-D-glucan have predictive values that need to be further investigated in COPD patients. Antifungal monotherapy using azole voriconazole is recommended as a first-line treatment of IPA. This review assesses the use of voriconazole in COPD patients.

Voriconazole therapeutic drug monitoring in patients with invasive mycoses improves efficacy and safety outcomes

BACKGROUND

Voriconazole is the therapy of choice for aspergillosis and a new treatment option for candidiasis. Liver disease, age, genetic polymorphism of the cytochrome CYP2C19, and comedications influence voriconazole metabolism. Large variations in voriconazole pharmacokinetics may be associated with decreased efficacy or with toxicity.

METHODS

This study was conducted to assess the utility of measuring voriconazole blood levels with individualized dose adjustments.

RESULTS

A total of 181 measurements with high-pressure liquid chromatography were performed during 2388 treatment days in 52 patients. A large variability in voriconazole trough blood levels was observed, ranging from <or=1 mg/L (the minimum inhibitory concentration at which, for most fungal pathogens, 90% of isolates are susceptible) in 25% of cases to >5.5 mg/L (a level possibly associated with toxicity) in 31% of cases. Lack of response to therapy was more frequent in patients with voriconazole levels <or=1 mg/L (6 [46%] of 13 patients, including 5 patients with aspergillosis, 4 of whom were treated orally with a median dosage of 6 mg/kg per day) than in those with voriconazole levels >1 mg/L (15 [12%] of 39 patients; P=.02). Blood levels >1 mg/L were reached after increasing the voriconazole dosage, with complete resolution of infection in all 6 cases. Among 16 patients with voriconazole trough blood levels >5.5 mg/L, 5 patients (31%) presented with an encephalopathy, including 4 patients who were treated intravenously with a median voriconazole dosage of 8 mg/kg per day, whereas none of the patients with levels <or=5.5 mg/L presented with neurological toxicity (P=.002). Comedication with omeprazole possibly contributed to voriconazole accumulation in 4 patients. In all cases, discontinuation of therapy resulted in prompt and complete neurological recovery.

CONCLUSIONS

Voriconazole therapeutic drug monitoring improves the efficacy and safety of therapy in severely ill patients with invasive mycoses.

Piperacillin-tazobactam for Pseudomonas aeruginosa infection: clinical implications of an extended-infusion dosing strategy

BACKGROUND

Piperacillin-tazobactam is frequently used to treat Pseudomonas aeruginosa infections in critically ill patients. In an effort to improve clinical outcomes, an extended-infusion dosing scheme for piperacillin-tazobactam therapy was devised using a Monte Carlo simulation and was adopted into clinical practice at Albany Medical Center (Albany, New York). This study evaluates the clinical implications of extended infusion of piperacillin-tazobactam therapy for critically ill patients with P. aeruginosa infection.

METHODS

We performed a cohort study of patients who received piperacillin-tazobactam therapy for a P. aeruginosa infection that was susceptible to piperacillin-tazobactam during the period January 2000-June 2004. Prior to February 2002, all patients received intermittent infusions of piperacillin-tazobactam (3.375 g intravenously for 30 min every 4 or 6 h); after this time, all patients received extended infusions of piperacillin-tazobactam (3.375 g intravenously for 4 h every 8 h). Data on demographic characteristics, disease severity, and microbiology were collected, and outcomes were compared between groups.

RESULTS

A total of 194 patients comprised the 2 study groups: 102 patients received extended infusions of piperacillin-tazobactam, and 92 patients received intermittent infusions of piperacillin-tazobactam. No differences in baseline clinical characteristics were noted between the 2 groups. Among patients with Acute Physiological and Chronic Health Evaluation-II scores > or =17, 14-day mortality rate was significantly lower among patients who received extended-infusion therapy than among patients who received intermittent-infusion therapy (12.2% vs. 31.6%, respectively; P=.04), and median duration of hospital stay after collection of samples for culture was significantly shorter for patients who received extended-infusion therapy than for patients who received intermittent-infusion therapy (21 days vs. 38 days; P=.02).Conclusions. These results indicate that extended-infusion piperacillin-tazobactam therapy is a suitable alternative to intermittent-infusion piperacillin-tazobactam therapy, and they strongly suggest that improved outcomes may be realized by administering extended-infusion piperacillin-tazobactam therapy to critically ill patients with P. aeruginosa infection.

