The effects of equine skin preparation on transdermal drug penetration in vitro

An increasing number of formulations are applied to equine skin, yet variable penetration can affect efficacy, or the incidence of adverse effects, or both. To investigate the effects of common methods of skin preparation on transdermal drug penetration in vitro, we clipped, harvested, and froze skin samples from 5 Thoroughbred geldings. Thawed samples were prepared as follows: control (no preparation); cleaned with aqueous chlorhexidine (Aq-C, 0.1% w/v); cleaned with alcoholic chlorhexidine (Al-C, 0.5% w/v); shaved (Sh); or tape-stripped (Ta) with the use of adhesive tape. The samples were then placed in diffusion cells, and 2 g of methylsalicylate (MeSa) gel (Dencorub) was applied to the stratum corneum side. The penetration of MeSa and its analyte, salicylate (Sa), through the skin samples was measured over 10 h. Compared with control skin, significantly more MeSa penetrated through skin prepared with Al-C or Sh (P < 0.01) or with Aq-C or Ta (P < 0.05), and significantly more Sa was recovered in the receptor phase from skin prepared with Aq-C, Al-C, or Sh (P < 0.05) or with Ta (P < 0.01). A significantly higher rate of penetration and shorter lag time were also noted for MeSa with all the prepared skin samples, compared with the control samples. The results show that clinical techniques routinely used to clean or prepare skin can significantly affect the rate and extent of penetration of a topically applied drug. This may result in greater systemic availability of active drug, which could lead to enhanced efficacy and, possibly, a higher incidence of adverse effects.     

The effects of skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro

This study investigated the effects of allergic skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro. Full-thickness lesional and nonlesional (normal) skin was removed from the dorsal lumbosacral and dorsocaudal thoracic regions, respectively, of five canine cadavers. The dogs were suspected of having flea allergy dermatitis based on their distribution and types of skin lesions. Nonlesional skin was confirmed to be histologically normal, and the histopathology of the lesional skin was consistent with allergic dermatitis. Excised skin was clipped, mounted in Franz-type diffusion cells, and the transdermal penetration of a saturated, radiolabelled hydrocortisone solution was measured over 30 h. When the penetration data for all five dogs were pooled, a restricted (or residual) maximal likelihood mixed model predicted that the permeability coefficient and pseudosteady-state flux of hydrocortisone was more than twice as great (95% confidence interval 1.55-2.71 times as great; P < 0.0001) through lesional compared with nonlesional skin. There was no significant difference in the lag time for hydrocortisone penetration through lesional compared with nonlesional skin of the dogs. This study has confirmed that the transdermal penetration of hydrocortisone may be altered, typically increased twofold, but could be as high as 10-fold, through lesional compared with nonlesional skin of dogs with suspected flea allergy dermatitis. This is likely to be affected by variables such as disease severity, concurrent infections and interindividual differences in skin characteristics.     

Regional differences in transdermal penetration of fentanyl through equine skin

The rate and regional differences for the penetration of fentanyl through equine skin was investigated in vitro using a commercial transdermal therapeutic system (TTS) or ‘patch’. Skin collected from the thorax, groin and leg (dorsal metacarpal) regions of five horses was placed in diffusion cells and a fentanyl TTS applied to each skin sample. Drug penetration through each skin sample over 48 h measured using high performance liquid chromatography (HPLC). Cumulative penetration (μg/cm²) was plotted against time (h) and used to regress the steady state flux (μg/cm²/h) of fentanyl through each skin site. Results showed similar fluxes for both the thorax (2.32 ± 0.17 μg/cm²/h and groin (2.21 ± 0.11 (μg/cm²/h) regions, but significantly lower flux (P = < 0.05) for the leg region (1.56 ± 0.120 μg/cm²/h. Interestingly, there was a significantly longer lag time for the penetration of fentanyl through the groin region (7.87 ± 0.51 h) compared to the other two sites (5.66 ± 0.97 h and 5.75 ± 0.43 h for the thorax and leg regions respectively). The results suggest that a fentanyl TTS applied to the leg region may have a small but significantly lower amount of fentanyl available systemically, compared to patches applied to the thorax or groin regions, which may affect the level of analgesia subsequently achieved in the horse.     

