<P> Obesity, age less than 16 years, past history of motion sickness and high levels of pre-operative anxiety are also risk factors for PONV . </P> <P> Because no currently available antiemetic is especially effective by itself, and successful control is often elusive, experts recommend a multimodal approach . Anaesthetic strategies to prevent vomiting include using regional anaesthesia wherever possible and avoiding medications that cause vomiting . Medications to treat and prevent postoperative nausea and vomiting is limited by both cost and the adverse effects . People with risk factors probably warrant preventative medication, whereas a "wait and see" strategy is appropriate for those without risk factors . </P> <P> Fasting guidelines often restrict the intake of any oral fluid after two to six hours preoperatively . However, it has been demonstrated in a large retrospective analysis in Torbay Hospital that unrestricted clear oral fluids right up until transfer to theatre could significantly reduce the incidence of postoperative nausea and vomiting without an increased risk in the adverse outcomes for which such conservative guidance exists . </P> <P> A Cochrane review found droperidol, metoclopramide, ondansetron, tropisetron, dolasetron, dexamethasone, cyclizine, and granisetron effective for preventing PONV . </P>

Which type of drug is used to treat possible postoperative nausea and vomiting