Pseudohyperphosphatemia associated with high-dose liposomal amphotericin B therapy

Biochemical assessment of phosphate homeostasis

Phosphate homeostasis is a requirement for normal life. Phosphate is involved in the synthesis of membrane lipids, DNA, RNA, and energy-rich molecules (ATP and GTP), and the regulation of protein activity by phosphorylation/dephosphorylation. Moreover, phosphate is a component of apatite crystals, which provide stability to the bone, and is essential for normal growth. Phosphate balance in the body is the difference between net phosphate absorption through the intestine and phosphate excretion through the kidney. Numerous disorders, both genetic and acquired, may alter phosphate homeostasis. In affected individuals, it is crucial to identify the underlying mechanism(s) to provide adequate treatment; however, phosphate homeostasis assessment remains challenging. Besides the measurement of key hormones involved in the control of phosphate homeostasis (parathyroid hormone, vitamin D and metabolites, fibroblast growth factor 23), assessing the magnitude of phosphate reabsorption by the kidney is a crucial step. It makes it possible to distinguish between a primary disorder of renal phosphate reabsorption, associated with an intrinsic defect or endocrine disturbance, and a nutritional cause of phosphate deficiency. This strategy is described, and the potential consequences for therapeutic decisions are discussed.

Severe Hyperphosphatemia in a Patient with Mild Acute Kidney Injury

Hyperphosphatemia may arise from various conditions including exogenous ingestion, extracellular shifts due to cell death or alterations in acid-base status, increased bone resorption, hormonal dysregulations leading to reduced renal excretion, reduced kidney function, or faulty measurement techniques. We herein present a case of a young pregnant woman who presented with mild acute kidney injury (AKI), invasive mucormycosis receiving liposomal amphotericin, and hyperphosphatemia out of proportion to the degree of kidney injury. While the patient was given routine phosphate-binding agent by her primary care team for presumed AKI-associated hyperphosphatemia, a full investigation by the renal consulting team for contributing factors other than kidney injury revealed that she actually had pseudohyperphosphatemia associated with the use of liposomal amphotericin. Erroneous treatment of pseudohyperphosphatemia may have been detrimental to this pregnant patient. A literature review for conditions associated with pseudohyperphosphatemia other than the use of liposomal amphotericin will be discussed.

Interferences in the measurement of circulating phosphate: a literature review

Background

Inorganic phosphate in blood is currently determined by the reaction with molybdate. This report aims at reviewing conditions underlying spuriously altered levels of circulating inorganic phosphate.

Content

A systematic search of the Excerpta Medica, the National Library Database and the Web of Science database was conducted without language restriction from the earliest publication date available through January 31, 2020.

Summary

For the analysis, 80 reports published in English (n = 77), French (n = 1), German (n = 1) and Spanish (n = 1) were retained. Well-documented pseudohyperphosphatemia was observed in individuals exposed to liposomal amphotericin, in patients affected by a gammopathy, in patients with hyperlipidemia and in patients with hyperbilirubinemia. An unexplained elevated inorganic phosphate level sometimes provided a clue to the diagnosis of a gammopathy. Well-documented cases of pseudohypophosphatemia were observed in patients on large amounts of intravenous mannitol. Finally, pseudohypophosphatemia was occasionally observed on treatment with liposomal amphotericin and in patients with a gammopathy.

Outlook

In order to avoid unnecessary testing and treatment, the phenomenon of spuriously altered inorganic phosphate should be recognized. An unexplained hyperphosphatemia may provide a clue to the diagnosis of a gammopathy or a severe hyperlipidemia.

Disorders of phosphate metabolism

Phosphate in both inorganic and organic form is essential for several functions in the body. Plasma phosphate level is maintained by a complex interaction between intestinal absorption, renal tubular reabsorption, and the transcellular movement of phosphate between intracellular fluid and bone storage pools. This homeostasis is regulated by several hormones, principally the parathyroid hormone, 1,25-dihydroxyvitamin D and fibroblast growth factor 23. Abnormalities in phosphate regulation can lead to serious and fatal complications. In this review phosphate homeostasis and the aetiology, pathophysiology, clinical features, investigation and management of hypophosphataemia and hyperphosphataemia will be discussed.

Clinical Pharmacokinetics, Pharmacodynamics, Safety and Efficacy of Liposomal Amphotericin B

Since its introduction in the 1990s, liposomal amphotericin B (LAmB) continues to be an important agent for the treatment of invasive fungal diseases caused by a wide variety of yeasts and molds. This liposomal formulation was developed to improve the tolerability of intravenous amphotericin B, while optimizing its clinical efficacy. Since then, numerous clinical studies have been conducted, collecting a comprehensive body of evidence on its efficacy, safety, and tolerability in the preclinical and clinical setting. Nevertheless, insights into the pharmacokinetics and pharmacodynamics of LAmB continue to evolve and can be utilized to develop strategies that optimize efficacy while maintaining the compound's safety. In this article, we review the clinical pharmacokinetics, pharmacodynamics, safety, and efficacy of LAmB in a wide variety of patient populations and in different indications, and provide an assessment of areas with a need for further clinical research.

