Lipophilic drug derivatives in liposomes

The drug molecules can be classified into four categories, i.e. highly hydrophilic, highly lipophilic, amphiphilic and those with biphasic insolubility. These are located differently in the liposomes and exhibit different entrapment and release behaviour. Problems like poor entrapment efficiency in addition to physical as well as chemical instability have been found to be associated with the liposomal entrapment of drug molecules other than those that are highly lipophilic. Therefore, a number of problem drugs have been synthesised into lipophilic derivatives and targeted to the phospholipid bilayer. Some other approaches have also been used for the purpose, which include ion pair formation and pharmacosomes. The present review discusses the advantages of incorporating drugs in the lipid domain of the vesicle. Taking examples of different drug classes, the success and limitations of the approach is discussed.