The natural history of nephrocalcinosis in premature infants treated with loop diuretics

Mechanisms Underlying Calcium Nephrolithiasis

Nephrolithiasis is a worldwide problem with increasing prevalence, enormous costs, and significant morbidity. Calcium-containing kidney stones are by far the most common kidney stones encountered in clinical practice. Consequently, hypercalciuria is the greatest risk factor for kidney stone formation. Hypercalciuria can result from enhanced intestinal absorption, increased bone resorption, or altered renal tubular transport. Kidney stone formation is complex and driven by high concentrations of calcium-oxalate or calcium-phosphate in the urine. After discussing the mechanism mediating renal calcium salt precipitation, we review recent discoveries in renal tubular calcium transport from the proximal tubule, thick ascending limb, and distal convolution. Furthermore, we address how calcium is absorbed from the intestine and mobilized from bone. The effect of acidosis on bone calcium resorption and urinary calcium excretion is also considered. Although recent discoveries provide insight into these processes, much remains to be understood in order to provide improved therapies for hypercalciuria and prevent kidney stone formation. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Drug-Induced Urolithiasis in Pediatric Patients

Drug-induced nephrolithiasis is a rare condition in children. The involved drugs may be divided into two different categories according to the mechanism involved in calculi formation. The first one includes poorly soluble drugs that favor the crystallization and calculi formation. The second category includes drugs that enhance calculi formation through their metabolic effects. The diagnosis of these specific calculi depends on a detailed medical history, associated comorbidities and the patient's history of drug consumption. There are several risk factors associated with drug-induced stones, such as high dose of consumed drugs and long duration of treatment. Moreover, there are some specific risk factors, including urinary pH and the amount of fluid consumed by children. There are limited data regarding pediatric lithogenic drugs, and hence, our aim was to perform a comprehensive review of the literature to summarize these drugs and identify the possible mechanisms involved in calculi formation and discuss the management and preventive measures for these calculi.

Association between furosemide in premature infants and sensorineural hearing loss and nephrocalcinosis: a systematic review

Furosemide is a potent loop diuretic commonly and variably used by neonatologists to improve oxygenation and lung compliance in premature infants. There are several safety concerns with use of furosemide in premature infants, specifically the risk of sensorineural hearing loss (SNHL), and nephrocalcinosis/nephrolithiasis (NC/NL). We conducted a systematic review of all trials and observational studies examining the association between these outcomes with exposure to furosemide in premature infants.

We searched MEDLINE, EMBASE, CINAHL, and clinicaltrials.gov. We included studies reporting either SNHL or NC/NL in premature infants (< 37 weeks completed gestational age) who received at least one dose of enteral or intravenous furosemide. Thirty-two studies met full inclusion criteria for the review, including 12 studies examining SNHL and 20 studies examining NC/NL. Only one randomized controlled trial was identified in this review. We found no evidence that furosemide exposure increases the risk of SNHL or NC/NL in premature infants, with varying quality of studies and found the strength of evidence for both outcomes to be low. The most common limitation in these studies was the lack of control for confounding factors.

The evidence for the risk of SNHL and NC/NL in premature infants exposed to furosemide is low. Further randomized controlled trials of furosemide in premature infants are urgently needed to adequately assess the risk of SNHL and NC/NL, provide evidence for improved FDA labeling, and promote safer prescribing practices.

Clinical pharmacology of furosemide in neonates: a review

Furosemide is the diuretic most used in newborn infants. It blocks the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle increasing urinary excretion of Na⁺ and Cl⁻. This article aimed to review the published data on the clinical pharmacology of furosemide in neonates to provide a critical, comprehensive, authoritative and, updated survey on the metabolism, pharmacokinetics, pharmacodynamics and side-effects of furosemide in neonates. The bibliographic search was performed using PubMed and EMBASE databases as search engines; January 2013 was the cutoff point. Furosemide half-life (t_1/2) is 6 to 20-fold longer, clearance (Cl) is 1.2 to 14-fold smaller and volume of distribution (Vd) is 1.3 to 6-fold larger than the adult values. t_1/2 shortens and Cl increases as the neonatal maturation proceeds. Continuous intravenous infusion of furosemide yields more controlled diuresis than the intermittent intravenous infusion. Furosemide may be administered by inhalation to infants with chronic lung disease to improve pulmonary mechanics. Furosemide stimulates prostaglandin E2 synthesis, a potent dilator of the patent ductus arteriosus, and the administration of furosemide to any preterm infants should be carefully weighed against the risk of precipitation of a symptomatic patent ductus arteriosus. Infants with low birthweight treated with chronic furosemide are at risk for the development of intra-renal calcifications.

Development of an animal model of nephrocalcinosis via selective dietary sodium and chloride depletion

BACKGROUND

Nephrocalcinosis (NC) is an important clinical problem seen in critically ill preterm neonates treated with loop diuretics. No reliable animal models are available to study the pathogenesis of NC in preterm infants. The purpose of this study was to develop a reproducible and clinically relevant animal model of NC for these patients and to explore the impact of extracellular fluid (ECF) volume contraction induced by sodium and chloride depletion in this process.

