Oral Lipid Based Formulations PDF Download

The work presented in this thesis has provided additional information regarding the utilisation of lipid-based self-emulsifying formulations for lipophilic drugs, making use of fenofibrate as a model. Specifically the work focused on lipid-based formulation in the context of the emerging "Lipid Formulation Classification System" (LFCS) which has been previously proposed as a new means of classifying lipid-based formulations. This is the first study to address lipid formulations using a small group of related excipients to cover a wide range of lipid formulations. The roles of the lipid phase, the effect of the ratio of lipid to surfactant and the presence of cosolvent on the performance of formulations were investigated. A series of phase diagrams were constructed to examine the phase behaviour during dispersion of anhydrous formulations. Type II, IIIA, IIIB and IV (SEDDS & SMEDDS) were investigated using medium chain glycerides (MCGs), polysorbates and propylene glycol (PG) as excipients. Equilibrium solubilities of the drug were determined in mixtures equivalent to diluted formulations to examine the likelihood of precipitation on dispersion. These data were compared with drug precipitation data obtained in dynamic dispersion experiments. Precipitation was measured over time after 1 in 100 dilutions of formulations in aqueous media. Aqueous dispersion of Type II lipid formulations resulted in turbid emulsions, followed subsequently by very slow precipitation of fraction of the drug dose. Type IIIA formulations, which carried less drug in solution at equilibrium, nevertheless typically maintained drugs in a metastable state for several hours or even days. These studies suggested that Type II and Type IIIA formulations were the most appropriate for fenofibrate. Diluted formulations were also subjected to in vitro digestion to predict the fate of the drug in the gastrointestinal (GI) tract after exposure of the formulation to pancreataic enzymes and bile. In vitro digestion experiments were carried out using a pH-stat maintained pH 7.5 for 30 minutes using intestinal fluids simulating the fed and fasted states (FeSSIF and FaSSIF). The digestion rate was higher in Type II & IIIA systems. Formulations with higher content of hydrophillic materials (Type IIIB or Type IV) resulted in more rapid precipitation, and extensive precipitation of drug from Type IV formulations took place rapidly. The high concentration of surfactant and or cosolvent lowered the rate of digestion but considerable precipitation occurred due to lack of solvent capacity of diluted formulations. Digestion experiments suggested that drug was in a supersaturated state which could be maintained in the presence of mixed bile salt micelles. The fate of fenofibrate is dependent on the choice of lipid formulation as exemplified by the LFCS. In particular the current study suggests that Type IIIB or Type IV formulation may be unsuitable for highly lipophilic drugs, but in vitro tests suggested that after digestion there was a considerable risk of precipitation from all formulations.