Effects of eight vehicles on transdermal lidocaine penetration in sheep skin in vitro

This study investigated the effects of vehicles on penetration and retention of lidocaine applied to sheep skin in vitro. Thoracic skin from two sheep was clipped of wool and stored at −20 °C, until used. Skin samples were defrosted and mounted in Franz‐type diffusion cells, and then one of the following formulations, each saturated with lidocaine, was added: sodium lauryl sulphate (SLS) 0.5% in water, SLS 1% in water, dimethyl sulphoxide (DMSO) 50% in water (wt/wt), DMSO 100%, isopropyl myristate 100% (IPM), water alone, diethylene glycol monoethyl ether (DGME) 50% in water (wt/wt) and DGME 100%. The penetration of lidocaine in each skin sample was measured over 8 h. Significantly greater lidocaine skin concentrations and flux (J_SS) were achieved with the nonaqueous vehicles, DMSO 100% (P < 0.00001 and P < 0.01, respectively), followed by DGME 100% and IPM (P < 0.00001 and P < 0.01, respectively). The lag time (t_lag) for lidocaine penetration in the DMSO 100% vehicle was significantly shorter (P < 0.01) compared with all other vehicles except water. Improved transdermal penetration of lidocaine in the DMSO 100% vehicle was likely due to skin barrier disruption, as determined by differences in pre‐ and post‐treatment transepidermal water loss (TEWL). This study has shown that nonaqueous vehicles enhanced penetration of lidocaine in sheep skin to a greater extent than aqueous vehicles, which has implications for topically applied local anaesthesia in sheep.     

The effects of surface preparation on the penetration of hydrocortisone through canine skin

This study investigated the effects of common skin surface preparations on the penetration kinetics of hydrocortisone through canine skin. Thoracic skin from five dogs was clipped of hair, divided between five treatment groups and prepared as follows: shaved (S); tape-stripped with adhesive bandage (TS); cleaned with aqueous chlorhexidine (Aq-C); cleaned with alcoholic chlorhexidine (Al-C); or allocated to the control group and had no further preparation performed (C). The skin samples were mounted in Franz-type diffusion cells and transdermal hydrocortisone penetration was measured over 30h. The pseudo-steady-state flux (J(SS)) of hydrocortisone through S, Al-C, Aq-C and TS skin was, respectively, 2.3 (P=0.021), 2.2 (P=0.037), 2.0 (P=0.070) and 1.5 (P=0.351) times greater than through the control skin, but there were no significant differences in the lag times (t(lag)) for hydrocortisone penetration between the groups. The study has shown that some skin surface preparations can significantly increase the subsequent penetration of hydrocortisone through canine skin in vitro.     

The effects of vehicle and region of application on in vitro penetration of testosterone through canine skin

The effects of the vehicles phosphate-buffered saline (PBS), ethanol (EtOH; 50% in PBS w/w) and propylene glycol (PG; 50% in PBS w/w) and the region of administration on in vitro transdermal penetration of testosterone was investigated in the dog. Skin was harvested from the thorax, neck (dorsal part) and groin regions of greyhounds after euthanasia and stored at -20 degrees C until required. The skin was then de-frosted and placed into Franz-type diffusion cells which were maintained at approximately 32 degrees C by a water-bath. Saturated solutions of testosterone, containing trace amounts of radiolabelled (14C) testosterone, in each vehicle were applied to the outer (stratum corneum) surface of each skin sample and aliquots of receptor fluid were collected at 0, 2, 4, 8, 16, 20, 22 and 24h and analysed for testosterone by scintillation counting. The maximum flux (J(max)) of testosterone was significantly higher for all sites when dissolved in a vehicle containing 50% EtOH or 50% PG, compared to PBS. In contrast, higher residues of testosterone were found remaining within the skin when PBS was used as a vehicle. This study shows that variability in percutaneous penetration of testosterone could be expected with formulation design and site of application.     

