Formulation Strategies to Improve the Bioavailability of Poorly Absorbed Drugs with Special Emphasis on Self-Emulsifying Systems

Table 2

Lipid formulation classification system.

Parameters	Increasing hydrophilic content →
	Types of lipid formulations
	Type I	Type II	Type IIIA	Type IIIB	Type IV
Example/reference	[30]	[31]	[19]	[32]	[29]
Triglycerides or mixed glycerides (%w/w)	100	40–80	40–80	<20	—
Water-insoluble surfactants (%w/w) (HLB < 12)	—	20–60	—	—	0–20
Water-soluble surfactants (%w/w) (HLB > 11)	—	—	20–40	20–50	30–80
Hydrophilic; cosolvents (%w/w)	—	—	0–40	20–50	0–50
Particle size of dispersion (nm)	Coarse	250–2000	100–250	50–100	<50
Characteristics	Nondispersing	SEDDS without water-soluble components	SEDDS/SMEDDS with water-soluble components	SMEDDS with water-soluble components and low oil content.	Oil-free formulations
Significance of aqueous; dilution	Limited importance	Solvent capacity unaffected	Some loss of solvent capacity	Significant phase changes and potential loss of solvent capacity	—
Significance of digestibility	Crucial requirement	Not crucial but likely to occur	Not crucial but may be inhibited.	Not required and not likely to occur	Not likely to occur
Advantages	GRAS status; simple; excellent capsule compatibility	Unlikely to lose solvent capacity on dispersion	Clear or almost clear dispersion. Absorption without digestion	Clear dispersion. Absorption without digestion	Good solvent capacity for many drugs; disperse to micellar solution
Disadvantages	Poor solvent capacity (unless drug is highly lipophilic)	Turbid o/w dispersion	Possible loss of solvent capacity on dispersion. Less easily digested	Likely loss of solvent capacity on dispersion	Loss of solvent capacity on dispersion; may not be digestible