Pseudohypophosphatemia associated with high-dose liposomal amphotericin B therapy

BACKGROUND

Hypophosphatemia is commonly observed in critically ill patients. Inorganic phosphorus is quantified by spectrophotometric measurement of a phosphomolybdate complex, a method with multiple documented interferents. Our clinical laboratory was contacted to investigate a case of asymptomatic hypophosphatemia in a patient receiving high-dose liposomal amphotericin B therapy (L-AMB).

METHODS

In vitro experiments were performed by spiking L-AMB into residual plasma specimens. Phosphate was measured on the Beckman Coulter AU and Ortho Diagnostics Vitros instruments.

RESULTS

When measured on the AU, phosphate in plasma with approximately 250mcg/mL of L-AMB demonstrated a median negative bias of 3.45mg/dL relative to unspiked samples. In contrast, Vitros phosphate measurements demonstrated excellent agreement for specimens with and without L-AMB (median bias -0.2mg/dL).

CONCLUSIONS

High L-AMB concentrations induced a significant negative bias on phosphate measured by the AU assay, but did not affect the Vitros assay. Laboratorians and clinicians should be aware of this phenomenon in patients receiving L-AMB who develop unexplained hypophosphatemia.

Case-control study and case series of pseudohyperphosphatemia during exposure to liposomal amphotericin B

Pseudohyperphosphatemia due to an interaction between liposomal amphotericin B and the Beckman Coulter PHOSm assay occurs sporadically and remains underrecognized in clinical practice. This retrospective case-control study compares the incidences of hyperphosphatemia in adult inpatients exposed to liposomal amphotericin B or a triazole. A case series of patients with confirmed pseudohyperphosphatemia is described. A total of 80 exposures to liposomal amphotericin B and 726 exposures to triazoles were identified. Among subjects without chronic kidney disease and no concomitant acute kidney injury, hyperphosphatemia occurred more often during liposomal amphotericin B therapy than during triazole therapy (40% [14/35 cases] versus 10% [47/475 cases] of cases; P < 0.01; adjusted odds ratio, 5.2 [95% confidence interval {CI}, 2.3 to 11.9]). Among individuals with chronic kidney disease and no concomitant acute kidney injury, hyperphosphatemia also occurred more often during liposomal amphotericin B exposure (59% [10/17 cases] versus 20% [34/172 cases] of cases; P < 0.01; adjusted odds ratio, 6.0 [95% CI, 2.0 to 18.0]). When acute kidney injury occurred during antifungal exposure, the frequencies of hyperphosphatemia were not different between treatments. Seven episodes of unexpected hyperphosphatemia during liposomal amphotericin B exposure prompted a confirmatory test using an endpoint-based assay that found lower serum phosphorus levels (median difference of 2.5 mg/dl [range, 0.6 to 3.6 mg/dl]). Liposomal amphotericin B exposure confers a higher likelihood of developing hyperphosphatemia than that with exposure to a triazole antifungal, which is likely attributable to pseudohyperphosphatemia. Elevated phosphorus levels in patients receiving liposomal amphotericin B at institutions using the Beckman Coulter PHOSm assay should be interpreted cautiously.

Pseudohyperphosphatemia in children treated with liposomal amphotericin B

PURPOSE

The results of a study to determine the frequency of pseudohyperphosphatemia in a sample of pediatric patients treated with i.v. liposomal amphotericin B are reported.

METHODS

A single-site retrospective study was conducted to identify evidence of pseudohyperphosphatemia in the medical records of patients 18 years of age or younger who received at least five doses of amphotericin B liposome; the maximum dose was calculated for each regimen and categorized as either ≤5 or >5 mg/kg/day. The primary objective was to ascertain the rate of pseudohyperphosphatemia (i.e., abnormally high serum phosphate without elevated serum calcium). The secondary objective was to compare rates of pseudohyperphosphatemia at the higher and lower amphotericin B dosage levels. A multivariate generalized estimating equation (GEE) regression model was used to identify potential predictors of pseudohyperphosphatemia.

RESULTS

Data were collected on 72 courses of amphotericin B liposome administered during a 13-month period to 47 patients; based on a review of chart notations and clinical data, it was determined that 36 regimens (50%) involved pseudohyperphosphatemia. The GEE model revealed no significant association between pseudohyperphosphatemia and any evaluated variable, including age, weight, duration of therapy, and concurrent use of medications known to alter serum phosphorus.

