Percutaneous absorption of drugs. IV. Percutaneous absorption of drugs from oily vehicles

Safety Assessment of Salicylic Acid, Butyloctyl Salicylate, Calcium Salicylate, C12–15 Alkyl Salicylate, Capryloyl Salicylic Acid, Hexyldodecyl Salicylate, Isocetyl Salicylate, Isodecyl Salicylate, Magnesium Salicylate, MEA-Salicylate, Ethylhexyl Salicylate, Potassium Salicylate, Methyl Salicylate, Myristyl Salicylate, Sodium Salicylate, TEA-Salicylate, and Tridecyl Salicylate

Salicylic Acid is an aromatic acid used in cosmetic formulations as a denaturant, hair-conditioning agent, and skin-conditioning agent—miscellaneous in a wide range of cosmetic products at concentrations ranging from 0.0008% to 3%. The Calcium, Magnesium, and MEA salts are preservatives, and Potassium Salicylate is a cosmetic biocide and preservative, not currently in use. Sodium Salicylate is used as a denaturant and preservative (0.09% to 2%). The TEA salt of Salicylic Acid is used as an ultraviolet (UV) light absorber (0.0001% to 0.75%). Several Salicylic Acid esters are used as skin conditioning agents—miscellaneous (Capryloyl, 0.1% to 1%; C12–15 Alkyl, no current use; Isocetyl, 3% to 5%; Isodecyl, no current use; and Tridecyl, no current use). Butyloctyl Salicylate (0.5% to 5%) and Hexyldodecyl Salicylate (no current use) are hair-conditioning agents and skin-conditioning agents—miscellaneous. Ethylhexyl Salicylate (formerly known as Octyl Salicylate) is used as a fragrance ingredient, sunscreen agent, and UV light absorber (0.001% to 8%), and Methyl Salicylate is used as a denaturant and flavoring agent (0.0001% to 0.6%). Myristyl Salicylate has no reported function. Isodecyl Salicylate is used in three formulations, but no concentration of use information was reported. Salicylates are absorbed percutaneously. Around 10% of applied salicylates can remain in the skin. Salicylic Acid is reported to enhance percutaneous penetration of some agents (e.g., vitamin A), but not others (e.g., hydrocortisone). Little acute toxicity (LD50 in rats; >2 g/kg) via a dermal exposure route is seen for Salicylic Acid, Methyl Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate. Short-term oral, inhalation, and parenteral exposures to salicylates sufficient to produce high blood concentrations are associated primarily with liver and kidney damage. Subchronic dermal exposures to undiluted Methyl Salicylate were associated with kidney damage. Chronic oral exposure to Methyl Salicylate produced bone lesions as a function of the level of exposure in 2-year rat studies; liver damage was seen in dogs exposed to 0.15 g/kg/day in one study; kidney and liver weight increases in another study at the same exposure; but no liver or kidney abnormalities in a study at 0.167 g/kg/day. Applications of Isodecyl, Tridecyl, and Butyloctyl Salicylate were not irritating to rabbit skin, whereas undiluted Ethylhexyl Salicylate produced minimal to mild irritation. Methyl Salicylate at a 1% concentration with a 70% ethanol vehicle were irritating, whereas a 6% concentration in polyethylene glycol produced little or no irritation. Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were not ocular irritants. Although Salicylic Acid at a concentration of 20% in acetone was positive in the local lymph node assay, a concentration of 20% in acetone/olive oil was not. Methyl Salicylate was negative at concentrations up to 25% in this assay, independent of vehicle. Maximization tests of Methyl Salicylate, Ethylhexyl Salicylate, and Butyloctyl Salicylate produced no sensitization in guinea pigs. Neither Salicylic Acid nor Tridecyl Salicylate were photosensitizers. Salicylic Acid, produced when aspirin