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SELECTED ARTICLES FROM THE RECENT LITERATURE 2006
9/22/06
Itraconazole affects fexofenadine catabolism
Summary
Background – Fexofenadine (Fex), marketed as Allegra, is a commonly used, very effective antihistamine. Fex is disposed of by several drug transporters, including P-glycoprotein. Therefore, it is important to know the effects on Fex pharmacokinetics of co-treatment with itraconazole (Itr) and diltiazem (Dil), 2 commonly used drugs, which have been found to inhibit P-glycoprotein activity.
Findings – Shimizu et al of Hirosaki Univ Hospital in Japan carried out a randomized, 3-way, crossover study of the effects of 5 days pre-treatment with either Itr 100 mg b.i.d., Dil 100 mg b.i.d. or placebo b.i.d. on the pharmacokinetics of a 120 mg dose of Fex in 8 healthy volunteers. They found that this pre-treatment with Itr but not with Dil led to an increased mean peak plasma levels of Fex (p<0.005). The area under the Fex plasma concentration – time curve was also significantly greater after Itr pre-treatment (<0.0001) but not after Dil pre-treatment.
Reference
Br J Clin Pharmacol 2006;61:538-44
Editor's Comments
These findings indicate that co-treatment with Itr, a commonly used anti-fungal drug, will result in decreased Fex disposal, leading to increased plasma Fex levels. Fortunately, these increased Fex levels should be well tolerated since previous studies have shown no adverse effects when twice the usual 180 mg adult daily dose (and maybe even higher doses) have been taken.
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