Lefamulin: A Novel Oral and Intravenous Pleuromutilin for the Treatment of Community-Acquired Bacterial Pneumonia

Lefamulin is a novel oral and intravenous (IV) pleuromutilin developed as a twice-daily treatment for community-acquired bacterial pneumonia (CABP). It is a semi-synthetic pleuromutilin with a chemical structure that contains a tricyclic core of five-, six-, and eight-membered rings and a 2-(4-amino-2-hydroxycyclohexyl)sulfanylacetate side chain extending from C14 of the tricyclic core. Lefamulin inhibits bacterial protein synthesis by binding to the 50S bacterial ribosomal subunit in the peptidyl transferase center (PTC). The pleuromutilin tricyclic core binds to a pocket close to the A site, while the C14 side chain extends to the P site causing a tightening of the rotational movement in the binding pocket referred to as an induced-fit mechanism. Lefamulin displays broad-spectrum antibacterial activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria as well as against atypical bacteria that commonly cause CABP. Pleuromutilin antibiotics exhibit low rates of resistance development and lack cross-resistance to other antimicrobial classes due to their unique mechanism of action. However, pleuromutilin activity is affected by mutations in 23S rRNA, 50S ribosomal subunit proteins rpl C and rpl D, ATP-binding cassette (ABC)-F transporter proteins such as vga (A), and the methyltransferase cfr . The pharmacokinetic properties of lefamulin include: volume of distribution ( V d ) ranging from 82.9 to 202.8 L, total clearance (CL T ) of 19.5 to 21.4 L/h, and terminal elimination half-life ( t 1/2 ) of 6.9–13.2 h; protein binding of lefamulin is high and non-linear. The oral bioavailability of lefamulin has been estimated as 24% in fasted subjects and 19% in fed subjects. A single oral dose of lefamulin 600 mg administered in fasted patients achieved a maximum plasma concentration ( C max ) of 1.2–1.5 mg/L with a time of maximum concentration ( T max ) ranging from 0.8 to 1.8 h, and an area under the plasma concentration-time curve from 0 to infinity (AUC 0−∞ ) of 8.5–8.8 mg h/L. The pharmacodynamic parameter predictive of lefamulin efficacy is the free plasma area under the concentration-time curve divided by the minimum inhibitory concentration ( f AUC 24h /MIC). Lefamulin efficacy has been demonstrated using various animal models including neutropenic murine thigh infection, pneumonia, lung infection, and bacteremia. Lefamulin clinical safety and efficacy was investigated through a Phase II clinical trial of acute bacterial skin and skin s