Enhanced taxane uptake into bladder tissues following co-administration with either mitomycin C, doxorubicin or gemcitabine: association to exfoliation processes.

OBJECTIVE: To investigate the effect of three anticancer drugs (mitomycin c (MMC), doxorubicin or gemcitabine) on bladder wall morphology and the uptake of paclitaxel or docetaxel following coadministration. The primary objective of this study was to measure the uptake of MMC, doxorubicin or gemcitabine with or without exposure of the tissue to amine terminated cationic nanoparticles (CNPs) and to investigate any possible exfoliation effects of the three drugs on intact bladder tissue. The secondary objective was to investigate the uptake of taxane drugs (docetaxel, DTX) and paclitaxel, (PTX) from surfactant micelle formulations in the presence of MMC, doxorubicin or gemcitabine. MATERIALS AND METHODS: Sections of fresh pig bladder tissue were incubated in Franz diffusion cells with the urothelial side exposed to solutions of doxorubicin, MMC and gemcitabine containing radioactive drug for 90 min. Some tissue samples were simultaneously exposed to each of the three drugs in combination with the surfactant micelle formulations of PTX (Taxol) or DTX (Taxotere). Tissue sections were then cryostat sectioned for drug quantitation by liquid scintillation counting or fixed for scanning electron microscopy and haematoxylin and eosin staining. RESULTS: All three drugs caused exfoliation of the urothelial layer of bladder tissues. Drug uptake studies showed that all three drugs effectively penetrated the lamina propria through to the muscular layer over a 2-h incubation and these levels were unaffected by pre-treatment with CNPs. The uptake levels of the taxane drugs PTX and DTX were significantly enhanced following simultaneous treatment of bladders with MMC, doxorubicin or gemcitabine. CONCLUSION: The exfoliation effects of MMC, doxorubicin and gemcitabine allow for good tissue penetration of these drugs with no additional effect from CNP treatment of bladders. The observed exfoliation effect of these amine-containing drugs probably arises from a cationic interaction with the mucus and urothelium cell layer in a manner similar to that previously reported for CNPs. These studies suggest that the lack of long-term clinical efficacy of these drugs may not arise from poor intravesical drug penetration but may result from a rapid diffusion of the drugs into the deeper vascularised muscular region with rapid drug clearance. The enhanced uptake of PTX or DTX following co-administration with MMC, doxorubicin or gemcitabine probably arises from the removal of the urothelial barrier by exfoliation allowing for improved taxane partitioning into superficial layers. These effects may allow for dual drug intravesical strategies offering greatly improved taxane uptake and potential additive drug effects for improved efficacy.

Tissue Permeability Effects Associated with the Use of Mucoadhesive Cationic Nanoformulations of Docetaxel in the Bladder.

PURPOSE: Recently, efficacy studies in mice have shown that amine-terminated cationic (CNP) nanoparticulate carriers of DTX offer an improved formulation of the drug for intravesical delivery. It is hypothesized that this improved efficacy may arise from a carrier mediated bladder exfoliation process that removes the urothelial barrier allowing for increased drug uptake into bladder tissue. The objective of this study was to investigate exfoliation processes in fresh pig's bladders (ex vivo) exposed to three cationic polyglycerols with increasing degrees of amination (denoted 350, 580 and 780). The study also compared the tissue depth profile of DTX uptake into these tissues using these different carriers. MATERIALS AND METHODS: Aminated polyglycerols were synthesized and characterized in the laboratory with low (CNP-360), medium (CNP-580) and high (CNP-780) levels of amine content. CNP-based DTX solutions and commercial DTX solutions in polysorbate 80 (Taxotere®) were doped with (3)H-radiolabeled DTX and prepared by solvent evaporation from acetonitrile, followed by drying and reconstitution in pH 6.4 buffer. Sections of fresh pig's bladder tissue were clamped into Franz diffusion cells and the urothelial side was exposed to the DTX solutions for 2 h. Tissue sections were then frozen for sectioning by cryotome sectioning and subsequently processed for drug analysis by liquid scintillation counting. Alternatively tissue sections were fixed in 2% glutaraldehyde and 2% paraformaldehyde in 0.1 M sodium cacodylate buffer for the purposes of scanning electron microscopy (SEM). RESULTS: Exposure of the urothelial surface to the amine-terminated polyglycerol solutions resulted in the exfoliation of bladder tissues in a time- and concentration-dependent manner. Exfoliation was significantly more pronounced when using CNPs with a medium or high levels of amination whereas only minor levels of exfoliation were seen with low levels. Following incubation of tissues in Tween-based commercial formulations (Taxotere) of DTX (0.5 mg/mL) the drug was detectable at low levels (10-40 µg/g tissue) in all depths of tissue. Similar drug uptake was observed using the CNP-360 formulation. However drug uptake levels were increased to 60-100 µg/g tissue when samples were incubated with either the CNP-580 or CNP-780 formulations. CONCLUSION: The use of cationic polyglycerols with higher levels of amine termination allows for an enhanced uptake of DTX into bladder tissues as compared to commercial (Taxotere) formulations. These increased drug levels probably arise from exfoliation processes resulting in a temporary elimination of the urothelial permeability barrier and increased drug penetration into the tissue.

