Absorption enhancers terpenes

Gao S, Singh J. In vitro percutaneous absorption enhancement of the lipophilic drug tamoxifen by terpenes. / Control Release 1998 51 193-199. 

Terpenes are widely used chemical penetration enhancers (Williams and Barry, 1991b Barry and Williams, 1993). Structural formulas of terpaies used as penetration enhancers are presented in Figure 12.6. Terpenes are of low cutaneous irritancy, provide excellent enhancement ability, and appear to be promising candidates for pharmaceutical formulations (El-Kattan etal., 2001 Gao and Singh, 1998 Zhao and Singh, 1999). Table 12.4 lists the in vitro percutaneous absorption enhancement of drugs using terpenes. 

The penetration-enhancing activities of monoterpenes, sesquiterpenes, and diter-penes were evaluated. Terpenes with relatively high lipophilic index exhibited absorption-promoting effects however, extremely high Upophilicity led to lower enhancing activities (Takayama et al., 1991). It was suggested that the difference in percutaneous absorption enhancing efficiency of terpenes arose from the difference in their thermodynamic activities in the vehicle (Obata et al., 1993). 

Zhao, K. and Singh, J. (1998). In vitro percutaneous absorption enhancement of tamoxifen by terpenes eugenol, D-limonene, and menthone, J. Controlled Release, 55 253-260. 

Table 12.4 In VHro Percutaneous Absorption of Drugs Using Terpenes as a Skin Penetration Enhancer...

There are few smdies on the in vivo efficacy and irritancy of terpenes used as an enhancer in percutaneous absorption. The percutaneous absorption-promoting effect and skin irritancy of cyclic monoterpenes were investigated in rats and with rabbits, respectively (Okabe etal., 1990). Plasma concentration of the drug (ketoprofen) markedly increased with the addition of the hydrocarbons of cyclic monoterpenes such as trans- -methane and d-limonene. Irritancy of cyclic monoterpenes in rabbits was evaluated using the Draize scoring method. No skin irritation was observed when ethanol-containing hydrocarbons of cyclic monoterpenes (trans-p-menthane and d-limonene) were applied to dorsal skin. 

Cal K, Kupiec K, Sznitowska M (2006) Effects of physicochemical properties of cyclic terpenes on their ex vivo skin absorption and elimination kinetics. J Dermatol Sci 41 137-142 Moghimi HR, Williams AC, Barry BW (1996) A lamellar matrix model for stratum comeum intercellular lipids III. Effects of terpene penetration enhancers on the release of 5-fluorouracil and oestradiol from the matrix. Int J Pharm 145 37-47... 

---