Liposome-encapsulation has been suggested as method to improve the efficacy of ciprofloxacin against the intracellular pathogen, Francisella tularensis. Early work with a prototype formulation, evaluated for use against the F. tularensis live vaccine strain, showed that a single dose of liposomal ciprofloxacin given by the intranasal or inhalational route could provide protection in a mouse model of pneumonic tularemia. Liposomal ciprofloxacin offered better protection than ciprofloxacin given by the same routes. Liposomal ciprofloxacin has been further developed by Aradigm Corporation for Pseudomonas aeruginosa infections in patients with cystic fibrosis and non-cystic fibrosis bronchiectasis. This advanced development formulation is safe, effective and well tolerated in human clinical trials. Further evaluation of the advanced liposomal ciprofloxacin formulation against the highly virulent F. tularensis Schu S4 strain has shown that aerosolised CFI (Ciprofloxacin encapsulated in liposomes for inhalation) provides significantly better protection than oral ciprofloxacin. Thus, liposomal ciprofloxacin is a promising treatment for tularemia and further research with the aim of enabling licensure under the animal rule is warranted.

Liposome-encapsulated ciprofloxacin for inhalation (CFI) was investigated as a putative postexposure therapeutic for two strains ofFrancisella tularensis. The efficacies of oral ciprofloxacin and intranasally instilled CFI could not be distinguished in a mouse model of infection with theF. tularensislive vaccine strain (LVS), where a single dose of either formulation offered full protection against a lethal challenge. However, mouse studies with the more virulent Schu S4 strain ofF. tularensisdemonstrated that a higher level of protection against a lethal aerosol infection is provided by CFI than by oral ciprofloxacin. In addition, using this infection model, it was possible to discriminate the efficacy of intranasally instilled CFI from that of aerosolized CFI, with aerosolized CFI providing full protection after just a single dose. The improved efficacy of CFI compared to oral ciprofloxacin is likely due to the high sustained concentrations of ciprofloxacin in the lung. In summary, CFI may be a promising therapy, perhaps enabling the prophylactic regimen to be shortened, for use in the event of a deliberate release ofF. tularensis. The prophylactic efficacy of CFI against other biological warfare (BW) threat agents also warrants investigation.

Inhalation of Yersinia pestis can lead to pneumonic plague, which without treatment is inevitably fatal. Two novel formulations of liposome-encapsulated ciprofloxacin, ‘ciprofloxacin for inhalation’ (CFI, Lipoquin®) and ‘dual release ciprofloxacin for inhalation’ (DRCFI, Pulmaquin®) containing CFI and ciprofloxacin solution, are in development. These were evaluated as potential therapies for infection with Y. pestis. In a murine model of pneumonic plague, human-like doses of aerosolized CFI, aerosolized DRCFI or intraperitoneal (i.p.) ciprofloxacin were administered at 24 hours (representing prophylaxis) or 42 hours (representing treatment) post-challenge. All three therapies provided a high level of protection when administered 24 hours post-challenge. A single dose of CFI, but not DRCFI, significantly improved survival compared to a single dose of ciprofloxacin. Furthermore, single doses of CFI and DRCFI reduced bacterial burden in lungs and spleens to below the detectable limit at 60 hours post-challenge. When therapy was delayed until 42 hours post-challenge, a single dose of CFI or DRCFI offered minimal protection. However, single doses of CFI or DRCFI were able to significantly reduce the bacterial burden in the spleen compared to empty liposomes. A three-day treatment regimen of ciprofloxacin, CFI, or DRCFI resulted in high levels of protection (90% -100% survival). This study suggests that CFI and DRCFI may be useful therapies for Y. pestis infection, both as prophylaxis and for the treatment of plague.

Background/Objectives: Q fever, caused by Coxiella burnetii, is typically treated with doxycycline, but its efficacy is limited in chronic cases and may be poorly tolerated. Systemic ciprofloxacin shows limited activity for acute Q fever. However, inhaled liposomal formulations may provide therapeutic benefit. Methods: Two inhaled ciprofloxacin formulations (Lipoquin^® and Apulmiq^®) were evaluated in an A/J mouse model of Q fever and compared with intraperitoneal ciprofloxacin and oral doxycycline. Initially, pharmacokinetic studies were performed to determine an appropriate dosing regimen for the inhaled ciprofloxacin formulations. A separate cohort of mice were then infected with C. burnetii and treated once daily via nebulisation with Lipoquin or Apulmiq, initiated at 24, 48, or 72 h post-challenge. Clinical signs, weight change, splenomegaly, bacterial burden, and lung histopathology were evaluated. Results: Pharmacokinetic analysis confirmed sustained lung concentrations of inhaled ciprofloxacin, supporting once-daily dosing. Inhaled Lipoquin and Apulmiq significantly reduced clinical signs, weight loss, splenomegaly, and pulmonary bacterial burden compared to untreated controls and doxycycline-treated mice. Histopathology revealed decreased lung inflammation and lesion severity following inhalational dosing. Systemic ciprofloxacin slightly reduced splenic bacterial burden but was less effective in controlling pulmonary infection. Conclusions: Inhaled liposomal ciprofloxacin demonstrated superior protection and reduced respiratory manifestations of Q fever compared to doxycycline and systemic ciprofloxacin. These findings suggest inhaled formulations may represent a viable alternative for the treatment of Q fever pneumonia. Further studies are needed to evaluate clinical applicability and long-term outcomes.