The use of tissue sealants to deliver antibiotics to an orthopaedic surgical site with a titanium implant.

BACKGROUND: Orthopaedic surgery is associated with unacceptable infection rates that respond poorly to systemic antibiotics. The objective of this study was to use an animal model for orthopaedic implant infection to examine the ability of a new-generation fibrin tissue sealant to effectively deliver antibiotics to the surgical site. METHODS: The antibiotics cefazolin, fusidic acid or 5-fluorouracil were blended into Vitagel tissue sealant. The release rate of the drugs was measured using HPLC methods and bioactivity was measured by the zone of inhibition method with pathogenic Staphylococcus aureus. The antibiotic activity of the drug-loaded sealant was then tested in rats using infected orthopaedic surgical sites (titanium clip on spine). Efficacy was evaluated by residual bacterial counts on clips, clinical observations of infection, and histological findings. RESULTS: The drugs were released in a controlled manner over 2-4 days. All three antibiotics demonstrated strong antibacterial activity when released from the sealants. None of the treated animals demonstrated systemic illness. Post mortem dissection revealed a well-encapsulated abscess surrounding the titanium clip with erosion of the bony process. Using an inoculum of 1-5 × 10(3) CFU, treatment with antibiotic-loaded fibrin sealant demonstrated reduced infective swelling and reduced bacterial counts on surgical clip swabs compared to control rats or rats treated with antibiotic only. This model allowed for almost 100 % infectivity with a 0 % mortality rate due to infection, mimicking the clinical features of human implant infection. CONCLUSION: The results support the use of antibiotic-loaded commercially available fibrin sealants to prevent infection after implant surgery.

Tissue uptake of docetaxel loaded hydrophobically derivatized hyperbranched polyglycerols and their effects on the morphology of the bladder urothelium.

Recently, we have reported that docetaxel (DTX) loaded, amine terminated hyperbranched polyglycerol (HPG-C(8/10)-MePEG-NH(2)) nanoparticles significantly increased drug uptake in mouse bladder tissues and was the most effective formulation to significantly inhibit tumor growth in an orthotopic model of bladder cancer. The objective of this study was to investigate the effects of HPG-C(8/10)-MePEG-NH(2) nanoparticles on bladder urothelial morphology and integrity, DTX uptake and permeability in bladder tissue and the extent of bladder urothelial recovery following exposure to, and then washout of, HPG-C(8/10)-MePEG-NH(2) nanoparticles. HPG-C(8/10)-MePEG-NH(2) nanoparticles significantly increased the uptake of DTX in both isolated pig bladder as well as in live mouse bladder tissues. Furthermore, HPG-C(8/10)-MePEG-NH(2) nanoparticles were demonstrated to increase the permeability of the urinary bladder wall by causing changes to the urothelial barrier function and morphology through opening of tight junctions and exfoliation of the superficial umbrella cells. These data suggest that exfoliation may be triggered by an apoptosis mechanism, which was followed by a rapid recovery of the urothelium within 24 h post-instillation of HPG-C(8/10)-MePEG-NH(2) nanoparticles. HPG-C(8/10)-MePEG-NH(2) nanoparticles cause significant but rapidly recoverable changes in the bladder urothelial morphology, which we believe may make them suitable for increasing drug permeability of bladder tissue and intravesical drug delivery.

In vivo evaluation of mucoadhesive nanoparticulate docetaxel for intravesical treatment of non-muscle-invasive bladder cancer.

