Antidepressant benefit may show within 2 weeks.(Clinical Rounds)

TORONTO -- Most clinical recommendations advise that patients who start an antidepressant be given 4-6 weeks to see whether they respond and have improvement.

But an analysis of more than 5,000 patients treated in clinical trials with a variety of antidepressants suggests that most patients who respond well start to improve within 2 weeks, Dr. Armin Szegedi said at the annual meeting of the American Psychiatric Association.

"This is a very strong, clinically relevant, and, perhaps to many, a surprising finding," Dr. Szegedi, executive director of clinical projects, psychiatry, at Organon International Inc., Rosalind, N.J., said in an interview.

The analysis included patients who were treated with six different, selective serotonin reuptake inhibitors, including parox-etine (Paxil) and fluoxetine; two tricyclic antidepressants, amitriptyline and doxepin; and venlafaxine (Effexor), a selective norepinephrine reuptake inhibitor.

Regardless of the kind of drug used, patients showed a notable improvement by 2 weeks, or they had only about a 10%-20% chance of ever responding well, Dr. Szegedi said in a poster presentation given at the meeting.

The general recommendation that patients need to continue a trial of an antidepressant for a full 6 weeks before it is given up as a failure and the patient switched never was based on data, but rather, on expert opinion, Dr. Szegedi said.

And most have assumed that drugs with different mechanisms of action would have different times of onset. "Unfortunately, the data do not back that up," he said in the interview.