Antihistamines fexofenadine

Scherer, C.R., Lerche, C., Decher, N., Dennis, A.T., Maier, P., Picker, E., Busch, A.E., Wollnik, B. and Steinmeyer, K. (2002) The antihistamine fexofenadine does not affect l(Kr) currents in a case report of drug-induced cardiac arrhythmia. British Journal of Pharmacology, 137, 892-900. 

ANTACIDS ANTIHISTAMINES-FEXOFENADINE 1 fexofenadine levels 1 absorption Be aware... 

Dicpinigaitis PV, Gayle YE (2003b) Effed of the second-generation antihistamine, fexofenadine, on cough reflex sensitivity and pulmonary function. Br J din Pharmacol 56 501-504 Doherty MJ, Mister R, Pearson MG, Calverley PM (2000) Capsaicin responsiveness and cough in asthma and chrome obstmetive pulmonary disease. Thorax 55 643-649... 

Antifungals Voriconazole (Rengelshausen et al. 2005) Antihistamines Fexofenadine (studies have indicated mixed results, with some reporting that plasma levels are increased while others indicating that plasma levels are decreased) (Dresser et al. 2003 Hamman et al. 2001 Wang et al. 2002)... 

Antihistamines bind to the same active site of the enzyme that binds histamine in the cell, but they evoke a different response. An antihistamine like fexofenadine (trade name Allegra), for example, inhibits vasodilation, so it is used to treat the symptoms of the common cold and allergies. Unlike many antihistamines, fexofenadine does not cause drowsiness because it binds to histamine receptors but does not cross the blood-brain barrier, so it does not affect the central nervous system. Cimetidine (trade name Tagamet) is a histamine mimic that blocks the secretion of hydrochloric acid in the stomach, so it is used to treat individuals with ulcers. 

The latter approach is used in the enantioselective determination of a Phase I metabolite of the antihistaminic drug, terfenadine. Terfenadine is metabolized to several Phase I compounds (Fig. 7-13), among which the carboxylic acid MDL 16.455 is an active metabolite for which plasma concentrations must often be determined. Although terfenadine can be separated directly on Chiralpak AD - an amy-lose-based CSP - the adsorption of the metabolite MDL 16.455 is too high to permit adequate resolution. By derivatizing the plasma sample with diazomethane, the carboxylic acid is converted selectively to the methyl ester, which can be separated in the presence of all other plasma compounds on the above-mentioned CSP Chiralpak AD [24] (Fig. 7-14). Recently, MDL 16.455 has been introduced as a new antihistaminic drug, fexofenadine. 

Antihistamines are drags used to counteract the effects of histamine on body organs and structures. Examples of antihistamines include diphenhydramine (Benadryl), loratadine (Claritin), fexofenadine (Allegra), and cetirizine (Zyrtec). A new antihistamine, deslorata-dine (Clarinex), is die active metabolite of loratadine and is intended to eventually replace loratadine (Claritin). Topical corticosteroid nasal sprays such as fluticasone propionate (Flonase) or triamcinolone ace-tonide (Nasacort AQ) are also used for nasal allergy symptoms. See Chapter 56 for more information on die topical corticosteroids. 

First-generation antihistamines are effective, but associated sedation and psychomotor impairment limit chronic use. Efficacy and safety of second-generation antihistamines in children have been demonstrated in clinical trials.33 Cetirizine is indicated for children 6 months of age and older, loratadine for children 2 years of age and older, and fexofenadine for children 6 years of age and older.15... 

The mechanisms of the beneficial effect of HRl antihistamines in asthma have been investigated in a mice model. Fexofenadine was found to suppress allergic immune/inflammatory responses in sensitized mice [60]. Treatment with fexofenadine diminished Th2-like response that typically follows sensitization and challenge with... 

Fexofenadine (Allegra) Antihistamine Filgrastim Leukocyte-stimulat-... 

Cetirizine is a non-sedating antihistamine drug that may be used for symptomatic relief in allergic rhinitis (hay fever) as it reduces rhinorrhoea and sneezing. Fexofenadine is an active metabolite of terfenadine (another antihistamine). 

Antagonists. Most of the so-called Hi-antihistamines also block other receptors, including M-cholinoceptors and D-receptors. Hi-antihistamines are used for the symptomatic relief of allergies (e.g., bamipine, chlorpheniramine, clemastine, dimethindene, mebhydroline pheniramine) as antiemetics (meclizine, dimenhydrinate, p. 330), as over-the-counter hypnotics (e.g., diphenhydramine, p. 222). Promethazine represents the transition to the neuroleptic phenothiazines (p. 236). Unwanted effects of most Hi-antihistamines are lassitude (impaired driving skills) and atropine-like reactions (e.g., dry mouth, constipation). At the usual therapeutic doses, astemizole, cetrizine, fexofenadine, and loratidine are practically devoid of sedative and anticholinergic effects. Hj-antihistamines (cimetidine, ranitidine, famotidine, nizatidine) inhibit gastric acid secretion, and thus are useful in the treatment of peptic ulcers. 

B. Although scopolamine effectively combats motion sickness, it is an antimuscarinic agent, not an antihistamine. Dimenhydrinate is an antihistamine with signihcant antimuscarinic properties that are likely to contribute to its anti-motion sickness activity. Chlorpheniramine, fexofenadine, and tripelennamine are antihistamines without signihcant efficacy in the treatment of motion sickness. 

Geriatric Considerations - Summary Clearance and half-life are altered in older adults therefore reduce starting dose. More sedating than fexofenadine and lorata-dine consider an alternate second-generation antihistamine. 

Fexofenadine inhibited antigen-induced bronchospasm and histamine release from mast cells. No anticholinergic or alpha adrenergic-receptor blocking effects were observed. Moreover, no sedative or other CNS effects were observed. Fexofenadine does not cross the blood-brain barrier. It inhibits skin wheal and flare responses produced by histamine injection. Following single and twice daily oral administration, antihistaminic effects occurred within 1 hour, achieved a maximum at 2-3 hours, and lasted a minimum of 12 hours. 

One can find many more examples where a subtle modification in a side chain leads to a new drug that produces a drastically different therapeutic or toxicological outcome. This is clearly illustrated by the nonsedating antihistamine terfenadine (Seldane), which produces cardiotoxicity when given with certain drugs that inhibits its metabolism. This product is no longer marketed. It has been replaced by its safer but no less effective carboxylic oxidative metabolite fexofenadine (Allegra). 

Occasionally a metabolite may provide a safer or more effective pharmaceutical than the parent compound selected for development. For example, fexofenadine, a widely sold nonsedating antihistamine, is the active metabolite of terfenadine. Fexofenadine is a safer drug than terfenadine and has replaced it on the market. 

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