Monitoring
Liver function tests should be followed on a monthly basis while on azole therapy.
A serum itraconazole level should be checked 2 to 3 weeks after starting therapy to ensure adequate absorption. A serum concentration of more than 1 microgram/mL is considered therapeutic. Repeat levels are generally not needed unless failure of therapy or symptomatic toxicity. Similarly, in patients with central nervous system disease being treated with voriconazole, it is advisable to check a trough level 1 to 2 weeks after starting therapy. Although there are no trials evaluating voriconazole therapeutic drug monitoring in blastomycosis, a serum trough concentration between 1 microgram/mL and 5 to 6 micrograms/mL is likely optimal to balance therapeutic efficacy and risk of toxicity.[53]
While on amphotericin-B therapy, serum potassium, magnesium, and creatinine should be monitored at least twice weekly.
If a urine, serum, cerebrospinal fluid (CSF) or bronchoalveolar lavage Blastomyces dermatitidis antigen was measured and positive at diagnosis, repeating levels every 1 to 3 months can be used to monitor response to therapy. Ideally the antigen is eliminated.
Radiographic abnormalities should be followed up with repeat exams every 1 to 3 months until resolution.
It is important to monitor for drug interactions between the azole antifungals and other medications metabolized by the cytochrome P450 system, particularly warfarin (using INR) or statins (symptoms of rhabdomyolysis). However, routine laboratory monitoring for rhabdomyolysis is not warranted.
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