Prescription Medications
Since the body's allergic reaction is caused by histamine,which triggers the full-blown allergic
reaction,medications called antihistamines are specific against allergies.They block histamine's activity and prevent its effects on the body. First-generation antihistamine
- Chlorpheniramine (Piriton)
- Brompheniramine (Dimetane, Dimetap)
- Dimenhydrinate (Dramamine)
- Hydroxyzine (Atarax)
- Triprolidine Hydrochloride (Actiefed)
The most common side effect of
first-generation Antihistamines is sedation, it may interfere with the patient's daytime activities.,.In recent year the second-generation antihistamines have been designed to be "non-sedating".
Second-generation antihistamine
- Terfenadine (Servinadine,Seldan)
- Loratadine (Claritin)
- Cetirizine (Zyrtec)
- Azelastine (Astelin,Azep)
Second-generation antihistamineTerfenadine(Servinadine,seldane), loratadine(claritin)are largely excluded from the brain when given in
therapeutic doses,because they do not cross the blood-brain barrier appreciably. The lack of sedation is in contrast of the profound sedating side effects of first-generation antihistamines and may be of
significant clinical benefit. Rarely,terfenadine and astemizole cause prolongation of the QT interval with resultant polymorphic ventricular tachycardia. The mechanism underlying terfenadine-related cases
is understood and seems similar for astemizole. The tachycardia can occur when terfenadine is taken in higher-than-recommended dosages or in situations in which hepatic metabolism is impaired either
by disease or by coadministration of drugs that inhibit CYP3A4,the specific cytochrome P450 thought to be responsible for terfenadine metabolism. The drugs that most commonly inhibit CYP3A4-mediated terfenadine
metabolism are the macrolite antibiotics [most notably erythromycin ethylsuccinate] and clarithromycin(Biacin) and antifungal agents[most notably ketoconazole(Nizoral) and itraconazole(Sporanox)].
Azithromycin(Zithromax) and Fluconazole(Diflucan).
Zyrtec(Cetirizine) is an active metabolite of hydroxyzine( the first-generation antihistamine) that does not significantly penetrate the central
nervous system and has less propensity to sedation.
Thrid-generation antihistamine
- Telfast,Allegra(Fexofenadine)
The third-generation antihistamine
fexofenadine (Telfast,Allegra) is the active metabolite of terfenadine. It is non-sedative,dose not cause QT prolongation when given in hight dose or when administered concomitantly with ketoconazole or
erythromycin.
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