Antihistamines in Dermatology

Abstract

Along with antibiotics, antihistamines are the most widely used systemic drugs in dermatology. This is attributable to the major role played by histamine in common diseases such as urticaria and atopic eczema. Of the currently recognised four subtypes of G protein-coupled histamine receptors, only the H₁ and H₂ subtypes have been positively identified in human skin. Traditionally believed to be competitive antagonists of histamine, H₁ and H₂ antihistamines are now considered to behave as inverse agonists. By consensus, H₁ antihistamines are classified as ‘first generation’ (associated with troublesome side-effects including somnolence, anti-adrenergic and atropine-like actions) and ‘second-generation’ compounds (in which these side-effects are reduced or absent). The main indications for H₁ antihistamines in skin are suppression of pruritus in urticaria and atopic eczema, both of which are associated with increased mast cell numbers and tissue histamine levels. However the evidence basis for use in atopic eczema is ambiguous and controversial, even though these drugs are widely used in practice. Currently, significant side-effects are mainly confined to the first-generation compounds and are especially troublesome in the elderly. Psychomotor impairment may persist throughout the day following administration. Anti-cholinergic and anti-α-adrenergic blockade and cardiotoxicity (torsade de pointes) may also occur with first-generation antihistamines. Two early low-sedation second-generation antihistamines caused arrhythmias in a small number of patients but these compounds have now been withdrawn. Generally, the second-generation H₁ antihistamines are well tolerated.

Chronic Urticaria: Recent Advances

“…Their clinical pharmacology and correct usage in urticaria has recently been reviewed [48]. Pruritus is the main symptom of most types of urticaria, and its diurnal periodicity should be determined in every patient.…”

“…Doxepin should be used with extreme caution in patients with heart disease and in the elderly, and should never be withdrawn abruptly. It is also important to emphasize the importance of regular dosage of H1 antihistamines to avoid the problem of development of subsensitivity ("pseudotachyphylaxis") [48]. For a small number of patients, especially those with CIU rather than a physical urticaria, even off-label dosages of H1 antihistamines are poorly effective.…”

Effects of Torilis japonica Extract on DNCB-induced Contact Dermatitis in BALB/c Mice

“…Histamine is involved in induction of itching and edema 40) . Histamine is detected commonly in AD skin lesions 53) . AD patients indicated high levels of histamine in plasma compared with healthy controls 54) .…”

Pathogenesis and Management of Pruritus in PBC and PSC

“…The nonspecific antipruritic effect observed in a few patients may result from their sedative properties [100] . However, dryness of mucous membranes is a common adverse effect of antihistamines, which further limits its use in PBC patients with sicca symptoms.…”