Review Article

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

Table 1

Strategies for the formulation of poorly absorbed drugs.

TechnologyPotential advantagePotential disadvantageReferences

Conventional micronizationKnown technology,
freedom to operate,
solid dosage form possible
Poor control of the size distribution of the particles, insufficient improvement in dissolution rate[24]

Nanocrystals obtained by ball-millingEstablished products in the market,
experienced technology,
solid dosage form possible
Available only under license, secondary process required to avoid aggregation of nanocrystals[7, 8]

Nanocrystals obtained by dense gas technologyAlternative nanocrystal processing method, still room to develop new IPUnproven technology,
secondary process required to avoid aggregation of nanocrystals
[8]

‘‘Solid solutions’’—drug immobilized in polymerFreedom to operate,
new extrusion technology offers solvent-free continuous process,
fast and continuous process,
low cost
Physical stability of product questionable, possibility of crystallization of drug or polymer[25]

Self-dispersing ‘‘solid solutions’’ with surfactantsSteric hindrance to aggregation built into product, amenable to extrusionPhysical stability of product
questionable, drug may crystallize
[10, 25, 26]

Nanoparticles and solid lipid nanoparticlesControlled-release of drug,
reduced variability
Low drug loading,
drug expulsion after polymorphic transition,
high water content
[27]

Lipid solutions (LFCS Type I lipid systems)GRAS status, simple,
safe, and effective for lipophilic actives; drug is presented in solution avoiding the dissolution step, excellent capsule compatibility
Poor solvent capacity, limited to highly lipophilic or very potentdrugs,
requires encapsulation
[6, 19]

Self-emulsifying drug delivery systems (SEDDS) and SMEDDS (LCFS Type II or Type III lipid systems)Prior art available,
dispersion leads to rapid absorption and reduced variability,
absorption not dependent on digestion
Surfactant may be poorly tolerated in chronic use,
soft gel or hard gel capsule can be used but seal must be effective, possible loss of solvent capacity on dispersion (Type III)
[6]

Solid or semisolid SEDDSCould be prepared as a free flowing powder, filled in capsules or compressed into tablet form, reduced problem of capsule leakageSurfactant may be poorly tolerated in chronic use,
physical stability of product
questionable, drug or polymer may crystallize
[25, 28]

Surfactant-cosolvent systems (LFCS Type IV ‘‘lipid’’ systems)
Relatively high solvent capacity for many drugs (due to surfactant), disperses to micellar solution, reduced variability and irritancy (due to dispersion of surfactant by cosolvent)Surfactant may be poorly tolerated in chronic use, loss of solvent capacity on dispersion, significant threat of drug precipitation on dilution[6, 29]