Summary 3- Sneha Subramanian
Journal of Controlled Release 84 (2002) 69–78
http://www.elsevier.com/ locate / jconrel
A facile method of delivery of liposomes by nebulization
Tejas R. Desaia, Robert E.W. Hancockb, Warren H. Finlaya ,*
aDepartment of Mechanical Engineering, Aerosol Research Laboratory of Alberta, University of Alberta, Edmonton, Alberta,
Canada T6G 2G8
bDepartment of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
Received 17 May 2002; accepted 30 August 2002
In this experiment, aerosol technology is studied to treat immune mediated pulmonary disorders. Use of liposomes and its different formulations has increased the potential of aerosol technology along with an array of potent drugs. Use of liposomal delivery has many advantages over conventional delivery like reduced toxicity, sustained release, increased potency and uniform deposition. There are many devices which are used for aerosol drug delivery like dry powder inhalers, dry powder inhalers and nebulisers. Among these nebulisers are considered to be the most appropriate for liposomal drug delivery as the liposome doesn’t require any further processing in this technique. The properties of aerosol developed by the nebuliser will depend on various factors like type of nebuliser, local conditions, aerosol output rate as well as the type of phospholipid used. Various liposomal formulations have been studied in the past few years for carrying therapeutic agents like anti-inflammatory and bronchodilators.
Liposome technology has long-term stability problem. The liposome undergoes chemical changes which lead to the leakage of entrapped drug. Thus, drug delivery through liposomes and nebulisers are hampered. To overcome this stability problem, freeze drying was developed by Darwis and Kellaway which was found to overcome this stability problem. But it is also found that lyophilisation leads to loss of encapsulated drug, thus, reducing the effect of aerosol. It is also found to increase the cost of production which is not feasible from a commercial viewpoint. In the previous study, liposomes were studied to be delivered in dry powdered form and were relied on the spontaneous formation of liposome on dispersion of micronized phospholipid powders. Bronchodilator like salbutamol sulphate and microbial agent like cyproflaxin were used in dry powdered formulation containing lactose, phospholipid and drug. In this study, aqueous dispersions of liposomes are formed for their use in nebulisation. Various liposome formulations using various phospholipids and exhibiting various physiochemical properties were also studied.
- Preparation of dry powder liposomes
The dry powdered liposomes were prepared using phospholipids, lactose and drug in measured quantities. It was then followed by jet milling. The various formulations used in this study were DMPC, DMPG, DPPC and combination of EPC+DMPC and DMPC+DMPG in a molar ratio of 1:1. Drugs like ciprofloxacin, CM3 peptide and salbutamol sulphate in the contration of 7mg/ml, 1mg/ml and 2mg/ml respectively were used. Drug, phospholipids and pharmatose 325M were micronized at a pressure of 90 p.s.i. the powder was then collected in the collection vessel and was stored at a low temperature (-20°C) and low humidity environment for further experiments.
- Preparation of liposomal dispersions
Liposomal dispersions were formed by mixing phospholipid powders and saline and then vortexing them at room temperature for 1 minute. The liposomes were then hydrated and were allowed to anneal for 15mins before nebulisation. The encapsulation was studied by centrifugating the liposomal dispersions and then by assaying the supernatant and pallete by UV spectrophotometry.
Nebulisation of liposome dispersion
The nebulisation of the fresh liposome dispersion was made by PARI LC STAR jet nebuliser. 2.5ml of liposomal dispersions were used in this nebuliser unit. Tghe aerosols produced were collected by respiguard filters. Isotonic water was used to extract this aerosols from the nebuliser. The nebuliser efficiency was calculated using the following formula:
Nebulisation efficiency (%) = aerosolised drug x 100
Total drug placed in nebuliser
Nebulisation tends to loss of drug due to leakage. Hence, drug entrapment was checked after nebulisation which is called as encapsulated delivery. Here, the collected sample was centrifuged and the drug in supernatant and pallete were determined by UV spectrometry. The drug entrapment was thus calculated as the ratio of amount of drug in pallet to the sum of the amount of drug in the pallet and the supernatant.
- Sizing of aerosol droplets
For determining aerosol particle size, the nebulised was directly connected to the cascade impactor. Each sample was nebulised for about 30s and was then allowed to equilibrate. Constant humidity and temperature was maintained in the chamber. Each liposome sample was checked for aerosol size and drug entrapment.
Results and discussion
Liposomes of different formulations were prepared using diffefent concentrations and types of phospholipids. These liposomes were then tested for drug encapsulation, drug leakage, size and aerosol droplet size. Nebulisation efficiencies of different phospholipids and ciprofloxacin is shown in the graph below
It can be seen the EPC+DMPG formulation has the maximum efficiency in nebulisation while DMPC+ DMPG having the least efficiency. Formulation having DMPG is showing the maximum drug entrapment. Thus, it can be concluded that sample having DMPG shows lower drug leakage. The following graph shows the entrapment of ciprofloxacin which is derived from different liposomal formulations after nebulisation.
Again it is observed that formulations containing DMPG shows maximum entrapment delivery. This may be due to the negatively charged bilayers of DMPG that cause electrostatic separation of bilayers, thus improving drug encapsulation. The encapsulation also depends on the phase transition temperature of the phospholipid used. Phospholipids having phase transition temperature below 25°C shows better entrapment as the spontaneous liposome formation is happening in the room temperature. The figure.2 also shows that after nebulisation there is loss of drug by leakage. This may be due to the shock waves and kinematics discontinuities associated with impaction on nebuliser baffles. Leakage may also be due the dilution effect. Liposomal formulation containing DPPC shows maximum leakage. Thus, from the following results it can be concluded that liposomal formulation containing DMPG is most suitable for delivering ciprofloxacin.
The mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) for the formulation containing DMPG was also calculated.
Similar studies were carried out for other drugd like CM3 peptide and salbutamol sulphate.
In this experiment, the best phospholipid formulation for drugs lige ciprofloxacin, CM3 peptide and salbutamol sulphate was calculated. The best formulations for these drugs were DMPG, DMPG+EPC and DMPG+DMPC. They showed good drug encapsulation efficiency and minimum leakage after nebulisation. Output of entrapment was also found to be dependent on phase transition temperature of the lipid.