The pharmacokinetics of fluconazole during haemodialysis in uraemic patients

Post-Dialysis Parenteral Antimicrobial Therapy in Patients Receiving Intermittent High-Flux Hemodialysis

Patients with end-stage renal disease (ESRD) requiring intermittent hemodialysis (IHD) are at increased risk of infection, which represents a leading cause of mortality in this population. The use of additional vascular access devices such as peripherally inserted central catheters to treat such infections should be minimized in patients with ESRD requiring IHD in order to mitigate complications such as infection and thrombosis and to maintain venous patency for hemodialysis access. Intravenous antimicrobial dosing following IHD has the advantages of avoiding additional access devices and providing convenience for patients and providers. Vancomycin, cefazolin, and aminoglycosides have historically been regarded as the primary intravenous antimicrobials administered with IHD given their relatively low cost, convenient dosing, and longevity of clinical use. Despite this, a growing body of literature is evaluating the use of an expanded list of antimicrobials that may be employed using post-dialysis dosing for patients requiring IHD; however, the available data are largely limited to pharmacokinetic studies and small cohorts of infected patients or uninfected subjects. Post-dialytic dosing of intravenous antimicrobials may be considered on a patient-by-patient basis after careful consideration of clinical, microbiological, and logistical factors that may influence the probability of treatment success. This document reviews and evaluates currently available information on the post-dialytic administration of an expanded list of intravenous antimicrobials in the setting of thrice-weekly, high-flux IHD.

Pharmacokinetics of antifungal drugs: practical implications for optimized treatment of patients

Introduction

Because of the high mortality of invasive fungal infections (IFIs), appropriate exposure to antifungals appears to be crucial for therapeutic efficacy and safety.

Materials and methods

This review summarises published pharmacokinetic data on systemically administered antifungals focusing on co-morbidities, target-site penetration, and combination antifungal therapy.

Conclusions and discussion

Amphotericin B is eliminated unchanged via urine and faeces. Flucytosine and fluconazole display low protein binding and are eliminated by the kidney. Itraconazole, voriconazole, posaconazole and isavuconazole are metabolised in the liver. Azoles are substrates and inhibitors of cytochrome P450 (CYP) isoenzymes and are therefore involved in numerous drug–drug interactions. Anidulafungin is spontaneously degraded in the plasma. Caspofungin and micafungin undergo enzymatic metabolism in the liver, which is independent of CYP. Although several drug–drug interactions occur during caspofungin and micafungin treatment, echinocandins display a lower potential for drug–drug interactions. Flucytosine and azoles penetrate into most of relevant tissues. Amphotericin B accumulates in the liver and in the spleen. Its concentrations in lung and kidney are intermediate and relatively low myocardium and brain. Tissue distribution of echinocandins is similar to that of amphotericin. Combination antifungal therapy is established for cryptococcosis but controversial in other IFIs such as invasive aspergillosis and mucormycosis.

Influence of sustained low-efficiency diafiltration (SLED-f) on interstitial fluid concentrations of fluconazole in a critically ill patient: Use of microdialysis

Acute kidney injury is a common complication in critically ill patients, and hybrid techniques including sustained low-efficiency dialysis/diafiltration (SLED-f) are being increasingly utilised in intensive care units. Most fungal infections occur in the interstitial fluid (ISF) of tissues and successful treatment of a fungal infection relies on the ability of an antifungal agent to achieve adequate concentrations at the site of infection. Tissue distribution of antimicrobials is impaired in critically ill patients owing to a variety of disease-related physiological changes, e.g. sepsis. Fluconazole is a widely used antifungal agent used to treat Candida spp. infections in critically ill patients. The implications for ISF concentrations of enhanced elimination during renal replacement therapy have not yet been reported for fluconazole. The aim of this single-patient case report was to describe the influence of SLED-f on subcutaneous (SC) ISF concentrations of fluconazole and the implications for achieving pharmacokinetic/pharmacodynamic targets. Serial blood and ISF samples were collected at pre- and post-filter ports within the SLED-f circuit and subcutaneously inserted microdialysis probe, respectively. Fluconazole concentrations were measured using a validated chromatography method. The SC ISF-to-plasma partition coefficient of fluconazole in this patient was 0.91, indicating rapid equilibrium. SC ISF fluconazole concentrations consistently decreased after initiating SLED-f. The majority of the fluconazole was eliminated from the SC ISF as a result of redistribution. Considering the extensive tissue re-distribution of fluconazole and observed elimination from tissue compartments, higher doses may be required to treat deep-seated fungal infections.

