Effectiveness of Low Doses of Paroxetine Controlled Release in the Treatment of Major Depressive Disorder

Context: Paroxetine controlled release (CR) is approved for the treatment of major depressive disorder (MDD) in the dosage range of 25 to 62.5 mg daily. However, lower daily doses (12.5 mg and 25 mg) of this formulation have not been investigated in the treatment of MDD. If the 12.5-mg and 25-mg doses are found to be efficacious, these lower doses may well convey a superior tolerability profile for paroxetine CR in the treatment of MDD.

Objective: To evaluate the antidepressant efficacy and tolerability profile of daily doses of paroxetine CR 12.5 mg and 25 mg versus placebo in the treatment of MDD.

Design and Setting: Randomized, double-blind, placebo-controlled clinical trial conducted in 40 clinical investigation centers in the United States.

Participants: 447 adult (>= 18 years of age) outpatients who met DSM-IV criteria for MDD and with a baseline 17-item Hamilton Rating Scale for Depression (HAM-D) score of at least 20 comprised the intent-to-treat study population (mean age = 38.8 years; 58.4% female; 75.6% white).

Intervention: Eligible patients completing a 1-week single-blind placebo run-in period were randomly assigned to receive once-a-day study medication (paroxetine CR 12.5 mg [N = 156], paroxetine CR 25 mg [N = 154], or placebo [N = 149]) in an 8-week, double-blind, parallel cell comparison.

Main Outcome Measures: The primary efficacy measure was the change from baseline to study endpoint (week 8) as measured by the HAM-D. Secondary efficacy measures included change from baseline to study endpoint as assessed by both the depressed mood item on the HAM-D and the Clinical Global Impressions (CGI) Severity of Illness scale (CGI-S). The proportion of patients considered at study endpoint to be in response (CGI-Improvement score of 1 or 2) or in remission (HAM-D <= 7) in the 3 treatment groups was also compared. Quality of life was assessed by the change from baseline in total score of the short form of the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q). Safety observations were made by assessing the proportion of patients who had adverse experiences, including laboratory and electrocardiographic abnormalities, during the treatment period.

Results: The primary efficacy analysis revealed that both the 12.5-mg and the 25-mg paroxetine CR treatment groups were associated with significant therapeutic effects (change in HAM-D score) from baseline to study endpoint (LOCF: p = .038, 95% CI = -3.38 to -0.09 and p = .005, 95% CI = -4.06 to -0.74, respectively). Results from the Wilcoxon rank sum test of the depressed mood item of the HAM-D (p = .011, 95% CI = -0.57 to -0.07) demonstrated significant efficacy in the 25-mg treatment group but not in the 12.5-mg group. However, LOCF analysis of the CGI-S revealed significant therapeutic effects for both the 12.5-mg (p = .018, 95% CI = -0.61 to -0.06) and 25-mg (p < .001, 95% CI = -0.78 to -0.22) treatment groups. Significantly more patients in the 25-mg paroxetine CR-treated group than in the placebo-treated group met criteria for response (CGI-Improvement score of 1 or 2, p = .035, OR = 1.68, 95% CI = 1.04 to 2.73) as well as for remission (HAM-D score <= 7, p = .013, OR = 1.96, 95% CI = 1.15 to 3.33). Neither HAM-D remission analysis nor CGI responder analysis showed statistical separation from placebo for paroxetine CR 12.5-mg treatment. Quality of life improvements were statistically significant for the 25-mg treatment (p = .041, 95% CI = 0.17 to 8.03) on the Q-LES-Q total score. Post hoc LOCF analyses of HAM-D sleep disturbance, psychic anxiety, and anxiety/somatization factors revealed significant improvements from baseline in the paroxetine CR 25-mg and 12.5-mg treatment groups. The types of adverse events reported in the 12.5-mg and 25-mg groups were similar to those reported with paroxetine CR at the customary 25-mg to 62.5-mg range; however, the lower doses of paroxetine CR were associated with a relatively reduced incident rate of these adverse events and an overall improved tolerability compared with the incident rate and tolerability profile associated with the customary dose range of paroxetine CR (25 to 62.5 mg).

Conclusion: Paroxetine CR, at 12.5 mg/day and 25 mg/day, demonstrated significant antidepressant effects.