Percutaneous retinoid absorption and embryotoxicity

Guidance for the pharmacological management of acne vulgaris

INTRODUCTION

Many international guidelines and expert consensuses are available to help the clinician diagnose and treat acne vulgaris; however, a simplified practical guidance that integrates current existing published recommendations is still lacking. This article aims to give practical and simplified insight into the treatment of acne.

AREAS COVERED

Herein, the author discusses the treatment of comedonal, papulopustular, and nodular/cystic/conglobate acne. The author also proposes a simplified treatment escalation strategy that is based on disease severity and extension, starting with topical treatments for mild cases and progressing over to systemic therapies in more severe cases.

EXPERT OPINION

The ideal acne treatment would simultaneously and safely target all the pathogenic factors implicated in the appearance of acne lesions with minimal side effects. Since no such treatment currently exists, combination therapies are usually recommended for most types of acne. A major limitation in choosing an appropriate treatment plan is the discrepant use of classification systems across the published literature making it difficult to draw clear and succinct conclusions about the recommendations given. Acne is not a traditional infectious disease and so while antibiotics may improve symptoms, they do not reliably resolve the condition. Thus, there is currently a tendency to opt for antibiotic-sparing treatment strategies whenever possible.

Pregnancy and dermatologic therapy

Dermatologists should be familiar with medication safety in pregnancy to be able to prescribe safely and confidently to pregnant women or women who may become pregnant during the course of treatment for dermatologic conditions. Topical medications should be considered first-line therapy for pregnant women, but certain systemic medications are safe to use in pregnancy and may be prescribed if necessary. Dermatologic surgery may be performed during the second trimester of pregnancy with proper positioning, but elective procedures should be delayed until the postpartum period.

Vitamin A: a multifunctional tool for development

Extensive research carried out over the last 100 years has established that the fat-soluble organic compound vitamin A plays crucial roles in early development, organogenesis, cell proliferation, differentiation and apoptosis as well as in tissue homeostasis. Given its importance during development, the delivery of vitamin A to the embryo is very tightly regulated with perturbations leading to severe malformations. This review discusses the roles of vitamin A during human development and the molecular mechanisms controlling its biological effects, hence bridging the gap between human development and molecular genetic work carried out in animal models. Vitamin A delivery during pregnancy and its developmental teratology in humans are thus discussed alongside work on model organisms, such as chicken or mice, revealing the molecular layout and functions of vitamin A metabolism and signaling. We conclude that, during development, vitamin A-derived signals are very tightly controlled in time and space and that this complex regulation is achieved by elaborate autoregulatory loops and by sophisticated interactions with other signaling cascades.

The Use of Dermatologic Drugs in Pregnancy and Lactation

Physicians are generally reluctant to prescribe dermatologic drugs to pregnant or nursing women because treatment is often elective and can be harmful to the patient, her fetus, or nursing infant; concerns for potential litigation also give pause. Yet, some effective dermatologic drugs have been determined to be safe during pregnancy and lactation. Of great practicality is an easily accessed reference guide that condenses information on such drugs into a set of tables that list pregnancy and teratogenicity ratings. Indications and contraindications are ordered in relation to the phases and trimesters of pregnancy. A discussion of the necessity of considering stages of childbearing in choosing drug therapies introduces the tables. A summary list of cautions spells out the steps physicians should take in treating women of childbearing age.

Minor malformations characteristic of the retinoic acid embryopathy and other birth outcomes in children of women exposed to topical tretinoin during early pregnancy

