NEW YORK (Reuters Health) Many patients treated with DAAs for hepatitis C (HCV) are at clinically significant risk for drug-drug interactions (DDIs), a new study suggests. HeinerWedemeyer, MD, PhD, of the Hannover Medical School in Germany and one of the study’s authors, notes that drug interactions can lead to treatment failure, a problem that is particularly acute because it is unclear how to treat patients who fail treatment with DAAs. In a report published online Nov. 26 in the journal Clinical Infectious Diseases, Dr. Wedemeyer and colleagues note that the first generation of DAAs approved for the treatment of hepatitis C – boeprevir and telaprevir – are often at risk for DDI. As more DAA drugs have been released, the researchers added, they have become the standard of care for HCV in the United States and much of Europe. The investigators noted that although newer DAAs are generally considered to have lower DDIs, the actual DDI risk of these newer DAA regimens in combination with patients is unknown. To explore the true extent to which clinically significant DDIs occur, the researchers surveyed 261 HCV-infected patients, including 115 patients recruited after the approval of boeprevir and telaprevir in 2011 and 146 patients enrolled after the approval of sofosbuvir in 2014. Researchers asked patients about their medication use and then assessed the potential DDI risk for patient medication and several types of DAA therapy. The results of the study showed that: ▲ Patients took an average of 2 medications, while 20% of patients did not use any other medications. The four most commonly used medications were: pantoprazole (18.8%), ambitasvir (16.5%), thyroxine (16.5%) and hydrochlorothiazide (10%); ▲ Patients on sofosbuvir/ribavirin had the lowest risk of clinically significant DDI at 9.6% and required close monitoring or dose adjustment. The risk of clinically significant DDI was highest in patients using Ombitasvir/paritaprevir/ritonavir in combination with or without dasabusvir (66.3%); ▲ The risk of clinically significant DDI in patients using sofosbuvir/simeprevir, sofosbuvir/dasabusvir and sofosbuvir/radiprevir was 31.4%, 36.8% and 40.2 %, respectively. 36.8 percent and 40.2 percent, respectively. ”Many physicians are unaware of potential drug interactions,” Dr. Wedemeyer noted, “and we must clarify all potential issues that contribute to treatment failure, even if only for cost reasons.” Dr. Wedemeyer and colleagues will continue to study the next wave of HCV drugs, which are expected to be approved this year or next. They will also be looking at data related to patient use of DAAs to explore how often clinically significant DDIs actually occur. “We need real data to identify safety signals, which are very important in this area.”