DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

Table 65–7
Half-Life of Antihistamines
FIRST-GENERATION
t 1/2
IN ADULTS
H 1
BLOCKERS
(hours)
Hydroxyzine 7-10
Diphenhydramine 2-8
Promethazine 16-19
Cyproheptadine 1-4
Doxepin 17
SECOND-GENERATION
H 1
BLOCKERS
Cetirizine 8.3
Levocetirizine 8-9
Loratadine 8
Desloratadine 27
Fexofenadine 14.4
H 2
BLOCKERS
Cimetidine 2
Ranitidine 2-3
Famotidine 2.5-4
Nizatidine 1-2
Doxepin 17
making them useful for the control of pruritus. First-generation
sedating H 1
receptor antagonists include hydroxyzine, diphenhydramine
(BENADRYL, others), promethazine, and cyproheptadine.
Doxepin, which has tricyclic antidepressant and sedative and antihistaminic
effects (see Chapter 15), is a good alternative to traditional
oral antihistamines for severe pruritus. A 5% topical cream formulation
of doxepin (PRUDOXIN, ZONALON), which can be used in
conjunction with low- to moderate-potency topical glucocorticoids,
also is available. Allergic contact dermatitis to doxepin has been
reported. The anti-pruritic effect from topical doxepin is comparable
to that of low-dose oral doxepin therapy.
Second-generation H 1
receptor antagonists lack
anticholinergic side effects and are described as nonsedating
largely because they do not cross the blood-brain
barrier. They include cetirizine (ZYRTEC, others), levocetirizine
dichloride (XYZAL), loratadine (CLARITIN, others),
desloratadine (CLARINEX), and fexofenadine
hydrochloride (ALLEGRA, others). While secondgeneration
“nonsedating” H 1
receptor blockers are as
effective as the first-generation H 1
blockers, they are
metabolized by CYP3A4 and, to a lesser extent, by
CYP2D6 and should not be co-administered with medications
that inhibit these enzymes (e.g., imidazole antifungals,
macrolide antibiotics).
ANTIMICROBIAL AGENTS
Antibiotics
These drugs commonly are used to treat superficial cutaneous
infections (Table 65–8) (pyoderma) and noninfectious
diseases, including acne rosacea, perioral
dermatitis, hidradenitis suppurativa, auto-immune blistering
diseases, sarcoidosis, and pyoderma gangrenosum
(Carter, 2003). Topical agents are very effective for the
treatment of superficial bacterial infections and acne vulgaris.
Systemic antibiotics also are prescribed commonly
for acne and deeper bacterial infections. The pharmacology
of individual antibacterial agents is discussed in
Section VI, Chemotherapy of Infectious Diseases. Only
the topical and systemic antibacterial agents principally
used in dermatology are discussed here.
Acne vulgaris is the most common dermatological
disorder treated with either topical or systemic
antibiotics. The anaerobe P. acnes is a component of
normal skin flora that proliferates in the obstructed,
lipid-rich lumen of the pilosebaceous unit, where O 2
tension is low. P. acnes generates free fatty acids that
Table 65–8
Recommended Cutaneous Antifungal Therapy
CONDITION TOPICAL THERAPY ORAL THERAPY
Tinea corporis, localized Azoles, allylamines —
Tinea corporis, widespread — Griseofulvin, terbinafine, itraconazole, fluconazole
Tinea pedis Azoles, allylamines Griseofulvin, terbinafine, itraconazole, fluconazole
Onychomycosis — Griseofulvin, terbinafine, itraconazole, fluconazole
Candidiasis, localized Azoles —
Candidiasis, widespread and mucocutaneous — Ketoconazole, itraconazole, fluconazole
Tinea versicolor, localized
Azoles, allylamines
Tinea versicolor, widespread — Ketoconazole, itraconazole, fluconazole