Enhancement of propranolol hydrochloride and diazepam skin absorption in vitro. II: Drug, vehicle, and enhancer penetration kinetics

The fluxes of representative hydrophilic (propranolol hydrochloride) and lipophilic (diazepam or indomethacin) drugs, administered as ethanolic solutions containing putative penetration enhancers (n-nonane, 1-nonanol, and 1-decanol), were measured across hairless mouse skin in vitro. Propranolol transport was augmented significantly by the presence of 4% (v/v) alkane or alkanol in the vehicle; diazepam and indomethacin, on the other hand, were enhanced only by n-nonane. Experiments with saturated solutions of the drugs as the donor phase revealed that the actions of the enhancers were taking place in the skin and were not a result of an alteration of solute thermodynamic activity in the vehicle. In separate runs, the impact of n-nonane and 1-nonanol on the percutaneous penetration of ethanol was determined. Temporal effects identical to those on the flux of propranolol were observed. A further measurement revealed that the penetration of 1-decanol, when administered as a 4% (v/v) solution in ethanol, followed a profile similar to that of the solvent (which, in turn, was comparable with that of the independently assessed propranolol hydrochloride). Thus, considerable linkage exists between the transport of a hydrophilic drug and the major vehicle component in the presence of n-nonane and 1-nonanol. The lipophilic drugs, conversely, were promoted only by n-nonane and only after most of the ethanol had been absorbed. The results show that an apparent synergy of transport between a putative enhancer and a cosolvent may not always lead to augmented drug flux. Study of the transport of all key formulation components is recommended, therefore, to optimize vehicles for transdermal drug delivery.

Percutaneous absorption of [14C]chlordane from soil

The objective was to determine percutaneous absorption of chlordane in vitro and in vivo from soil into and through skin. The data are needed to calculate the absorbed dose of chlordane from soil, which is then used to assess the toxicity risk. Chlordane, an insecticide for which residues exist in soil, is restricted currently to use for termite control. Chlordane is highly lipophilic with little or no movement out of soil. Soil (Yolo County 65-California-57-8; 26% sand, 26% clay, 48% silt, 0.9% organic) was passed through 10-, 20-, and 48-mesh sieves. Soil then retained by 80-mesh was mixed with 14C-labeled chemical at 67 ppm. Acetone solutions were prepared for comparative analysis. Human cadaver skin was dermatomed to 500 microns and used in glass diffusion cells with human plasma as the receptor fluid (3 ml/h flow rate) for a 24-h skin application time. Chlordane concentration within skin from in vitro studies was 0.34 +/- 0.31% from soil and 10.8 +/- 8.2% from acetone vehicle (p less than .01). Individual variation from human skin sources was evident (p less than .008). Chlordane accumulation in human plasma receptor fluid was the same for soil (0.04 +/- 0.05%) and acetone (0.07% +/- 0.06%) formulations. Most of the remaining chlordane was recovered in the soap and water skin surface wash. In contrast, in vivo percutaneous absorption of chlordane in the rhesus monkey was the same for soil (4.2 +/- 1.8%) and acetone (6.0 +/- 2.8%) formulations (p = .29, nonsignificant). Multiple soap and water washings were necessary to remove chlordane from skin, suggesting that a single wash may not adequately remove all the chlordane.