PURPOSE: The present work describes the development and in vitro and in vivo evaluation of a mucoadhesive nanoparticulate docetaxel (DTX) formulation for intravesical bladder cancer therapy. EXPERIMENTAL DESIGN: Mucoadhesive formulations based on hyperbranched polyglycerols (HPG), hydrophobically derivatized with C(8)/C(10) alkyl chains in the core and modified with methoxy-polyethylene glycol (MePEG) and amine groups in the shell (HPG-C(8/10)-MePEG-NH(2)) were synthesized and DTX was loaded into these by a solvent evaporation method. Both low-grade (RT4, MGHU3) and high-grade (UMUC3) human urothelial carcinoma cell lines were treated with various concentrations of DTX formulations in vitro. KU7 cells that stably express firefly luciferase (KU7-luc) were inoculated in female nude mice by intravesical instillation and quantified using bioluminescence imaging. Mice with established KU7-luc tumors were given a single intravesical instillation with PBS, Taxotere (DTX from Sanofi-aventis), and DTX-loaded HPG-C(8/10)-MePEG and/or HPG-C(8/10)-MePEG-NH(2). Drug uptake was conducted using LC/MS-MS (liquid chromatography/tandem mass spectrometry) and tumor microenvironment and uptake of rhodamine labeled HPGs was assessed. RESULTS: In vitro, all DTX formulations potently inhibited bladder cancer proliferation. However, in vivo, DTX-loaded HPG-C(8/10)-MePEG-NH(2) (mucoadhesive DTX) was the most effective formulation to inhibit tumor growth in an orthotopic model of bladder cancer. Furthermore, mucoadhesive DTX significantly increased drug uptake in mouse bladder tissues. In addition, rhodamine labeled HPG-C(8/10)-MePEG-NH(2) showed enhanced uptake of these nanoparticles in bladder tumor tissues. CONCLUSIONS: Our data show promising in vivo antitumor efficacy and provide preclinical proof of principle for the intravesical application of mucoadhesive nanoparticulate DTX formulation in the treatment of bladder cancer.

In vitro and in vivo evaluation of intravesical docetaxel loaded hydrophobically derivatized hyperbranched polyglycerols in an orthotopic model of bladder cancer.

The objective of this study was to evaluate the tolerability, to establish a dosing regimen, and to evaluate the efficacy of intravesical docetaxel (DTX) formulations in a mouse model of bladder cancer. DTX in commercial formulation (Taxotere, DTX in Tween 80) or loaded in hyperbranched polyglycerols (HPGs) was evaluated. The synthesis and characterization of HPGs with hydrophobic cores and derivatized with methoxy poly(ethylene glycol) in the shell and further functionalized with amine groups (HPG-C(8/10)-MePEG and HPG-C(8/10)-MePEG-NH(2)) is described. Intravesical DTX in either commercial or HPGs formulations (up to 1.0 mg/mL) was instilled in mice with orthotopic bladder cancer xenografts and was well tolerated with no apparent signs of local or systemic toxicities. Furthermore, a single dose of intravesical DTX (0.5 mg/mL) loaded in HPGs was significantly more effective in reducing the tumor growth in an orthotopic model of bladder cancer than the commercial formulation of Taxotere. In addition, DTX-loaded HPG-C(8/10)-MePEG-NH(2) was found to be more effective at lower instillation dose than DTX (0.2 mg/mL)-loaded HPG-C(8/10)-MePEG. Overall, our data show promising antitumor efficacy and safety in a recently validated orthotopic model of bladder cancer. Further research is warranted to evaluate its safety and efficacy in early phase clinical trials in patients refractory to standard intravesical therapy.

The use of bone cement for the localized, controlled release of the antibiotics vancomycin, linezolid, or fusidic acid: effect of additives on drug release rates and mechanical strength.