METHODS

Three-week-old weanling Sprague-Dawley rats were fed diets deficient in either chloride or sodium or both. A subgroup of rats from each dietary group was injected daily with furosemide (40 mg/kg i.p.).

RESULTS

Rats fed a control diet, with or without furosemide, or a chloride-depleted diet alone, did not develop NC. By contrast, 50% of the rats injected with furosemide and fed the chloride-depleted diet developed NC. Moreover, 94% of the rats fed the combined sodium- and chloride-depleted diet developed NC, independently of furosemide use. NC was associated with the development of severe ECF volume contraction; hypochloremic, hypokalemic, metabolic alkalosis; increased phosphaturia; and growth retardation.

CONCLUSION

Severe ECF volume contraction induced by chronic sodium and chloride depletion appears to play an important role in the pathogenesis of NC.

Nephrocalcinosis in preterm neonates

The prevalence of nephrocalcinosis (NC) in preterm neonates in recent reports is 7-41%. The wide range in prevalence is a consequence of different study populations and ultrasound equipment and criteria, in addition to a moderate interobserver variation. NC in preterm neonates has a multifactorial aetiology, consisting of low gestational age and birth weight, often in combination with severe respiratory disease, and occurs as a result of an imbalance between stone-promoting and stone-inhibiting factors. A limited number of histological studies suggest that calcium oxalate crystals play an important role in NC in premature neonates. In 85% of children resolution of NC occurs in the first years of life. Prematurity, per se, is associated with high blood pressure, relatively small kidneys, and (distal) tubular dysfunction. In addition, NC in preterm neonates can have long-term sequelae for glomerular and tubular function. Long-term follow-up of blood pressure and renal function of prematurely born children, especially with neonatal NC, is recommended. Prevention of NC with (low) oral doses of citrate has not resulted in a significant decrease in the prevalence of NC; a higher citrate dosage deserves further study. Future research pertaining to prevention of NC in preterm neonates is crucial.

Nephrocalcinosis in a preterm infant

Bilateral medullary echogenic foci are not uncommonly seen in renal ultrasounds of sick, preterm neonates. Often, the likely diagnosis is nephrocalcinosis. We present one such case. The long term outcome in this population is unknown, but is generally thought to be essentially good.

Neonatal nephrocalcinosis: long term follow up

AIMS

To assess the spontaneous resolution of neonatal nephrocalcinosis and its long term effects on renal function.

METHODS

Fourteen very low birthweight preterm babies with nephrocalcinosis were followed up at 5-7 years of age; 14 controls were matched for sex, gestation, and birth weight. Height, weight, blood pressure, and renal symptomatology were recorded, and a renal ultrasound scan was performed. Early morning urine osmolality and creatinine ratios of albumin, phosphate, calcium, oxalate and beta microglobulin were determined. Urea and electrolytes in the study group were determined, and glomerular filtration rate (GFR) and TmP/GFR (tubular reabsorption of phosphate per GFR) were calculated. Statistical analysis was performed on a group basis using the Mann-Whitney confidence interval.

RESULTS

Mean age was 6.9 years (range 5.81-7.68). An early morning urine osmolality >700 mOsm/kg was achieved in all cases. In two cases and four controls, the calcium/creatinine ratio was >0.7 mmol/mmol. In all cases, the GFR was normal (median 132.6 ml/min/1.73 m(2) (range 104.1-173.1)). Median TmP/GFR was 1.22 mmol/l (0.73-1.61), with two having levels below the normal range. These did not have persisting nephrocalcinosis. Nephrocalcinosis was found in three of the 12 cases scanned and one control. There were no significant differences in urine biochemistry.

CONCLUSIONS

Resolution of nephrocalcinosis occurred in 75% of cases. No evidence was found to suggest that nephrocalcinosis is associated with renal dysfunction in the long term. There was evidence of hypercalciuria in the cases and controls, suggesting that prematurity may be a risk factor.

Kidney stone disease

About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. Stones ultimately arise because of an unwanted phase change of these substances from liquid to solid state. Here we focus on the mechanisms of pathogenesis involved in CaOx, CaP, UA, and cystine stone formation, including recent developments in our understanding of related changes in human kidney tissue and of underlying genetic causes, in addition to current therapeutics.