Pharmacokinetics of fluconazole in critically ill patients with acute kidney injury receiving sustained low-efficiency diafiltration

Fluconazole is a widely used antifungal agent in critically ill patients. It is predominantly (60-80%) excreted unchanged in urine. Sustained low-efficiency diafiltration (SLED-f) is increasingly being utilised in critically ill patients because of its practical advantages over continuous renal replacement therapy. To date, the effect of SLED-f on fluconazole pharmacokinetics and dosing has not been studied. The objective of this study was to describe the pharmacokinetics of fluconazole in critically ill patients with acute kidney injury receiving SLED-f and to compare this with other forms of renal replacement therapy. Serial blood samples were collected at pre- and post-filter ports within the SLED-f circuit during SLED-f and from an arterial catheter before and after SLED-f from three patients during one session. Fluconazole concentrations were measured using a validated chromatography method. Median clearance (CL) and 24-h area under the concentration-time curve (AUC0-24) were 2.1L/h and 152 mg·h/L, respectively, whilst receiving SLED-f. Moreover, 72% of fluconazole was cleared by a single SLED-f session (6h) compared with previous reports of 33-38% clearance by a 4-h intermittent haemodialysis session. CL and AUC0-24 were comparable with previous observations in a pre-dilution mode of continuous venovenous haemodiafiltration. The observed rebound concentration of fluconazole post SLED-f was <2%. Although a definitive dosing recommendation is not possible due to the small patient number, it is clear that doses >200mg daily are likely to be required to achieve the PK/PD target for common pathogens because of significant fluconazole clearance by SLED-f.

Fluconazole dosing in continuous veno-venous haemofiltration (CVVHF): need for a high daily dose of 800 mg

To cover intermediate sensitive Candida glabrata in ICU patients, fluconazole plasma peak levels at least in the range of 16-32 microg/ml appear necessary for treatment. Previous studies did not reach these fluconazole levels under continuous veno-venous haemofiltration (CVVHF) with dosages of 200-600 mg fluconzole daily. In the present study, nine patients simultaneously requiring CVVHF for treatment of acute oligoanuric renal failure and antimycotic therapy of Candida septicemia received fluconazole 800 mg/day. Fluconazole plasma levels were determined to evaluate whether this dosage is adequate to reach the advised fluconazole levels. Patients were dialysed on two consecutive days with an ultrafiltration rate (UF) of 1000 ml/h or 2000 ml/h, respectively, in a randomized order. The predilution was 800 ml/h and 1800 ml/h, respectively. The treatment was tolerated without adverse effects. All patients reached plasma fluconazole concentrations between 16 and 32 microg/ml, remaining in this range for a minimum of 1 up to 24 h with a mean of 9.6 h and a UF rate of 2000 ml/h, and 15.7 h with a UF rate of 1000 ml/h. So far, there are no in vivo data on the fluconazole plasma concentrations required for effective treatment. However, our data demonstrate, that at least the fluconazole concentrations desirable on the basis of in vitro susceptibility testing can be reached in critically ill patients on CVVHF in an ICU setting. However, in these patients, 800 mg fluconazole/day are necessary to achieve fungicidal drug concentrations.

FHD: an index to evaluate drug elimination by hemodialysis

BACKGROUND

In hemodialyzed patients, physicians have to (1) adjust drug dosage for a creatinine clearance lower than 10-15 ml/min and (2) know whether or not the drug will be removed by the dialysis session to decide whether it may be administered before or after the session on dialysis days. However, of several indices being used to evaluate drug removal by dialysis none is appropriate and we suggest a novel index named F(HD), which reflects the role of hemodialysis clearance of a drug in its overall clearance during the session.

METHODS

Pharmacokinetic simulations were performed to test the influence of dialysis on the pharmacokinetics of some drugs, whether F(HD) was considered or not, to determine when to administer the drug. F(HD) was then calculated for several drugs and its value compared with other indices. Five hemodialysis patients from our department for whom the time of drug administration was determined according to F(HD) were included in a small study and their drugs' trough concentrations were monitored.

RESULTS

F(HD) emphasized that considering hemodialysis clearance alone may lead to false interpretations of the potential dialyzability of some drugs. In our patients, who received their treatment according to the 'F(HD) rule', monitoring of trough levels gave satisfactory results.

CONCLUSION

The use of the 'F(HD) rule' should be tested on a long-term administration basis to confirm our conclusion. F(HD )could be the index of choice to determine when to administer a drug, before or after the session, in hemodialysis patients.

