Several classes of antiemetics are available today. The most important are:

NK1 Antagonists

Neurokinine (substance P, NK1) antagonists have shown impressive antiemetic characteristics for various stimuli in the animal model. However, early clinical data have been disappointing, except for aprepitant (Emend®), which has demonstrated superiority over ondansetron in chemotherapy induced nausea and vomiting.

Serotonin (5HT3) Antagonists

Ondansetron (Zofran®) is the best studied drug of this class. It is equally effective compared to droperidol and dexamethasone, has no sedating side-effects but may increase the incidence of mild headache in about 3% of patients ( Apfel et al. New Engl J Med 2004) . Phamaco-economic evaluation revealed that in selected patients 4 mg ondansetron is considerably more cost-effective than placebo but slightly less cost effective than droperidol which has lower acquisition costs (Hill et al. Anesthesiology 2000). Because repeating ondansetron is of limited effectiveness (Kovac et al. J Clin Anesth 1999) it seems reasonable to use ondansetron predominantly as a rescue treatment ( White PF, New Engl J Med 2004 ).

Dexamethasone

Although the mechanism of its antiemetic action is unclear, meta-analyses have shown that a single dose of 8-10 mg dexamethasone is effective (Henzi et al. Anesth Analg 2000, Eberhart et al. Anaesthesist 2000) with no known increase in side-effects. Recent dose response trials suggest that doses between 2.5 and 5 mg are sufficient. IMPACT has recently demonstrated that 4 mg dexamethasone given at the beginning of surgery is as effective as 4 mg ondansetron or 1.25 mg droperidol ( Apfel et al. New Engl J Med 2004 ). Since dexamethasone is cheap, causes no increase of side-effects as far as known and is equally effective as the other antiemetics it may be considered as the first line drug for the prevention of PONV. Also, there is some evidence from Wang et al. Anesth Analg 2000 and the IMPACT data (unpublished observation) that dexamethasone has a delayed onset of antiemetic actions which might need a few hours to work. It may therefore not be a very good option for the treatment of established PONV.

Dimenhydrinate

Dimenhydrinate (Vomex A®, Dramamine®, a aminophylline salt of diphenhydramine) appears to be equally effective as droperidol (Apfel et al. Br J Anaesth 2002 , Kranke et al. Acta Anaesthesiol Scand 2002). It is a relatively old but cheap drug with some sedating side-effects. It may therefore be a good choice for the prevention of PONV. For treatment of established PONV it may be wise to use only half a dose, e.g. 25-30 mg i.v.

Droperidol

The use of 1.25 mg droperidol intravenously was associated with greater effectiveness, lower costs, and similar patient satisfaction compared with 0.625 mg droperidol intravenously and 4 mg ondansetron intravenously (Hill et al. Anesthesiology 2000). IMPACT has recently demonstrated that 1.25 mg droperidol given at the beginning of surgery is as effective as 4 mg dexamethasone or 4 mg ondansetron ( Apfel et al. New Engl J Med 2004 ).

However, low-dose droperidol may cause dysphoria (Melnick et al. Anesth Analg 1989, Lim et al. Anaesth Intensive Care 1999), and the FDA has recently added a black box warning to the drug's labeling to indicate that it may be associated with torsade de pointes; despite there is little evidence that antiemetic doses trigger this condition (Gan et al. Anesthesiology 2002).

Metoclopramide

Metoclopramide (Reglan®, Paspertin®) has been and is still widely used despite numerous studies including a meta-analysis have pointed out its limited efficacy (Henzi et al. Can J Anaesth 1999).