Cutaneous metabolism of theophylline by the human skin

Percutaneous absorption of theophylline in human skin from five sources was examined by use of a flow-through in vitro diffusion system. The metabolites and unchanged drug were estimated by thin-layer chromatography. Correlation was evident in the percentage of the applied dose that diffused through the five skin samples (range 2.8 +/- 0.5%-7.7 +/- 0.8%); however, the percentage of applied dose absorbed varied between different skin samples (range 3.6 +/- 0.9%-33.4 +/- 2.4%). Between 0.2 +/- 0.1%-4.6 +/- 0.2% of the doses applied were metabolized, and over 60% of the total metabolites formed diffused through the skin. The uptake and metabolism of theophylline by microsomes obtained from four of the human skin samples were measured. All preparations showed detectable activities for the metabolism of theophylline. Microsomal preparations from skin sources A, B, and E, and B, C, and E biotransformed theophylline to 1,3,7-trimethyluric acid and 1,3-dimethyluric acid, respectively. The activities of microsomes from skin samples C and E on the drug produced the pharmacologically active metabolite 3-methylxanthine. The specific activities of the microsomes from skin sources A-E for the formation of 1,3-dimethyluric acid and 3-methylxanthine varied fivefold. However, the variation in specific activities of the microsomes for the formation of 1,3,7-trimethyluric acid was twofold (range 2.8 +/- 0.1-6.2 +/- 0.5 pmol/min per mg protein). These metabolic data may be of value in the development of transdermal theophylline systems. The results indicate that a high level of absorption enhancement will be required before transdermal theophylline preparations could produce therapeutic plasma concentrations.

Simplified experimental human dermatophytosis model

The authors have improved and simplified previous methods for producing localized mycotic skin infections in an attempt to compare topical antifungal agents for their bioequivalency. Healthy human volunteers who had negative results for commercial, purified Trichophyton antigen (Trichophytin) were inoculated with Trichophyton mentagrophytes on two sites on each forearm in a randomized study designed to compare the antifungal activities of two ciclopirox olamine formulations. The lesions, easily induced by the authors' method, were localized and did not spread under the occlusive dressings. Infections established at the four sites on 26 subjects were treated twice daily for 14 days with the two active drug formulations and their vehicles. There were no significant differences in culture-documented cure rates or alleviation of clinical signs and symptoms between ciclopirox olamine lotion and cream. Each drug was significantly better than its vehicle. The authors' method seems to be effective and suitable for therapeutic studies.

Effect of a new topical cyclosporin formulation on human allergic contact dermatitis

We studied the effect of a new topical cyclosporin (CS) formulation on the suppression of allergic contact dermatitis. 4 test sites were outlined on the back of healthy male volunteers. For 7 consecutive days, the test sites were treated as follows: #1: CS formulation (10%), #2: placebo formulation, #3: flumethasone pivalate (FP) formulation (0.02%; #4: no treatment. On day 8, we challenged all test sites in the diphenylcyclopropenone (DCP) sensitized individuals. Photographic and clinical documentation was performed daily. 24 h after the DCP skin challenge, a marked redness accompanied by severe itching and slight pain occurred in the test sites pretreated with CS (#1) and placebo (#2). A considerably milder reaction was noted in the untreated test site (#4) and only a faint redness was noted in the test site pretreated with FP (#3). After 36 h, a further increase in the cutaneous reaction was documented in CS and placebo pretreated test sites (#1, 2). In agreement with other workers, topical CS did not suppress experimentally-induced allergic contact dermatitis in man. On the contrary, in CS and placebo pretreated areas (#1, 2), an increased cutaneous reaction was observed. This observation may be explained by the extensive pretreatment with the topical formulation of CS and placebo, which possibly caused a profound perturbation of the stratum corneum, enabling excessive allergen penetration compared to the untreated area with intact stratum corneum.

The local side effects of transdermally absorbed nicotine

Percutaneous nicotine administration induces predominant sudorific and rubiform responses in the skin which may be accompanied by subtle piloerection, hyperalgesia and pruritus (although these signs are not overtly manifest). These dermal responses are complex and mechanisms have been proposed for the direct nicotine-stimulation of sweat glands, piloerection and vasoconstriction. These reactions are accompanied by secondary activation and release of vasodilator peptides which produce a predominating vasodilator tone following topical administration, this response masking the direct axon reflex-mediated vasoconstriction.

