To determine if the loud noise generated by magnetic resonance (MR) imaging equipment is capable of inducing hearing loss, the hearing of 24 patients was tested before and after MR imaging. Fourteen patients were imaged without ear protection, and six (43%) suffered a temporary, mild loss of hearing (less than or equal to 15 dB at at least one frequency). Ten patients were imaged with ear protection, and only one experienced any hearing loss. Therefore, the noise generated by MR imagers may cause temporary hearing loss, and earplugs can prevent this loss. All threshold changes had returned to within 10 dB of baseline by 15 minutes after completion of the second audiometric test.
The renal handling of vancomycin is unknown. Previously reported studies have not achieved steady-state conditions with constant vancomycin concentrations. We measured systemic vancomycin clearance simultaneously with the renal clearances of vancomycin, creatinine, inulin, and para-aminohippurate in nine healthy subjects at steady-state serum vancomycin concentrations of 7 and 14 mg/L. For all steady-state observations the renal clearance of vancomycin was 89 +/- 11 ml/min (mean +/- SE), the clearance of inulin 105 +/- 9 ml/min, the clearance of creatinine 117 +/- 9 ml/min, and the clearance of para-aminohippuric acid 496 +/- 41 ml/min. The systemic clearance of vancomycin was 131 +/- 7 ml/min. The clearances of creatinine, inulin, and para-aminohippuric acid and the renal clearance of vancomycin were not statistically different at both steady-state vancomycin concentrations. The ratio of the renal clearance of vancomycin to the clearance of inulin was 0.89 +/- 0.06 and to creatinine clearance 0.79 +/- 0.05. Both ratios were independent of vancomycin concentration, urine flow rate, and filtration fraction. The systemic clearance of vancomycin was 10% greater at serum vancomycin concentrations of 14 mg/L than at 7 mg/L (p less than 0.05) because of an increase in the nonrenal clearance. Therefore in healthy subjects, 30% of the systemic vancomycin clearance is by nonrenal mechanisms and this nonrenal clearance is concentration dependent. Assuming protein binding to be between 10% and 20%, renal vancomycin excretion is predominantly by glomerular filtration. Small amounts of tubular vancomycin transport cannot be excluded by these techniques.
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