Bupropion - Adverse Effects

Adverse Effects

Seizure is the most controversial side effect of bupropion, and was responsible for its initial withdrawal from the market. The risk of seizure is highly dose-dependent: 0.1% at 100–300 mg of bupropion, 0.4% at 300–450 mg, and 2% at 600 mg. For comparison, the incidence of the first unprovoked seizure in the general population is 0.07 to 0.09%. The risk of seizure for other antidepressants is as follows: 0.1–0.6% for imipramine, depending on dosage; 0–0.06% for amitriptyline, depending on dosage; 0.5% for clomipramine; 0.4% for maprotiline; and 0.2% for fluoxetine and fluvoxamine. Experiments on mice indicate that increased susceptibility to seizure is a general side effect of chronically using antidepressants that inhibit norepinephrine transporters, such as imipramine, desipramine and reboxetine. Clinical depression itself was reported to increase the occurrence of seizures two-to-sevenfold compared with the general population; in this light, the above statistics could indicate that low to moderate doses of antidepressants, including bupropion, may actually have an anti-convulsive action.

The prescribing information notes that hypertension, sometimes severe, was observed in some patients, both with and without pre-existing hypertension. The frequency of this adverse effect was under 1% and not significantly higher than that found with placebo. In a group of cardiac patients with depression, high doses of bupropion (400–500 mg/day) caused a rise in supine blood pressure but had no effect on pulse rate. No statistically significant changes in blood pressure or heart rate occurred in patients with or without heart conditions at a lower dose of 300 mg/day. In a study of bupropion for ADHD, a rise of systolic blood pressure by 6 mm Hg and of heart rate by 7 beats per minute (both statistically significant) were observed. A study of smokers hospitalized for heart disease found a 1.5-fold increase (close to being statistically significant) in subsequent cardiovascular events in the bupropion group, compared with the placebo group, but found no difference in blood pressure. Although the cardiovascular side effects of bupropion appear to be mild, it cannot be recommended for patients with heart disease, since the safety comparison with SSRIs (such as sertraline and fluoxetine, which may have a preventative effect after a myocardial infarction) is not in its favor.

In the UK, more than 7,600 reports of suspected adverse reactions were collected in the first two years after bupropion's approval by the MHRA as part of the Yellow Card Scheme, which monitored side effects. Approximately 540,000 people were treated with bupropion for smoking cessation during that period. The MHRA received 60 reports of "suspected adverse reactions to Zyban which had a fatal outcome". The agency concluded that "in the majority of cases the individual's underlying condition may provide an alternative explanation." This is consistent with a large, 9,300-patient safety study that showed that the mortality of smokers taking bupropion is not higher than the natural mortality of smokers of the same age.

Other isolated adverse effects have been reported. Three cases of liver toxicity have been described, a very low incidence given the widespread use of the drug. A single case of clitoral priapism (clitorism) has been reported in the literature.

The common adverse effects associated with 12-hour sustained-release bupropion (with the greatest difference from placebo) are dry mouth, nausea, insomnia, tremor, excessive sweating and tinnitus. Those that most often resulted in interruption of the treatment in the same trial were rash (2.4%) and nausea (0.8%).