Dosage adjustment of fluconazole during continuous renal replacement therapy (CAVH, CVVH, CAVHD, CVVHD)

Continuous arterio-venous haemofiltration (CAVH), continuous veno-venous haemofiltration (CVVH), continuous arterio-venous haemodialysis (CAVHD) and continuous veno-venous haemodialysis (CVVHD) are increasingly used in patients with acute renal failure (ARF). The elimination rate of fluconazole varies considerably depending on the procedure used. (In Germany, fluconazole is approved for the treatment of life-threatening fungal infections caused by Candida spp. and Cryptococcus neoformans at a dosage of up to 800 mg day-1.) The elimination rate of fluconazole by CVVHD depends on the combined dialysate/ultrafiltrate flow rate, but is much higher than achieved with CVVH and intermittent dialysis, with a fluconazole clearance in patients with CVVHD 2 l h-1 exceeding the values of healthy persons. To achieve therapeutic plasma levels during continuous renal replacement therapy, the same loading dose as in patients without renal failure should be administered, followed by a maintenance dose that is adjusted for anuric patients by multiplying by a factor that takes into account the extracorporeal elimination of the absorbed dose (CAVH, CVVH x 2.2, ultrafiltrate flow 0.5 l h-1; CAVHD, CVVHD x 3.8, combined dialysate/ultrafiltrate flow 1.5 l h-1). Despite the broad therapeutic margin of fluconazole, drug monitoring is recommended to achieve therapeutic drug levels in life-threatening indications because there have been only a few investigations of this, all involving relatively low dosages (up to 200 mg day-1).

[Pharmacokinetics and dosage of fluconazole in continuous hemofiltration (CAVH, CVVH) and hemodialysis (CAVHD, CVVHD)]

Continuous haemofiltration (CAVH, CVVH) and haemodialysis (CAVHD, CVVHD) are increasingly used in patients with acute renal failure (ARF). The elimination rates of fluconazole vary considerably among the different procedures. In CVVHD, the elimination rate is, depending on the combined dialysate/ultrafiltrate flow rate, the most marked compared to CVVH and intermittent dialysis with a fluconazole clearance exceeding the values of healthy persons in CVVHD 2 L/h. To achieve therapeutic plasma levels during continuous renal replacement therapy, the same loading dose as in patients without renal failure should be applied, followed by the adjusted maintenance dose for anuric patients multiplied by a factor taking the extracorporeal elimination of the absorbed dose into account (CAVH, CVVH: x 2.2, ultrafiltrate flow 0.5 L/h; CAVHD, CVVHD: x 3.8, combined dialysate/ultrafiltrate flow 1.5 L/h). Despite the broad therapeutic margin of fluconazole, drug monitoring is recommended with respect to the very limited number of investigations with relatively low dosages up to 200 mg/day and--which is of paramount importance--to achieve therapeutic drug levels in vital indications.

