Enteric absorption and pharmacokinetics of oseltamivir in critically ill patients with pandemic (H1N1) influenza.
BACKGROUND
Whether the enteric absorption of the neuraminidase inhibitor oseltamivir is impaired in critically ill patients is unknown. We documented the pharmacokinetic profile of oseltamivir in patients admitted to intensive care units (ICUs) with suspected or confirmed pandemic (H1N1) influenza.


METHODS
We included 41 patients 18 years of age and older with suspected or confirmed pandemic (H1N1) influenza who were admitted for ventilatory support to nine ICUs in three cities in Canada and Spain. Using tandem mass spectrometry, we assessed plasma levels of oseltamivir free base and its active metabolite carboxylate at baseline (before gastric administration of the drug) and at 2, 4, 6, 9 and 12 hours after the fourth or later dose.


RESULTS
Among the 36 patients who did not require dialysis, the median concentration of oseltamivir free base was 10.4 (interquartile range [IQR] 4.8-14.9) microg/L; the median concentration of the carboxylate metabolite was 404 (IQR 257-900) microg/L. The volume of distribution of the carboxylate metabolite did not increase with increasing body weight (R2=0.00, p=0.87). The rate of elimination of oseltamivir carboxylate was modestly correlated with estimations of creatinine clearance (R2=0.27, p<0.001). Drug clearance in the five patients who required continuous renal replacement therapy was about one-sixth that in the 36 patients with relatively normal renal function.


CONCLUSIONS
Oseltamivir was well absorbed enterically in critically ill patients admitted to the ICU with suspected or confirmed pandemic (H1N1) influenza. The dosage of 75 mg twice daily achieved plasma levels that were comparable to those in ambulatory patients and were far in excess of concentrations required to maximally inhibit neuraminidase activity of the virus. Adjustment of the dosage in patients with renal dysfunction requiring continuous renal replacement therapy is appropriate; adjustment for obesity does not appear to be necessary.
Department of Pharmacy, St. Boniface General Hospital, and Department of Internal Medicine, the Faculty of Pharmacy, University of Manitoba, Winnipeg, Manitoba.
Robert E
RE
Ariano
Daniel S
DS
Sitar
Sheryl A
SA
Zelenitsky
Ryan
R
Zarychanski
Amarnath
A
Pisipati
Stéphane
S
Ahern
Salmaan
S
Kanji
Jordi
J
Rello
Anand
A
Kumar
D000293:Adolescent; D000328:Adult; D000998:Antiviral Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D016638:Critical Illness; D004196:Disease Outbreaks; D004334:Drug Administration Schedule; D005260:Female; D041981:Gastrointestinal Tract / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D007251:Influenza, Human / Q000188:drug therapy / Q000453:epidemiology / Q000821:virology; D007362:Intensive Care Units / Q000706:statistics & numerical data; D007668:Kidney / Q000378:metabolism; D008297:Male; D053139:Oseltamivir / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D053719:Tandem Mass Spectrometry; D055815:Young Adult
D000998:Antiviral Agents; D053139:Oseltamivir