Terfenadine

Oral
Allergic conditions

CrCl	Dosage
<40	Half the usual daily dose

Porphyria.

Child and elderly. Avoid in patients with cardiac or significant hepatic disease, electrolyte imbalance, or known or suspected prolongation of the QT interval. Lactation, pregnancy.

Anxiety, palpitations, insomnia, mild GI distubances, erythema multiforme and galactorrhoea.
Potentially Fatal: Ventricular arrhythmias including torsades de pointes. Palpitations, dizziness, syncope or convulsions may indicate arrhythmias. Hepatitis.

Potentially Fatal: Increased risk of ventricular arrhythmia with triazole and imidazole antifungals, macrolide antibacterials, streptogramin antibacterials, SSRI, HIV-protease inhibitors and non-nucleoside reverse transcriptase inhibitors, arrhythmogenic drugs, diuretics, astemizole and zileutron.

Grapefruit juice may inhibit the metabolism of terfenadine.

Description: Terfenadine, a piperidine derivative, is a non-sedating H₁ receptor antagonist antihistamine.
Pharmacokinetics:
Absorption: Rapidly absorbed from GI tract. Peak plasma concentrations: within 2 hr.
Distribution: Protein binding: 97% (terfenadine). Does not appear to cross the blood-brain barrier to significant extent. Limited amounts of fexofenadine, but not terfenadine detected in breast milk. Elimination half-life: 16-23 hr (terfenadine).
Metabolism: Prodrug and undergoes extensive first-pass metabolism in the liver to active (carboxylic acid derivative fexofenadine) and inactive metabolites.
Excretion: Excreted in the urine and faeces (traces of unchanged drug and metabolites)

Antihistamines & Antiallergics