Efficient entrapment of amikacin and teicoplanin in liposomes

Liposomes for Antibiotic Encapsulation and Delivery

When antibiotics are administered, orally or intravenously, they pass through different organs and layers of tissue on their way to the site of infection; this can cause dilution and/or intoxication. To overcome these problems, drug delivery vehicles have been used to encapsulate and deliver antibiotics, improving their therapeutic index while minimizing their adverse effects. Liposomes are self-assembled lipid vesicles made from at least one bilayer of phospholipids with an inner aqueous compartment. Liposomes are attractive vehicles to deliver antibiotics because they can encapsulate both hydrophobic and hydrophilic antibiotics, they have low toxicity, and they can change the biodistribution of the drug. Furthermore, liposomes have been approved by regulatory agencies. However, most developmental and mechanistic research in the field has been focused on encapsulation and delivery of anticancer drugs, a class of molecules that differ significantly in chemistry from antibiotics. In this critical Review, we discuss the state of knowledge regarding the design of liposomes for encapsulation and delivery of antibiotics and offer insight into the challenges and promises of using liposomes for antibiotic delivery.

Liposomal Nanovesicles for Efficient Encapsulation of Staphylococcal Antibiotics

Liposomes are attractive vehicles for localized delivery of antibiotics. There exists, however, a gap in knowledge when it comes to achieving high liposomal loading efficiencies for antibiotics. To address this issue, we investigated three antibiotics of clinical relevance against staphylococcal infections with different hydrophilicity and chemical structure, namely, vancomycin hydrochloride, teicoplanin, and rifampin. We categorized the suitability of different encapsulation techniques on the basis of encapsulation efficiency, lipid requirement (important for avoiding lipid toxicity), and mass yield (percentage of mass retained during the preparation process). The moderately hydrophobic (teicoplanin) and highly hydrophobic (rifampin) antibiotics varied significantly in their encapsulation load (max 23.4 and 15.5%, respectively) and mass yield (max 74.1 and 71.8%, respectively), favoring techniques that maximized partition between the aqueous core and the lipid bilayer or those that produce oligolamellar vesicles, whereas vancomycin hydrochloride, a highly hydrophilic molecule, showed little preference to any of the protocols. In addition, we report significant bias introduced by the choice of analytical method adopted to quantify the encapsulation efficiency (underestimation of up to 24% or overestimation by up to 57.9% for vancomycin and underestimation of up to 61.1% for rifampin) and further propose ultrafiltration and bursting by methanol as the method with minimal bias for quantification of encapsulation efficiency in liposomes. The knowledge generated in this work provides critical insight into the more practical, albeit less investigated, aspects of designing vesicles for localized antibiotic delivery and can be extended to other nanovehicles that may suffer from the same biases in analytical protocols.

Preparation, properties and the effects of amikacin, netilmicin and tobramycin in free and liposomal formulations on Gram-negative and Gram-positive bacteria

The most common problems limiting the medical use of aminoglycosides have been the nephro- and oto-toxicities and the increasing bacterial resistance. It has been shown that encapsulation of drugs into liposomes enhances their efficacy while reducing their toxicities. The present in vitro study was designed to evaluate the antimicrobial activities of free and liposomal amikacin, netilmicin and tobramycin. We, therefore, encapsulated these drugs into liposomes prepared by sonication. The drug contained in liposomes was measured by enzyme multiplied immunoassay technique (EMIT) after lysis of the vesicles by 0.2% Triton X-100. The comparative encapsulation efficiency of the three antibiotic preparations was assessed. Aminoglycosides kinetic release from liposomes in presence of normal human sera was also studied in vitro over a 48 h period at 37 degrees C under 5% CO(2). The MICs of these encapsulated drugs to Pseudomonas aeruginosa, Xanthomonas maltophilia, Escherichia coli, Streptococcus faecalis and Staphylococcus aureus were determined and compared to those of respective free drugs using an agar dilution method. The amikacin and tobramycin encapsulation efficiencies were significantly (P </= 0.05) higher (5.36% +/- 0.17 and 5.06% +/- 0.10) than those of netilmicin (3% +/- 0.18). However, in presence of sera, liposomal retention of netilmicin was significantly (P </= 0.05) lower (61.88 +/- 0.14%) than that of amikacin (81.45 +/- 0.64%) and tobramycin (94.07 +/- 0.18%) after 1 h of incubation and then remained nearly constant over an 48 h period of the study. The MICs of liposomal netilmicin against all bacterial strains tested were reduced, compared to those of free netilmicin. However, liposomal amikacin and tobramycin MICs were nearly similar to those of free respective drugs. Overall, liposomal netilmicin appears to be a promising approach in the management of Gram-positive and Gram-negative bacterial infections and should be further evaluated in in vivo experiments.