In-vitro skin pharmacokinetics of acitretin: percutaneous absorption studies in intact and modified skin from three different species using different receptor solutions

The aromatic synthetic retinoid acid derivative, acitretin, is efficacious in several cutaneous diseases. Its toxicological profile makes a topical form with no or reduced systemic adverse effects desirable. Direct application of a topical acitretin formulation might result in therapeutic skin concentrations at the site of the disease while minimizing systemic exposure. The present studies define the percutaneous absorption characteristics of acitretin from an isopropylmyristate formulation. We investigated, in-vitro, (1) the role of receptor solution variations, (2) the role of skin modifications, (3) the influence of skin from three different species on the absorption of topically applied acitretin and (4) the drug distribution within the skin. Addition of solubilizers (Polyethylenglycol-20 and albumin) to the receptor solutions improved the flux of acitretin through monkey skin, whereas the acitretin concentration in the skin was not affected by the various receptor solutions used. Acitretin flux through tape-stripped monkey skin and dermis was only slightly higher than through intact skin. Acitretin concentration in human skin was significantly higher than in rhesus monkey or guinea-pig skin. Topical application of acitretin can produce dermal concentrations in excess of those achieved by therapeutic oral doses.

Skin aging. Effect on transepidermal water loss, stratum corneum hydration, skin surface pH, and casual sebum content

This study investigates the effect of cutaneous aging on transepidermal water loss, stratum corneum hydration (capacitance), skin surface pH, and causal sebum content. Because the physiologic condition of skin varies considerably with anatomic region and skin aging might demonstrate regional variability, all factors were studied on 11 anatomic locations in 14 young adult (seven female and seven male subjects; 26.7 +/- 2.8 years [mean +/- SD]) and 15 aged human volunteers (seven female and seven male subjects; 70.5 +/- 13.8 years). Significant anatomic variability was noted for all factors in both age groups. However, no significant differences between the two groups were noted for sebum, capacitance, and pH on most anatomic regions. Transepidermal water loss, however, was significantly lower in the aged population on all anatomic regions tested, except for the postauricular region and the palm. Comparing male and female volunteers, none of the four factors showed significant differences. Of all measured factors, only transepidermal water loss showed significant age-related differences on most anatomic regions studied. The additionally observed differences between the age groups on the ankle for pH and sebum might be related to the stasis frequently observed on the lower limbs in aged individuals.

Contact dermatitis caused by allergy to ophthalmic drugs and contact lens solutions

Although a common cause of allergic reactions, topically applied ophthalmic drugs and contact lens solutions are seldom verified as such. This review documents reported allergens and suggests an 'ophthalmic tray', based on the literature search, to simplify patch test verification. The criteria for literature selection were that each patient had a history of allergic reaction to local application of ophthalmic drugs or contact lens solutions, and tested positive to putative allergen patch tests. We established 38 chemicals causing allergic reactions. 5 authors published suggestions for patch test trays.

Effect of sodium lauryl sulfate-induced skin irritation on in vivo percutaneous penetration of four drugs

The influence of sodium lauryl sulfate-induced irritant contact dermatitis on in vivo percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment, 450 microliters saturated solutions of HC, IM, IB, or AC in isopropylmyristate were applied to the pretreated skin for 24 h. Systemic absorption was determined by urinary and fecal excretion of compounds. Drug concentrations in stratum corneum (obtained by tape cellophane stripping after decontamination of the application site) and in epidermis/dermis (punch biopsy) were also investigated. Systemic absorption of topically applied drugs (as evaluated by urinary and fecal excretion) in SLS-irritated skin was significantly increased for HC (factor 2.6) followed by IB (1.9 times) and IM (1.6 times) but not increased for AC. However, drug concentrations in the viable epidermis and dermis were 70% lower in SLS-irritated than normal skin for HC, but not different for IB, IM, and AC. Thus, the influence of the state of the skin (irritant dermatitis versus healthy) on percutaneous penetration was different for diverse drugs. The general assumption that percutaneous penetration and drug tissue concentrations were higher in diseased versus healthy skin was not found to be true in our irritated-skin model.

