Measurement of ceftazidime concentration in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry. Application to critically ill patients and patients with osteoarticular infections.

Ceftazidime is an antibiotic belonging to the third generation of the cephalosporin family. It is indicated in the treatment of serious, simple or mixed bacterial infections, and its administration in continuous or intermittent infusion allows optimization of the concentration of antibiotic to keep it above the minimum inhibitory concentration. We developed and validated a chromatographic method by ultra-performance liquid chromatography-tandem mass spectrometry to measure ceftazidime concentration in human plasma. Following extraction with acetonitrile and 1,2-dichloroethane, the chromatographic separation was achieved using an Acquity ® UPLC ® BEH(TM) (2.1 × 100 mm i.d., 1.7 µm) reverse-phase C18 column, with a water-acetonitrile linear gradient containing 0.1% formic acid at a 0.4 mL/min flow rate. Ceftazidime and its internal standard (cefotaxime) were detected by electrospray ionization mass spectrometry in positive ion multiple reaction monitoring mode using mass-to-charge transitions of 547.0 → 467.9/396.1 and 456.0 → 395.8/324.1, respectively. The limit of quantification was 0.58 mg/L and linearity was observed in the range 0.58-160 mg/L. Coefficients of variation and absolute relative biases were <9.8 and 8.4%. The mean recovery for ceftazidime was 74.4 ± 8.1%. Evaluation of the matrix effect showed ion enhancement, and no carry-over was observed. The validated method could be applied to daily clinical laboratory practice to measure the concentration of ceftazidime in plasma.

Postresection parathyroid hormone and parathyroid hormone decline accurately predict hypocalcemia after thyroidectomy.

Hypocalcemia is the most frequent complication after total thyroidectomy. Parathyroid hormone (PTH) measurement has been proposed as an early predictor of this condition. Total thyroidectomy was performed in 39 patients. Hypocalcemia was present in 15 cases (38%). Patients undergoing hemithyroidectomy (n = 13) were considered control subjects not developing hypocalcemia. PTH was measured before surgery and 10 minutes after resection of the gland using a rapid (15 minutes) chemiluminescent immunometric assay. Patients developing hypocalcemia had lower calcium and postresection PTH levels and higher PTH decline than patients not developing hypocalcemia (P < .0001). PTH decline (cutoff value, 62.5%) had the better sensitivity (93.3%) for predicting hypocalcemia, allowing for a fairly safe early discharge. However, the best overall results corresponded to the combination of postresection PTH level (< or = 18 pg/mL [< or = 1.9 pmol/L]) and PTH decline (>62.5%), with a sensitivity of 90% and a specificity of 97.9%. Perioperative PTH measures can accurately predict hypocalcemia after thyroidectomy, granting the laboratory a key role in the immediate decision about calcium supplementation for patients at risk.