Panic disorder is a chronic condition for many patients and can be socially, emotionally and occupationally disabling. Until recently, clomipramine and alprazolam were the only drugs approved for its treatment. While widely used in the US and Europe, both belong to drug classes (tricyclics and benzodiazepines) with well-recognised side effects that can be problematic and thus limit their use. Recently, paroxetine became the first selective serotonin reuptake inhibitor to receive approval and licensing for panic disorder.

The short- and long-term efficacy and tolerability of paroxetine in panic disorder has been established in clinical trials of almost 1,000 patients meeting Diagnostic and Statistical Manual (DSM)-IIIR criteria for panic disorder, with or without agoraphobia. In a 12-week double-blind study of 120 panic patients receiving standardised cognitive therapy, paroxetine was significantly more effective than placebo in reducing panic attack frequency. In a 12-week placebo-controlled comparison in 367 panic patients, paroxetine was at least as effective as clomipramine and better tolerated. There was also some evidence that paroxetine had an earlier onset of action than clomipramine.

A 9-month extension of the placebo-controlled comparison with clomipramine showed that the efficacy of paroxetine and clomipramine is maintained when treatment is continued into the longer term. In a relapse prevention study, 105 responders to 3 months' treatment with paroxetine or placebo were re-randomised, either to continue existing treatment or to receive placebo for 3 months. Only 5% of patients who continued to take paroxetine experienced a relapse compared with 30% of those who switched to placebo (P = 0.002). Paroxetine was generally well tolerated. In the short-term trials, the frequency of withdrawals due to adverse events (7.3%) was lower than that for placebo (11.4%) or clomipramine (14.9%). In the longer term, the dropout rate due to adverse events increased in the clomipramine group (19.0%) but was unchanged in the paroxetine group (7.4%). Since most patients with panic disorder will require prolonged treatment, the long-term tolerability of paroxetine and its lack of potential for dependence are important advantages that will encourage good compliance with treatment and improve the quality of life of patients.