Chemical and pharmacologic skin irritation in man. A reflectance spectroscopic study

Attention is increasingly being focused on the relationship of dissociation constant (pKa) of chemicals and skin irritation presumably caused by pH effects at epidermal levels. Human skin studies of irritation have utilized both subjective visual-palpation scores and reflectance spectroscopy (RS) or laser Doppler velocimetry (LDV) respectively. Several studies document that erythema determined subjectively and objectively correlates with the degree of skin irritancy, but others report lack of correlation between LDV and irritancy scored subjectively. In this study, pharmacological and chemical in vivo skin irritation was evaluated utilizing an improved reflectance spectrophotometer equipped with computerized data analysis. In 16 white females, a model for skin irritation was induced by a 24-h patch application of 4 basic chemicals, imipramine, norephedrine, nicotine and 8-aminoquinoline, with pKa'S ranging from 3.8 to 9.5. Skin pigmentation (melanin) and the relative amounts of oxygenized (arterial) and deoxygenized (venous) hemoglobin present in the erythematous skin were calculated. A clear increase in the hemoglobin content was observed in chemical and vehicle exposed sites. Although skin irritation is a complex phenomenon involving chemical and solution properties, percutaneous absorption and the biological drug response, high pKa (p greater than 0.01) was predictive of acute skin irritation in man using computerized analysis of reflectance spectroscopy. A high correlation between visual score and RS was found (r = 0.91).

Cutaneous responses to topical methyl nicotinate in human forearm and vulvar skin

In order to identify and define differences in percutaneous absorption and microcirculatory sensitivity between forearm and vulvar skin we studied the response of human forearm and vulvar (labium majus) skin to topical methyl nicotinate (MN) in 11 healthy premenopausal volunteers. MN-induced erythema was assessed by laser Doppler velocimetry (LDV). The following parameters were compared: 1) basal cutaneous blood flow, 2) the time to peak response, 3) the magnitude of LDV peak response, 4) the area under the LDV response-time curve and 5) the decay time to 75% of peak response. Basal cutaneous blood flow at the vulva was higher than at the forearm (P less than 0.05); the magnitude of peak response was lower at the vulva than at the forearm (P less than 0.01); the area under the curve was lower at the vulva than at the forearm (P less than 0.001); the decay time to 75% of peak response was shorter at the vulva than at the forearm (P less than 0.001). The time to peak response showed no significant differences between sites. The results indicate that the MN-induced vasodilatation is less intense and lasts shorter in vulvar compared to forearm skin.

Evaluation of vulvar irritancy potential of a menstrual pad containing sodium bicarbonate in short-term application

The effect on the skin of menstrual pads containing sodium bicarbonate as a fragrance substitute and of sodium bicarbonate alone was studied in 50 healthy women. Skin changes were monitored by transepidermal water loss, capacitance, laser Doppler flowmetry, skin surface pH and visual scoring. No clinical signs developed after the volunteers had been patched with the menstrual pads for 24 hours. No subclinical vulvar skin irritant reactions were observed with bioengineering methods. The menstrual pads containing sodium bicarbonate as a deodorant did not significantly affect the vulva in short-term use.

Degradation of newly synthesized high molecular mass hyaluronan in the epidermal and dermal compartments of human skin in organ culture

Human whole skin was labeled for 24 h with [6-3H]-glucosamine in organ culture and epidermis, dermis and culture medium were separately analyzed for the molecular mass and content of the [3H]-labeled hyaluronan (HA). Gel filtration on Sephacryl S-1000 of HA purified by HPLC showed a large proportion of the newly synthesized HA to be of a very high molecular mass (greater than 2 X 10(6) Da) in both epidermis and dermis, whereas HA in the medium was of a smaller size. After 24 h chase, most of the high molecular mass HA, and 42-48% of total labeled HA disappeared from both tissue compartments. The size of labeled HA recovered in the chase media was further reduced but the content roughly corresponded to that lost from tissue. The amount of unlabeled HA was not significantly altered in epidermis, whereas in dermis it was reduced to about 10% of the initial values during 5-d culture. The results demonstrate that HA of both epidermis and dermis is synthesized as a very high molecular mass compound but rapidly undergoes a limited degradation into large fragments. The fragmentation of HA is suggested to enhance its diffusion from the tissues, particularly dermis.

