Do individualized medication effectiveness tests (n-of-1 trials) change clinical decisions about which drugs to use for osteoarthritis and chronic pain?

To assess the impact of individualized medication effectiveness tests (IMETs, or n-of-1 trials), on patients' short-term decision making about medications for chronic pain. Survey evaluation of patients undergoing a double-blind, crossover comparison of drug versus placebo, drug versus drug, or drug versus drug combination using paracetamol and ibuprofen in 3 pairs of treatment periods, randomized within pairs. General practice patients (supplemented by a few from 2 tertiary pain clinics) with either chronic pain (> or =3 months), or osteoarthritis (with pain for > or =1 month) severe enough to warrant consideration of long-term nonsteroidal antiinflammatory drug (NSAID) use but for whom there was doubt about the efficacy of NSAID or alternative. Pain and stiffness in sites nominated by the patient, global pain, use of escape analgesia, and side effects. Of 116 IMETs started, 71 were completed. Drug management changed for 46 of 71 (65%). The most common change was to add paracetamol or to substitute the NSAID or COX-2 inhibitor with paracetamol (25 of 71 patients and 54% of changes). Of the 37 who were using NSAIDs or COX-2 inhibitors before the IMET, 12 (32%) ceased these afterward. Paracetamol was as effective or more effective than ibuprofen in 37 (68%) of the 54 IMETs directly comparing these drugs. IMETs provide useful information for clinical decisions. Paracetamol continues to be useful for patients with chronic pain whose optimal drug choice is in doubt. Our results provide a new (individual) perspective on the well-known recommendation for paracetamol as first-line treatment for chronic pain and demonstrate that it is feasible to provide IMETs nationally by mail and telephone.