Hemodiafiltration for vancomycin overdose in a neonate with end-stage renal failure

Pharmacokinetics of Vancomycin in Pediatric Patients Receiving Intermittent Hemodialysis or Hemodiafiltration

INTRODUCTION

Vancomycin is a common antibiotic used to treat hemodialysis (HD) or hemodiafiltration (HDF)-related infections in pediatric patients, but optimal dosing remains unknown. This is the first observational study to characterize the pharmacokinetics and evaluate dosing of vancomycin in this population.

METHODS

Eligible patients received IV vancomycin 10 mg/kg per dose postdialysis followed by a series of serum vancomycin concentrations collected before, immediately after, 1 hour after, and 4 hours after dialysis. The pharmacokinetic parameters were estimated using 1- and 2-compartment models and a nonlinear least-squares algorithm.

RESULTS

Among 42 vancomycin courses in 16 patients, 1 compartment model had the best fit for observed data. The net drug removal was 43 ± 13% (39% for HD and 50% for HDF) from an average 3-hour HD/HDF session. The mean elimination constant was 0.28 h-1 (standard deviation [SD], 0.11 h-1) during the intradialytic period compared with 0.0049 h-1 (SD, 0.004 h-1) when off dialysis. The mean volume of distribution was 0.65 (SD, 0.19) L/kg. Duration of dialysis session and mode of dialysis (HD vs. HDF) were significant predictors of vancomycin pharmacokinetic parameters. Half-life was shorter for HDF compared with HD (2.1 vs. 3.5 hours).

CONCLUSIONS

Based on the simulations, an initial vancomycin dose of 10 mg/kg per dose and redosing postdialysis was optimal to achieve a vancomycin concentration range of 5 to 12 mg/L at 4 hours postdialysis and 24-hour area under the curve over minimum inhibitory concentration of ≥400 hours. Therapeutic drug monitoring is necessary to account for residual variability in vancomycin elimination in pediatric patients receiving HD/HDF.

Dosing Recommendations for Pediatric Patients With Renal Impairment

A treatment gap exists for pediatric patients with renal impairment. Alterations in renal clearance and metabolism of drugs render standard dosage regimens inappropriate and may lead to drug toxicity, but these studies are not routinely conducted during drug development. The objective of this study was to examine the clinical evidence behind current renal impairment dosage recommendations for pediatric patients in a standard pediatric dosing handbook. The sources of recommendations and comparisons included the pediatric dosing handbook (Lexicomp), the U.S. Food and Drug Administration-approved manufacturer's labels, and published studies in the literature. One hundred twenty-six drugs in Lexicomp had pediatric renal dosing recommendations. Only 14% (18 of 126) of Lexicomp pediatric renal dosing recommendations referenced a pediatric clinical study, and 15% of manufacturer's labels (19 of 126) described specific dosing regimens for renally impaired pediatric patients. Forty-two products had published information on pediatric renal dosing, but 19 (45%) were case studies. When pediatric clinical studies were not referenced in Lexicomp, the renal dosing recommendations followed the adult and pediatric dosing recommendations on the manufacturer's label. Clinical evidence in pediatric patients does not exist for most renal dosing recommendations in a widely used pediatric dosing handbook, and the adult renal dosing recommendations from the manufacturer's label are currently the primary source of pediatric renal dosing information.

Have advances in extracorporeal removal techniques changed the indications for their use in poisonings?

During the past 25 years, numerous changes have taken place in the use of hemodialysis as a therapeutic modality. Advances in technologies and a progression in our collective understanding of the pharmacokinetics of certain xenobiotics have resulted in alterations in the indications, effectiveness, and safety of hemodialysis. However, these changes have not necessarily been reflected in the current published data regarding treatment of intoxications. Reported clearance rates often reflect what was achievable in the 1970s and 1980s, and more recent reports are frequently lacking. Our goal in this review is to summarize the changes in hemodialysis and in other extracorporeal removal technologies and highlight the effects of these changes on the current indications for hemodialysis of the poisoned patient. Changes in dialysis performance that are reviewed in this article include the use of high-efficiency and high-flux dialysis membranes, improved hemodynamic stability because of ultrafiltration control, and the use of bicarbonate as a source of base. We review the indications for hemodialysis for removal of specific toxins, including vancomycin, methotrexate, carbamazepine, and valproic acid.

