The self-emulsifying process is depends on:
1. The nature of the oil–surfactant pair
2. The surfactant concentration
3. The temperature at which selfemulsificationoccurs
Oils
Oils are the most important excipients in theSEDDS formulation, because they may be able
to solubilize the lipophilic drug in definite quantity, and facilitate self-emulsification. By
this, the amount of lipophilic drug transport can be increased via the intestinal lymphaticsyst
em, therefore absorption from the GI tract also increased by basing on the nature oftriglyceri
de oils. In the formulation of SEDDs we have to use both long-chain triglycerideand medium-chain triglyceride oils with different degrees of diffusion. Modified or hydrolyzed vegetable oils have contributed widely to the success of SEDDSs, due to their excellent emulsification systems, and better drug solubility properties. At present Novelsemi-synthetic medium-chain triglyceride oils have surfactant properties and are widely used in stead of the regular medium- chain triglyceride. Deckelbaum (1990) showing that MCT is more soluble and have a higher mobility in the lipid/water interfaces than LCT allied with a more rapid hydrolysis of MCT. In general, while using LCT, a higher concentration of cremophor RH40 was required to form microemulsions compared with MCT.
Surfactant
Numerous compounds exhibiting surfactant properties might be working for the design of
self-emulsifying systems, but the choice is limited at the same time as very few surfactants are orally suitable, because Safety is a major determining factor in choosing asurfactant. Emulsifiers of natural origin are preferred since they are considered to be safer than the synthetic surfactant. The most extensively suggested ones being the non-ionic surfactants with a relatively high hydrophilic lipophilic balance (HLB) (e.g., Tween,Labrasol, Labrafac CM 10, Cremophore, etc.). The strength of surfactant usually ranges preferred since they are considered to be safer than the synthetic surfactant. The most extensively suggested ones being the non-ionicsurfactants with a relatively high hydrophiliclipophilicbalance (HLB) (e.g., Tween,Labrasol, Labrafac CM 10, Cremophore, etc.).The strength of surfactant usually ranges.
Cosurfactant/Cosolvents
Cosurfactant/Cosolvents like Spans,capyrol90, lauroglycol, diethyleneglycol,monoethyl
ether (transcutol), propyleneglycol, polyethylene glycol, polyoxyethylene,propylenecarbonat
e, tetrahydrofurfurylalcohol polyethylene glycol ether (Glycofurol),etc., might help to dissolve large amounts of hydrophilic surfactants or the hydrophobicdrug in the lipid base. These solvent sometimes play the role of the cosurfactants in the microemulsion systems.
Formulation of SEDDSs
With a large variety of liquid or waxyexcipients available, ranging from oils through biological lipids, hydrophobic and hydrophilic surfactants, to water-soluble cosolvents, there are
many different combinations that could be formulated for encapsulation in hard or softgelatin or mixtures which disperse to give finencolloidal emulsions. The following should be
considered in the formulation of a SEDDS11:
1. The solubility of the drug in different oil, surfactants and cosolvents.
2. The selection of oil, surfactant and Cosolvent based on the solubility of the drug and the
preparation of the phase diagram.
3. The preparation of SEDDSformulation by dissolving the drug ina mix of oil, surfactant and cosolvent.
4. The addition of a drug to a SEDDS iscritical because the drug interfereswith the self-emulsification process toa certain extent, which leads to achange in the optimal oil–surfactantratio. So, the design of an optimal SEDDS requires preformulation solubility and phase-diagram studies.In the case of prolonged SEDDS,
The following should be considered in the formulation of a SEDDS:
1. The solubility of the drug in different oil, surfactants and cosurfactant/co‐solvents.
2. The selection of oil, surfactant and co‐solvent based on the solubility of the drug and the
preparation of the phase diagram.
3. The preparation of SEDDS formulation by dissolving the drugin a mix of oil, surfactant and co‐surfactant/co‐solvents.The addition of a drug to a SEDDS is critical because the drug
interferes with the self‐emulsification process to a certain extent,which leads to a change in the optimal oil–surfactant ratio. So, the design of an optimal SEDDS requires pre formulation‐solubility and phase‐diagram studies. In the case of prolonged SEDDS, formulation is made by adding the polymer or gelling agent.
Mechanism of self emulsification
According to Reiss 16, self‐emulsification occurs when the entropy change that favors dispersion is greater than the energy required to increase the surface area of the dispersion. The free energy of the conventional emulsion is a direct function of the energy required to
create a new surface between the oil and water phases and can be described by the equation:
Where, DG is the free energy associated with the process (ignoringthe free energy of mixing),N is the number of droplets of radius rand s represents the interfacial energy. The two phases of emulsiontend to separate with time to reduce the interfacial area, and subsequently, the emulsion is stabilized by emulsifying agents,which form a monolayer of emulsion droplets, and hence reduces the interfacial energy, as well as providing a barrier to prevent coalescence.In the case of self‐emulsifying systems, the free energy required to form the emulsion is either very low and positive, or negative (then,the emulsification process occurs spontaneously).Emulsificationrequiring very little input energy involves Destabilization through contraction of local inter facial regions. For emulsification to occur, it is necessary for the inter facial structure to have no resistance to surface shearing
