Preparation, characterization, and antibacterial activity of tigecycline-loaded, ultrasound-activated microbubbles

Central nervous system infectious disease caused by the multidrug-resistant Acinetobacter baumannii (AB) seriously threatens human life in clinic. Tigecycline has good sensitivity in killing AB, but due to its wide tissue distribution and blood-brain barrier, concentration in cerebrospinal fluid is low, therefore, the clinical effect is limited. Herein, we designed micro-bubbled tigecycline, aimed to enhance its anti-MDRAB effects under ultrasound. The lipid microbubbles with different ratios of lipids to drugs (a ratio of 10:1, 20:1, and 40:1) were prepared by the mechanical shaking method. The morphology, zeta potential and particle size of microbubbles were tested to screen out the much better formulation. Encapsulation efficiency and drug loading amount were determined by ultracentrifugation combined with high-performance liquid chromatography. Then the in vitro antibacterial activity against AB was conducted using the selected ultrasound-activated microbubble. Results showed the selected microbubbles with high encapsulation efficiency and good stability. The mechanical shaking method is feasible for preparation of drug-loaded and ultrasound-activated lipid microbubbles. Using 0.2 mg/mL microbubbles, combined with 1 MHz, 2.5 W/cm2 and 1 min of ultrasound exhibited a potent anit-AB in vitro. This study indicates that tigecycline treatment in form of ultrasound-activated microbubble is a promising strategy against AB infections.