OBJECTIVE: To compare pain relief and stability of pain control in patients with chronic low back pain treated with scheduled 12 hourly doses of controlled-release codeine or as required doses of a fixed combination of acetaminophen and codeine.PATIENTS AND METHODS: Patients were assigned to five days of treatment with controlled-release codeine (Codeine Contin; Purdue Frederick) 100 mg q12h or placebo q12h in a randomized, double-blind, parallel group study. Acetaminophen 325 mg q4h prn was available as rescue to the codeine group and acetaminophen 325 mg plus codeine 30 mg q4h prn was available to the placebo group. Pain intensity was assessed pretreatment and four times daily using a four-point categorical scale. Acceptability of therapy was assessed twice daily on a five-point scale.RESULTS: Of 104 patients enrolled, 82 were able to be evaluated for safety and efficacy. Sum of pain intensity differences scores were significantly lower on controlled-release codeine than on as required acetaminophen plus codeine at all assessments. The number of changes in pain intensity throughout the day was higher with acetaminophen plus codeine than with codeine alone (8.6±0.7 versus 6.1±0.6, respectively, P=0.011). Mean total daily codeine dose was 200 mg in the codeine group and 71.1±6.6 mg in the acetaminophen plus codeine group (P=0.0001). Mean total daily prn acetaminophen consumption was 542.2±86.5 mg in the codeine group and 770.8±71.5 mg in the fixed combination group (P=0.0452).CONCLUSION: Twelve hourly dosing of controlled-release codeine provides greater and more stable pain relief in patients with chronic low back pain than as required dosing of an acetaminophen plus codeine combination.