Pharmacokinetic/pharmacodynamic profile of voriconazole

Voriconazole is the first available second-generation triazole with potent activity against a broad spectrum of clinically significant fungal pathogens, including Aspergillus,Candida, Cryptococcus neoformans, and some less common moulds. Voriconazole is rapidly absorbed within 2 hours after oral administration and the oral bioavailability is over 90%, thus allowing switching between oral and intravenous formulations when clinically appropriate. Voriconazole shows nonlinear pharmacokinetics due to its capacity-limited elimination, and its pharmacokinetics are therefore dependent upon the administered dose. With increasing dose, voriconazole shows a superproportional increase in area under the plasma concentration-time curve (AUC). In doses used in children (age < 12 years) voriconazole pharmacokinetics appear to be linear. Steady-state plasma concentrations are reached approximately 5 days after both intravenous and oral administration; however, steady state is reached within 24 hours with voriconazole administered as an intravenous loading dose. The volume of distribution of voriconazole is 2-4.6 L/kg, suggesting extensive distribution into extracellular and intracellular compartments. Voriconazole was measured in tissue samples of brain, liver, kidney, heart, lung as well as cerebrospinal fluid. The plasma protein binding is about 60% and independent of dose or plasma concentrations. Clearance is hepatic via N-oxidation by the hepatic cytochrome P450 (CYP) isoenzymes, CYP2C19, CYP2C9 and CYP3A4. The elimination half-life of voriconazole is approximately 6 hours, and approximately 80% of the total dose is recovered in the urine, almost completely as metabolites. As with other azole drugs, the potential for drug interactions is considerable. Voriconazole shows time-dependent fungistatic activity against Candida species and time-dependent slow fungicidal activity against Aspergillus species. A short post-antifungal effect of voriconazole is evident only for Aspergillus species. The predictive pharmacokinetic/pharmacodynamic parameter for voriconazole treatment efficacy in Candida infections is the free drug AUC from 0 to 24 hour : minimum inhibitory concentration ratio.

Variability of voriconazole plasma levels measured by new high-performance liquid chromatography and bioassay methods

Voriconazole (VRC) is a broad-spectrum antifungal triazole with nonlinear pharmacokinetics. The utility of measurement of voriconazole blood levels for optimizing therapy is a matter of debate. Available high-performance liquid chromatography (HPLC) and bioassay methods are technically complex, time-consuming, or have a narrow analytical range. Objectives of the present study were to develop new, simple analytical methods and to assess variability of voriconazole blood levels in patients with invasive mycoses. Acetonitrile precipitation, reverse-phase separation, and UV detection were used for HPLC. A voriconazole-hypersusceptible Candida albicans mutant lacking multidrug efflux transporters (cdr1Delta/cdr1Delta, cdr2Delta/cdr2Delta, flu1Delta/flu1Delta, and mdr1Delta/mdr1Delta) and calcineurin subunit A (cnaDelta/cnaDelta) was used for bioassay. Mean intra-/interrun accuracies over the VRC concentration range from 0.25 to 16 mg/liter were 93.7% +/- 5.0%/96.5% +/- 2.4% (HPLC) and 94.9% +/- 6.1%/94.7% +/- 3.3% (bioassay). Mean intra-/interrun coefficients of variation were 5.2% +/- 1.5%/5.4% +/- 0.9% and 6.5% +/- 2.5%/4.0% +/- 1.6% for HPLC and bioassay, respectively. The coefficient of concordance between HPLC and bioassay was 0.96. Sequential measurements in 10 patients with invasive mycoses showed important inter- and intraindividual variations of estimated voriconazole area under the concentration-time curve (AUC): median, 43.9 mg x h/liter (range, 12.9 to 71.1) on the first and 27.4 mg x h/liter (range, 2.9 to 93.1) on the last day of therapy. During therapy, AUC decreased in five patients, increased in three, and remained unchanged in two. A toxic encephalopathy probably related to the increase of the VRC AUC (from 71.1 to 93.1 mg x h/liter) was observed. The VRC AUC decreased (from 12.9 to 2.9 mg x h/liter) in a patient with persistent signs of invasive aspergillosis. These preliminary observations suggest that voriconazole over- or underexposure resulting from variability of blood levels might have clinical implications. Simple HPLC and bioassay methods offer new tools for monitoring voriconazole therapy.

Voriconazole: review of a broad spectrum triazole antifungal agent

Voriconazole is a second-generation triazole antifungal agent, structurally derived from fluconazole with an extended spectrum of activity against a wide variety of yeasts and moulds. Developed for the treatment of life-threatening fungal infections, it appears to be an effective therapy option for invasive aspergillosis, fluconazole-resistant candidiasis and refractory or less-common invasive fungal infections. It is available for both oral and intravenous administration and is characterised by an acceptable safety and tolerability spectrum.