Liposomes have useful properties that promote them for the use as a drug delivery system, particularly in the targeted administration for potentially toxic drugs with a narrow therapeutic index.
Medical research has supported the use of liposomes for the administration of some medications, such as antitumor drugs, to enhance efficacy and reduce related toxicity.
For medications with a narrow therapeutic index, a drug carrier is often needed to help in the drug delivery to increase the safety and efficacy of administration. A carrier may alter the temporal or spatial delivery, changing the biodistribution of the pharmacokinetics of the drug.
There are several benefits that promote the use of liposomes in pharmaceutical preparations, including:
- Improved solubility of lipophilic and amphiphilic drugs
- Passive targeting to immune system cells
- Sustained release for systemic and local administration
- Mechanism to avoid or target certain sites
- Improved tissue penetration and charged/hydrophilic molecule transfer
There are three different types of liposomes: multilamellar (MLV), small unilamellar vesicles (SUV) and large unilamellar vesicles (LUV). Different types are used for different drugs and target cells.
Liposomal drugs can also be formulated to improve bioavailability for target cells in the circulation or particular disease sites, such as tumors. These formulations have been used favorably as anticancer agents, and several clinical research studies have supported their use, linking the formulations to less toxicity than the free drug.
For example, anthracyclines help to stop the growth of rapidly dividing cells, including cancer cells and natural cells found in the body. As a result of this, these medications are effective in cancer treatment but have high toxicity. Targeting the therapy to affected cells with liposome carriers can help to reduce side effects.
Liposomes can be used as a carrier for drugs such as foramphotericin B, used in the treatment of fungal infection. Foramphotericin B has notably beneficial properties as an antifungal medication but its use in practice is limited by its toxicity, particularly ionosphere and neurotoxicity.
Using liposomes as carriers to encapsulate the drug helps to prevent the build-up of drugs in problematic organs, such as those in the central nervous system, reducing the risk of toxicity dramatically. Additionally, the liposomes naturally target the mononuclear phagocytic system where the fungus usually exists, leading to passive drug targeting.
Liposomes are an ideal vehicle of drug administration to allow targeted therapy to certain areas of the body.
For example, a parasitic infection of macrophages, Leishmaniasis, is a potentially fatal condition and the drugs used to treat the condition can be difficult to handle because the toxic dose is only incrementally higher than the required effective dose. Drug delivery with liposomes would be an ideal solution because the liposomes naturally target the macrophages and, therefore, be directed towards the infection.
As antibiotics are largely orally available, there is less need for liposome encapsulation. At present, it is only considered beneficial for potentially toxic antibiotics with intravenous administration. Instead, alternative methods of administration, such as topical or inhaled, are usually preferred.
Several antibiotics have been linked to less toxicity when delivered in a liposome-encapsulated formulation, including ribavirin, azidothymidine and acyclovir.
As the design and technologies for the use of liposomes continue to develop, the possible applications are expanding and leading to possibilities of administering antisense oligonucleotides, cloned genes and recombinant proteins.