Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Navoban (Sandoz)
5 mg capsules
1 mg/1 mL in 5 mL ampoules
Indication: prevention of nausea and vomiting
Oncologists now have a choice of serotonin (5-HT3) receptor antagonists to help reduce the nausea and vomiting associated with chemotherapy. Unfortunately, there is a dearth of comparative data to guide the prescriber in the selection of tropisetron or the previously marketed ondansetron (see 'New drugs' AustPrescr 1991;14:70).
Anticancer treatments are believed to cause vomiting by triggering the release of serotonin from the gut. This acts on 5-HT3 receptors in the gut and brainstem so receptor antagonists will reduce the emetic effects of anticancer treatment.
Compared to an antiemetic 'cocktail' of drugs including metoclopramide, tropisetron is probably as effective in the control of acute vomiting, but less effective in controlling acute nausea, and delayed nausea and vomiting. However, the antiemetic 'cocktail' may cause more adverse effects than a single daily dose of tropisetron.
Oral tropisetron is rapidly absorbed from the gut, but its bio availability varies due to saturation of first pass metabolism. The elimination of tropisetron may also vary between individuals as its metabolism can be influenced by polymorphism. About 8% of Caucasians are slow metabolisers and in these patients the elimination half-life may be 45 hours compared with 8 hours in extensive metabolisers. In extensive metabolisers, most of the dose is excreted in the urine - 8% as unchanged drug and 70% as metabolites. In poor metabolisers, a greater proportion of unchanged drug is excreted. Higher plasma concentrations can be expected in patients with impaired renal function.
Tropisetron appears to be well tolerated. The most frequently reported adverse effects are headache, constipation, diarrhoea and fatigue.