The role of continuous renal replacement therapy in the treatment of poisoning

Extracorporeal elimination of drugs and toxins is a critical component in the management of poisonings, though specific techniques and indications remain a matter of debate. Conventional hemodialysis is frequently the treatment of choice because of its widespread availability and proven effectiveness for certain drugs and toxins. With the increased availability of continuous renal replacement therapy (CRRT) modalities, there is yet another therapeutic option, but one that has yet to find a definitive role in this field. The continuous nature of these therapies is attractive for the management of acute renal failure, but the relatively slower clearance rates as compared to conventional hemodialysis is a distinct drawback in patients with acute xenobiotic-induced toxicity. There are abundant case reports as well as a few small case series in the medical literature documenting the use of CRRT, but specific techniques and the clinical outcomes vary considerably. Therefore one cannot draw definitive conclusions regarding benefit. Some patients, particularly those who are hemodynamically unstable and are not candidates for conventional hemodialysis, may warrant a trial of CRRT. However, at the present time, routine use for the treatment of poisoning is not supported. Controlled trials to better clarify its role would be beneficial, though such studies would be extremely difficult to conduct in this field. We believe that the intelligent application of extracorporeal modalities requires a thorough knowledge of drug pharmacokinetics, of the techniques utilized, and a skeptical analysis of the available literature.

The Effect of Detection Approaches on the Reported Incidence of Tenfold Errors

BACKGROUND

Tenfold errors in calculation of paediatric drug doses are often life threatening. The magnitude and characteristics of this phenomenon have not been fully described.

OBJECTIVES

The objective of this study was to describe the incidence and nature of paediatric tenfold errors and to describe the effect of different detection approaches on the detection of such errors.

METHODS

To evaluate the incidence of tenfold errors, data were collected from three different studies on medication errors all conducted at a large tertiary care paediatric hospital: (i) a study investigating medication event reports to the hospital's Medication Incident Committee; (ii) a study auditing the charts of 1532 patients in the emergency department (ED) and; (iii) a prospective study of medication errors occurring during mock code resuscitations in the ED.

RESULTS

In the first study, 20 tenfold errors were reported during the surveyed period. Almost all errors were prescribing errors. The calculated incidence was 1 per 22 500 doses prescribed. In chart auditing study in the ED, two tenfold errors where found in 1678 orders. In the prospective study, four tenfold errors were identified in eight mock resuscitations (125 orders for drugs).

CONCLUSION

The incidence of tenfold errors in paediatrics varies dramatically when different detection approaches are used. The rate of tenfold errors may be especially high in resuscitation situations and is underestimated by spontaneous reporting.

Comparison of solute clearance in three modes of continuous renal replacement therapy

OBJECTIVES

To compare the clearances of low molecular weight molecules using three modalities of continuous renal replacement therapy (CRRT) at the low blood flow rates typically used in pediatric patients.

DESIGN

A controlled, in vitro laboratory study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

AN69 dialysis hemofilter.

INTERVENTIONS

CRRT was performed using a 0.6 m(2) AN69 hemofilter. Human whole blood and plasma were combined to achieve a hematocrit of approximately 30%. Urea and creatinine were added to obtain concentrations of approximately 54 mmol/L of blood urea nitrogen and 1770 micromol/L of creatinine. Clearance data for urea and creatinine at a blood flow rate of 60 mL/min were generated using predilution continuous venovenous hemofiltration (CVVH), postdilution CVVH, and continuous venovenous hemodialysis (CVVHD).

MEASUREMENTS AND MAIN RESULTS

Clearance of all three modalities was compared at a replacement solution (CVVH) or dialysate (CVVHD) flow rate of 16.7% of the blood flow rate. Both postdilution CVVH and CVVHD had a urea clearance of 11.3 mL/min, which was 15% greater than the 9.8 mL/min urea clearance of predilution CVVH (p <.005). Creatinine clearance with postdilution CVVH (10.7 mL/min) was 15% greater than the 9.0 mL/min clearance produced by predilution CVVH (p < 0.01). Predilution CVVH and CVVHD were compared at a flow rate of either replacement solution (CVVH) or dialysate (CVVHD) of 33% and 50% of the blood flow rate. Postdilution CVVH was not performed at high ultrafiltration rates due to the potential problem of hemoconcentration. CVVHD clearances of urea and creatinine were statistically superior to predilution CVVH at both flow rates.

