Fexofenadine Cimetidine

Miscellaneous Amitriptyline, cimetidine, fexofenadine, lidocaine, loperamide, quinine, telmisartan, terfenadine... 

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. 

Yasui-Furukori N, Uno T, Sugawara K, et al. Different effects of three transporting inhibitors, verapamil, cimetidine, and probenecid, on fexofenadine pharmacokinetics. Clin Pharmacol Ther 2005 77 17-23. 

Transporter absorptive effects predominant Examples. Acyclovir, Amiloride -, Amoxicillin Atenolol Atropine, Bidisomide Bisphosphonates Captoprit, Cefazolin Cetirizine Cimetidine Ciprofloxacin, Cloxacillin Dicloxacillin Erythromycin - -, Famotidine Fexofenadine Folinic acid Furosemide, Ganciclovir Hydrochlorothiazide, Lisinopril Metformin Methotrexate, Nadolol Penicillins Pravastatin Ranitidine Tetracycline Trimethoprim Valsartan Zalcitabine... 

Cimetidine 400 mg twice daily for 6 days did not cause any changes in the plasma pharmacokinetics of a single 120-mg dose of fexofenadine in 12 healthy subjects. However, the renal clearance of fexofenadine was decreased by 39%. ... 

Cimetidine is a non-specific cytochrome P450 isoenzyme inhibitor, but it would seem that in most cases, with the exception of loratadine, these enzyme inhibitory effects do not significantly affect the metabolism of antihistamines. More recent evidence has shown cimetidine can also affect drug transporter proteins, in particular it may inhibit organic cation transporters. However, it probably does not affect anion transporter proteins since it does not affect the plasma pharmacokinetics of fexofenadine, which is a substrate of these transporters. ... 

There would seem to be no good reason for avoiding the concurrent use of either cetirizine, ebastine, fexofenadine, hydroxyzine, or loratadine with cimetidine, or chiorphenamine with ranitidine, nor would any of the other H2-receptor antagonists be expected to interact with any of these antihistamines. 

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. 

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