Antifungal therapeutic drug monitoring: When, how, and why

Phase 1 drug-drug interaction study to assess the effect of CYP3A4 inhibition and pan-CYP induction on the pharmacokinetics and safety of fosmanogepix in healthy participants

Immunocompromised patients are susceptible to fungal infections, and drug-drug interactions with antifungals may occur due to concomitant medications. Fosmanogepix [FMGX; active moiety manogepix (MGX)] targets glycosylphosphatidylinositol-anchored mannoprotein synthesis and maturation, essential for fungal virulence. This phase 1, fixed-sequence study in healthy participants evaluated the effect of strong CYP3A4 inhibitor itraconazole [Cohort 1 (n = 18); FMGX 500 mg intravenous (IV) twice a day (BID )+ itraconazole 200 mg oral once a day (QD)] and pan-CYP inducer rifampin [Cohort 2 (n = 18); FMGX 1,000 mg IV BID + rifampin 600 mg oral QD] on the pharmacokinetics of FMGX and MGX. In cohort 1, geometric mean (GM) MGX Cmax, AUC0-t, and AUCinf were almost similar with and without itraconazole administration. In Cohort 2, GM MGX Cmax was slightly lower and AUC0-t and AUCinf were significantly lower after rifampin administration, with the least squares GM ratio associated 90% confidence intervals (CIs) below 80 - 125% (no effect window). No deaths, serious adverse events (SAEs), or FMGX-related withdrawals were reported. In both cohorts, a total of 188 AEs (n = 30; 186 mild; two moderate) were reported. In all, 37 of 188 AEs (n = 12) were considered FMGX related (most frequent: headache, nausea, and hot flush). Administration of FMGX alone and with itraconazole or rifampin was safe and well tolerated. A strong CYP3A4 inhibitor had no effect on FMGX or MGX exposure. A strong pan-CYP inducer had no effect on FMGX exposure but demonstrated ~45% decrease in MGX exposure.

CLINICAL TRIALS

This study is registered with ClinicalTrials.gov as NCT04166669 and with EudraCT as number 2019-003586-17.

Voriconazole Pharmacokinetics in Critically Ill Patients and Extracorporeal Membrane Oxygenation Support: A Retrospective Comparative Case-Control Study

Voriconazole, an antifungal agent, displays high intra- and inter-individual variability. The predictive pharmacokinetic (PK) index requires a minimum plasma concentration (C_min) in patient serum of between 1-5.5 mg/L. It is common to encounter fungal infections in patients undergoing extracorporeal membrane oxygenation (ECMO) support, and data regarding voriconazole PK changes during ECMO are scarce. Our study compared voriconazole PKs in patients with and without ECMO support in a retrospective cohort of critically-ill patients. Fifteen patients with 26 voriconazole C_min determinations in the non-ECMO group and nine patients with 27 voriconazole C_min determinations in the ECMO group were recruited. The ECMO group had lower C_min (0.38 ± 2.98 vs. 3.62 ± 3.88, p < 0.001) and higher infratherapeutic C_min values (16 vs. 1, p < 0.001) than the non-ECMO group. Multivariate analysis identified ECMO support (-0.668, CI₉₅ -0.978--0.358) and plasma albumin levels (-0.023, CI₉₅ -0.046--0.001) as risk factors for low C_min values. When comparing pre- and post-therapeutic drug optimisation samples from the ECMO group, the dose required to achieve therapeutic C_min was 6.44 mg/kg twice a day. Therapeutic drug optimisation is essential to improve target attainment.

Nasopharyngeal cryptococcosis in a cat: interlaboratory variation in cryptococcal antigen assay test results

Case summary

An indoor-only 6-year-old spayed female domestic cat was evaluated for a history of stertorous respiration. Skull radiographs revealed increased soft tissue density within the caudal aspect of the left nasal cavity. CT and rhinoscopy revealed a mass lesion in the choana, plus a smaller lesion, nearly completely occluding flow through the nasal passages. Rhinoscopy was used to collect a biopsy specimen from a fleshy, tan–yellow mass visualized in the caudal nasopharynx. Histopathology was diagnostic for Cryptococcus species infection and systemic antifungal therapy with fluconazole was initiated. Following a series of discordant results, serum samples were submitted to a veterinary diagnostic laboratory that utilized a cryptococcal antigen latex agglutination system with pretreatment of serum with pronase. Twenty-three months after the initial diagnosis, the cat’s serum cryptococcal antigen titer declined to 1:5 and the cat has responded well to continuing treatment.

Relevance and novel information

This case illustrates challenges associated with discordant test results for cryptococcal antigen among laboratories. Discordancies may be due to differences in assay design, or the underlying disease state itself, or whether serum is pre-treated with pronase; with some tests relying on the training and experience of the operator if the cryptococcal antigen detection test requires a subjective interpretation. It also resolves some confusion in the literature related to the assay types available and terminology used to describe them, and emphasizes the importance of considering cryptococcosis as an important differential for cats with upper respiratory signs, without nasal discharge, even if the cat is kept exclusively indoors.

Advances in antifungal drug measurement by liquid chromatography-mass spectrometry

Fungal infections, especially invasive types, have become a serious healthcare problem as the immunocompromised population increases. There are five main classes of antifungal drugs: polyenes, flucytosine, allylamines, azoles, and echinocandins. Therapeutic drug monitoring (TDM) is justified for flucytosine and triazoles due to their large inter- and intra-individual pharmacokinetic variability and their high tendency for drug-drug interactions. Available methods for measuring these drugs include bioassay, liquid chromatography and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The LC-MS/MS approach is preferred due to its superior analytic sensitivity and specificity. In this review, we highlight TDM methods by LC-MS/MS for these antifungal drugs searchable in PubMed by December 1, 2018. LC-MS/MS methods that were developed for other purposes such as pharmacokinetics or toxicokinetics were also included. We have critically analyzed these methods with an emphasis on sensitivity, specificity, simplicity, throughput and robustness.