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Antimicrobial Agents and Chemotherapy, January 1998, p. 129-134, Vol. 42, No. 1
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Optimizing the Correlation between Results of Testing In Vitro and Therapeutic Outcome In Vivo for Fluconazole by Testing Critical Isolates in a Murine Model of Invasive Candidiasis

John H. Rex,1,* Page W. Nelson,1 Victor L. Paetznick,1 Mario Lozano-Chiu,1 A. Espinel-Ingroff,2 and Elias J. Anaissie3

Division of Infectious Diseases, Department of Internal Medicine, Center for the Study of Emerging and Reemerging Pathogens, University of Texas Medical School, Houston, Texas 770301; Division of Infectious Diseases, Medical College of Virginia-VCU, Richmond, Virginia 232983; and Section of Oncologic Emergencies, Division of Hematology/Oncology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 772052

Received 7 July 1997/Returned for modification 12 August 1997/Accepted 17 October 1997

The trailing growth phenomenon seen when determining the susceptibilities of Candida isolates to the azole antifungal agents makes consistent endpoint determination difficult, and the M27-A method of the National Committee for Clinical Laboratory Standards addresses this problem by requiring an 80% reduction in growth after 48 h of incubation. For some isolates, however, minor variations of this endpoint criterion can produce up to 128-fold variations in the resulting MIC. To investigate the significance of this effect, isolates of Candida that exhibited various forms of trailing growth when tested against fluconazole were identified. The isolates were examined in a murine model of invasive candidiasis and were ranked by their relative response to fluconazole by using both improvement in survival and reduction in fungal burden in the kidney. The resulting rank order of in vivo response did not match the MICs obtained by using the M27-A criterion, and these MICs significantly overestimated the resistance of three of the six isolates tested. However, if the MIC was determined after 24 h of incubation and the endpoint required a less restrictive 50% reduction in growth, MICs which better matched the in vivo response pattern could be obtained. Minor variations in the M27-A endpoint criterion are thus required to optimize the in vitro-in vivo correlation for isolates that demonstrate significant trailing growth when tested against fluconazole.

* Corresponding author. Mailing address: 6431 Fannin, 1728 JFB, Houston, TX 77030. Phone: (713) 500-6738. Fax: (713) 500-5495. E-mail: jrex{at}heart.med.uth.tmc.edu.

Antimicrobial Agents and Chemotherapy, January 1998, p. 129-134, Vol. 42, No. 1
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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