Bone cement containing antibiotics is commonly used to treat orthopedic related infections. However, effective treatment (especially of resistant bacteria, methacillin-resistant Staphylococcus aureus (MRSA)) is compromised by very low levels of drug release so that typically less than 10% of loaded drug is released over a 6-week period. The objective of this study was to investigate the effect of incorporation of water soluble excipients (polyethylene glycol, sodium chloride, or dextran) into antibiotic-loaded cement on mechanical strength and drug release properties. Poly(methyl methylacrylate) cement implants containing various amounts of drug (vancomycin, linezolid or fusidic acid (all MRSA active)) and excipients were cast in the form of beads or films and characterized using differential scanning calorimetry. Mechanical strength as assessed by Young's modulus was determined by thermo-mechanical analysis. Drug release was measured by incubation in phosphate buffered saline with analysis by HPLC methods. The inclusion of sodium chloride up to 20% w/w caused only minor reductions in Young's modulus. Vancomycin and linezolid released very slowly from unmodified bone cement beads (less than 3% released by 4 weeks) whereas fusidic acid released more quickly (approximately 8% released by 4 weeks). The inclusion of sodium chloride or dextran in bone cement resulted in major increases in the release rate of vancomycin, linezolid and fusidic acid. These studies support the inclusion of sodium chloride and dextran in bone cement to increase the release rate of vancomycin, linezolid, or fusidic acid without compromising the mechanical strength of the composite material.

Effectiveness of liposomal paclitaxel against MCF-7 breast cancer cells.

Paclitaxel is an effective chemotherapeutic agent that is widely used for the treatment of several cancers, including breast, ovarian, and non-small-cell lung cancer. Due to its high lipophilicity, paclitaxel is difficult to administer and requires solubilization with Cremophor EL (polyethoxylated castor oil) and ethanol, which often lead to adverse side effects, including life-threatening anaphylaxis. Incorporation of paclitaxel in dimyristoylphosphatidylcholine:dimyristoylphosphatidylglycerol (DPPC:DMPG) liposomes can facilitate its delivery to cancer cells and eliminate the adverse reactions associated with the Cremophor EL vehicle. Accordingly, the effectiveness of liposomal paclitaxel on MCF-7 breast cancer cells was examined. The results from this study showed that (i) the lipid components of the liposomal formulation were nontoxic, (ii) the cytotoxic effects of liposomal paclitaxel were improved when compared with those seen with conventional paclitaxel, and (iii) the intracellular paclitaxel levels were higher in MCF-7 cells treated with the liposomal paclitaxel formulation. The results of these studies showed that delivery of paclitaxel as a liposomal formulation could be a promising strategy for enhancing its chemotherapeutic effects.

Paclitaxel incorporated in hydrophobically derivatized hyperbranched polyglycerols for intravesical bladder cancer therapy.

OBJECTIVE: To develop paclitaxel incorporated into unimolecular micelles based on hydrophobically derivatized hyperbranched polyglycerols (dHPGs) for use as mucoadhesive intravesical agents against non-muscle-invasive bladder cancer. MATERIALS AND METHODS: Two different types of dHPGs (HPG- C10-polyethylene glycol (PEG) and polyethyleneimine (PEI)-C18-HPG) were synthesized and paclitaxel was loaded into these using a solvent evaporation method. After physicochemical characterization of the resulting nanoparticles, four human bladder cancer cell lines were incubated with various concentrations of paclitaxel incorporated in dHPGs and the results were compared with those of paclitaxel formulated in Cremophor-EL (Taxol(R), Bristol-Myers-Squibb). In vivo, nude mice with orthotopic KU7-luc tumours were intravesically instilled with phosphate buffered saline, Taxol, or paclitaxel/HPG-C10-PEG. RESULTS: dHPGs are mucoadhesive nanoparticles with hydrodynamic radii of <10 nm and incorporation of paclitaxel did not affect their size. The release profiles of paclitaxel from dHPGs were characterized by a rapid-release phase followed by a slower sustained-release phase. While the PEI-C18-HPG formulation released only approximately 40% of the initially incorporated paclitaxel, up to 80% was released from HPG-C10-PEG. Moreover, only paclitaxel/HPG-C10-PEG was stable in acidic urine. In vitro, all paclitaxel formulations potently decreased bladder cancer proliferation although paclitaxel/HPG-C10-PEG was slightly less cytotoxic than standard Taxol. By contrast, in vivo, the mucoadhesive HPG-C10-PEG formulation of paclitaxel was significantly more effective in reducing orthotopic tumour growth than Taxol and was well tolerated. CONCLUSION: Intravesical administration of mucoadhesive nanoparticulate formulations of paclitaxel might be a promising approach for instillation therapy of patients with non-muscle-invasive bladder cancer.

Unimolecular micelles based on hydrophobically derivatized hyperbranched polyglycerols: ligand binding properties.

