Drug Exposure and Minimum Inhibitory Concentration in the Treatment of MAC Lung Disease

This is an observational cohort study conducted to enrol consenting adult patients with culture-positive MAC lung disease in study hospital (n=100). The diagnosis and treatment of MAC lung disease will adhere to the ATS/ERS/ESCMID/IDSA and Chinese national guidelines (9, 10). Patients treated with a regimen composed of macrolides, rifamycin and ethambutol at minimum are screened for eligibility. Detailed demographic, behaviour, clinical and laboratory information will be recorded at baseline. Respiratory samples (sputum and/or bronchoalveolar lavage fluid) will be collected at baseline and once every 3 months until treatment completion for mycobacterial culture using BACTEC MGIT 960. Time to mycobacterial culture positivity (TTP) will be recorded to estimate the bacterial load as an alternative for colony forming units count. MIC determination will be performed for baseline, six-month and/or the last available positive culture during treatment with the Sensititre™ SLOMYCO2 Susceptibility Testing Plate, to assess the development of acquired drug resistance.

Drug concentrations will be measured for all study patients at one month after treatment initiation. Rich blood sampling (0, 1, 2, 4, 6 and 8 hours after drug intake) will be implemented for the first 30 patients aged < 65 years to enable the development of population pharmacokinetic models. A limited sampling strategy (2 and 6 hours after drug intake) will be applied for the rest patients to increase the feasibility of study. Additional blood sampling will be given for patients with poor treatment response at six months with limited sampling strategy. The developed pharmacokinetic models will be used to accurately calculate the area under the plasma concentration versus time curve (AUC) and peak plasma concentration (Cmax), as the main exposure variables. To comprehensively assess the response to MAC treatment, mycobacterial culture, lung function test, computerized tomography (CT) scan and questionnaires for well-being will be taken regularly in this study. The final treatment outcome is recorded at the end of MAC treatment and defined according to an NTM-NET consensus statement (8). Post-treatment visits are given at 6 and 12 months after treatment completion to assess the recurrence of MAC lung disease.

Together with bacteria MIC and clinical data, the Cmax/MIC and AUC/MIC for antimycobacterial drugs will be explored to deepen our understandings on the correlation of pharmacokinetic and/or pharmacodynamic indices with treatment response, which may guide development of new dosing strategies.

Inclusion criteria

• Culture-positive MAC lung disease
• MAC treatment at the Shanghai Pulmonary Hospital
• A regimen composed of at least the core drugs, i.e., macrolides, rifamycin and ethambutol, in doses not lower than recommended according to the ATS/ERS/ESCMID/IDSA and Chinese national guidelines
• Written informed consent

Exclusion criteria

• Pregnancy
• Confirmed mixed infection with mycobacterial species, including M.tuberculosis and other NTM species
• Ongoing with any antimycobacterial treatment for more than one month, including tuberculosis and NTM
• Patients admitted to the intensive care unit
• Off-label use for any study drugs, such as inhalation of amikacin