促渗剂促进药物透皮吸收机理的研究进展

综述了促渗剂促进药物透皮吸收机理的研究概况,着重介绍了氮酮、油酸和萜烯等常用促渗剂的促渗机理研究进展,并提出透皮吸收机理研究发展趋势,为该领域进一步深入研究提供参考.     

Effect of solute lipophilicity on penetration through canine skin

OBJECTIVE: To investigate the effect of lipophilicity on the percutaneous penetration of a homologous series of alcohols through canine skin. DESIGN: Skin harvested from Greyhound thorax was placed in Franz-type diffusion cells and the in vitro passage of radiolabelled (14C) alcohols (ethanol, butanol, hexanol and octanol (Log P 0.19-3.0)) through separate skin sections was measured in replicates of five. Permeability coefficient (kP, cm/h), maximum flux (Jmax, mol/cm2/h) and residue remaining within the skin were determined. RESULTS: The kP increased with increasing lipophilicity (6.2 x 10(-4) +/- 1.6 x 10(-4) cm/h for ethanol to 1.8 x 10(-2) +/- 3.6 x 10(-3) cm/h for octanol). Alcohol residues remaining within each skin sample followed a similar pattern. An exponential decrease in Jmax with increasing lipophilicity was observed. CONCLUSION: Changes in canine skin permeability occur with increasing alcohol lipophilicity. This finding has practical consequences for the design of topical formulations and optimisation of drug delivery through animal skin.     

Effects of freezing on mechanical properties of rat skin.

Two test specimens of skin were cut from the lateral aspect of each hind limb of 9 rats. Specimens were contiguous, thereby providing matched pairs. One specimen was immediately placed in liquid nitrogen for 5 minutes, then stored at -70 C and tested within 3 to 4 weeks. Within 5 minutes of harvest, the second specimen was used for immediate material testing. Basic engineering material tests were used to measure strength, loading response, and elastic and viscous properties. Each matched pair of tissues was used for the same procedure. Quasistatic uniaxial tensile tests were used to apply deformations to the test specimens, and resulting loads were recorded. Stress and strain were calculated from the recorded data, providing information on yield strength, ultimate strength, fracture strength, and loading response. Each matched pair of specimens represented 1 repetition; 6 repetitions were made of each observation. Statistical analysis indicated that tissue freezing significantly (P less than 0.05) increased fracture strength, but did not affect strength, ultimate strength, or loading response. Dynamic vibration response tests were used to find mechanical mobility of the specimens, thereby providing information on elastic and viscous behaviors, which were quantified by calculation of spring and damping coefficients, respectively. As before, 6 repetitions were used. Statistical analysis indicated that tissue freezing did not affect these coefficients.     

松萝酸体外透皮试验研究

采用简化体外透皮释放测定装置 ,初步研究了松萝酸在透皮促渗剂作用下的透皮吸收作用。结果表明单一的透皮促进剂氮酮 ( Azone)及以氮酮为主的复合透皮促进剂 ( 2 % Azone 2 0 %丙二醇 ,2 % Azone 2 0 %二甲基亚砜 ,2 % Azone 2 0 %尿素 )对松萝酸的透皮吸收均无促进作用     

Extent of skin penetration byDermatophilus congolensis in bovine streptothricosis

Summary Hyphae ofDermatophilus congolensis were noted in the upper epidermis especially in the stratum corneum and sometimes reaching the basement membrane (dermo-epidermal junction). Hyphae and coccoid forms were also seen in hair follicle sheaths and sebaceous glands which formed the main avenues for dermal invasion. Dermatophilus organisms were seen in the papillary layer of the dermis in areas where the basement membrane of the epidermis had disintegrated but none were seen in areas where the basement membrane was intact.

