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Chapter 48: Dermatological Pharmacology

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The rate-limiting step in the absorption of drugs through the skin is passage through the

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a. dermis.

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b. epidermis.

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c. stratum corneum.

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d. hypodermis.

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e. sweat glands.

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Answer is c. Passage through the outermost layer (stratum corneum) is the rate-limiting step for percutaneous absorption. Permeability generally is inversely proportional to the thickness of the stratum corneum. Drug penetration is higher on the face, intertriginous areas, and perineum due to minimal stratum corneum thickness in these regions.

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A 35-year-old man has a fungal infection of his toenails. A systemic antifungal preparation, griseofulvin, is prescribed because

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a. topical antifungal preparations are irritating.

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b. topical antifungal agents are expensive.

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c. systemic antifungal agents produce high drug concentrations in the nails.

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d. systemic antifungal agents have no adverse effects.

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e. topical antifungal preparation are easily washed off the nails.

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Answer is c. Systemic therapy is necessary for effective management of onychomycosis (see Chapter 43). Griseofulvin is deposited in keratin precursor cells; when these cells differentiate, the drug is tightly bound to, and persists in, keratin, providing prolonged resistance to fungal invasion. For this reason, the new growth of hair or nails is the first to become free of disease. As the fungus-containing keratin is shed, it is replaced by normal tissue.

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A 23-year-old woman with recalcitrant acne is being treated with an oral dose of isotretinoin. She should be warned against

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a. getting pregnant.

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b. sun exposure.

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c. close contact with her 1-year-old child.

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d. flying in an airplane.

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e. eating broccoli.

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Answer is a. Isotretinoin is approved for the treatment of recalcitrant and nodular acne vulgaris. Systemic retinoids are highly teratogenic. There is no safe dose during pregnancy. Common malformations include craniofacial, cardiovascular, thymic, and central nervous system (CNS) abnormalities. Although there appears to be minimal, if any, risk of retinoid embryopathy in fetuses conceived by males taking systemic retinoids, it is commonly recommended that men avoid retinoid therapy when actively trying to father children.

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A 53-year-old woman with psoriasis is treated with methotrexate. Aside from monitoring her blood count for evidence of bone ...

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