Association of hypocalcemia with a change in gentamicin administration in neonates

Gentamicin Inhibits Ca2+ Channel TRPV5 and Induces Calciuresis Independent of the Calcium-Sensing Receptor-Claudin-14 Pathway

BACKGROUND

Treatment with the aminoglycoside antibiotic gentamicin can be associated with severe adverse effects, including renal Ca²⁺ wasting. The underlying mechanism is unknown but it has been proposed to involve activation of the Ca²⁺-sensing receptor (CaSR) in the thick ascending limb, which would increase expression of claudin-14 (CLDN14) and limit Ca²⁺ reabsorption. However, no direct evidence for this hypothesis has been presented.

METHODS

We studied the effect of gentamicin in vivo using mouse models with impaired Ca²⁺ reabsorption in the proximal tubule and the thick ascending limb. We used a Cldn14 promoter luciferase reporter assay to study CaSR activation and investigated the effect of gentamicin on activity of the distal nephron Ca²⁺ channel transient receptor potential vanilloid 5 (TRPV5), as determined by patch clamp in HEK293 cells.

RESULTS

Gentamicin increased urinary Ca²⁺ excretion in wild-type mice after acute and chronic administration. This calciuretic effect was unaltered in mice with genetic CaSR overactivation and was present in furosemide-treated animals, whereas the calciuretic effect in Cldn14^-/- mice and mice with impaired proximal tubular Ca²⁺ reabsorption (claudin-2 [CLDN2]-deficient Cldn2^-/- mice) was equivalent to that of wild-type mice. In vitro, gentamicin failed to activate the CaSR. In contrast, patch clamp analysis revealed that gentamicin strongly inhibited rabbit and human TRPV5 activity and chronic gentamicin administration downregulated distal nephron Ca²⁺ transporters.

CONCLUSIONS

Gentamicin does not cause hypercalciuria via activation of the CaSR-CLDN14 pathway or by interfering with proximal tubular CLDN2-dependent Ca²⁺ reabsorption. Instead, gentamicin blocks distal Ca²⁺ reabsorption by direct inhibition of the Ca²⁺ channel TRPV5. These findings offer new insights into Ca²⁺ wasting in patients treated with gentamicin.

Calcemia and Inflammatory Markers in Early-Onset Neonatal Infection

INTRODUCTION

Ionised hypocalcemia (S-Ca2+) has been repeatedly observed in neonates with sepsis. Our aim was to evaluate total calcemia (S-Ca) and its relationship to laboratory markers of infection.

METHODS

We retrospectively evaluated total calcemia (S-Ca) and its relationship to laboratory markers of sepsis/infection (serum levels of C-reactive protein - S-CRP and procalcitonin - S-PCT) in 29 full-term neonates with early-onset neonatal infection hospitalized at our neonatology ward between 2012 and 2016. The control group consisted of 705 neonates without infection.

RESULTS

In neonates with early-onset infection , the S-Ca on day 1, 2 and 3 was significantly lower (p < 0.0001; p < 0.0001; p = 0.05 versus controls) same as the pooled S-Ca (p < 0.0001 versus controls). There was a weak negative correlation between pooled S-Ca and S-PCT, or pooled S-Ca and S-CRP (r = -0.22, p = 0.06; r = -0.19, p = 0.09).

CONCLUSION

S-Ca was decreased in neonates with early-onset infection and did show a slight tendency to inverse correlation with S-CRP and S-PCT. Pediatricians must be aware of the fact that a drop in total S-Ca should alert their attention to the risk of neonatal infection, and, likewise, that the children with neonatal infection are at a higher risk of hypocalcemia with all its consequences.

Evidence That Antibiotics Bind to Human Mitochondrial Ribosomal RNA Has Implications for Aminoglycoside Toxicity

Aminoglycosides are a well known antibiotic family used to treat bacterial infections in humans and animals, but which can be toxic. By binding to the decoding site of helix44 of the small subunit RNA of the bacterial ribosome, the aminoglycoside antibiotics inhibit protein synthesis, cause misreading, or obstruct peptidyl-tRNA translocation. Although aminoglycosides bind helix69 of the bacterial large subunit RNA as well, little is known about their interaction with the homologous human helix69. To probe the role this binding event plays in toxicity, changes to thermal stability, base stacking, and conformation upon aminoglycoside binding to the human cytoplasmic helix69 were compared with those of the human mitochondrial and Escherichia coli helix69. Surprisingly, binding of gentamicin and kanamycin A to the chemically synthesized terminal hairpins of the human cytoplasmic, human mitochondrial, and E. coli helix69 revealed similar dissociation constants (1.3-1.7 and 4.0-5.4 μM, respectively). In addition, aminoglycoside binding enhanced conformational stability of the human mitochondrial helix69 by increasing base stacking. Proton one-dimensional and two-dimensional NMR suggested significant and specific conformational changes of human mitochondrial and E. coli helix69 upon aminoglycoside binding, as compared with human cytoplasmic helix69. The conformational changes and similar aminoglycoside binding affinities observed for human mitochondrial helix69 and E. coli helix69, as well as the increase in structural stability shown for the former, suggest that this binding event is important to understanding aminoglycoside toxicity.

Serum calcium values in term and late-preterm neonates receiving gentamicin

Since noting an apparent increase in hypocalcemia in neonates receiving gentamicin every 24 h (q 24 h) for > or = 4 days, we have prospectively monitored serum calcium (Ca) values in these patients receiving prolonged gentamicin therapy. This study is a retrospective analysis of those values measured during gentamicin treatment. The study included neonates with gestational age > or = 35 weeks who received > or = 4 days of gentamicin therapy and in whom at least one serum Ca value was measured > or = 47 h after initiation of therapy. Hypocalcemia was defined as a serum Ca level < 8 mg/dl (2 mmol/l). Data were analyzed by Student t-test, chi-square test, and Pearson product moment correlation. There were 1,624 neonates that met the study criteria. Ca was < 8 mg/dl in 241 (15%). Ca < 8 mg/dl was more likely in boys than in girls (16.4% vs 11.8%, P = 0.01) and in neonates < 37 weeks gestational age (GA) than in those > or = 37 weeks GA (23.9% vs 14.1%, P = 0.01). A second Ca value was obtained in 883 neonates (54%); 23.2% of neonates with initial Ca < 8 mg/dl remained hypocalcemic, and 30% of these were receiving oral Ca supplementation. The second Ca value was < 8 mg/dl in eight neonates in whom initial Ca was > or = 8 mg/dl. Hypocalcemia is not uncommon in neonates receiving gentamicin therapy, and it may occur more frequently in boys and late-preterm infants. These data suggest that the monitoring of serum Ca levels should be considered when gentamicin is given > or = 4 days.

Antimicrobial resistance in Gram-negative bacilli isolated from infant formulas

A total of 90 samples of infant formula (IF) were collected from the lactary of a teaching hospital, during a 4-month period from July to August 1999. The sanitary conditions of the formulas were analyzed, and a physiological characterization of Gram-negative bacillus isolates and antimicrobial susceptibility testing were performed. Colony counts were considered to be unacceptable for the majority of the IF samples and the contamination rates were related to inadequate handling. Coliforms (35 degrees C and 45 degrees C growth) were detected in most of the IF tested. Klebsiella pneumoniae, Citrobacter freundii, Cedacea davisae, Klebsiella planticola and Enterobacter cloacae were the isolates most commonly identified. Antimicrobial susceptibility testing showed significant resistance rates, particularly to amoxicillin/clavulanic acid, cefoxitin, cephalotin or ampicillin. One extended-spectrum beta-lactamase-producing K. pneumoniae strain was also recovered.