Enhancing effect of combining two pyrrolidone vehicles on transdermal drug delivery

Improved transdermal delivery of prostaglandin E1 through hairless mouse skin: combined use of carboxymethyl-ethyl-β-cyclodextrin and penetration enhancers

The optimal prescription of transdermal preparations of prostaglandin E1 (PGE1) for treatment of peripheral vascular diseases has been investigated. The chemical stability of PGE1 in fatty alcohol/propylene glycol (FAPG) ointment was markedly improved by carboxymethyl-ethyl-β-cyclodextrin (CME-β-CyD). Application of a PGE1 ointment containing the penetration enhancer, 1-dodecylazacycloheptane-2-one (Azone) or 1-[2-(decylthio)ethyl]azacyclopentane-2-one (HPE-101), onto the skin of hairless mice showed the increase of blood flow in the skin due to the vasodilating action of PGE1. In particular, the ointment containing a PGE1-CME-β-CyD complex supplemented with HPE-101 showed the most prominent increase of the blood flow. Compared with other ointments, this ointment was found to show significantly greater transfer of HPE-101 into in-vitro preparations of the skin of hairless mice. Transfer of PGE1 into the skin was thought to be facilitated by this increased transfer of HPE-101. These results suggest that a combination of CME-β-CyD and HPE-101 is useful for designing PGE1 ointments for topical application with good chemical stability and percutaneous permeability.

Evaluation of chemical enhancers in the transdermal delivery of lidocaine

The effect of various classes of chemical enhancers was investigated for the transdermal delivery of the anesthetic lidocaine across pig and human skin in vitro. The lipid disrupting agents (LDA) oleic acid, oleyl alcohol, butenediol, and decanoic acid by themselves or in combination with isopropyl myristate (IPM) showed no significant flux enhancement. However, the binary system of IPM/n-methyl pyrrolidone (IPM/NMP) improved drug transport. At 2% lidocaine dose, this synergistic enhancement peaked at 25:75 (v/v) IPM:NMP with a steady state flux of 57.6 +/- 8.4 microg cm(-2) h(-1) through human skin. This observed flux corresponds to a four-fold enhancement over a 100% NMP solution and over 25-fold increase over 100% IPM at the same drug concentration (p < 0.001). NMP was also found to co-transport through human skin with lidocaine free base and improve enhancement due to LDA. These findings allow a more rational approach for designing oil-based formulations for the transdermal delivery of lidocaine free base and similar drugs.

Role of n-methyl Pyrrolidone in the Enhancement of Aqueous Phase Transdermal Transport

The role of n-methyl pyrrolidone (NMP) as an enhancer for permeants delivered from an aqueous phase was investigated in the transdermal delivery of the local anesthetics lidocaine free base, lidocaine-hydrochloride (HCl), and prilocaine-HCl. Lidocaine free-base flux increased from H2O/NMP binary systems containing over 50% (v/v) NMP with significant flux enhancement observed above 80% NMP. In this range, drug flux was found to correlate with NMP flux. The addition of oleic acid (1% w/v) further enhanced lidocaine flux sixfold, in these formulations. The H2O/NMP (50% v/v) system enhanced the transport of water-soluble hydrochloride salt derivatives of lidocaine and prilocaine by factors of 4.3 and 2.6, respectively, indicating that NMP was capable of enhancing hydrophilic and hydrophobic drugs from an aqueous phase. These findings were consistent with the model that NMP flux across the stratum corneum improves the transport of formulation solutes.

Novel microemulsion enhancer formulation for simultaneous transdermal delivery of hydrophilic and hydrophobic drugs

PURPOSE

Microemulsion (ME) systems allow for the microscopic co-incorporation of aqueous and organic phase liquids. In this study, the phase diagrams of four novel ME systems were characterized.

METHODS

Water and IPM composed the aqueous and organic phases respectively, whereas Tween 80 served as a nonionic surfactant. Transdermal enhancers such as n-methyl pyrrolidone (NMP) and oleyl alcohol were incorporated into all systems without disruption of the stable emulsion.

RESULTS

A comparison of a W/O ME with an O/W ME of the same system for lidocaine delivery indicated that the O/W ME provides significantly greater flux (p < 0.025). The water phase was found to be a crucial component for flux of hydrophobic drugs (lidocaine free base, estradiol) as well as hydrophilic drugs (lidocaine HCl, diltiazem HCl). Furthermore, the simultaneous delivery of both a hydrophilic drug and a hydrophobic drug from the ME system is indistinguishable from either drug alone. Enhancement of drug permeability from the O/W ME system was 17-fold for lidocaine free base, 30-fold for lidocaine HCl, 58-fold for estradiol, and 520-fold for diltiazem HCl.

CONCLUSIONS

The novel microemulsion systems in this study potentially offers many beneficial characteristics for transdermal drug delivery.

Analysis of the combined effect of 1-menthol and ethanol as skin permeation enhancers based on a two-layer skin model

The combined effects of 1-menthol and ethanol as a skin permeation enhancer were evaluated with two equations describing the permeability coefficient through full-thickness skin (PFT) and the full-thickness skin/vehicle concentration ratio (CFT/CV) of drugs as a function of their octanol/vehicle partition coefficient (KOV). A two-layer model was applied for skin, which consists of a stratum corneum (SC) with lipid and porous pathways and a viable epidermis and dermis (ED). The two equations contain one variable (KOV) and nine coefficients, six of which (three diffusion coefficients, the porosity of the SC, and two terms of the linear free energy relationship) were considered different, dependent on the drug vehicle. In vitro permeation of four drugs (morphine hydrochloride, atenolol, nifedipine, and vinpocetine) was determined using excised hairless rat skin and four aqueous vehicles (water, 5% 1-menthol, 40% ethanol, and 5% 1-menthol-40% ethanol) to measure each PFT. Drug concentrations in full-thickness skin were also measured to obtain CFT/CV. A nonlinear least-squares method was employed to determine six coefficients using the two equations and experimentally obtained PFT and CFT/CV. The addition of 1-menthol to water and 40% ethanol increased the diffusion coefficient of drugs in lipid and pore pathways of SC, whereas the addition of ethanol to water and 5% 1-menthol increased the drug solubility in the vehicle, decreased the skin polarity, and increased the contribution of the pore pathway to whole-skin permeation.