title: Isotretinoin therapy and the incidence of acne relapse: a nested case-control study.
abstract: BACKGROUND
  Previous studies on predictors of acne relapse in patients treated with isotretinoin had either small sample sizes, short follow-up periods, or lacked population-based data.
  
  
  OBJECTIVE
  To identify and quantify predictors of acne relapse, and predictors of receiving a second isotretinoin treatment.
  
  
  METHODS
  Using the Régie de l'Assurance Maladie du Québec (RAMQ) and Quebec's hospital discharge (Med-Echo) administrative databases, a population-based cohort of 17 351 first-time isotretinoin users was assembled between 1984 and 2003. A nested case-control analysis was performed to determine predictors of acne relapse (as defined by receiving an antiacne medication). A second nested case-control analysis was performed to determine predictors of receiving a second isotretinoin treatment. The index date of cases was the calendar date of dispensing an antiacne medication (isotretinoin or other). Five controls were matched to each case on follow-up time. Rate ratios were estimated using conditional logistic regression.
  
  
  RESULTS
  A total of 7100 (41%) subjects experienced an acne relapse. These were matched to 35 500 controls. Being male, under 16 years of age and living in an urban area, and receiving isotretinoin cumulative doses greater than 2450 mg and an isotretinoin treatment longer than 121 days were statistically associated (P < 0.05) with acne relapse. The publishing of the different Canadian acne guidelines had no impact on the incidence of acne relapse (P > 0.05). A total of 4443 (26%) subjects required a second isotretinoin treatment. These were matched to 22 215 controls. There was a greater probability of receiving a second isotretinoin treatment after the publishing of the Canadian acne guidelines (P < 0.05).
  
  
  CONCLUSIONS
  A relatively high rate of subjects experienced an acne relapse after an isotretinoin treatment.
authors.affiliation: Faculty of Pharmacy, University of Montreal, Montreal, Quebec, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Azoulay
authors.forename: D
authors.initials: D
authors.lastname: Oraichi
authors.forename: A
authors.initials: A
authors.lastname: Bérard
mesh_terms: D000152:Acne Vulgaris / Q000188:drug therapy*; D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D015331:Cohort Studies; D003879:Dermatologic Agents / Q000008:administration & dosage / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D005500:Follow-Up Studies; D006801:Humans; D015474:Isotretinoin / Q000008:administration & dosage / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D016896:Treatment Outcome
chemical_list: D003879:Dermatologic Agents; D015474:Isotretinoin