CMAJ study: Increased dosage of Tamiflu required in treating H1N1 influenza patients

Canadian Medical Association JournalFeb 17 2010

An increased dosage of Tamiflu (oseltamivir) for patients with critical illness is unlikely to be required in the treatment of pandemic (H1N1) influenza, contrary to current international guidelines, found a new study http://www.cmaj.ca/cgi/doi/10.1503/cmaj.092127 in CMAJ (Canadian Medical Association Journal) www.cmaj.ca.

World Health Organization (WHO) guidelines recommend that all critically ill patients should be treated with Tamiflu and if the patient was unresponsive to standard doses or critically ill, a higher dose should be considered.

The CMAJ study looked at the gastrointestinal absorption of Tamiflu in 44 patients, 18 years of age or older, with suspected or confirmed pandemic (H1N1) influenza who were admitted to nine ICUs in two cities in Canada (Winnipeg and Ottawa) and Tarragona, Spain because of respiratory failure. As critically ill patients may have gastrointestinal absorption issues, guidelines suggest higher doses of Tamiflu.

"Studying the absorption ability of Tamiflu in the critically ill became a priority with the large number of patients needing ICU and ventilation support," writes lead author Dr. Anand Kumar, Health Sciences Centre, University of Manitoba and coauthors. "Also, the number of obese patients suffering from H1N1 related critical illnesses were large which raised the question about whether the dose should be adjusted upwards with increased body weight."

Blood sampling indicated that the 75 mg twice daily dosage of Tamiflu was well absorbed in critically ill patients with respiratory failure. Blood levels of the antiviral were similar or higher than levels in ambulatory patients with a similar dosage. Patients with kidney dysfunction requiring dialysis needed an adjusted dose but adjustment for obesity was not required.

"The findings of this study suggest that an increased Tamiflu dosage is unlikely to be necessary in such cases based on either insufficient drug absorption or altered distribution pharmacokinetics," conclude the authors.