This paper discusses the binding and release properties of hydrophobically modified hyperbranched polyglycerol-polyethylene glycol copolymers that were originally developed as human serum albumin (HSA) substitutes. Their unimolecular micellar nature in aqueous solution has been proven by size measurements and other spectroscopic methods. These polymers aggregate weakly in solution, but the aggregates are broken down by low shear forces or by encapsulating a hydrophobic ligand within the polymer. The small molecule binding properties of these polymers are compared with those of HSA. The preliminary in vitro paclitaxel release studies showed very promising sustained drug release characteristics achieved by these unimolecular micelles.

Bactericidal efficacy of liposomal aminoglycosides against Burkholderia cenocepacia.

OBJECTIVES: Burkholderia cenocepacia (formally a genotype of Burkholderia cepacia complex called genomovar III) has emerged as a serious opportunistic pathogen in individuals with cystic fibrosis. We developed a liposomal antibiotic formulation composed of 1,2-distearoyl-sn-glycero-3-phosphocholine and cholesterol (molar ratio 2:1) to overcome B. cenocepacia's resistance to commonly used aminoglycosidic antibiotics. METHODS: The dehydration-rehydration vesicles technique was used to entrap antibiotics in liposomes. The size of liposome formulations was measured and encapsulation efficiencies were determined by microbiological assays. MICs of free and liposomal antibiotics against the clinical isolates of B. cenocepacia were determined by the standard broth dilution method and in vitro time--kill studies were performed using free and liposomal antibiotics at one, two or four times the MICs. We studied the mechanism of action of these formulations by using transmission electron microscopy (TEM), fluorescence-activated cell sorter (FACS) analysis, lipid-mixing assay and immunocytochemistry. RESULTS: The encapsulation efficiencies of amikacin, gentamicin and tobramycin into liposomes were 52.08 +/- 5.4%, 27.72 +/- 1.14% and 28.08 +/- 1.54%, respectively. The liposome formulations were more stable in PBS at 4 degrees C than in PBS, bronchoalveolar lavage fluid or plasma at 37 degrees C. The TEM studies along with lipid-mixing assays and FACS analysis indicated the lipid contact of the liposomal bilayers and bacterial cell membranes. Most importantly, our liposomal formulations reduced MICs for highly antibiotic-resistant strains and enhanced the antibiotics' penetration into the bacterial cells. For instance, bacterial eradication by liposomal tobramycin was 4-fold higher than free tobramycin. CONCLUSIONS: A liposomal drug delivery system might enhance the efficacy of commonly used aminoglycosides.

Mechanism of enhanced activity of liposome-entrapped aminoglycosides against resistant strains of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is inherently resistant to most conventional antibiotics. The mechanism of resistance of this bacterium is mainly associated with the low permeability of its outer membrane to these agents. We sought to assess the bactericidal efficacy of liposome-entrapped aminoglycosides against resistant clinical strains of P. aeruginosa and to define the mechanism of liposome-bacterium interactions. Aminoglycosides were incorporated into liposomes, and the bactericidal efficacies of both free and liposomal drugs were evaluated. To define the mechanism of liposome-bacterium interactions, transmission electron microscopy (TEM), flow cytometry, lipid mixing assay, and immunocytochemistry were employed. Encapsulation of aminoglycosides into liposomes significantly increased their antibacterial activity against the resistant strains used in this study (MICs of > or =32 versus < or =8 microg/ml). TEM observations showed that liposomes interact intimately with the outer membrane of P. aeruginosa, leading to the membrane deformation. The flow cytometry and lipid mixing assays confirmed liposome-bacterial membrane fusion, which increased as a function of incubation time. The maximum fusion rate was 54.3% +/- 1.5% for an antibiotic-sensitive strain of P. aeruginosa and 57.8% +/- 1.9% for a drug-resistant strain. The fusion between liposomes and P. aeruginosa significantly enhanced the antibiotics' penetration into the bacterial cells (3.2 +/- 2.3 versus 24.2 +/- 6.2 gold particles/bacterium, P < or = 0.001). Our data suggest that liposome-entrapped antibiotics could successfully resolve infections caused by antibiotic-resistant P. aeruginosa through an enhanced mechanism of drug entry into the bacterial cells.

Antibacterial activity of liposomal gentamicin against Pseudomonas aeruginosa: a time-kill study.

