Treatment with paroxetine (Paxil), which belongs to the selective serotonin reuptake inhibitor (SSRI) class of antidepressant drugs, increases DNA fragmentation in sperm, according to research presented on Tuesday at the 64th annual meeting of the American Society for Reproductive Medicine in San Francisco.

Although the study did not directly evaluate male fertility, the five-fold increase in the number of men who developed abnormal sperm DNA while being treated with paroxetine is "troubling" and "suggests an adverse effect on fertility," co-investigator Dr Cigdem Tanrikut, from Harvard Medical School in Boston, said.

In a clinical trial she described as "the first study to assess the impact of an SSRI on semen parametres in healthy men," 35 men took paroxetine for 5 weeks. The drug was administered in once-daily doses of 10 mg the first week, 20 mg in the second week, 30 mg the third and fourth week, and 20 mg in the fifth week.

Tests were conducted on semen samples obtained prior to starting paroxetine and after 4 weeks of treatment. The average DNA fragmentation score increased from 13.8 per cent before paroxetine was begun to 30.3 per cent at week 4, a statistically significant amount.

The percentage of men who had a fragmentation score of 30 per cent or higher before treatment rose from 10 per cent to 50 per cent.

Semen analyses conducted throughout the study, however, showed normal volume, concentration, movement and appearance.

Paroxetine was also associated with significant sexual dysfunction, with one third of men reporting problems with erectile function and nearly half reporting ejaculatory difficulties.

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