Solubility and in vitro transdermal diffusion of riboflavin assisted by PAMAM dendrimers

PAMAM dendrimers of full generation (Gn) and half generation (Gn.5) were used as solubility enhancers of riboflavin (B₂ vitamin) in methanol. They were found to weakly enhance solubility of B₂ (7.2-10.3 times) according to the order: G2≫G2.5>G3≫G3.5>G4. The homogeneous mixtures of Gn (or Gn.5) with B₂ of 1:1 molar ratio were obtained by removal of methanol to form oily host-guest complexes. The complexes were released from o/w emulsions and the transdermal permeation of B(2) through polyvinyldifluoride (PVDF) and pig ear skin (PES) membranes was estimated. PAMAM dendrimers were demonstrated to promote permeation of B₂ according to the order: G2>G3≫G2.5>G3.5>G4 (none). The permeation of fluorescein labeled dendrimers is faster than B₂; the diffusion of G2 dendrimer through PES was the slowest of all studied Gn dendrimers, presumably due to absorption inside the skin. On the other hand the G2 was the best permeation enhancer for B₂. The water soluble PAMAM dendrimers G2 and G3 can be successfully applied in cosmetic and dermatologic emulsions for this weakly water soluble vitamin.