A prospective study on Therapeutic Drug Monitoring guided decision making Of voriconazole therapy for invasive fungal diseases.

Therapeutic Drug monitoring plays an important role in optimizing pharmacotherapy of some drugs by guiding healthcare providers by modifying drug dosing strategies. This procedure involves measuring the concentration of a drug and its metabolite in various biological samples to ensure that the drug levels are within a target therapeutic range to achieve treatment success yet avoid dose related toxicity. Monitoring of effectiveness and safety of patients on voriconazole is mainly based on clinical judgement as the therapeutic drug monitoring facility is not available in majority of the public hospitals in India. But nonetheless, use of voriconazole is progressively increasing especially in immunosuppressed patients and it would be worthwhile to evaluate clinical outcomes in those patients using therapeutic drug monitoring. In tropical countries like India where the patient burden suffering from invasive fungal diseases requiring voriconazole therapy is increasing, this study will generate evidence to document whether therapeutic drug monitoring for voriconazole is beneficial in identifying those patients requiring dose modification in resource limited settings like ours. The study may also help us in identifying early cases who are likely to be non responders or patients developing toxicity. These patient subgroups can have their drug doses modified or can be switched over to other alternatives. Lastly, we would like to add that there are very few documented studies regarding therapeutic drug monitoring of voriconazole in India and almost none in Eastern India. This few data is inconclusive for generalizing any recommendations in the whole country considering potential genetic variations. Given the potential impact of regional genetic variations, sufficient documentation is needed in Eastern India to define the utility of therapeutic drug monitoring of voriconazole in the Indian setting.

Voriconazole is a third-generation triazole antifungal agent, used for treatment and prevention of invasive fungal diseases. It is mainly used as first-line treatment for Allergic Bronchopulmonary Aspergillosis (ABPA), a severe fungal infection primarily caused by Aspergillus species. One of the distinctive features of voriconazole is its wide inter-patient variability in drug concentrations, which can be attributed to various factors like non-linear pharmacokinetics genetic polymorphism of its main metabolizing enzyme i.e. CYPC2C19 and patient characteristics such as age, weight and liver function. The large variability in voriconazole plasma concentrations together with the narrow therapeutic window make individualized dosing adjustments based on TDM necessary to optimize therapeutic response and to minimize the probability of toxicity.

Different methods, including agar well diffusion bioassays, high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS) and enzyme immunoassays (EIA) have been described for the determination of voriconazole in biological fluids.

Though some international organizations like the Japanese Antimicrobial Therapeutic Drug Monitoring Committee guidelines have suggested trough plasma voriconazole concentration based monitoring while few other studies have failed to show evidence of its utility. To the best of our knowledge, only one published study from New Delhi on pediatric patients with hematological malignancies failed to show any significant differences in outcome. However, the study had a small sample size.

Monitoring of effectiveness and safety of patients on voriconazole is mainly based on clinical judgment as TDM facility of voriconazole is not available in majority of the public hospitals of India. But none the less, use of voriconazole is progressively increasing especially in immune-suppressed patients and it would be worthwhile to evaluate clinical outcomes in those with TDM. We foresee that by TDM early detection of patients with sub or supra therapeutic concentrations can lead to better clinical outcomes. Therefore, in the backdrop of such conflicting evidence about its utility we propose to undertake a prospective study to evaluate the effectiveness and safety of TDM in patients on voriconazole for invasive fungal diseases.