• disease severity;
  • electronic monitors;
  • medication adherence;
  • psoriasis;
  • randomized controlled trial


Background  Patients are commonly nonadherent to medication regimens. In dermatology, there has been little study of the effect of nonadherence on outcomes.

Objectives  To test the association between adherence behaviour and changes in severity of psoriasis.

Methods  Twenty-four subjects with psoriasis were enrolled in an 8-week, left/right, controlled trial of salicylic acid plus topical tacrolimus ointment vs. salicylic acid plus placebo. Subjects were given salicylic acid to apply to all lesions. The salicylic acid was supplied in a bottle with a medication event monitoring system cap in order to assess adherence to the salicylic acid. The primary outcome for this study was the relationship between the change in the disease severity (change in sum score of erythema, scale and thickness scores for a target plaque) and medication adherence.

Results  The mean initial disease severity was 5·8 on a nine-point sum score scale. For the topical tacrolimus-treated side, a decrease in adherence rate of 10% was associated with a 1-point increase in severity (P < 0·05). For the placebo-treated side, adherence was not significantly correlated with changes in severity.

Conclusions  Nonadherence may have a significant role in altering clinical trial data, skewing it towards ineffectiveness. Improved outcomes in psoriasis may be achievable through interventions that improve patients' adherence to treatment.