---

Sumario Hifas deDermatophilus congolensis fueron vistas en la epidermis superior, especialmente, en el estrato córneo y algunas veces se encontraron en la membrana basal (union dermo-epidermo). Las hifas y las formas cocoides fueron tambien vistas en las vainas de los folículos pilósos y glándulas sebáceas, las cuales formaban las mas grandes “avenidas” para la invasión dermal. Los organismos Dermatophilus fueron vistos en la capa papilar de la dermis en areas en donde la membrana basal de la epidermis se habia desintegrado, pero, ningun organismo fue visto en areas en donde la membrana basal estaba intacta.

---

Résumé Les hyphes deDermatophilus congolensis sont trouvées dans la couche supérieure de l'épiderme, en particulier dans lestratum corneum, et quelquefois atteignent la membrane basale (frontière dermo-épidermique). Des hyphes et des formes cocco?des sont vues aussi dans la gaine des follicules pileux et dans les glandes sébacées qui constituent les principales voies d'invasion du derme. Ces mêmes éléments microbiens s'observent aussi dans la couche papillaire du derme, dans les zones ou la membrane basale de l'épiderme a été détruite; par contre on ne les trouve jamais dans les zones où cette membrane est restée intacte.

     

The effects of thyroid hormones on the skin of beagle dogs

The effects of hypothyroidism on canine skin were determined by comparing morphologic, morphometric, and hair cycle differences in skin biopsy samples from 3 groups of age- and gender-matched Beagle dogs: (1) euthyroid dogs; (2) dogs made hypothyroid by administration of 131I; and (3) dogs made hypothyroid and maintained in a euthyroid state by treatment with synthetic thyroxine. After 10 months of observation, there was slower regrowth of hair 2 months after clipping in the untreated-hypothyroid dogs. Untreated-hypothyroid dogs had a greater number of follicles in telogen and fewer hair shafts (ie, a greater number of hairless telogen follicles) than did the control group. The control dogs had a greater number of telogen follicles but the same number of hair shafts as the treated-hypothyroid group. Treated-hypothyroid dogs had the greatest number of follicles in the growing stage of the hair cycle (anagen). This study suggests that, at least in Beagles, induced hypothyroidism does not affect the pelage as dramatically as has been described in naturally occurring disease. This is because normal Beagles retain hair shafts in follicles for long periods, and the alopecia of hypothyroidism appears to evolve slowly because of the prolongation of this haired telogen stage. The evaluation of thyroxine-treated hypothyroid dogs demonstrates that thyroid hormone supplementation of Beagle dogs with induced hypothyroidism stimulates hair growth.     

氮酮促进洛美沙星仔猪皮肤吸收机理的研究

选用10～12日龄同品种仔猪,随机分组,于仔猪腹部皮肤涂搽含氮酮的洛美沙星透皮吸收剂, 分别于涂药前、涂药后2、4、6、12、24、48和72 h 在体取皮,应用透射电镜观察皮肤表皮结构变化,探讨氮酮促进洛美沙星透皮吸收的作用机理.结果表明,氮酮通过以下途径促进药物透皮吸收:(1)作用于表皮角质层细胞间脂质,使角质层变得疏松,细胞间距增大,外角质层细胞易于脱落,降低了皮肤对药物的屏障作用;(2)氮酮进入角质细胞内,与细胞内基质相作用,引起基底角质层肿胀,增加了角质细胞水化程度和药物存储空间.研究还发现,氮酮在体对仔猪皮肤的作用可维持72 h 以上;由氮酮引起皮肤结构的改变是一非损伤可复性过程.     

Temporal effects of freezing on plasma nitric oxide concentrations in ponies

The purpose of this study was to compare concentrations of nitric oxide (NO) in fresh plasma versus frozen plasma, and determine the temporal effects of freezing on jugular venous plasma NO concentrations in clinically healthy ponies. Twenty-eight helminth-naïve ponies, aged from 4 to 6 mo, were raised and maintained under parasite-free conditions. Blood was collected from the jugular vein, centrifuged, and the plasma supernatant was analyzed fresh for NO concentrations using a chemiluminescent method. The remaining samples were aliquoted into 12 samples and stored at −70°C until they were analyzed for NO concentration. Plasma NO concentration was measured at monthly intervals for 12 mo. There were significant differences in the plasma NO concentration across time compared with the baseline value at 1, 3, 4, 6, 7, and 11 mo. However, these values remained within the range for clinically healthy equids compared with concentrations of NO from horses with increased NO from diseased states.     

