♦ bacitracin

Bacitracin is a polypeptide antibiotic that is applied topically for the treatment or prevention of local skin infections caused by susceptible aerobic and anaerobic gram-positive organisms such as staphylococci, streptococci, anaerobic cocci, corynebacteria, and clostridia. It works by inhibiting bacterial cell wall synthesis, which leads to cell death. It can be either bactericidal or bacteriostatic, depending on the causative organism. Its antimicrobial spectrum is broadened in several available combination drug products. Most of these also contain neomycin and/or polymyxin B (see later in the chapter).

Adverse reactions are usually minimal; however, reactions ranging from skin rash to allergic anaphylactoid reactions have occurred. If itching, burning, inflammation, or other signs of sensitivity occur, discontinue bacitracin. This drug is available in ointment form and is usually applied to the affected area one to three times daily. It is also available in systemic and ophthalmic (see Chapter 57) formulations.

neomycin and polymyxin B

Neomycin and polymyxin B are two additional broad-spectrum antibiotics that are available as the nonprescription product known as Neosporin. Neosporin cream is a combination of these two drugs alone, whereas Neosporin ointment also contains bacitracin. Several brand name and generic combinations of these three topical antibiotics are available, and all are commonly used as topical antiseptics for minor skin wounds. Although neomycin/polymyxin B is still a very popular over-the-counter (OTC) product, there is evidence that use of the drug can increase the likelihood of future allergic reactions of the skin.

mupirocin

Mupirocin (Bactroban) is an antibacterial product available only by prescription. It is used on the skin for treatment of staphylococcal and streptococcal impetigo. It is used topically and intranasally to treat nasal colonization with MRSA. The drug is applied topically three times daily and intranasally twice daily to treat MRSA colonization. Adverse reactions are usually limited to local burning, itching, or minor pain.

♦ silver sulfadiazine

Silver sulfadiazine (Silvadene) has proved both effective and safe in the prevention and treatment of infections in burns. A major concern for burn victims is infection at the burn site. However, because increased systemic absorption of a drug can occur in compromised skin areas, topical burn drugs must not be too potent or toxic to avoid causing dangerous systemic effects. This is especially true when larger burned areas must be treated, because the drug may be applied over a large surface area of skin and therefore may be absorbed in greater quantities. On the other hand, the blood supply to burned areas is often drastically reduced, so that systemically administered antibiotics either cannot reach the site or do so only in quantities too low to be effective. Therefore, the only way of applying these drugs to ensure that they reach the burn site is to do so topically.

Silver sulfadiazine is a synthetic antimicrobial drug produced when silver nitrate reacts with the chemical sulfadiazine. It appears to act on the cell membrane and cell wall of susceptible bacteria and is used as an adjunct in the prevention and treatment of infection in second- and third-degree burns and less frequently in cellulitic or eczematous extremities. The adverse effects of silver sulfadiazine are similar to those of other topical drugs and include pain, burning, and itching. This drug should not be used in patients who are allergic to sulfonamide drugs. It is available only as a 1% cream and is applied topically to cleansed and débrided burned areas once or twice daily using a sterile-gloved hand.

♦ benzoyl peroxide

The microorganism that most commonly causes acne, P. acnes, is an anaerobic bacterium; that is, it needs an environment that is poor in oxygen to grow. Benzoyl peroxide is effective in combating such infection because it slowly and continuously liberates active oxygen in the skin, resulting in antibacterial, antiseptic, drying, and keratolytic actions. These actions create an environment that is unfavorable for the continued growth of the P. acnes bacteria, and they soon die. Drugs such as benzoyl peroxide that soften scales and loosen the outer horny layer of the skin are referred to as keratolytics.

Benzoyl peroxide generally produces signs of improvement within 4 to 6 weeks. Adverse effects tend to be related to dose (including overuse) and include peeling skin, red skin, or a sensation of warmth. Blistering or swelling of the skin is generally considered an allergic reaction to the product and is an indication to stop treatment. Overuse of this drug and also of tretinoin is common in teenage patients who are attempting to cure their acne quickly. The result can be painful, reddened skin, which usually resolves on return to use of these medications as prescribed.

Benzoyl peroxide is available in multiple topical dosage forms, including a cleansing bar, liquid, lotion, mask, cream, gel, and cleanser. It is also available in various combination drug products. It is usually applied topically one to four times daily, depending on the dosage form and prescriber’s instructions. Benzoyl peroxide is classified as a pregnancy category C drug.

clindamycin

Clindamycin (Cleocin T) is a topical form of the systemic antibiotic described in Chapter 39. Adverse reactions are usually limited to minor local skin reactions, including burning, itching, dryness, oiliness, and peeling. The drug is available in gel, lotion, suspension, pledgettes, and foam. Clindamycin is usually applied once or twice daily. It is classified as a pregnancy category B drug.

♦ isotretinoin

tretinoin

Tretinoin (retinoic acid, vitamin A acid) (Renova, Retin-A) is a derivative of vitamin A that is used to treat acne and ameliorate the dermatologic changes (e.g., fine wrinkling, mottled hyperpigmentation, roughness) associated with photodamage (sun damage). The drug appears to act as an irritant to the skin, in particular to the follicular epithelium. Specifically, it stimulates the turnover of epidermal cells, which results in skin peeling. While this is occurring, the free fatty acid levels of the skin are reduced, and horny cells of the outer epidermis cannot then adhere to one another. Without fatty acids and horny cells, acne and its comedo, or pimple, cannot exist.

Topically administered tretinoin has been shown to enhance the repair of skin damaged by ultraviolet (UV) radiation, or sunlight. It does this by increasing the formation of fibroblasts and collagen, both of which are needed to rebuild skin. The drug also may reduce collagen degradation by inhibiting the enzyme collagenase that breaks down collagen.

Tretinoin’s main adverse effects are local inflammatory reactions, which are reversible when therapy is discontinued. Common adverse effects are excessively red and edematous blisters, crusted skin, and temporary alterations in skin pigmentation. Tretinoin is available in many topical formulations, including creams, gels, and a liquid. Because of its potential to cause severe irritation and peeling, it may initially be applied once every 2 or 3 days, and treatment often starts with a lower-strength product.

Retin-A Micro has been approved for the treatment of acne vulgaris. This particular acne product contains tretinoin formulated inside a synthetic polymer called a Microsponge system. This system is made of round microscopic particles of synthetic polymer. These microspheres act as reservoirs for tretinoin, allowing the skin to absorb small amounts of the drug over time. Retin-A Micro is currently available only in gel form. All topical forms of tretinoin are classified as pregnancy category C drugs. They are not to be confused with the oral capsule form of tretinoin that is used to treat leukemia and is classified as a pregnancy category D drug. Another antiacne retinoid is adapalene, a topical solution.