Topical tretinoin (Retin-A) is used to treat acne and photodamaged skin. Its teratogenic potential is of concern due to its similarity to isotretinoin (Accutane), a recognized human teratogen. Through the California Teratogen Information Service and Clinical Research Program, between 1983 and 2003, 106 pregnant women with first-trimester exposure to topical tretinoin were prospectively ascertained and followed. Birth outcomes, including pregnancy loss, major structural defects, and pre- and postnatal growth were compared to 389 similarly and prospectively ascertained women with no topical tretinoin exposure during pregnancy. Because a distinct pattern of malformation had already been described for isotretinoin, we also compared exposed (n = 62) and unexposed (n = 191) infants on the prevalence of a specific subset of minor malformations selected to represent the spectrum of defects comprising the retinoic acid embyopathy. There were no significant differences between groups in the proportion of pregnancies ending in spontaneous abortion (6.6% in exposed vs. 8.5% in unexposed; P = 0.53), or infants with major structural defects (2.2% in exposed vs. 1.2% in unexposed; P = 0.62). In addition, the groups were similar in birth weight, length and head circumference, and there were no significant differences between groups in length of gestation. Furthermore, the prevalence of one or more retinoic acid-specific minor malformations did not differ significantly between groups (12.9% in exposed vs. 9.9% in unexposed; P = 0.51). First-trimester topical tretinoin exposure in this study was not associated with an increased risk of any adverse pregnancy outcome evaluated. Specifically, there was no indication that topical tretinoin is associated with an increased risk for minor malformations that are consistent with the retinoic acid embryopathy. Although it is impossible to exclude the possibility that some women/infants may be uniquely susceptible to topical tretinoin exposure, this study provides further reassurance for women who are inadvertently exposed early in pregnancy.

A developmental toxicity study of tretinoin administered topically and orally to pregnant Wistar rats

BACKGROUND

Although it is well established that oral tretinoin produces embryofetal developmental toxicity in various laboratory animals, the toxic potential of topical tretinoin has not been clearly established.

OBJECTIVE

This study of tretinoin administration to pregnant Wistar rats was conducted to determine whether topical tretinoin is associated with adverse effects on reproductive function or embryofetal growth and development and to compare outcomes with topical and oral tretinoin.

METHODS

Topical and oral tretinoin (1 to 20 mg/kg and 1 to 10 mg/kg, respectively) or vehicles alone were administered on gestational days 6 through 16 and 15, respectively.

RESULTS

Topical tretinoin: After topical treatment, dams receiving 10 mg/kg daily or greater had severe local and systemic toxicity prompting discontinuation of tretinoin. At doses of 2.5 mg/kg or greater, dam weight gain and food consumption were significantly less than those of control dams. Offspring of dams receiving 5 mg/kg weighed significantly less, and offspring of dams receiving 2.5 mg/kg or greater had a significantly greater occurrence of supernumerary ribs compared with control offspring. Oral tretinoin: After oral treatment, in the absence of maternal toxicity, significantly more offspring of dams receiving 5 mg/kg or greater had supernumerary ribs, and offspring of the 10 mg/kg treatment group had a greater incidence of cleft palate than had control offspring.

CONCLUSION

The local and systemic maternal toxicity found in association with supernumerary ribs and low weights in the offspring at topical tretinoin doses of 2.5 and 5 mg/kg suggests that these developmental effects may be nonspecific or maternally mediated. Oral tretinoin at doses of 10 mg/kg, however, is clearly associated with embryofetal alterations in the Wistar rat.

Tretinoin: a review of the nonclinical developmental toxicology experience

Tretinoin has been thoroughly evaluated for its potential as an embryofetal developmental toxicant. Oral tretinoin produces developmental anomalies in animal models; the minimal teratogenic dose is consistently 2.5 to 10 mg/kg. In contrast, topical application does not induce developmental malformations in laboratory animals. A structurally related compound, isotretinoin, is a potent toxicant in humans and animals; the lowest systemic dose that induces fetal anomalies varies more than 100-fold depending on the model. Oral isotretinoin is a more potent developmental toxicant than oral tretinoin in monkeys. Between-drug differences in the metabolism and transplacental transfer of the two retinoids account for the differences in toxicant potency. Pharmacokinetic studies reveal that absorption of tretinoin from the skin is poor and yields maternal plasma concentrations below the developmentally toxic threshold established after oral administration. Analysis of outcomes of developmental toxicology and pharmacokinetic studies suggests that the human risk of fetal anomalies is negligible after therapeutic application of topical tretinoin.

A developmental toxicity study of tretinoin emollient cream (Renova) applied topically to New Zealand white rabbits

BACKGROUND

Embryofetal developmental toxicity associated with oral administration of vitamin A analogs has led to concern about risks from topical application.

OBJECTIVE

This study was conducted to evaluate the potential developmental toxicity of tretinoin emollient cream when applied to the skin of pregnant New Zealand white rabbits during organogenesis (gestational days 7 through 19).

