Use of Opioid Analgesics Before and After Gastric Bypass Surgery in Sweden: a Population-Based Study

Morbid obesity is associated with various conditions causing musculoskeletal pain [1] often leading to use of prescription analgesics [2], including opioids. Bariatric surgery has proved to be an efficient intervention in the management of obesity resulting in lasting weight-loss and reduced obesity-related co-morbidity [3], improved physical function [4], and health-related quality-of-life (HRQoL) [5]. As a result, the number of post-bariatric surgery patients in the population is growing. Little is known regarding the use of opioid analgesics among patients who have undergone bariatric surgery. Recent studies has shown an increase in postoperative use of opioid analgesics both regarding the total dose and number of new persistent users [6‐9]. The anatomical changes after Roux-en-Y gastric bypass (RYGB) can lead to changes in the pharmacokinetic properties of opioid analgesics leading to faster and more complete absorption of morphine oral solution [10], which is similar to the changes seen with ethanol [11]. This raises concerns regarding a potentially increased risk of developing substance-use disorder (SUD) [12‐14]. The increased risk of side effects of non-steroidal anti-inflammatory drugs (NSAID) [15] after RYGB limits the pharmacological options available and likely pushes patients and prescribers toward opioids. It is thus important to gain a deeper understanding of the use of opioids after bariatric surgery.

The aim of this retrospective cohort study, including all patients undergoing gastric bypass surgery in Sweden between May 2007 and November 2013, was to describe the pattern of opioid use over time following surgery, and to see if the pattern differs between patients with a high opioid consumption prior to surgery (HOC) and those with a low consumption (LOC).

The study population comprised 35,612 persons (Table 1) who had undergone gastric bypass surgery (1628 HOC, and 33,984 LOC). After surgery, the number of HOC patients increased fairly consistently to 2218 at end of follow-up (Fig. 1).

When comparing mean daily opioid consumption in the total population prior to and after surgery, there was a statistically significant increase. In the HOC group, there was no difference between mean daily consumption before and after surgery. In the LOC group, however, there was a statistically significant increase in mean daily consumption after surgery. Furthermore, the amount of opioid consumed daily more than doubled after surgery in this group (Table 2). This increase remained when the 3-month periods immediately before and after surgery were excluded from the analysis.

In the group classed as high opioid consumers prior to surgery, 422 participants (25.9%) used 10 mg or less opioid analgesics after surgery (from a mean daily consumption before surgery of 22.9 to 3.0 mg after surgery) and 1206 participants (74.1%) continued or increased their consumption after surgery (mean daily consumption before surgery 31.5 to 43.8 mg after surgery).

In the LOC group 33,224 participants (97.8%) used 10 mg/day or less after surgery (from mean daily consumption 0.4 mg before surgery to 0.6 mg after surgery), and 760 LOCs (2.2%) became high opioid consumers after surgery (mean daily consumption 2.4 mg before surgery to 40.6 mg after surgery) (Figs. 2 and 3).

There was no significant difference in mean daily use before and after surgery between women and men (Table 2).

This study is one of few looking at the consumption of opioid analgesics in patients undergoing bariatric surgery. Our results show that there is an increase in opioid consumption after gastric bypass surgery, both the number of HOC patients and the amount of opioids consumed.

Previous studies have shown an unexpected increase in opioid analgesics consumption after bariatric surgery [6‐9]. Our results with a larger population are consistent with their findings. However, in our study, the ratio of high opioid consumers before surgery and of low opioid consumers before surgery that became high consumers after surgery is slightly lower compared to previous studies. This can most likely be attributed to differences in classification of HOC. It is worrying that 760 patients in the LOC group became high opioid consumers during the 2 years following surgery, especially since 169 had not taken opioids during the 2 years prior to surgery. The post-surgery increase in consumption of opioids in the LOC group was probably the result of painful postoperative complications but other causes such as substance-use disorder cannot be ruled out. Patients considering gastric bypass surgery in general and opioid naïve patients in particular should be informed of the possible risks regarding postoperative opioid use. Consumption of opioid analgesics in the HOC group as a whole did not change after surgery, but, as can be seen in Fig. 2 approximately 25% of these patients significantly decrease their consumption and the remainder increase it. Mean age among HOCs was significantly lower after surgery (Table 2); this potentially protective effect has been shown previously [8] but not repeatedly [7], and there are many potentially confounding factors that we in this study are unable to adjust for. The number of HOC individuals in the total population appeared to increase fairly consistently, and if the 3-month period after surgery is excluded, bariatric surgery does not seem to have had an impact on this increase (Fig. 1).

Future studies prompted by these results would be to compare opioid use in patients who have undergone gastric bypass surgery with an obese control group and an in-depth analysis of the group of opioid-naïve patients that after surgery became HOC to find out what caused this change.

The strength of this study is that it used cohort data from comprehensive nationwide registers covering all patients undergoing gastric bypass surgery in Sweden, as well as having complete information on dispensed opioid analgesics. Furthermore, we used a previously described and established method to calculate morphine equivalents. Limitation of this study is the lack of a control group with obesity. It should also be noted that we cannot be certain that all dispensed opioids have been used and that our data do not include opioids given during hospital admissions.

In this nationwide study, we have showed that there is an increase in consumption of opioid analgesics after gastric bypass surgery in Sweden. There was no difference in use of opioid analgesics between women and men. The increase in the number of individuals with high opioid consumption in the total population was mainly due to an increase in the group of patients with a low consumption prior to surgery. Mean daily opioid consumption remained unchanged in the group with high consumption prior to surgery.