Terfenadine

Definition
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H1 antagonist.

Half-life
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4–6 h

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Indication
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Rhinitis allergica, allergic skin reactions.

Limited indication
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Bronchial asthma, hypokalemia (previous compensation), known QT time reduction, combination with macrolides or azole antifungals, psoriasis vulgaris (worsening possible).

Dosage and method of use
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Adults/teenagers: 2 times/day 60-120 mg p.o.
Children 9-12 years: 2 times/day 30-60 mg p.o.
Children 6-9 years: 2 times/day 30 mg p.o.

Undesirable effects
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Gastrointestinal disturbances, hyperhidrosis, headache, pruritus, flushing, urticaria, depression, reaction limitation, seizures, fatigue, dizziness, visual disturbances, extrasystoles, cardiac arrhythmias, galactorrhea, bronchospasm, dry mouth, transaminase increase, dysmenorrhea, myalgias, alopecia, photosensitization.

Notice. Discontinue preparation if syncope occurs!

Interactions
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See Table 1.

Contraindication
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Hypersensitivity to the active substance, pregnancy, lactation, children < 6 years (Tbl.), children < 12 months (Tbl., suspension), severe liver dysfunction.

Preparations
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Hisfedin, Terfenadine ratiopharm

Note(s)
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In the meantime, terfenadine has been withdrawn from the market in various countries due to cardiac side effects. The successor of terfenadine (fexofenadine) is the metabolite of terfenadine responsible for the histamine H1 receptor antagonism. The unfavourable effects on the electrophysiology of the heart are due to the terfenadine mother substance, not to the antihistaminically active metabolite.

Literature
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del Cuvillo A et al (2006) Comparative pharmacology of the H1 antihistamines. J Investig Allergol Clin Immunol 16: 3-12
Borchard U (2003) New H1 antihistamines in comparison. Allergology 1: 23-32

Tables
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Essential interactions of terfenadine

Clarithromycin	QT extension
Erythromycin	QT prolongation, cardiac arrhythmia, avoid combination
Fluconazole	Cardiac arrhythmia
Fluvoxamine	torsades de pointes
Itraconazole	Cardiac arrhythmia, torsades de pointes, avoid combination
Josamycin	QT prolongation, cardiac arrhythmia, avoid combination
Ketoconazole	QT prolongation, cardiac arrhythmia, avoid combination
Miconazole	Cardiac arrhythmia, avoid combination
Oleandromycin	QT prolongation, cardiac arrhythmia
Roxithromycin	Cardiac arrhythmia
Sotalol	QT extension
Troleandromycin	QT extension