Cystic fibrosis (CF) is a common and lethal genetic disorder with a carrier frequency of 1 in 29 Caucasians. Chronic respiratory infections with Pseudomonas aeruginosa are the leading cause of morbidity and mortality in individuals with CF. Aminoglycoside antibiotics, including gentamicin, are highly effective against P. aeruginosa, but severe toxicity limits their use. One potential strategy for avoiding this problem is to encapsulate aminoglycosides in liposomes. In this study, we compared the bactericidal capacity of liposome-encapsulated gentamicin with that of free antibiotic against clinical isolates of P. aeruginosa. Liposome size, encapsulation efficiency and minimal inhibitory concentrations (MICs) of the free and liposomal gentamicin against gentamicin-sensitive and -resistant strains of P. aeruginosa were determined. In vitro time-kill studies were performed using free and liposomal gentamicin at 1, 2 or 4 times the MICs. The average liposomal size was 426.25 +/- 13.56 nm, with a gentamicin encapsulation efficiency of 4.51 +/- 0.54%. The MICs for liposomal gentamicin were significantly lower than those of corresponding free gentamicin. In addition, the time-kill values for liposomal gentamicin were either equivalent to or better than those of the free antibiotic. In conclusion, our liposomal gentamicin formulation is a more potent antipseudomonal drug with an improved killing time and prolonged antimicrobial activity.

Preparation and characterization of dehydration-rehydration vesicles loaded with aminoglycoside and macrolide antibiotics.

Enhanced activity of liposomes-encapsulated antibiotics against clinical isolates of Pseudomonas aeruginosa has been documented with liposomes of low encapsulation efficiency. We sought to construct liposomes with high yield entrapment of aminoglycoside and macrolide antibiotics as well as favorable stability in storage and physiological conditions. Liposome-entrapped aminoglycosides (amikacin, gentamicin, tobramycin) and a macrolide (erythromycin) were prepared by a modified dehydration-rehydration vesicles (DRVs) method, and their particle size and entrapment efficiency were determined. We studied in vitro stability of these vesicles over a 48 h period at 4 and 37 degrees C in phosphate-buffered saline (PBS) and in plasma at 37 degrees C. The mean particle size of DRVs loaded with antibiotics varied from 163.37+/-38.44 to 259.83+/-11.80 nm with no significant difference in regard with the type of the antibiotics encapsulated. Encapsulation efficiency of DRVs loaded with amikacin, gentamicin, tobramycin, and erythromycin were 29.27+/-1.17, 33+/-0.76, 22.33+/-1.48 and 32.06+/-0.82% of initial amount of the drug, respectively. These vesicles were stable regardless of the experimental temperature. Indeed, the liposomes retained more than 75% of the initially encapsulated drugs for the study period of 48 h. DRVs incubated in plasma however, released more antibiotics than those incubated in PBS. In conclusion, using this modified DRV method, we obtained small sized vesicles with high yield entrapment for aminoglycoside and macrolide antibiotics. The technique may be utilized to overcome the low encapsulation efficiency associated with aminoglycoside and macrolide antibiotics.

Liposome-mediated gentamicin delivery: development and activity against resistant strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients.

OBJECTIVES: Chronic pulmonary infection by Pseudomonas aeruginosa in cystic fibrosis patients is virtually impossible to eradicate by means of existing free antibiotics. We sought to assess the antibacterial activities of liposomal gentamicin against clinical isolates of P. aeruginosa. METHODS: Gentamicin was encapsulated into liposomes with different lipid compositions (1,2-dimyristoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-distearoyl-sn-glycero-3-phosphocholine) and cholesterol in the molar ratio of 2:1 by sonication. The in vitro stability of liposome-encapsulated gentamicin was studied over a 48 h period at 4 and 37 degrees C in PBS and at 37 degrees C in pooled plasma. The MICs of free and liposomal gentamicin for clinical isolates of P. aeruginosa were assessed by broth dilution. RESULTS: The encapsulation efficiency of all liposomal preparations was 4%-5.18% of the initial amount of the drug in solution. The liposomes retained 60%-70% of the encapsulated gentamicin for 48 h when they were incubated in normal human pooled plasma or PBS at 4 or 37 degrees C. The MICs of liposomal gentamicin for all clinical isolates of P. aeruginosa were lower than the MICs of free gentamicin. Importantly, liposomal gentamicin altered the susceptibilities of these clinical isolates from gentamicin resistant to either intermediate or susceptible. CONCLUSIONS: Taken together, these data indicate that liposomal gentamicin formulations could be more effective than the free drug in controlling pulmonary infections due to P. aeruginosa.