In 2006, the Centers for Disease Control and Prevention recommended discontinuing the use of adamantanes (amantadine and rimantadine) to treat influenza because of high levels of resistance to this class of antivirals. We examined changes in prescribing practices resulting from this recommendation and found that prescribing of adamantanes declined nationwide, with these drugs accounting for approximately 40% of the antivirals prescribed for influenza from 2000 to 2005 and only 2% in 2006. This finding provides evidence of a rapid change in clinical practice associated with the dissemination of treatment guidelines. Evaluating the effectiveness with which public health recommendations are translated into practice is important given the ongoing emergence of resistance to antiviral drugs and a novel H1N1 influenza virus.