Enhancement of transdermal delivery of phenylbutazone from liposomal gel formulations through deer skin

Phenylbutazone (PBZ) is a nonsteroidal anti‐inflammatory drug used in the treatment of chronic pain and arthritis. Topical and transdermal administration of PBZ would be beneficial in large animals in terms of minimizing gastro‐intestinal ulcerations and other side effects, easy administration to legs and joints and minimizing the dose to reduce systemic toxicity of the drug. A topical liposomal preparation with different concentrations of a mono‐substituted alkyl amide (MSA) and PBZ was formulated. The formulations were evaluated by in vitro skin‐permeation kinetics through deer skin using Franz diffusion cells. By increasing drug loading from 1% to 5% w/w, the steady‐state flux (μg/cm²/h) of PBZ was increased twofold (P < 0.001). Similarly, by increasing the MSA concentration from 0% to 4%, the steady‐state flux (μg/cm²/h) of PBZ was increased twofold (P < 0.001). Overall, by increasing the drug load and the use of an appropriate amount of the penetration enhancer, the steady‐state flux of PBZ through skin was increased fourfold (P < 0.001). MSA at both 2% and 4% w/w concentrations significantly increased the skin levels of PBZ as compared with control (P < 0.05). In conclusion, MSA served as an effective skin‐penetration enhancer in the liposomal gel of PBZ for deer.     

Regional differences in the in vitro penetration of methylsalicylate through equine skin

Commercial formulations of non-steroidal anti-inflammatory drugs (NSAIDs) are developed for human use but the extent to which they will pass through equine skin is unknown. Skin was harvested from five Thoroughbred geldings from the thorax, groin and leg (dorsal metacarpal) regions and frozen (-20 degrees C) until required. Two grams of methylsalicylate (MeSa) gel was applied to defrosted full-thickness samples in diffusion cells and the penetration of MeSa and its active metabolite, salicylate (Sa), through skin samples were measured over 24 h. Significantly higher (P < or = 0.02) total salicylate (AUC; MeSa + Sa) penetrated through skin from the leg region (5491.3 h mg/L), compared to thorax (3710.7 h mg/L) and groin (3571.5 h mg/L). In addition, there was a significantly higher (P0.01) rate of penetration of total Sa through leg skin in the first 6h after application. It was concluded that the commercial formulation of MeSa would achieve therapeutic levels of total salicylate beneath sites of topical application, with a faster and more pronounced response through the leg region, compared to the upper body.     

Regional differences in the in vitro penetration of hydrocortisone through equine skin

Little is known about the transdermal penetration of hydrocortisone in the horse and, although commercial formulations containing hydrocortisone are registered for topical use in the horse, there have been no studies investigating the movement of this glucocorticoid through different regions of equine skin. Skin was harvested from the thorax, groin and leg (dorsal metacarpal) regions of five Thoroughbred geldings and frozen (-20 degrees C) until required. Defrosted skin was placed in Franz-type diffusion cells and the amount of radiolabelled ((3)H) hydrocortisone, in a saturated solution of unlabelled hydrocortisone in 50% ethanol (w/w), which penetrated through and remained within skin samples was measured over 24 h. Significantly higher (P < 0.001) maximum flux (J(max); mol/cm(2)/h) was measured when hydrocortisone was applied to skin from the leg, compared to thorax and groin, although significantly less hydrocortisone (P < 0.001) was retained within skin from the leg at 24 h. Topical application of hydrocortisone in a vehicle containing ethanol would penetrate faster through leg skin from the lower leg when compared with the thorax or groin, which depending on cutaneous blood flow, may result in higher systemic drug concentrations or greater efficiency in treating local inflamed tissue.