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J Antimicrob Chemother. 2014 Nov;69(11):2988-94. doi: 10.1093/jac/dku242. Epub 2014 Jul 7.

Five year results of an international proficiency testing programme for measurement of antifungal drug concentrations.

Author information

1
Radboud University Medical Center, Department of Pharmacy, Radboud Institute for Health Sciences, Nijmegen, The Netherlands.
2
Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands.
3
Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands Dutch Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology (KKGT), The Hague, The Netherlands.
4
Dutch Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology (KKGT), The Hague, The Netherlands.
5
Radboud University Medical Center, Department of Pharmacy, Radboud Institute for Health Sciences, Nijmegen, The Netherlands Dutch Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology (KKGT), The Hague, The Netherlands.
6
Radboud University Medical Center, Department of Pharmacy, Radboud Institute for Health Sciences, Nijmegen, The Netherlands roger.bruggemann@radboudumc.nl.

Abstract

OBJECTIVES:

Since 2007 the Dutch Association for Quality Assessment in Therapeutic Drug Monitoring (KKGT) has organized an international interlaboratory proficiency testing (PT) programme for measurement of antifungal drugs in plasma. We describe the 5 year results of the laboratories' performance.

METHODS:

Twice a year, laboratories received a set of blind plasma samples containing low or high concentrations of fluconazole, itraconazole, hydroxyitraconazole, posaconazole, voriconazole and flucytosine. Participating laboratories were asked to report their results within 6 weeks after dispatch and provide details of their analytical methods. Results deviating >20% from the weighed-in concentration were considered inaccurate. Four-way ANOVA was performed to assess the effect of antifungal drug measured, concentration, analytical method and performing laboratory on the absolute inaccuracy. In 2012, a questionnaire based on the CLSI guidelines was dispatched with the request to provide input on sources of error.

RESULTS:

Fifty-seven laboratories (13 countries) reported 2251 results (287 fluconazole, 451 itraconazole, 348 hydroxyitraconazole, 402 posaconazole, 652 voriconazole and 111 flucytosine) in 5 years. Analyses were performed using HPLC (55.0%), LC-MS(/MS) (43.4%), UPLC (1.4%) or GC-MS (0.2%). Overall, 432 (19.2%) analyses were inaccurate. The performing laboratory was the only factor clearly associated with inaccuracies. The questionnaire results indicated that laboratories encounter significant problems analysing low concentrations (15.4% of all inaccuracies).

CONCLUSIONS:

Results of the PT programme suggest that one out of five measurements is inaccurate. The performing laboratory is the main determinant of inaccuracy, suggesting that internal quality assurance is pivotal in preventing inaccuracies, irrespective of the antifungal drug measured, concentration and analytical equipment.

KEYWORDS:

analytical method; pharmacokinetics; therapeutic drug monitoring

PMID:
25006236
DOI:
10.1093/jac/dku242
[Indexed for MEDLINE]

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