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1) When monitoring vancomycin you need to know what type of filter is
being used. The standars filters do not remove much, but the newer
"high-flux" filters do remove some. What is generally done in practice
is to measure a RANDOM concentration approximately 4-5 days post dose to
ensure the patient is therapeutic, and help you decide when the next
dose will be needed. (Peaks are not necessary and full of error!!) Most
patients can get away with 15mg/kg every 7 days, although i do see
patients that require a dose every 4 or 5 days, depending on residual
renal function.
2) The same goes for hemodialysis give 15mg/kg every dose, check a
random level in 4-5 days. Unless it is a high-flux filter vanco will
not be significantly removed.
The tricky part of this comes in the interpretation of the vanco
concentration, as a "metabolite" of vancomycin accumulates and
cross-reacts with the most commonly used assay (Abbott's FPIA TDx
assay). The measured concentrations can be falsely high on the order of
50-70%....it becomes more significant as duration of therapy increases.
A new assay is out (Abbott's FPIA Vancomycin II), which utilizes a
monoclonal antibody that does not cross-react....so it is imperative
that you know which assay is being used when you measure serum
concentrations.
hope this helps,
Patrick Smith, PharmD
The Clinical Pharmacokinetics Lab
Buffalo, NY
some references for your entertainment:
Leader WG, Chandler MHH, Castiglia M. Pharmacokinetic optimisation of
vancomycin therapy. Clin Pharmacokinet 1995;28(4):327-42.
Smith PF, Petros WP, Soucie MP, Copeland KR. New modified flourescence
polarization immunoassay does not falsely elevate vancomycin
concentrations in patients with end-stage renal disease. Ther Drug
Monitor 1998;20:231-5.
Morse GD, Nairn DK, Bertino JS, Walshe JJ. Overestimation of vancomycin
concentrations utilizing fluorescence polarization immunoassay in
patients on peritoneal dialysis. Ther Drug Monit 1987; (9)2:212-15.
Najjar TA, Al-Dhuwailie AA, Tekle A. Comparison of high-performance
liquid chromatography with fluorescence polarization immunoassay for the
analysis of vancomycin in patients with chronic renal failure. J
Chromatogr B 1995;672:295-9.
Anne L, Hu M, Chan K, Colin L, Gottwald K. Potential problem with
fluorescence polarization immunoassay cross-reactivity to vancomycin
degradation product CDP-1: Its detection in sera of renally impaired
patients. Ther Drug Monit 1989: (11)5:585-591.
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)