METHODS

Twenty rabbits each were randomly assigned to a control group (group I) or to receive vehicle (group II) or tretinoin emollient cream topically at dosages of 10 (0.05 mg/kg*, group III) or 100 (0.5 mg/kg*, group IV) times that used clinically in humans. Does and fetuses were examined for tretinoin-induced toxic effects, and maternal plasma tretinoin and metabolite levels were measured.

RESULTS

The rate of abortion was increased significantly in does in group IV (p < or = 0.01) compared with the control group. Dosage-dependent increases in incidence and severity of skin reactions occurred in groups administered the vehicle and the two dosages of tretinoin. Does in groups III and IV had clinical and necropsy observations that were considered direct or indirect effects of tretinoin administration, persistent weight loss, and reduced feed consumption. Maternal endogenous plasma tretinoin levels were below the lower limit of quantitation of 5 ng/ml and were not significantly altered with treatment. Group IV had significantly reduced mean fetal body weight (p < or = 0.01) and a greater frequency of resorptions compared with group I. Although external, visceral, or skeletal alterations occurred at significantly greater levels in group III, they were unrelated to tretinoin administration because the fetal incidences were not dosage dependent, and the litter incidence did not significantly differ from the control group values.

CONCLUSION

Maternally toxic dosages of tretinoin were associated with an increased incidence of abortions and resorptions and reduced fetal body weight, two end points of developmental toxicity. Consistent with the absence of detectable tretinoin plasma levels, however, no changes in fetal morphology were attributable to tretinoin administration. *The milligrams per kilogram dosage refers to the amount of active ingredient (tretinoin). The 0.05 mg/kg and 0.5 mg/kg groups were treated with 0.005% and 0.05% wt/wt tretinoin emollient cream formulation. The 0.05% tretinoin emollient cream is the Renova clinical formulation. The 10 and 100 times clinical multiples refer to Renova clinical multiples and are based on a 50 kg adult patient's applying 500 mg of 0.05% tretinoin emollient cream formulation daily to yield a clinical dosage of 0.005 mg/kg.

Dermatologic drug use during pregnancy and lactation

Physicians are often asked to prescribe medication for women during the childbearing years. This article reviews which dermatologic drugs have been reported to interfere with contraceptive efficacy, which should be avoided, and which have the fewest contraindications for use during pregnancy and lactation. Corticosteroids and tretinoin are discussed in detail. Sources and guidelines for choices of dermatologic drugs for women of childbearing age are presented.

Teratogenicity of low doses of all-trans retinoic acid in presomite mouse embryos

This study was designed to examine the developmental dose response for all-trans retinoic acid (TRA) administered at presomite stages in mouse embryos. Previous studies using hamsters [Shenefelt (1972) Teratology 5:103-118] have shown that developmental stages corresponding to those present early on gestational day (GD) 7 in mice are most sensitive to retinoid-induced teratogenesis. Our preliminary studies showed that at this treatment time, gavage dosages of 7.5 mg/kg maternal body weight administered to C57B1/6N mice, an inbred strain, resulted in severe craniofacial malformations representing the holoprosencephaly, aprosencephaly spectrum. Additionally, in an outbred mouse strain, CD-1, exencephaly was induced by dosages of 2.5 mg/kg TRA and above. Readily detectable abnormalities of the eyes, including anophthalmia and severe microphthalmia and iridial colobomata, were induced by even lower doses cf TRA in the C57B1/6N strain. Incidences of micro/anophthalamia were 6.7%, 8.1%, 12.9%, and 32.4% at 0, 0.313, 0.625, and 1.25 mg/kg, respectively. The dosages required to induce significant incidences of exencephaly (2.5 mg/kg) and severe ocular abnormalities (1.25 mg/kg) on GD 7 in mice are approximately 50-100-fold less than those that are commonly used to examine the teratogenicity of this compound at later developmental stages in this species. The trend toward an increase in the incidence of severe ocular malformations at the lowest dose examined and the fact that subtle ocular malformations were not taken into account for this study suggest that even lower dosages may be effective.(ABSTRACT TRUNCATED AT 250 WORDS)