• Number of Participants With a 50% Reduction in PASI (Psoriasis Area and Severity Index) Score Compared With Baseline PASI Score (PASI50 Response) [ Time Frame: Baseline and 12, 24, 36, 52, 76, 100, 160, and 208 weeks after the first dose of adalimumab ] [ Designated as safety issue: No ]
  PASI scores range from 0 (best outcome) to 72 (worst outcome including erythema, induration, desquamation, and area affected). Baseline is defined as the last available PASI value prior to the first dose of study drug (adalimumab or placebo) in Study M04-688 (NCT00338754).
  
  

• Number of Participants With a 75% Reduction in PASI (Psoriasis Area and Severity Index) Score Compared With Baseline PASI Score (PASI75 Response) [ Time Frame: Baseline and 12, 24, 36, 52, 76, 100, 160, and 208 weeks after the first dose of adalimumab ] [ Designated as safety issue: No ]
  PASI scores range from 0 (best outcome) to 72 (worst outcome including erythema, induration, desquamation, and area affected). Baseline is defined as the last available PASI value prior to the first dose of study drug (adalimumab or placebo) in Study M04-688 (NCT00338754).
  
  
• Number of Participants With a 90% Reduction in PASI (Psoriasis Area and Severity Index) Score Compared With Baseline PASI Score (PASI90 Response) [ Time Frame: Baseline and 12, 24, 36, 52, 76, 100, 160, and 208 weeks after the first dose of adalimumab ] [ Designated as safety issue: No ]
  PASI scores range from 0 (best outcome) to 72 (worst outcome including erythema, induration, desquamation, and area affected). Baseline is defined as the last available PASI value prior to the first dose of study drug (adalimumab or placebo) in Study M04-688 (NCT00338754).
  
  

This was a continuation trial of adalimumab in participants with moderate to severe chronic plaque psoriasis who had completed Study M04-688 (NCT00338754), a 24-week, double-blind, placebo-controlled study. This study was an open-label extension study that continued until the approval of adalimumab for the treatment of psoriasis in Japan.

During Study M04-688 (NCT00338754), participants received 24 weeks of treatment with adalimumab 40 mg every other week (eow) with or without a loading dose, adalimumab 80 mg eow, or placebo.

At the start of this study, participants who had received adalimumab 40 mg eow or adalimumab 80 mg eow in Study M04-688 (NCT00338754) continued on the same treatment regimen. Participants who had received placebo during Study M04-688 (NCT00338754) were re-randomized at the start of this study to receive adalimumab 40 mg eow or adalimumab 80 mg eow.

Participants in the adalimumab 40 mg eow treatment group who failed to achieve a PASI50 response (>= 50% reduction in the Psoriasis Area and Severity Index score from Baseline of Study M04-688 [NCT00338754]) at or anytime after Week 12 of this study were given the option to increase their dose to adalimumab 80 mg eow. Once the dose was escalated, there was no option to de-escalate dosing back to 40 mg eow. Participants who failed to achieve PASI50 responses while receiving adalimumab 80 mg eow may have been discontinued from the study after evaluating the risk/benefit of further treatment with adalimumab.

At Week 28 of this study, it was mandatory for all participants who started the study in the adalimumab 80 mg eow treatment group (i.e., not including the dose escalators described above) to reduce their dose to adalimumab 40 mg eow, regardless of their response status. Following this mandatory dose reduction, if these participants failed to achieve or maintain PASI50 response, they were permitted to escalate their dose to adalimumab 80 mg eow. There was no option to de-escalate dosing back to 40 mg eow following dose escalation.

Data in this clinical trial results disclosure are analyzed as observed according to treatment received at the start of this study (i.e., adalimumab 40 mg eow or adalimumab 80 mg eow) regardless of subsequent dose escalation. Data are summarized according to participants' cumulative exposure to adalimumab in Study M04-688 (NCT00338754) and this study.