A clear-cut therapeutic range has not been described. British guidelines (1) suggest the use of area under the curve (AUC- estimated from measurements at 1, 4 and 24 hours) over the minimal inhibitory concentration (MIC) of the organism and that >100 using the EUCAST method is associated with higher treatment success. A Brazilian study published recently describes serum levels between 20 and 40 mg/L in patients with neurocryptococcosis and that CSF levels correlate with serum levels. (2) Others (European Conference on Infections in Leukemia) suggest trough levels of > 10-15 mg/L as an alternative (see http://www.ecil-leukaemia.com/telechargements2015/ECIL6-Triazole-TDM-07-12-2015-Lewis-R-et-al.pdf ).
1. Ashbee HR et al. Therapeutic Drug Monitoring (TDM) of Antifungal Agents: Guidelines From the British Society for Medical Mycology. J Antimicrob Chemother. 2014 May;69(5):1162-76. doi: 10.1093/jac/dkt508. Epub 2013 Dec 29.
2.Schiave LA, et al. Fluconazole levels in serum and cerebrospinal fluid according to daily dosage in patients with cryptococcosis and other fungal infections. Braz J Infect Dis. 2018 Jan-Feb;22(1):11-15. doi: 10.1016/j.bjid.2017.10.003. Epub 2017 Nov 13.