5-Flucytosine Longitudinal Antifungal Susceptibility Testing of Cryptococcus neoformans: A Substudy of the EnACT Trial Testing Oral Amphotericin

Thomas C McHale; Andrew Akampurira; Elliot S Gerlach; Atukunda Mucunguzi; Melanie R Nicol; Darlisha A Williams; Kirsten Nielsen; Tihana Bicanic; Ann Fieberg; Biyue Dai; David B Meya; David R Boulware; ENACT Trial Team

doi:10.1093/ofid/ofad596

5-Flucytosine Longitudinal Antifungal Susceptibility Testing of Cryptococcus neoformans: A Substudy of the EnACT Trial Testing Oral Amphotericin

Open Forum Infect Dis. 2023 Nov 29;10(12):ofad596. doi: 10.1093/ofid/ofad596. eCollection 2023 Dec.

Authors

Collaborators

ENACT Trial Team:
Enock Kagimu, Abdu K Musubire, Lillian Tugume, Kenneth Ssebambulidde, John Kasibante, Laura Nsangi, Timothy Mugabi, Jane Gakuru, Sarah Kimuda, Derrick Kasozi, Suzan Namombwe, Isaac Turyasingura, Morris K Rutakingirwa, Edward Mpoza, Enos Kigozi, Conrad Muzoora, Jayne Ellis, Caleb P Skipper, Darlisha A Williams, Kathy H Hullsiek, Mahsa Abassi, Asmus Tukundane, Jane F Ndyetukira, Cynthia Ahimbisibwe, Alisat Sadiq, Florence Kugonza, Shifa Nabbale, Tadeo Kiiza, Alice Namudde, Tony Luggya, Richard Kwizera, Michael Okiror, Dora Babirye, Catherine Nanteza, Susan Mulwana, Rhona Muyise, John Kisembo, Andrew Luswata, Carol Namujju, Eva Laker, Stewart Walukaga, Minda Liu, Nicole Engen, Abduljewad Wele, Irene Rwomushana, Mable Kabahubya, Michael Ssemusu, James Mwesigye, Joan Rukundo, Samuel Jjunju

Affiliations

¹ Department of Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
² Infectious Diseases Institute, Makerere University, Kampala, Uganda.
³ Department of Microbiology & Immunology, University of Minnesota, Minneapolis, Minnesota, USA.
⁴ Department of Experimental and Clinical Pharmacology, University of Minnesota, Minneapolis, Minnesota, USA.
⁵ Institute of Infection and Immunity, St Georges, University of London, London, UK.
⁶ Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, Minnesota, USA.

Abstract

Background: The EnACT trial was a phase 2 randomized clinical trial conducted in Uganda, which evaluated a novel orally delivered lipid nanocrystal (LNC) amphotericin B in combination with flucytosine for the treatment of cryptococcal meningitis. When flucytosine (5FC) is used as monotherapy in cryptococcosis, 5FC can induce resistant Cryptococcus mutants. Oral amphotericin B uses a novel drug delivery mechanism, and we assessed whether resistance to 5FC develops during oral LNC-amphotericin B therapy.

Methods: We enrolled Ugandans with HIV diagnosed with cryptococcal meningitis and who were randomized to receive 5FC and either standard intravenous (IV) amphotericin B or oral LNC-amphotericin B. We used broth microdilution to measure the minimum inhibitory concentration (MIC) of the first and last cryptococcal isolates in each participant. Breakpoints are inferred from 5FC in Candida albicans. We measured cerebral spinal fluid (CSF) 5FC concentrations by liquid chromatography and tandem mass spectrometry.

Results: Cryptococcus 5FC MIC₅₀ was 4 µg/mL, and MIC₉₀ was 8 µg/mL. After 2 weeks of therapy, there was no evidence of 5FC resistance developing, defined as a >4-fold change in susceptibility in any Cryptococcus isolate tested. The median CSF 5FC concentration to MIC ratio (interquartile range) was 3.0 (1.7-5.5) µg/mL. There was no association between 5FC/MIC ratio and early fungicidal activity of the quantitative rate of CSF yeast clearance (R² = 0.004; P = .63).

Conclusions: There is no evidence of baseline resistance to 5FC or incident resistance during combination therapy with oral or IV amphotericin B in Uganda. Oral amphotericin B can safely be used in combination with 5FC.

Keywords: 5-flucytosine resistance; antifungal resistance; antifungal susceptibility testing; cryptococcal meningitis.

Abstract

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