is rapidly hydrolyzed after absorption from the gut, was reported to be the causative agent in aspirin teratogenesis in animals. Dermal exposures to Methyl Salicylate, oral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate, and parenteral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate are all associated with reproductive and developmental toxicity as a function of blood levels reached as a result of exposure. An exposure assessment of a representative cosmetic product used on a daily basis estimated that the exposure from the cosmetic product would be only 20% of the level seen with ingestion of a “baby” aspirin (81 mg) on a daily basis. Studies of the genotoxic potential of Salicylic Acid, Sodium Salicylate, Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were generally negative. Methyl Salicylate, in a mouse skin-painting study, did not induce neoplasms. Likewise, Methyl Salicylate was negative in a mouse pulmonary tumor system. In clinical tests, Salicylic Acid (2%) produced minimal cumulative irritation and slight or no irritation(1.5%); TEA-Salicylate (8%) produced no irritation; Methyl Salicylate (>12%) produced pain and erythema, a 1% aerosol produced erythema, but an 8% solution was not irritating; Ethylhexyl Salicylate (4%) and undiluted Tridecyl Salicylate produced no irritation. In atopic patients, Methyl Salicylate caused irritation as a function of concentration (no irritation at concentrations of 15% or less). In normal skin, Salicylic Acid, Methyl Salicylate, and Ethylhexyl (Octyl) Salicylate are not sensitizers. Salicylic Acid is not a photosensitizer, nor is it phototoxic. Salicylic Acid and Ethylhexyl Salicylate are low-level photoprotective agents. Salicylic Acid is well-documented to have keratolytic action on normal human skin. Because of the possible use of these ingredients as exfoliating agents, a concern exists that repeated use may effectively increase exposure of the dermis and epidermis to UV radiation. It was concluded that the prudent course of action would be to advise the cosmetics industry that there is a risk of increased UV radiation damage with the use of any exfoliant, including Salicylic Acid and the listed salicylates, and that steps need to be taken to formulate cosmetic products with these ingredients as exfoliating agents so as not to increase sun sensitivity, or when increased sun sensitivity would be expected, to include directions for the daily use of sun protection. The available data were not sufficient to establish a limit on concentration of these ingredients, or to identify the minimum pH of formulations containing these ingredients, such that no skin irritation would occur, but it was recognized that it is possible to formulate cosmetic products in a way such that significant irritation would not be likely, and it was concluded that the cosmetics industry should formulate products containing these ingredients so as to be nonirritating. Although simultaneous use of several products containing Salicylic Acid could produce exposures greater than would be seen with use of baby aspirin (an exposure generally considered to not present a reproductive or developmental toxicity risk), it was not considered likely that consumers would simultaneously use multiple cosmetic products containing Salicylic Acid. Based on the available information, the Cosmetic Ingredient Review Expert Panel reached the conclusion that these ingredients are safe as used when formulated to avoid skin irritation and when formulated to avoid increasing the skin's sun sensitivity, or, when increased sun sensitivity would be expected, directions for use include the daily use of sun protection.

