Percutaneous absorption of bromhexine in rats

The percutaneous absorption of bromhexine (BH), an expectorant drug, through rat skin was examined in vitro and in vivo. BH in free base form penetrated better than the hydrochloride through the skin. When the in vitro penetration of BH was compared using Plastibase, macrogol and sucrose ester of fatty acid F-160 (DK-ester) formulations, the DK-ester formulation showed the best penetration of BH of the three. The addition of Azone (3%) or lauric acid (BH: lauric acid molar ratio, 1:1) considerably increased BH penetration to a relatively large penetration rate. The plasma levels of BH after in vivo application of the DK-ester formulation with Azone or lauric acid (0.6 g/3.8 cm2) were also higher than those after the formulation without an enhancer, and a constant plasma level (20-50 ng/ml) was obtained during the application for 48 h. However, the bioavailability was low, 2.5 and 2.7% respectively. When the amount of BH remaining in DK-ester ointment and the skin after an 18-h application was measured, the BH content in the ointment was 88.6 +/- 8.0% for the formulation without Azone and 93.7 +/- 6.9% for that with Azone. The low penetration and low bioavailability observed will thus be due to the high drug retention of the base.     

Percutaneous absorption of clonazepam in rabbit

The percutaneous (p.c.) absorption of clonazepam (CZP), an antiepileptic drug, was investigated in rabbits. CZP was efficiently absorbed from a gel ointment (0.5% CZP, 1g, 9 cm2) with Azone and therapeutic plasma concentrations were maintained for 27 h. The bioavailability of CZP from the gel ointment was 47.2 +/- 3.1%, which was significantly larger than that (3.3 +/- 0.5%) after the ointment without Azone or that (12.5 +/- 3.6%) after oral administration. About a half of CZP in the ointment with Azone was absorbed during a 24 h application. The maximum and minimum plasma concentrations and the area under the plasma concentration-time curve gradually increased during repeated application of the ointment (2% CZP, 0.25 g/d, 2.25 cm2), probably due to the accumulation of drug in the skin and body. The efficient absorption and sustained plasma concentration of CZP after application suggest that a once a day p.c. administration regimen is possible by using the ointment with Azone.     

Percutaneous absorption of 1,3-dinitroglycerin and a trial of pharmacokinetic analysis

In order to estimate the pharmaceutical usefulness of 1,3-glyceryl dinitrate (1,3-GDN), an active metabolite of nitroglycerin, a trial transdermal delivery system designed to sustain a suitable plasma concentration of 1,3-GDN was produced using a porous membrane (Hipore 2100 or 4500) and it was a gel base or ethylhexyl acrylate-based adhesive (adhesive) and it was applied to rats. Additionally, for practical use of the transdermal system, a simple pharmacokinetic model to describe plasma 1,3-GDN levels after percutaneous (p.c.) application is presented. As a result, the drug was penetrated through the rat skin in vitro at a zero-order rate, although the penetration rate from the gel base was significantly greater than that from the adhesive. In vivo, the drug was rapidly absorbed through the rat skin, with a peak plasma level of 581 +/- 151 and 265 +/- 62 ng/ml for the gel ointment and adhesive systems without a porous membrane, respectively. The plasma levels after application of the systems with a membrane were relatively constant for a long time, indicating that the membranes act as a controlled-release barrier. The bioavailability of 1,3-GDN after gel base systems with and without a membrane was relatively high. The model presented was successfully able to describe the time course of plasma 1,3-GDN concentrations following p.c. application of the systems.     

Percutaneous absorption of ketoprofen from acrylic gel patches containing d-limonene and ethanol as absorption enhancers.

The percutaneous absorption of ketoprofen (KPF) from gel patches containing d-limonene and ethanol was investigated in rats. Plasma levels of KPF varied with the kind of polymers which constitute the gel patch, and the highest level was observed when the copolymer of ethylacrylate (EA) and diethyleneglycolmethacrylate (DEGMA) was used as a vehicle. The amount of KPF permeating through the rat skin from the gel patch was well correlated with that of ethanol. Permeations were enhanced with increase in the amount of d-limonene distributed from the vehicle to the skin tissue. The amount of d-limonene accumulated in the skin varied greatly with the kind of polymers; the highest accumulation was observed with the EA-DEGMA copolymer, and decreased with increasing affinity of d-limonene to the polymers. The reason EA-DEGMA copolymer showed the highest percutaneous absorption of KPF from gel patches containing d-limonene may be the hydrophilic nature of this polymer which showed the lowest affinity to d-limonene.     

Formulation optimization and in situ absorption in rat intestinal tract of quercetin-loaded microemulsion

A new microemulsion system has been developed to increase the solubility and oral absorption of quercetin, a poorly water-soluble drug. The formulation of quercetin-loaded microemulsion was optimized by a simplex lattice experiment design. The optimized microemulsion formulation consisted of oil (7%, w/w), surfactant (48%, w/w), and cosurfactant (45%, w/w). Under this condition, the mean droplet diameter of microemulsion was 38.9 nm and solubility of quercetin in the microemulsion was 4.138 mg/ml. The in situ absorption property of quercetin-loaded microemulsion in rat intestine was studied and the results showed there was significant difference in absorption parameters such as K_a, t_1/2 and uptake percentages between microemulsion and micelle solution containing quercetin. The study on absorption percentage in different regions of rat intestine attested that the colon had the best permeability, followed by ileum, duodenum in order. It can be concluded that microemulsion can improve the solubility and oral absorption of quercetin, a poorly water-soluble drug.     

Theory of two-photon absorption and emission second-order saturation effect

A simplified theory of small-signal two-photon absorption is developed, based on the solution of rate equations involving an infinitely short-living intimediate state. It is shown that in a first approximation this theory leads to results identical to those obtained using second-order perturbation techniques. Moreover, the present approach leads to a built-in saturation effect at high intensities depending on the parameters of the laser and of the absorbing medium. An analysis expression is given for the intensity dependent saturation.