Liposomes as drug delivery systems for the treatment of TB

TB is an infectious disease that is far from being eradicated and controlled. The treatment for TB is associated with noncompliance to therapy because it consists of a long-term treatment with a multidrug combination and is associated with the appearance of several side effects. Liposomal formulations are being developed with first- and second-line antibiotics, and might be an extremely useful alternative to current therapies. This article will thus focus on the role of liposomes as nanodelivery systems for the treatment of TB. Among several advantages, these nanocarriers allow an increase in the bioavailability of antibiotics, which may lead to a reduction in the time of treatment. Results obtained with such nanosystems, although preliminary, are promising and are perspective of the use of inhalation for TB treatment.

Treatment of osteomyelitis by liposomal gentamicin-impregnated calcium sulfate

OBJECTIVES

Traditional therapy of staphylococcal osteomyelitis is ineffective in producing complete sterilization of infected bones due to the formation of the Staphylococcus aureus biofilms. The aim of this study was to develop a new drug-delivery system of antibiotics for treatment of chronic experimental osteomyelitis.

METHODS

In the current work, cationic liposomal gentamicin was prepared and impregnated in calcium sulfate (CS), and tested for anti-biofilm activities in vitro and in vivo.

RESULTS AND CONCLUSIONS

The combination of liposomal gentamicin and CS showed initial burst-release of active liposomal gentamicin and had continuous-release (12 days). Liposomal gentamicin released from CS had the same anti-biofilm activity with the liposomal gentamicin prepared freshly. Meanwhile, both agents were more effective relative to free gentamicin at low drug concentration. Therapeutic trials with antibiotics given intravenously revealed that free gentamicin for 14 days was ineffective in sterilizing bone. Treatment with liposomal gentamicin for 14 days resulted in recovery of 33.3% of treated animals, which was the lower slightly than the result treated with implantation of gentamicin-impregnated CS (66.7%). Complete sterilization of bone tissues on cultures (100% cure) was obtained only in the group of liposomal gentamicin-impregnated CS treated for 14 days. The new drug-delivery system was effective in preventing biofilm infection in a contaminated defect, and it could also be used clinically for bacterial infections in the conditions like plaque formation or in arresting biofilm formation in the implanted devices or dead bone of osteomyelitis.

Treatment of experimental osteomyelitis by liposomal antibiotics

OBJECTIVES

Traditional antibiotic therapy of staphylococcal osteomyelitis by a single drug or a drug combination is ineffective in producing complete sterilization of infected bones. The aim of this study was to develop a non-traditional delivery system of antibiotics for treatment of chronic experimental osteomyelitis.

METHODS

In the current work, ciprofloxacin and vancomycin were encapsulated in a cationic, anionic or neutral liposomal formulation. For prolonged circulation in serum, liposomal dispersions (<100 nm in diameter) were sonicated for different times (20, 40, 60 or 80 s), and tested for antibacterial activities.

RESULTS AND CONCLUSIONS

Liposomes sonicated for 40 s gave the highest antibacterial activities in vitro. Since cationic liposomes trapped the highest percentage of antibiotics, and enhanced antibacterial activity above that of the free drugs, they were used for therapeutic trials to treat chronic staphylococcal osteomyelitis induced in rabbits. Therapeutic trials with antibiotics given intravenously revealed that, free ciprofloxacin or vancomycin given alone for 14 days was ineffective in sterilizing bone. Combination therapy with free ciprofloxacin and vancomycin for 14 days was more effective. However, this group showed renal dysfunction and severe diarrhoea, which resulted in loss of 33.3% of treated animals. Treatment with liposomal forms of either drug for 7 days was ineffective. Meanwhile, combination therapy in liposomal form for 7 days was more effective. Complete sterilization of bone tissues on cultures (100% cure) was obtained only in the group treated for 14 days with the combination of both drugs in liposomal form. Moreover, liposomal formulations showed much lower nephrotoxicity and a lower incidence of severe diarrhoea than that induced by free drugs.