To the Editors: Therapeutic drug monitoring (TDM) is necessary for optimizing triazole antifungal therapy in immunocompromised children. However, frequent blood sampling can be invasive and distressing, and particularly burdensome for children undergoing intensive cancer treatments or recipients of hematopoietic cell transplants (HCT).1 Noninvasive TDM methods, such as saliva sampling, offer a promising alternative due to their ease of collection and accessibility.2,3 To date, no published studies have investigated the feasibility of measuring posaconazole concentrations using saliva. Therefore, we aimed to determine whether posaconazole can be detected in the saliva of children undergoing cancer therapy or allogenic HCT. In a 2-year prospective pharmacokinetic study (2023–2025), paired serum and saliva samples were collected after written informed consent from oncology or HCT patients aged 1–98%) in comparison to voriconazole (~58%) and fluconazole (~10%).4 A recent review found that both voriconazole and fluconazole can be reliably detected in saliva.3 For fluconazole, saliva-to-serum concentration ratios averaged 1.21 (±0.31 standard deviation; range: 0.99–1.45). Itraconazole is structurally like posaconazole, has high protein binding (>99%) and has poor detectability in saliva. Two studies in adults detected itraconazole in saliva after oral suspension but not with capsules, likely due to the topical effect. In addition, the active metabolite of itraconazole was not detected, limiting the use of saliva for monitoring this antifungal.3 Overall, our findings show that saliva testing is not feasible for noninvasive TDM of posaconazole in immunocompromised children.
Weerdenburg et al. (Mon,) studied this question.