Correction: Predictors of opioid efficacy in patients with chronic pain: A prospective multicenter observational cohort study.

[This corrects the article DOI: 10.1371/journal.pone.0171723.].

Predictors of opioid efficacy in patients with chronic pain: A prospective multicenter observational cohort study.

Opioids are increasingly used for treatment of chronic pain. However, they are only effective in a subset of patients and have multiple side effects. Thus, studies using biomarkers for response are highly warranted. The current study prospectively examined 63 opioid-naïve patients initiating opioid use for diverse types of chronic pain at five European centers. Quantitative sensory testing, electroencephalography (EEG) recordings, and assessment of pain catastrophizing were performed prior to treatment. The co-primary outcomes were change from baseline in ratings of chronic pain and quality of life after 14 days of opioid treatment. Secondary outcomes included patient's global impression of clinical change and side effects. Logistic regression models adjusted for age and sex were used to identify biomarkers predictive for successful treatment, defined as at least a 30% reduction in average pain intensity or an improvement in quality of life of at least 10 scale points. Fifty-nine patients (94%) completed the study. The mean age was 55 ± 16 years and 69% were females. Pain reduction was predicted by cold pain intensity (OR: 0.69; P = 0.01), pain catastrophizing (OR: 0.82; P = 0.03), relative delta (OR: 0.76; P = 0.03) and beta EEG activity (OR: 1.18; P = 0.04) induced by experimental cold pain. None of the study variables were related to improvement in quality of life. For the first time, individual pain processing characteristics have been linked to opioid response in a mixed chronic pain population. This has the potential to personalize treatment of chronic pain and restrict opioid use to patients with high likelihood for response.

Incisional self-administration of bupivacaine or ropivacaine provides effective analgesia after inguinal hernia repair.

PURPOSE: To evaluate the safety and applicability of two local anesthetic (LA) solutions self-administered for pain treatment after inguinal hernia repair (IHR) by balloon-pumps via catheters placed in the surgical wound. Effectiveness of analgesia was also compared. METHODS: Two groups of patients for IHR were included in the randomized, double-blind study. An epidural catheter was placed in the surgical wound, tunneled subcutaneously and connected to a balloon-pump containing either 0.25% bupivacaine (B) or 0.25% ropivacaine (R). Postoperatively, the patient self-administered the LA into the wound. Administration could be repeated after 20 min. If moderate to severe pain still persisted, rescue medication (piritramid) was given intravenously. The variables recorded in both groups were: visual analogue scale (VAS), pain scores at rest and with movement, number of applications, wound healing, patients' satisfaction. RESULTS: During the first 24 hr, median number of LA applications in 26 B patients was 4 (range 1-6) and in 25 R patients 3 (range 1-5). Both groups showed low VAS pain scores: less than 2 at rest, less than 4 with movement. Eighty percent of patients of each group would choose this type of analgesia again. Two patients from B Group and three from R Group needed rescue medication. No wound infection was observed. There were no statistically significant differences between the groups. CONCLUSION: Self-administration of the LA solution via a catheter in the surgical wound is an effective method of pain relief after IHR with little side-effects.