Clinical pharmacokinetics of fluconazole in superficial and systemic mycoses

The bis triazole agent fluconazole is used widely in the treatment of superficial and deep mycoses. A single oral dose of fluconazole 150 mg gives a mean long term clinical cure rate of 84 +/- 5% and is considered a valuable alternative to other topical antifungal drugs for vaginal candidiasis. A clinical cure rate of 90.4% for oropharyngeal candidiasis was obtained with 100mg daily for a minimum of 14 days; however, as for the other azoles the rate of relapse was large (40%) in immunocompromised patients. A daily dose of 100mg for at last 3 weeks gave satisfying outcomes for oesophageal candidiasis. Most patients (71 to 86%) with signs and symptoms of urinary tract candidiasis show beneficial clinical results when given oral fluconazole 50mg for several weeks. Fluconazole 50 to 150 mg given for weeks or months results in over 90% clinical cure or improvement for cutaneous mycosis including tinea, pityriasis, cryptococcosis and candidiasis. Prolonged (6 to 12 months) fluconazole 150 mg once a week is needed to treat onychomycosis successfully. Higher oral doses (200 to 400 mg daily) for long periods are generally used to treat deep mycoses such as meningitis, ophthalmitis, pneumonia, hepatosplenic mycosis and endocarditis. Fluconazole is effective for treating the fungal peritonitis which can complicate continuous ambulatory peritoneal dialysis (CAPD). A regimen of 50 mg intraperitoneally or 100 mg orally was used in these patients with impaired renal function. The dosage schedules used to treat disseminated fungal infections due to systemic mycoses with different or multiple foci of infections vary widely, with doses of 50 to 400 mg given orally or intravenously for between 1 week and several months. The most recent clinical reports have investigated the use of prophylaxis with fluconazole 100 to 400 mg daily, in immunocompromised patients. Fluconazole is found in body fluids such as vaginal secretions, breast milk, saliva, sputum and cerebrospinal fluid at concentrations comparable with those determined in blood after single or multiple doses. There is an excellent linear plasma concentration-dose relationship, but the mycological and clinical responses do not appear to be well correlated with the dose. A total maximum daily dose of 1600 mg is recommended to avoid neurological toxicity. Data from pharmacokinetic studies conducted in patients, mainly those with AIDS, and using a 1-compartment model give very constant parameters similar to those obtained in healthy individuals. Bioavailability, measured in HIV-positive patients and those with AIDS, exceeded 93% for tablets, suspension and suppositories. The time to reach peak plasma concentrations (tmax) was 2.4 to 3.7 hours. The peak plasma drug concentration (Cmax) obtained after a 100 mg oral dose was 2 mg/L. Areas under the concentration-time curve (AUC) obtained in different studies all correlate well with the dose (r = 0.926). The AUC determined after 200 and 25 mg suppositories were similarly well correlated. Hypochlorhydria does not affect the absorption of fluconazole, neither does food intake, race (Japanese or Caucasian) or gastrointestinal resection. Binding to plasma protein is low (11.14%) and is increased to 23% in cancer patients. Fluconazole is rapidly distributed to the tissue, where it accumulates. Tissues fall into 1 of 4 groups of increasing drug concentration: blood, bone and brain have the lowest concentrations, and spleen has the highest. The volume of distribution (Vd) remains stable at 46.3 +/- 7.9L and is considered to be an 'invariant' parameter across species. Fluconazole is poorly metabolised and is mainly eliminated unchanged in the urine. The percentage of the dose recovered in the urine in 48 hours is close to 60%. Concentrations in the urine are high and the half-life (t1/2) is long (37.2 +/- 5.5h) in patients, mainly those with AIDS, which is not significantly different from the t1/2 (31.4 +/- 4.7 hours) in healthy individuals. (ABSTRACT TRUN

Clinical pharmacokinetics of fluconazole

Fluconazole was recently developed for the treatment of superficial and systemic fungal infections. Triazole groups and insertion of 2 fluoride atoms increase the polarity and hydrosolubility of the drug, allowing it to be used in a parenteral form. Bioassay methods using Candida pseudotropicalis as a test organism were the first techniques used for the determination of fluconazole in body fluids. Gas chromatographic and high performance liquid chromatographic methods were later developed with better accuracy and sensitivity. Prediction of efficacious concentrations in patients from the minimum inhibitory concentrations in vitro seems to be uncertain because of low efficacy of the drug on some yeasts in vitro compared with efficacy in vivo in animal models. Oral forms (capsule and solution) are quickly absorbed and bioavailability is nearly complete (about 90%). Plasma protein binding is low (11 to 12%) and fluconazole circulates as active drug. Distribution is extensive throughout the tissues and allows the treatment of a variety of systemic fungal infections. The average elimination half-life (t1/2) of 31.6 +/- 4.9h is long, with a minimum of 6 days needed to reach steady-state; thus, a loading dose (equal to double the maintenance dose) is recommended. The metabolism of fluconazole is not qualitatively or quantitatively significant. The main route of elimination is renal. The mean +/- SD (calculated from published data) total and renal clearance values are 19.5 +/- 4.7 and 14.7 +/- 3.7 ml/min (1.17 +/- 0.28 and 0.88 +/- 0.22 L/h), respectively. Concentrations of fluconazole in blood after administration of single doses correlated well with the administered dose. There was very little interassay variation between the data reported in literature. Concentrations in blood after multiple doses also exhibit little variation and the accumulation factor was between 2.1 and 2.8. Fluconazole was found in many body fluids, especially in cerebrospinal fluid and dialysis fluid, allowing the treatment of systemic fungal infections such as coccidioidal meningitis and fungal peritonitis. Concentrations of 1 to 3 mg/L and 20 mg/L are the extreme values expected in clinical practice. In renal insufficiency the fluconazole t1/2 is longer, requiring dosage adjustment in relation to creatinine clearance. In continuous ambulatory peritoneal dialysis a 150mg dose in a 2L dialysis solution every 2 days has been proposed. In haemodialysis, a dose of 100 or 200mg should be given at the end of each dialysis session. Neither old age nor irradiation affect fluconazole pharmacokinetics, but the t1/2 was shorter in children.(ABSTRACT TRUNCATED AT 400 WORDS)