Final Report on the Safety Assessment of Myristyl Myristate and Isopropyl Myristate

Acute oral and dermal toxicity tests indicated that Myristyl Myristate is nontoxic to rats. This cosmetic ingredient produced minimal to mild skin irritation, minimal eye irritation in rabbits, and no sensitization in guinea pigs. Studies with rabbits indicated that undiluted Isopropyl Myristate was a mild irritant after 24 h and moderate to severe when applied for three consecutive days. Isopropyl Myristate was minimally irritating to the rabbits' eye, and was not a skin sensitizer in studies with guinea pigs. In limited studies, Isopropyl Myristate was not carcinogenic on the skin of mice, but a mixture of Isopropyl Myristate and isopropyl alcohol significantly accelerated the carcinogenic activity of benzo(a)pyrene on the skin.

Human studies with Isopropyl Myristate indicated that it was not a human skin irritant or sensitizer when applied in a product formulation containing 15-58% of the ingredient. A product containing 43% Isopropyl Myristate produced no phototoxicity and no photo-contact allergenicity in human studies.

From the available information, it is concluded that Myristyl Myristate and Isopropyl Myristate are safe as cosmetic ingredients in the present practices of use.

Percutaneous absorption of salicylic acid after repeated (14-day) in vivo administration to normal, acnegenic or aged human skin

The objective of the present work was to determine the relative bioavailability of salicylic acid (SA) after repeated (14-day) topical application to subjects who presented normal, acnegenic, or photodamaged facial skin. To emulate exposure characteristics likely to be encountered by subjects in these two subpopulations, individuals presenting facial acne were treated with 2% SA in a hydroalcoholic vehicle, and volunteers with aged or photodamaged skin received a comparable topical dose of SA in a cream (moisturizer-like) vehicle. Plasma concentration-time profiles and cumulative urinary excretion of SA were measured after the last dose in subjects who had received 15 consecutive daily topical applications of 27 mg of SA or oral doses of 81 mg of acetylsalicylic acid (ASA). The rate and extent of percutaneous absorption of SA were not affected by facial skin condition. Faster rates of absorption (Cmax) were obtained with a hydroalcoholic compared with a cream vehicle. Systemic SA exposures were at least five-fold higher with oral ASA than topical SA. Based on systemic salicylate concentrations resulting from ingestion of 81 mg of ASA, these results support that patients without gross skin disorders are at minimal risk of adverse systemic effects from routine use of topical products containing 2% SA.

A biophysically based dermatopharmacokinetic compartment model for quantifying percutaneous penetration and absorption of topically applied agents. I. Theory

We present a general comprehensive mathematical model to stimulate and predict percutaneous absorption and subsequent disposition of chemicals in vivo that is chiefly based on biophysical parameters estimated or measured with in vitro and ex vivo perfused skin preparations. Current physicochemical principles of drug diffusion and partitioning across the skin barrier, solute and solvent concentration dynamics, the influence of solute and solvent on the stratum corneum barrier, and dynamic vascular perfusion effects are integrated in this model. Such a comprehensive approach is necessary to achieve optimal biological relevance in a quantitative model of percutaneous absorption, particularly when a chemical is applied as a binary (solute and solvent) or more complex formulation or chemical mixture. The proposed model should have applications in (a) designing drugs and permeation enhancers for passive or active (e.g., electrically assisted) transdermal drug delivery, (b) assessing the systemic exposure of topical drugs used in dermatology, and (c) integration into other mathematical models being developed to assess the risk after topical exposure to mixtures of environmental pollutants. We also have included experimental data to provide a preliminary illustration of the performance of the model.

Enhancing effects of lipophilic vehicles on skin penetration of methyl nicotinate in vivo

Vehicle effects may be caused by thermodynamic effects and by specific (penetration enhancing) effects. To investigate the effects of various lipophilic vehicles on drug penetration, an in vivo permeability study was conducted with methyl nicotinate as the model drug. The drug was dissolved in the respective vehicles at concentrations that provide equal drug escaping tendencies. Drug solutions were applied to the upper arms of volunteers with a glass chamber system. To avoid drug depletion effects, drug disappearance rates were measured under steady-state conditions by the difference method. Enhancement factors were calculated from the steady-state flux values (i.e., drug disappearance rates per area unit) and compared with results from non-steady-state experiments. Significant enhancing effects (p < 0.01) were observed with dibutyl adipate, caprylic/capric acid triglycerides containing 5% phospholipids, isopropyl myristate, and mineral oil. Caprylic/capric acid triglycerides, cetearyl isooctanoate, and the standard vehicle dimethicone 100 were without effect on drug penetration. The explanation for the observed enhancing effects may be an interaction of the lipophilic liquids with the lipid bilayers of the stratum corneum that leads to a decrease of the barrier resistance.

Effect of repeated skin application on percutaneous absorption of salicylic acid

Various concentrations of salicylic acid in hydrophilic ointment were applied repeatedly at daily or weekly intervals to rats in vivo. Salicylic acid absorption through treated skin was monitored by determining the penetration fluxes of salicylic acid through skin excised at various times. A gradual decrease in the salicylic acid penetration flux was observed following weekly applications of either 5 or 10% salicylic acid in hydrophilic ointment. The penetration flux of 1% salicylic acid remained constant. In the daily applications of 5 and 10% salicylic acid, the penetration flux increased after approximately 2 days of treatment and declined thereafter. The penetration flux of salicylic acid from the 1% salicylic acid increased slightly after 3--4 days of treatment.