Quantitation of paclitaxel in micro-sample rat plasma by a sensitive reversed-phase HPLC assay

A sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of paclitaxel in micro-samples of rat plasma in order to study the mechanism of enhanced systemic exposure of paclitaxel co-administered with P-glycoprotein inhibitors. The assay involved solid-phase extraction procedures using 2'-methylpaclitaxel as the internal standard. Chromatographic separations were achieved using a ZORBAX ODS C18 column and mobile phase consisting of acetonitrile, methanol and ammonium acetate buffer (10 mM, pH 5.0) (48.5:16.5:35) pumped at 0.8 ml/min. The effluents were measured for UV absorption at 227 nm, with retention times of 8.5 and 11.0 min for paclitaxel and 2'-methylpaclitaxel, respectively. The chromatographic separation was excellent, with no endogenous interference. The standard curves showed a good linearity (r=0.9994) over the concentration ranges of 10-1,000 ng/ml. At 1,000 ng/ml, the absolute recoveries of paclitaxel and 2'-methylpaclitaxel are 89 and 90%, respectively. The intra- and inter-day variabilities of paclitaxel were both less than 15%. This validated method for the assay of paclitaxel in micro-sample rat plasma made it feasible to study the pharmacokinetics of the drug in a single rat.

Terpenes in propylene glycol as skin-penetration enhancers: permeation and partition of haloperidol, Fourier transform infrared spectroscopy, and differential scanning calorimetry

The respective alcoholic terpenes carvacrol, linalool, and alpha-terpineol were used at 5% w/v in propylene glycol (PG) to increase the in vitro permeation of haloperidol (HP) through human skin. The possible enhancement mechanism was then elucidated with HP-stratum corneum (SC) binding studies, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The greatest increase in the permeation of HP was achieved with linalool followed by carvacrol and terpineol. HP permeation with linalool was predicted to reach a therapeutic plasma concentration and therapeutic daily-permeated amounts. Carvacrol increased lag time, which was attributed to slow redistribution of the enhancer within SC. Carvacrol increased the partition of the drug to the pulverized SC. Pure PG extracted lipids from SC but less than that achieved by the terpenes in PG. Terpenes extracted lipids to a similar extent. An increase in bilayer cohesion in the remaining lipids present in the SC could be attributed to the alignment of terpenes within the lipid bilayer. The higher permeation with linalool was attributed to its molecular orientation within the lipid bilayer. Terpenes showed different rates of SC dehydration but did not change the percentages of secondary structures of keratin.

Terpenes in ethanol: haloperidol permeation and partition through human skin and stratum corneum changes

Carvacrol, linalool and alpha-terpineol (5% w/v) in 50% ethanol were used to enhance the permeation of haloperidol (HP) through human skin in vitro and their enhancement mechanism was investigated with HP-stratum corneum (SC) binding studies, fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Carvacrol followed by terpineol and linalool enhanced flux and permeability coefficient but only carvacrol provided the required plasma concentration and the permeated daily doses. All terpenes increased the activity coefficient of HP in the skin. Carvacrol increased the lag time, which could be due to slow redistribution within SC. The thermogram of hydrated SC showed two lipid endotherms T1 and T2 at 65 and 78 degrees C and protein endotherm T3 at 97 degrees C. All endotherms were absent after SC treated for 48 h with 12 ml of terpene solutions and a decrease in melting points (m.p.) of lipids with a shift of protein endotherm were observed after 12 h treatment with 7 ml of terpene solutions. Linalool and terpineol decreased the m.p. of T1 to 33 degrees C. Carvacrol increased the T1 peak area, which was attributed to lateral lipid bilayer swelling. The IR spectra showed decreases in peak areas and heights of CH2 stretchings but did not show shift of these peaks, increase in their peak widths and shift in amide bands. All the three terpenes disrupted the lipid bilayer and extracted the lipids. Moreover, carvacrol increased the partition of HP whilst linalool and terpineol fluidized the lipids at skin temperature. There could be other possible protein-terpene interactions.

Effect of cetrimide and ascorbic acid on in vitro human skin permeation of haloperidol

Permeation of haloperidol through the human skin in vitro was studied with two enhancers, cetrimide and ascorbic acid, at various concentrations. Amber glass Franz-type diffusion cells were used for the permeation studies and haloperidol was made soluble in aqueous solution with the aid of lactic acid. Donor solutions were prepared by adding excess of haloperidol to 0.03% (v/v) lactic acid solution with or without enhancers at concentrations 0.1, 0.3 and 0.6% (w/v) and stirred for 36 h at 32 degrees C before filtering. Ascorbic acid gradually increased the solubility of the haloperidol from that of the control where as cetrimide did not show any effect. Cetrimide concentration dependent increase in the permeability coefficient of haloperidol was observed. Mechanism of enhancement by cetrimide was probed with the diffusion profile kinetics and Fourier transform infrared (FT-IR) spectroscopy. Cetrimide was found to increase the thermodynamic activity of the drug in the skin. IR spectra of the stratum corneum treated with cetrimide showed time-dependent decrease in the intensity of the spectrum and dose-dependent decrease of lipid band but no change in the protein conformation. Cetrimide appears to interact with both the dermal keratin and lipids and this interaction was found to be irreversible. Ascorbic acid although increased the flux of haloperidol to the same extent at all concentrations from that of the control, decreased the permeability coefficient and enhancer index in a concentration dependent manner and this is due to the increased solubility of the drug in the vehicle. Both the enhancers did not change the lag time from that of the control.

Effect of some enhancers on the permeation of haloperidol through rat skin in vitro

The objective of this work is to enhance the permeation of haloperidol through the rat skin in vitro by using various enhancers at a concentration of 1 mg/ml in the saturated drug solution and analysing the dose-dependent diffusion profile for the enhancers which significantly increased permeation at this concentration compared with the control. Enhancers belonging to various chemical classes like the vitamins (ascorbic acid), surfactants (cetrimide, polysorbate 20), sulfoxides (dimethyl sulfoxide), glycols (polyethylene glycol 400, propylene glycol) and amides (urea) were used. Amber glass Franz-type diffusion cells were used for the permeation studies and haloperidol was made soluble in aqueous solution with the aid of lactic acid. Ascorbic acid and cetrimide increased flux and permeability coefficient significantly. From the dose-dependent permeation studies, it was concluded that ascorbic acid enhanced the permeation by increasing the solubility of the drug in the vehicle thus providing a high concentration gradient across the skin, whereas cetrimide enhanced the permeation by increasing the thermodynamic activity which may be due to solubilization of skin lipids by micelles. Polysorbate 20 decreased the enhancer index by decreasing the thermodynamic activity. None of the enhancers changed the lag time except for urea which decreased the lag time probably by its binding with keratin. Dimethyl sulfoxide, polyethylene glycol 400 and propylene glycol did not have a significant effect on haloperidol permeation compared with control.