CONCLUSION

In children receiving amphotericin B liposome, half of the regimens were associated with pseudohyperphosphatemia. Although no factors were found to predict pseudohyperphosphatemia, on average, patients who developed the abnormality were significantly older and heavier and received a significantly higher absolute initial dosage of amphotericin B liposome than those who did not develop the condition.

Spurious electrolyte disorders: a diagnostic challenge for clinicians

Spurious electrolyte disorders refer to an artifactually elevated or decreased serum electrolyte values that do not correspond to their actual systemic levels. When a clinician is confronted with a case of electrolyte disturbance, the first question should be whether it is an artifact. Spurious electrolyte disorders (pseudohyponatremia, pseudohypernatremia, pseudohypokalemia, pseudohyperkalemia, pseudohypomagnesemia, pseudohypophosphatemia, pseudohyperphosphatemia, pseudohypocalcemia and pseudohypercalcemia) are not infrequently observed in clinical practice. The recognition that an electrolyte disturbance may be an artifact may prevent inappropriate therapeutic interventions that could potentially have unfavorable outcomes. Clinicians must be alert to the possibility of spurious laboratory abnormalities when faced with conflicting laboratory values or measurements that are discordant with the clinical presentation. Moreover, in the presence of conditions that predispose to spurious electrolyte disorders, the normal measured electrolyte levels should raise the suspicion that true electrolyte disorders may be present.

Pseudohyperphosphatemia associated with high-dose liposomal and lipid complex amphotericin B when tested with Synchron LX 20 (Beckman/Coulter) phosphorous assay

Although case reports of hyperphosphatemia have been previously described in patients receiving liposomal amphotericin B, this has not been reported in patients receiving the lipid complex formulation. We report a case of hyperphosphatemia that persisted despite switching from liposomal to lipid complex amphotericin B in a child with invasive zygomycosis. This case suggests that in the context of acute renal dysfunction, hyperphosphatemia may also be observed with lipid complex amphotericin B. This case highlights the importance of differentiating between pseudohyperphosphatemia and hyperphosphatemia to prevent complications.

Hyperphosphatemia in pediatric oncology patients receiving liposomal amphotericin B

OBJECTIVE

After transitioning our front-line amphotericin product to the liposomal formulation, we observed an increased incidence of hyperphosphatemia. We aimed to determine the incidence of hyperphosphatemia in children with oncologic disorders receiving an amphotericin B product and to establish whether the incidence varies depending on amphotericin formulation.

METHODS

This retrospective review of the medical record was conducted at a tertiary, free standing children's hospital. Pharmacy data revealed 159 patients receiving an amphotericin product between November 2006 and December 2008. Doses of amphotericin, serum phosphorous, calcium and creatinine concentrations were recorded at daily time points during the 10 days following both initiation and discontinuation of amphotericin. Administration of phosphate binders and total parenteral nutrition was noted. The incidence of hyperphosphatemia, defined as a serum value greater than the age-adjusted upper limit of normal, was compared among the amphotericin groups.

RESULTS

One hundred thirty-nine amphotericin recipients had a serum phosphorus measurement during amphotericin therapy. Final analysis included 117 children, of which 64 (55%) were oncology patients. Deoxycholate (mean maximum dose 1 mg/kg), lipid complex (mean maximum dose 4.8 mg/kg) and liposomal amphotericin (mean maximum dose 4.9 mg/kg) were used in 24 (20.5%), 37 (31.6%) and 56 (47.9%) of all patients, respectively. Hyperphosphatemia developed in 27% (32/117) of all patients, and in 33% (21/64) of oncology patients. Similar to within all recipients, among oncology patients, 45% (n=18) of liposomal recipients demonstrated hyperphosphatemia compared to 13% of those receiving lipid complex (n=3, p=0.007). No oncology patient received deoxycholate.

CONCLUSION

Nearly 45% of children with oncologic disorders receiving liposomal amphotericin developed hyperphosphatemia. The incidence is significantly greater for the liposomal formulation than either of the other amphotericin formulations.

A synopsis of phosphate disorders in the nursing home

Elderly patients are at an increased risk of developing both hypophosphatemia and hyperphosphatemia. Renal insufficiency predisposes elderly patients to elevated serum concentrations of phosphate. On the other hand, poor dietary intake and loss of phosphorus in the urine can lead to deficiency states. It is well documented that hyperphosphatemia is correlated with an increase in morbidity and mortality as a result of vascular calcification. This article reviews the etiology, pathophysiology, symptoms, and treatment of hypophosphatemia and hyperphosphatemia.