CONCLUSIONS

CVVHD was superior to predilution CVVH for clearance of urea and creatinine. Postdilution CVVH and CVVHD gave nearly equivalent clearances. At the low blood flow rates used in pediatric patients, which raise concerns about high ultrafiltration during postdilution CVVH causing excessive hemoconcentration and filter clotting, CVVHD appears to be the optimal modality for maximizing clearance of small solutes during CRRT.

Vancomycin

This review describes the use of vancomycin in neonates over the last three decades. Given the relation of late-onset neonatal septicaemia to outcome and the increase in coagulase-negative staphylococcal infection as causative organism, vancomycin remains an important antibacterial in the neonatal intensive care unit. The pharmacokinetic behaviour of vancomycin in neonates can be adequately described by a one- or two-compartment model and is mainly determined by postconceptional age and renal function. In neonates, a patent ductus arteriosus as well as treatment with indomethacin or extracorporeal membrane oxygenation (ECMO) leads to an increase in volume of distribution and a decrease in clearance. Microbiological studies in vitro have shown that an increase in vancomycin concentrations above the minimum inhibitory concentration does not result in more effective killing. The microbiological and clinical efficacy of vancomycin in neonates has only been studied explicitly in a restricted number of patients. There are no definitive data relating serum concentrations to effect in this patient group. Vancomycin-related nephrotoxicity and ototoxicity in neonates is rare, and no clear relation to serum concentrations has been demonstrated. Based on the pharmacokinetic profile of vancomycin in neonates, several administration regimens have been constructed. Recent guidelines have suggested that dosage can be independent of gestational age or postconceptional age in neonates without renal failure. In patients with renal failure, therapy can be adequately tailored by using a regimen based on serum creatinine. The usefulness of routine monitoring of peak serum concentrations is doubtful based on the current literature. Recent research demonstrates a shift towards taking only routine trough serum concentrations in order to optimise efficacy. Patients with renal failure and other special subpopulations, such as patients exposed to ECMO or indomethacin, need to be monitored more closely.

The development of pediatric nephrology

Pediatric nephrology, as a discipline, arose from descriptive studies of childhood glomerulonephritis in Europe and the field of pediatric metabolism in the United States. While pediatric scientists before 1950 were concerned with fluid and electrolyte metabolism, regulation of intracellular and extracellular fluid, acid-base homeostasis, and parenteral fluid therapy, the defined field of nephrology developed after the Second World War around six major advances: ACTH and glucocorticoid therapy for nephrotic syndrome; renal biopsy to diagnose glomerular disease; the role of immunologic factors in glomerular injury; the use of dialysis as renal replacement therapy; renal transplantation as the optimal form of therapy in children with end stage renal failure; and recognition of renal disease in the etiology of 80% of cases of childhood hypertension. These discoveries led to focused research, the definition of specific training in nephrology, establishment of an American, European, and an International Society of Pediatric Nephrology, as well as an American Sub-Board of Pediatric Nephrology, and the inception of a journal, Pediatric Nephrology, now in its 15th year. Major research themes have included developmental nephrology, transplantation immunology, and concerns about growth in children with renal disease. Many clinical entities have been described in detail, some of which are almost confined to children. The scientific basis of pediatric nephrology, ongoing patient care needs, and its technical aspects - renal biopsy, dialysis and transplantation - assure its continuing future as a major pediatric discipline on all continents.

Extracorporeal therapies for acute intoxications

Intoxications frequently perturb acid-base and electrolyte status, intravascular volume, and renal function. In selected cases, extracorporeal techniques effectively restore homeostasis and augment intoxicant removal. The use of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, is a new and effective treatment for patients exposed to toxic alcohols. In this section, practical approaches to commonly encountered intoxicants and the use of extracorporeal techniques are critically reviewed.

Management of hypophosphatemia induced by high-flux hemodiafiltration for the treatment of vancomycin toxicity: intravenous phosphorus therapy versus use of a phosphorus-enriched dialysate

Intensive high-flux hemodiafiltration is often used in the management of vancomycin toxicity. We describe two patients who developed hypophosphatemia as a consequence of this form of therapy. The first patient was treated with an intravenous phosphorus infusion. For the second patient, hypophosphatemia was corrected, during hemodiafiltration, with the use of a phosphorus-enriched dialysate. The latter dialysate was prepared by adding sodium phosphate salts to the "base concentrate" of a dual-concentrate, bicarbonate-based dialysate delivery system. This simple method was more efficient than intravenous therapy in ameliorating the hypophosphatemia secondary to aggressive hemodiafiltration treatment.