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Over-the-counter Antihistamine (Theraflu) / PI Interactions?
Jan 23, 2001

Hi docs...thanks for the great column. I'm on a combination of amprenavir + low-dose ritonavir, abacavir, lamivudine, and stavudine. The other day I was fighting a cold, and throughout the course of the day had 3 helpings of Theraflu (acetaminophen + pseudoephedrine + dextromethorphan). That night, I couldn't sleep, and the next morning continued to be extremely agitated, nervous, slightly dizzy, etc. Never had this reaction to Theraflu or other OTC remedies before going on meds. I'm wondering if the PI's I'm taking could have some interaction with the Theraflu (particularly, I'm suspecting, the pseudoephedrine), maybe increasing their concentrations? Thanks.

Response from Dr. Young

You've certainly described what sounds like a relative overdose of Theraflu (or one of it's components). All three parts of Theraflu are metabolized by the liver; though the official listing of drug interactions does not list either pseudoephedrine or dextromethorphan as interacting with the same liver pathway as ritonavir. I suspect that there is enough overlap in the metabolism of either pseudoephedrine or dextromethorphan and ritonavir that you experienced your symptoms. I'd either avoid Theraflu or use, say 1/2 the dose next time.Thanks for a great question. -BY

Benjamin Young, M.D., Ph.D.

should i be concerned?

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