Development of nephrocalcinosis in very low birth weight infants

Premature infants undergo intensive growth during the postnatal period. Adequate mineralization is dependent on sufficient intake of calcium (Ca) and phosphorus (P). However, Ca and P supplementation can be associated with some risks, for example development of nephrocalcinosis. We investigated pathophysiological risk factors in premature very low birth weight (VLBW) infants associated with the development of nephrocalcinosis. From June 1994 to September 1995 all preterm neonates with a birth weight below 1,500 g were screened prospectively. At regular intervals of 2 weeks, ultrasonography (US) of the kidneys was performed and parameters of mineral metabolism were assessed in blood and spot urine samples. For analysis, premature infants with nephrocalcinosis (group N) were compared with infants without nephrocalcinosis (group R) and with a retrospectively pair-matched subgroup of premature infants without nephrocalcinosis (control group C) taken from the same study. Nephrocalcinosis was detected in 20 of 114 preterm neonates (group N, 17.5%). Of these 20 infants with nephrocalcinosis, 16 presented with a tendency towards systemic acidosis (pH<7.25) on day 2-7, compared with only 4 of 20 premature infants of the control group. Premature infants of group N had a lower serum P at 2 weeks of life and 5 (versus 0 patients of the control group C) had transient hypophosphatemia (serum P<1.6 mmol/l). Moreover, the Ca/creatinine ratio in spot urine specimens tended to be higher (P<0.1) in patients developing nephrocalcinosis. There were no significant differences in the duration of ventilation, the length of stay in the intensive care unit, and duration and frequency of furosemide and steroid treatment between the groups N and C. VLBW premature infants developing nephrocalcinosis frequently presented with slightly impaired acid-base homoeostasis within the 1st week, followed by signs of impaired mineralization (and immature or impaired renal function) within 2 weeks. In VLBW premature infants, close observation of acid-base status and regular analysis of spot urine specimens (Ca, P, creatinine) during the first weeks of life may help to identify those premature infants at risk for nephrocalcinosis.

High incidence of nephrocalcinosis in extremely preterm infants treated with dexamethasone

BACKGROUND

The use of postnatal corticosteroids to treat or prevent chronic lung disease is common in very preterm infants. Medullary nephrocalcinosis has been noted as a possible side effect.

OBJECTIVE

This prospective study was designed to assess the incidence of nephrocalcinosis in extremely preterm infants exposed to dexamethasone.

PATIENTS AND METHODS

A prospective study of extremely preterm infants, recruited to a randomized trial of dexamethasone treatment for chronic lung disease, was initiated. Infants had US of the renal tract scheduled on entry into the study, at day 28 and at discharge or at the corrected gestational age of 36 weeks.

RESULTS

Thirty-three infants were enrolled in the study. Birth weight ranged between 440 and 990 g and gestation between 24 and 28 weeks. Nine infants died and six had incomplete data. Because there was no difference in incidence of calcification between those on the short course and those on the long course of dexamethasone, analysis was made on the entire cohort. One infant had nephrocalcinosis at the time of the initial US examination on day 26 of life. By day 28, nephrocalcinosis was present in 31% of those with complete data. By discharge, or corrected gestational age of 36 weeks, US evidence of nephrocalcinosis was present in 15 (83%) of 18 infants. All infants had at least one course of an aminoglycoside antibiotic during the study. All infants had parenteral nutrition. Only four infants received furosemide more regularly than single doses. The longest course was 10 days, received by an infant who did not develop nephrocalcinosis.

CONCLUSION

The incidence of nephrocalcinosis is high in this group of sick, extremely preterm infants. Dexamethasone may be a factor in the development of nephrocalcinosis. Future research should focus on the natural history of nephrocalcinosis in extremely preterm infants.

Nephrocalcinosis in preterm babies

OBJECTIVES

To determine prospectively the incidence and cause of nephrocalcinosis in preterm infants.

STUDY DESIGN

Inborn babies of gestation less than 32 weeks or birth weight less than 1500 g were eligible to be entered into a prospective observational study. Two renal ultrasound scans were performed, the first at 1 month postnatal age and the second at term or discharge. Data were collected on gestation, birth weight, sex, race, family history of renal calculi, oliguria on first day, respiratory support (ventilation, steroid, and oxygen dependency), and use of nephrotoxic drugs (gentamicin, vancomycin, and frusemide). Intake of fluid, calcium, and phosphate and plasma urea, creatinine, calcium, and phosphate were recorded for the first 6 weeks of life. Random urinary calcium/creatinine, oxalate/creatinine, and urate/creatinine ratios and tubular absorption of phosphate were measured once at term.

RESULTS

A total of 101 preterm infants were studied. Twenty three (23%) had abnormal ultrasound scans. Sixteen (16%) had nephrocalcinosis. On univariate analysis, gestational age, male sex, duration of ventilation, oxygen dependency, duration and frequency of gentamicin treatment, toxic gentamicin/vancomycin levels, and postnatal dexamethasone were significantly associated with nephrocalcinosis. In addition, babies with nephrocalcinosis had a lower intake of fluid, calcium, and phosphate, longer duration of total parenteral nutrition, and higher urinary oxalate/creatinine and urate/creatinine ratios than infants who did not have the condition. There was also a significant association with plasma urea and creatinine but not with plasma calcium or phosphate or urinary calcium. Multivariate analysis showed that the strongest predictors of nephrocalcinosis were duration of ventilation, toxic gentamicin/vancomycin levels, low fluid intake, and male sex.

CONCLUSION

16% of babies born at less than 32 weeks gestation developed nephrocalcinosis. The multifactorial origin, in particular, the association with extreme prematurity and severity of respiratory disease, is confirmed. In addition, an association with male sex, frequency and duration of gentamicin use, and high urinary oxalate and urate excretion is shown.