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Topical preparations constitute the sole treatment in many patients with acne and are part of the therapeutic regimen in almost all patients. This article reviews topical acne preparations and provides information that can help family physicians select agents or combinations of agents that are appropriate in various situations.
Understanding the pathophysiology of acne can help the physician tailor therapy to the individual patient. Acne lesions arise from pilosebaceous units, which consist of sebaceous glands and small hair follicles. These units are found everywhere on the body except the palms and soles.
Pilosebaceous density is greatest on the face, upper neck and chest, at roughly nine times the concentration found elsewhere on the body. Pilosebaceous units are present and active at birth as a reaction to maternal hormones. Thus, neonates can present with acne. The pilosebaceous units atrophy during childhood but, under the influence of androgens, reemerge during adolescence. Obstruction of the pilosebaceous canal is the primary cause of acne and occurs because of a variety of factors.
The first factor is sebum overproduction stimulated by hypersensitivity to androgenic steroids. The combination of sebum and desquamated cells provides an environment that is ripe for the growth of Propionibacterium acnes , the principal organism in inflammatory acne lesions.
Proliferation of P. The stages of acne are illustrated in Figure 3. Acne is usually diagnosed by the patient. The physician needs to determine if the condition is noninflammatory open and closed comedones , inflammatory papules or pustules or a mixture of both the most common situation.
Topical treatment is sufficient in most patients with acne, but systemic therapy is required in patients who have deep acne with nodules and cysts Figure 4. In most situations, the physician does not need to look for an underlying cause of acne. However, medications should be reviewed because corticosteroids, anabolic steroids, lithium and some oral contraceptives can contribute to the development of this condition.
In the treatment of acne, the vehicle cream, gel, lotion or solution may be as important as the active agent. Consequently, it is important to assess the patient's skin type. Creams are appropriate for patients with sensitive or dry skin who require a nonirritating, nondrying formulation.
Patients who have oily skin may be more comfortable with gels, which have a drying effect. However, gels may cause a burning-type irritation in some patients and may prevent certain kinds of cosmetics from adhering to the skin. Lotions can be used with any skin type, and they spread well over hair-bearing skin. Yet lotions contain propylene glycol and thus may have burning or drying effects.
Solutions are mainly used with topical antibiotics, which are often dissolved in alcohol. Like gels, solutions work best in patients with oily skin. Benzoyl peroxide, available over the counter and by prescription, has been a mainstay of acne treatment since the s Table 1. It is the topical agent most effective against P. Benzoyl peroxide can be obtained in various concentrations 2. The water-based formulations are less drying than the alcohol-based preparations. Benzoyl peroxide gels are applied once or twice daily.
Skin irritation is the most common side effect of benzoyl peroxide. This effect occurs more often at higher concentrations and tends to decrease with continued use. Contact allergy occurs in 1 to 2 percent of patients. Because benzoyl peroxide is an oxidizing agent, patients should be warned about potential bleaching of clothing and bed linens.
This problem can be avoided by applying benzoyl peroxide to a clean, dry face in the morning and putting it on the face again at dinner time, if needed. Salicylic acid is an ingredient of various over-the-counter preparations. It is available at a concentration of 0. This agent inhibits comedogenesis by promoting the desquamation of follicular epithelium. It has been shown to be as effective as benzoyl peroxide in the treatment of comedonal acne. Sulfur preparations have been used to treat acne since the time of Hippocrates.
Sulfur is combined with various other acne medications in many over-the-counter washes and cleansing bars. This agent has been shown to be effective in the treatment of inflammatory acne lesions, most likely as a result of keratolysis.
However, efficacy may also be related to an irritative effect. Preparations containing sulfur can cause some skin discoloration and can have a displeasing odor. Consequently, sulfur medications are now used less often in patients with acne.
The combination of sulfacetamide and sulfur Novacet, Sulfacet-R can be effective in the treatment of inflammatory skin lesions without the unpleasant side effects that occur with sulfur preparations alone. One study of sulfacetamide-sulfur lotion showed an 83 percent reduction in inflammatory lesions after 12 weeks of therapy. Azelaic acid is a decarboxylic acid that was first investigated in the s as a treatment for hyperpigmentation and was coincidentally found to be an effective acne treatment.
