Chemotherapy-induced nausea and vomiting (CINV) is a distressing and common adverse event associated with cancer treatment. Updated anti-emetic guidelines were published in 2007 by the National Comprehensive Cancer Network and in 2006 by the American Society of Clinical Oncology, which have included the use of the new and more effective anti-emetic agents (5-hydroxytryptamine-3 [5-HT 3 ] receptor antagonists and neurokinin-1 [NK-1] receptor antagonists). Aprepitant is a selective NK-1 receptor antagonist approved as part of combination therapy with a corticosteroid and a 5-HT 3 receptor antagonist for the prevention of acute and delayed CINV. Fosaprepitant (also known as MK-0517 and L-758,298) is a water-soluble phosphoryl prodrug for aprepitant, which, when administered intravenously, is converted to aprepitant within 30 min after intravenous administration via the action of ubiquitous phosphatases. Because fosaprepitant is rapidly converted to the active form (aprepitant), it is expected to provide the same aprepitant exposure in terms of AUC, and a correspondingly similar anti-emetic effect. Clinical studies have suggested that fosaprepitant could be appropriate as an intravenous alternative to the aprepitant oral capsule. In a study in healthy subjects, fosaprepitant was well tolerated up to 150 mg (1 mg/ ml), and fosaprepitant 115 mg was bioequivalent in its AUC to aprepitant 125 mg. Fosaprepitant 115 mg has been submitted for FDA approval as an alternative on day 1 of a 3-day oral aprepitant regimen, with oral aprepitant administered on days 2 and 3. Fosaprepitant may be a useful parenteral alternative to oral aprepitant. Further study is needed to clarify the use of fosaprepitant for the prevention of CINV, and to clarify optimal dosing regimens that may be appropriate substitutes for oral aprepitant. © 2007 Informa UK Ltd.