The FDA's approval of Insmed's inhaled formulation of amikacin for lung disease associated with Mycobacterium avium marked the agency's first use of the Limited Population Pathway for Antibacterial and Antifungal Drugs (LPAD) approval pathway.

Congress established the LPAD under the 21st Century Cures Act as a means of promoting the development and approval of antibacterial and antifungal drugs for serious or life-threatening infections in limited patient populations with unmet need. Earlier in the year, the agency issued a draft guidance on the LPAD, noting that products that are reviewed under this pathway can follow streamlined clinical development strategies that may involve smaller, shorter or fewer clinical trials.

In the case of Insmed's inhaled amikacin, the regulatory green light was granted on the basis of a 336-patient, open-label phase III trial. Patients with refractory M. avium-associated lung disease were randomized to inhaled amikacin plus a background regimen of antibiotics, or to background antibiotics alone. At 6 months, 29% of amikacin-treated patients had no evidence of mycobacteria in their sputum, compared with 9% of patients on background therapy alone.

Injected formulations of amikacin have been in commercial use since the 1970s for the treatment of multidrug-resistant Gram-negative bacteria, non-tubercular mycobacterial infections and other indications.

“We're seeing a lot of early interest among sponsors in using this new pathway, and it's our hope that it'll spur more development and approval of antibacterial drugs for treating serious or life-threatening infections in limited populations of patients with unmet medical needs,” says FDA commissioner Scott Gottlieb.