Evaluation of omadacycline against intracellular in an infection model in human macrophages.

Background: Omadacycline is an aminomethylcycline antibiotic in the tetracycline class that was approved by the US FDA in 2018 for the treatment of community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections. It is available in both IV and oral formulations. Omadacycline has broad-spectrum activity and clinical efficacy against infections caused by Gram-positive and Gram-negative pathogens. Omadacycline is being evaluated in a 3 month placebo-controlled Phase 2 clinical trial of oral omadacycline versus placebo in adults with non-tuberculous mycobacteria (NTM) pulmonary disease caused by (NCT04922554).

Objectives: To determine if omadacycline has intracellular antimicrobial activity against NTM, bacteria that can cause chronic lung disease, in an model of intracellular infection.

Methods: Two strains of were used to infect THP-1 macrophages. Intracellular was then challenged with omadacycline and control antibiotics at multiples of the MIC over time to evaluate intracellular killing.

Results: At 16 ×  the MIC at 72 h, omadacycline treatment of intracellular NTM yielded a log reduction in cfu of 1.1 (91.74% reduction in cfu) and 1.6 (97.65% reduction in cfu) consistent with killing observed with tigecycline, whereas amikacin and clarithromycin at 16 ×  the MIC did not show any reduction in cfu against the intracellular .

Conclusions: Omadacycline displayed intracellular activity against within macrophages. The activity was similar to that of tigecycline; as expected, intracellular killing was not observed with clarithromycin and amikacin.