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.
Zyban (Glaxo Wellcome)
150 mg sustained-release tablets
Approved indication: nicotine dependence
Australian Medicines Handbook Section 18.6.2
Bupropion is not a new drug. It was approved in the USA for the treatment of depression more than 10 years ago. The antidepressant effect probably involves the drug's action on neurotransmitters. These actions may also help smokers to quit; depressed smokers gave up smoking during the clinical trials of bupropion.
To study the usefulness of bupropion in assisting smoking cessation, 615 smokers were enrolled in a randomised placebo-controlled trial. All the participants were given counselling in addition to drug treatment. After seven weeks of treatment, 19% of the placebo group had given up smoking. In the bupropion group the success rate increased with the dose. Approximately 29% of those taking 100 mg daily gave up, compared with 39% of those taking 150 mg and 44%of those taking 300 mg. All the participants put on weight, but the least weight gain (1.5 kg) was in the patients taking the highest (300 mg) dose of bupropion.1
Bupropion has also been compared with nicotine patches. In this trial 244people were randomised to take bupropion, 244 used a nicotine patch, 245 used both medications and 160 were given placebos. During the nine weeks of treatment the participants were also counselled. When the participants were reviewed after six months, 35% of the bupropion group had stopped smoking compared with21% of those using the nicotine patch and 19% of the placebo group. In the combined treatment group, 39% had stopped smoking. Treatment with bupropion alone, or in combination with a nicotine patch, was significantly better than treatment with the patch alone.2
Patients begin bupropion when they are still smoking. They start with 150mg once a day, and after three days they take 150 mg twice a day. Smoking should stop in the second week of treatment. If the patient is still smoking after seven weeks they are unlikely to benefit by continuing bupropion.
There is extensive first-pass metabolism and metabolism is the main method of clearance. Less than 1% of the drug is excreted unchanged in the urine. Bupropion is metabolised by cytochrome P450 2B6. Although clinical interactions have not been studied, caution is needed when prescribing other drugs metabolized by this system. The metabolism of bupropion may be altered by drugs such as phenytoin and carbamazepine. There is a risk of seizures, so bupropion is contraindicated in patients with epilepsy or other conditions which alter the seizure threshold.
The drug's effect on neurotransmitters may cause insomnia as an adverse effect. In clinical trials 40% of patients complained of insomnia. Other complaints included altered concentration, anxiety and dizziness. Some patients will experience nausea and a dry mouth. Severe allergic reactions have also been reported. In the comparative study2 approximately 12% of the people taking bupropion stopped treatment because of its adverse effects.
As with other interventions for smoking, the effectiveness of bupropion declines with time. A year after the start of the placebo-controlled trial 23% of those given bupropion had not resumed smoking.1 In the comparative trial 30% of the bupropion group were still abstinent after one year.2
Bupropion has only been approved for short-term use by patients who are committed to stopping smoking. It should always be used in conjunction with counselling.