Pesticide-related dermatoses in agricultural workers

We need to improve education of farm workers and their families to the potential hazards of exposure to the chemicals and other agents that they are in contact with on a daily basis. Simple measures such as showers in the fields and a change of clothes after work might lower the cutaneous reactions to these chemicals significantly. To that end, physicians can better educate themselves to highlight this area more intensely to residents in training, to offer lectures on the subject at dermatology conferences, and to foster better communication between our public health agencies and the pesticide industry itself. Companies are often cooperative when made aware of the benefits of irritant- and allergic-potential testing. Pesticide registration should require from the companies patch-testing before the product comes to market to determine the threshold irritant concentration and irritant potential of the vehicle.

Effect of sodium lauryl sulfate-induced skin irritation on in vitro percutaneous absorption of four drugs

The influence of irritant contact dermatitis on percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated in vivo for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment animals were sacrificed. Percutaneous penetration was then measured using in vitro diffusion cells and the removed (pretreated) skin. The following parameters were determined: cumulative amount of compound penetrated, steady state flux, lag time, and permeability coefficient, skin concentration per unit area, and the relative amount of drug remaining in the skin (as a percentage of the cumulative amount of compound penetrated through the skin). SLS pretreatment resulted in moderate irritant dermatitis in all animals and increased in vivo transepidermal water loss 4.5 times. Flux was increased in SLS-pretreated skin as compared with controls for all four compounds, with the greatest enhancement for hydrocortisone (HC) (5.9 times), followed by indomethacin (IM) (4.6 times), ibuprofen (IB) (3.9 times), and acitretin (AC) (3.4 times). Skin concentrations increased to a smaller degree from 1.6 times (IB) and 2.6 times (HC) to 3.4 times (IM). However, AC skin concentrations were not different between the two groups. Thus, percutaneous penetration parameters were equivocally influenced by SLS-induced irritation. Increased skin concentrations were paralleled by even higher increases in flux.

Glyphosate skin binding, absorption, residual tissue distribution, and skin decontamination

Glyphosate is a broad-spectrum postemergence translocated herbicide. Its interactions with skin and potential systemic availability through percutaneous absorption was studied by skin binding, skin absorption, residual tissue distribution, and skin decontamination. Glyphosate in a final formulation (Roundup) undiluted and diluted with water 1:20 and 1:32, would not partition into powdered human stratum corneum (less than 1%). In vitro percutaneous absorption through human skin into human plasma as receptor fluid was no more than 2% over a concentration range of 0.5-154 micrograms/cm2 and a topical volume range of 0.014-0.14 ml/cm2. Disposition of glyphosate following iv administration of 93 and 9 micrograms doses to rhesus monkeys was mainly through urine excretion, 95 +/- 8 and 99 +/- 4% in 7 days, respectively. Percutaneous absorption in vivo in rhesus monkey was 0.8 +/- 0.6% for the low dose (25 micrograms/cm2) and 2.2 +/- 0.8% for the high dose (270 micrograms/cm2). No residual 14C was found in organs of the monkeys euthanized 7 days after the topical application. Washing the skin application site with soap and water removed 90 +/- 4% of applied dose, and washing with water only removed 84 +/- 3% of applied dose. Both soap and water and water only were equal in ability to remove glyphosate from skin over a 24 hr skin application period. About 50% of the initially applied dose could be recovered after 24 hr. Glyphosate is very soluble in water and insoluble in most organics (octanol/water log P = -1.70) and therefore not compatible with the lipid-laden stratum corneum.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic hydrocortisone/cortisol induces allergic skin reactions in presensitized subjects