Food and Drug Administration FDA labeled azelaic acid for the treatment of mild to moderate inflammatory acne. Although its exact mechanism of action is unknown, this agent has antibacterial and antikeratinizing activity, and it appears to be as effective as benzoyl peroxide or tretinoin Retin-A in the treatment of mild to moderate acne. Azelaic acid is available as a 20 percent cream Azelex , which is applied twice daily to a clean, dry affected area.
The agent is fairly well tolerated, with only about 5 percent of patients complaining of transient cutaneous irritation and erythema. Because azelaic acid decreases pigmentation, it should be used with caution in patients with darker complexions. Retinoids, which are derivatives of vitamin A, function by slowing the desquamation process, thereby decreasing the number of comedones and microcomedones.
Retinoids are the most effective comedolytic agents in use. They have been a mainstay of acne treatment for the past 25 years. Until recently, tretinoin was the only available topical retinoid. This agent is effective as monotherapy in patients with noninflammatory or mild to moderate inflammatory acne. Tretinoin is available as a cream, gel or liquid. The cream has the lowest potency, and the liquid has the highest potency. All tretinoin formulations can cause some skin irritation.
The liquid is the most irritating, and the cream is the least irritating. The concentration of the agent also affects the degree of irritation. Tretinoin should be applied in small amounts to clean, dry skin. Because the irritation associated with tretinoin is compounded by sun exposure, the formulation should be applied to affected areas once daily at bedtime.
To assess irritation, a test dose should be applied and then washed off an hour or two later. To minimize irritation, tretinoin should be started at a low concentration, which can then be titrated upward as needed.
Skin irritation usually decreases with continued therapy. Patients should be warned that they may suffer a pustular flare during the first few weeks of tretinoin therapy. Rather than being an indication to stop or alter therapy, this pustular flare is a sign of the accelerated resolution of existing acne.
Because of the known teratogenic effects of oral vitamin A products, the use of tretinoin in pregnancy has been an issue of concern. Tretinoin is listed as a pregnancy category C drug. However, a study of women exposed to tretinoin in the first trimester showed no increase in anomalies compared with control subjects.
Tretinoin is now available in a new delivery system Retin-A Micro that may minimize its irritative effects. This delivery system works by entrapping the drug in microspheres that bring the medication more directly to the follicle and serve as reservoirs for the medication.
Adapalene Differin is a topical retinoid that was labeled by the FDA in Its mechanism of action is similar to that of tretinoin. Adapalene comes in a 0. Studies have shown that 0. Like tretinoin, adapalene may cause skin irritation and initial exacerbation of acne lesions. Tazarotene Tazorac gel is a retinoid product that the FDA has labeled for use in the treatment of psoriasis and mild to moderate acne.
It comes in a 0. Studies comparing tazarotone with vehicle alone have shown that the medication is effective in treating noninflammatory acne lesions. Although comparative drug trials have not been performed, tazarotene and the standard form of tretinoin appear to have similar irritation rates. The use of tazarotene in pregnant women is not recommended. Topical antibiotics work directly by killing P. Through their bactericidal activity, they also have a mild indirect effect on comedogenesis.
These agents are available in a variety of forms and are applied once or twice daily. Topical erythromycin and clindamycin Cleocin T are the most commonly used agents and have similar efficacy in patients with acne.
Almost all topical antibiotics are associated with some minor skin irritation. This adverse effect may be influenced by the vehicle used. Combination therapy is often employed when patients have a mixture of comedonal and inflammatory acne lesions.
Because adequate clinical studies are lacking, it is difficult to compare various combination therapies. The combination of 5 percent benzoyl peroxide and 3 percent erythromycin Benzamycin is a highly effective acne treatment.
The agents come unmixed, and the pharmacist or patient must combine the erythromycin powder with the benzoyl peroxide gel. The mixture must be refrigerated.
