A case of linezolid-induced SIADH in elderly and a review of the literature.

INTRODUCTION: Linezolid is a synthetic oxazolidinone antimicrobial drug with a broad spectrum and a unique mechanism of inhibiting resistant pathogenic strains, and it was approved by the Food and Drug Administration (FDA) in April 2000. Several different systemic side effects were reported after the use of this medication. In this article, we report a case in which a syndrome of inappropriate antidiuretic hormone (SIADH) was developed after linezolid treatment was started. CASE PRESENTATION: We present the case of a 79-year-old woman who developed severe hyponatremia during linezolid treatment (0.6 g i.v. q12 h) after undergoing hemiarthroplasty for left femoral neck fracture. The patient's baseline serum sodium upon admission (138 mmol/L) decreased to 118 mmol/L, urine sodium was 102 mmol/L, plasma osmolality was 248 mOsm/kg and urine osmolarity was 310 mOsm/kg at day 4, thus a diagnosis of SIADH was made. The patient was not taking any other medication known to cause SIADH, and she did not present a comorbidity that could explain her condition. Her serum sodium increased to 135 and 137 mmol/L, respectively, 11 and 12 days after cessation of linezolid, strongly suggesting that SIADH was the cause in this case. CONCLUSIONS: This is the fourth case of linezolid-induced SIADH. A thorough workup was essential for the diagnosis to correctly differentiate between SIADH and other causes of hyponatremia, which helped us properly conducting follow-up treatments. SIADH is a rare but serious side effect of linezolid, and practicing physicians should be aware of this complication. It is necessary to periodically monitor the serum sodium.

[Effectiveness of eradication regimen based on the bacterial susceptibility and CYP2C19 genotype in children with refractory Helicobacter pylori infection].

Objective: To evaluate the effectiveness of eradication therapy based on Helicobacter pylori (Hp) susceptibility and CYP2C19 genotype in children with refractory Hp infection. Methods: In this prospective observational cohort study, 156 children with Hp refractory to amoxicillin+clarithromycin+omeprazole triple regimen in Baoding Children's Hospital from December 2017 to May 2018 were enrolled. Ninety-two of them underwent Hp culture and CYP2C19 detection. Seventy-five cases with positive Hp culture were defined as culture successful group and were treated according to Hp susceptibility and CYP2C19 genotype. Seventeen cases with negative Hp culture were defined as culture failed group and were treated only based on the results of CYP2C19 genotype. Sixty-four children who did not have Hp culture and CYP2C19 gene testing were defined as the empirical eradication therapy group and were treated with quadruple regimen (amoxicillin+metronidazole+omeprazole+bismuth). Bacterial resistance, CYP2C19 polymorphism and therapeutic effectiveness between the three groups were compared using chi-square test. Results: Among the 75 positive Hp culture results, 72 (96%) were resistant to clarithromycin, 3 (4%) were resistant to metronidazole, 5 (7%) were resistant to levofloxacin, 5 (7%) were resistant to rifampicin, 1 (1%) was resistant to tetracycline, and none was resistant to amoxicillin and furazolidone. The CYP2C19 polymorphism in 92 patients showed that 43 (47%) were extensive metabolizer (EM), 9 (10%) were poor metabolizer (PM), and 40 (43%) were intermediate metabolizer (IM). In terms of the effectiveness, eradication rate in the culture successful group,culture failed group and empirical eradication therapy group were 99% (74/75), 88% (15/17) and 72% (46/64), respectively (χ(2)=21.325, P<0.05). The eradication rate in the culture successful group was significantly higher than that in empirical eradication therapy group (χ(2)=21.005, P<0.05), while there was no difference between empirical eradication therapy group and culture failed group (χ(2)=1.154, P=0.283). Conclusion: Eradication regimen based on bacterial susceptibility and CYP2C19 genotype should be considered in children with refractory Hp infection.