To determine whether systemic hydrocortisone can elicit allergic skin reactions in patients with contact hypersensitivity to hydrocortisone, we studied four patients with contact hypersensitivity to hydrocortisone and hydrocortisone-17-butyrate and two patients with contact hypersensitivity to hydrocortisone-17-butyrate but not to hydrocortisone. Open oral provocation with 100 or 250 mg hydrocortisone in patients with hydrocortisone contact hypersensitivity elicited cutaneous reactions at sites of previous allergic dermatitis caused by hydrocortisone in two patients and at sites of earlier allergic patch test reactions caused by hydrocortisone in the other two patients. Provocations in two patients with contact hypersensitivity to hydrocortisone-17-butyrate but not to hydrocortisone remained negative. To determine whether the adrenal cortical hormone cortisol, which is identical to hydrocortisone, could induce similar skin reactions, one patient with hydrocortisone contact hypersensitivity underwent adrenocorticotropic hormone stimulation tests; as a control, one hydrocortisone-sensitive patient underwent analogous provocations with placebo. After an 8-hour infusion with the adrenocorticotropic hormone analog tetracosactide, a similar skin reaction to that seen with oral hydrocortisone was observed, whereas provocations with placebo remained negative. We conclude that both oral hydrocortisone and intrinsic cortisol are able to induce allergic skin reactions in presensitized subjects.

Percutaneous penetration of methyl nicotinate at three anatomic sites: evidence for an appendageal contribution to transport?

Percutaneous absorption of the vasodilator methyl nicotinate (MN) was evaluated in human volunteers at three anatomic sites (forehead, forearm and palm) using the technique of laser Doppler flowmetry (LDF). The experiments were designed to test the hypothesis that the kinetics and extent of skin penetration are dependent upon the appendageal density at the site of application. The LDF technique measured the increase in skin blood flow elicited by topically applied MN once the chemical had penetrated to the microvasculature. Significant differences in the measured LDF responses at the three sites were found, and further analysis of the data suggested that MN penetration was greatest through forehead skin, least through the palm and intermediate across the skin of the forearm. A correlation therefore existed between apparent MN absorption and appendageal density.

Sensitive and ethnic skin. A need for special skin-care agents?

Sensitive skin is a complex problem with genetic, individual, environmental, occupational, and ethnic implications. Further work is needed to rank irritants and irritant reactions to classify sensitive skin on the basis of standard models. The development of topical products designed for sensitive and ethnic skin may be advisable to optimize drug activity with minimal side effects. The availability of transdermal systems for drug delivery highlights the problem. Occlusive transdermal patch systems for delivery of clonidine show sensitization rates of 34% in white women, 18% in white men, 14% in black women, and 8% in black men. Besides ethnic differences in transcutaneous penetration, individual and ethnic skin sensitivity may play an important role in determining both patient compliance and therapeutic efficacy of drugs and cosmetics; furthermore, a drug formulation considering skin physiology may prevent unwanted local and general adverse effects.

In vivo biophysical characterization of skin physiological differences in races

The role of race in modulating skin responses has been investigated. Several parameters (skin thickness, transepidermal water loss, water content of the stratum corneum and skin biomechanics) have been measured using noninvasive tools in whites, Hispanics and blacks to assess whether the melanin content could induce changes in skin biophysical properties. Marked differences between races appear in stratum corneum water content and in skin extensibility, recovery and elastic modulus. Measurements done in different sun-exposed sites highlight the effects of solar irradiation on the skin and the role of melanin in preventing skin damage. The study shows that racial differences in skin physiology exist and are mainly related to the protective role of melanin present in races with darker skin. Moreover, differences in skin hydration are not fully explained according to the site and presence of hair.