Pexiganan

Pexiganan acetate (MSI 78) is a synthetic cationic peptide (22 amino acids) with antibacterial activity. It is an analogue of magainin 2, which is a host defence peptide isolated from frog skin. The drug is thought to act by disturbing the permeability of the cell membrane or cell wall. Pexiganan acetate has good in vitro activity against Gram-positive and Gram-negative aerobes; 99% of strains were susceptible to the agent using a break-point of 64 mg/L. 89 to 97% of anaerobes were susceptible to pexiganan acetate using the same break-point. After 7 passages in vitro, there was no evidence of resistance to pexiganan acetate among 2 strains of Staphylococcus aureus. In 2 phase III multicentre randomised double-blind trials in diabetic patients with infected foot ulcers, both topical pexiganan acetate 1% and oral ofloxacin 800 mg/day achieved clinical cure or improvement in about 90% of patients. Eradication of pathogens in the 2 studies was achieved in 82% of ofloxacin recipients and 66% of pexiganan acetate recipients at the end of therapy. Limited data indicate that pexiganan acetate is well tolerated.

Background: Pseudomonas aeruginosa is a gram-negative pathogen, associated with a severe mortality rate. It is also difficult to treat due to numerous resistance mechanisms to a wide range of antibiotics. Objective: Evaluate the activity of pexiganan, an antimicrobial peptide, in combination with two clinical antibiotics (azithromycin and tigecycline) that are not active against P. aeruginosa. Methods: Ten clinical P. aeruginosa were isolated from urinary tract infections, blood culture, skin infections and respiratory tract infections. Minimum inhibitory concentrations (MICs) and synergies were evaluated by broth microdilution, checkerboard assays and time-kill studies. In vitro synergy was confirmed with an in vivo experiment using a murine model of sepsis. Results: Pexiganan MICs were included between 2 and 16 mg/L. Tigecycline and azithromycin MICs were high as expected (4-64 mg/L and 32-256 mg/L, respectively). Pexiganan and azithromycin combination resulted to be additive or indifferent while tigecycline and pexiganan combination was synergic against seven out of ten P. aeruginosa and additive against the other strains. In vivo experiment confirmed the in vitro synergy, denoting a significative reduction of bacteria in mice treated with pexiganan and tigecycline combination. Conclusion: Antimicrobial peptides are molecules that could be useful in the fight against infections and pexiganan seems to be one of the most promising. Our results demonstrated that, in association with tigecycline, pexiganan administration could overcome antibiotic resistance and increase the effectiveness of treatment against P. aeruginosa sepsis.

Diabetic foot ulcers (DFUs) are major complications of Diabetes mellitus being responsible for significant morbidity and mortality. DFUs frequently become chronically infected by a complex community of bacteria, including multidrug-resistant and biofilm-producing strains of Staphylococcus aureus and Pseudomonas aeruginosa. Diabetic foot infections (DFI) are often recalcitrant to conventional antibiotics and alternative treatment strategies are urgently needed. Antimicrobial Peptides (AMPs), such as pexiganan and nisin, have been increasingly investigated and reported as effective antimicrobial agents. Here, we evaluated the antibacterial potential of pexiganan and nisin used in combination (dual-AMP) to control the growth of planktonic and biofilm co-cultures of S. aureus and P. aeruginosa clinical strains, co-isolated from a DFU. A DFU collagen three-dimensional (3D) model was used to evaluate the distribution and efficacy of AMPs locally delivered into the model. The concentration of pexiganan required to inhibit and eradicate both planktonic and biofilm-based bacterial cells was substantially reduced when used in combination with nisin. Moreover, incorporation of both AMPs in a guar gum delivery system (dual-AMP biogel) did not affect the dual-AMP antimicrobial activity. Importantly, the application of the dual-AMP biogel resulted in the eradication of the S. aureus strain from the model. In conclusion, data suggest that the local application of the dual-AMPs biogel constitutes a potential complementary therapy for the treatment of infected DFU.