Lipid-based formulations for oral delivery of lipophilic drugs.

In the last decade there has been a growing interest in lipid-based formulations to deliver challenging compounds such as lipophilic drugs. Following a brief clarification of the nomenclature, this review stresses the different mechanisms of how lipid-based excipients and formulations interact with the absorption process. Case studies are presented in which enhanced bioavailability was demonstrated in vivo using this pertinent formulation approach. It is emphasized that lipid-based delivery of challenging drugs requires a development in consecutive steps. Such a structured formulation development is crucial for optimal allocation of resources. Thus, lipid-based excipients are first evaluated in view of drug solubility, phase behavior, as well as with respect to known biological effects. Mixtures can be screened in simple dilution tests and are subsequently studied in more advanced biopharmaceutical tests. Once a lipid-based formulation principle is identified, different technologies are presented to encapsulate the fill mass either in soft or hard capsules. It is also possible to formulate lipid-based systems as a solid dosage form. Even though such solid lipid technologies seem very attractive, one has to assure that the final dosage form does not impair the biopharmaceutical potential of the lipid formulation principle.