Opioids prescribed for acute pain in a hospital setting cause unexpected in-hospital deaths, longer hospital stays, higher healthcare costs, and a greater likelihood of 30-day readmission (16). In our retrospective study, we used naloxone administration as a secondary measurement for opioid overdose in over 11,000 patients, enabling us to examine risk factors contributing to adverse events compared to the controlled population receiving opioids. While the patient group receiving naloxone had almost double the MME, we identified an additional seven statistically significant risk factors predisposing patients to adverse drug events, which included OSA, obstructive pulmonary disease, coadministration of benzodiazepines, BMI, CrCl, and substance use disorder history.
Per our study results, OSA was noted to be a statistically significant risk factor for adverse events with opioid administration. Of the patients that overdosed in the inpatient setting, 21.54% had a history of OSA compared to just 10.51% of patients who did not require naloxone use in the hospital (OR = 1.608, p = 0.0424). This is consistent with literature, which shows that patients with pre-existing OSA have a 1.4-fold risk of respiratory issues compared to control groups and is the cause of death in 50% of surgical patients within the first 24 hours of surgery (13). The u-opioid receptors responsible for opioid analgesia are also implicated in modulation of respiratory drive (17). Furthermore, obstructive apneas can also occur with opioids due to their direct inhibitory effect on genioglossus muscle activity and their impact on the central hypoglossal motor pool, along with the depression of the protective arousal response (17).
In our study, patients with iatrogenic opioid overdose were more than twice as likely to have concomitant obstructive pulmonary disease (47.69% vs. 22.75%). Our data suggests that obstructive pulmonary disease is more strongly associated with in-hospital opioid overdose compared to OSA. This may be due to the structural and functional changes associated with chronic obstructive pulmonary disease. Opioids administered to individuals with obstructive pulmonary disease may exacerbate respiratory depression, reduce mucous clearance due to cough suppression, and increase immunosuppressive events (18). A large cohort study identified an increase in all-cause mortality among recipients of 30 MME per day compared to those without advanced COPD (19). Another study found similar correlations with adverse effects, with a 2.27-fold risk of opioid-induced respiratory depression after surgery, in line with our findings (13).
The literature mentions a few types of medications which can negatively interact with opioids including benzodiazepines, muscle relaxers and gabapentinoids. Interestingly, in our study, only benzodiazepine/barbiturate use was associated with increased odds of iatrogenic opioid overdose (OR = 2.042, p = 0.0014), whereas gabapentinoid and muscle relaxant use was not found to be an independent risk factor for opioid overdose.
Benzodiazepines are the main culprit for adverse events when used alongside opioids for pain control. Both benzodiazepines and opioid analgesics are CNS depressants, with their coadministration demonstrating a potentiating effect on overdose (20). Two studies reported a 3.5 to 4-fold increased risk of overdose death with sedating nervous system medications; another study found increased cardiopulmonary and respiratory adverse events when opioids were combined with benzodiazepines (4, 11, 12). Muscle relaxers have been routinely co-prescribed with opioids, with one article highlighting that about 10% of those who use opioids for pain control are also prescribed muscle relaxers (21). This increases to 30% when the pain in question is specifically musculoskeletal (21). Regarding gabapentin, one study noted a 50% increase in opioid related death with concurrent use of gabapentin. This statistic nearly doubled when the gabapentin dose was high, supporting a drug-drug interaction between the two agents and thus its association with life-threatening consequences (11). Another study noted that continuation of home gabapentin or pregabalin was associated with a 6-fold increase in opioid-induced respiratory depression on surgical wards (22). Perhaps one contributing factor to the higher rates of opioid overdose in inpatients with recent benzodiazepine/barbiturate use is the longer half-life of these medications compared to gabapentinoids and muscle relaxants. For instance, the half-life of long-acting benzodiazepines ranges from 40-250 hours, whereas gabapentinoids and muscle relaxants generally have much shorter half-lives (23-25). In the inpatient population specifically, blood levels of gabapentinoids and muscle relaxants might not be high enough to potentiate effects of opioids after a few days, whereas benzodiazepines may be present in the bloodstream for longer.
BMI has also played a role in adverse events with opioid usage. Our research found that a BMI of greater than 30 was a statistically significant predictor of adverse events with opioid usage (OR = 3.656, p < 0.001). Patients with a higher BMI experience increased restrictive effects on lung function and a reduction in functional residual capacity. This is caused by reduced chest wall compliance due to added weight from adipose tissue and cephalad displacement of the diaphragm due to increased abdominal mass. This, in turn, can lead to atelectasis, hypoxemia, and diminished lung function (22, 26). One study found that not only was there a strong correlation of obesity and the use of opioids for pain control, but that correlation strengthened as BMI increased (27). Moreover, the duration of treatment with opioids was noted to be higher in those with obesity, leading to increased risk of opioid use disorder and mortality (27). Another study was able to discern that obesity, alongside other risk factors such as mild liver disease, Hispanic origin, and COPD, put patients at higher risk of cardiopulmonary and respiratory arrest in both medical and surgical settings (28).
Our research was able to identify that not only do patients with a CrCl < 29 (mL/min) benefit from renal dose adjustments with opioid usage, but that those with a CrCl of 30-59 (mL/min) were also at risk for adverse events, suggesting they might also benefit from dosage adjustments. In patients with kidney disease, the primary concern revolves around the accumulation of opioids and their active metabolites due to renal insufficiency. This accumulation is a consequence of decreased nephrons, glomerular filtration rate (GFR), tubular secretion, and renal blood flow required for the removal of opioids and their harmful metabolites. Furthermore, liver enzymes CYP2D6 and CYP3A4 undergo downregulation in advanced kidney disease, secondary to uremia (8). Agents such as oxycodone and hydromorphone should be used cautiously in patients with CrCl < 30 (mL/min) as there have been reports of drug accumulation leading to CNS toxicity and sedation if not properly dose adjusted (8, 9). However, opioids such as methadone and fentanyl seem safe to use, although dose adjustments are still highly recommended. Finally, opioids like codeine, morphine, and tramadol should be completely avoided due to accumulated active metabolites that can lead to adverse effects (8, 29).
In our study, the risk factor with the largest independent effect on risk of iatrogenic opioid overdose was history of substance use disorder (OR = 4.255, p < 0.0001). There may be a few reasons for this interaction. Firstly, substance use disorders are often comorbid with liver and renal disease, which may impair metabolism and excretion of opioids in these patients (30). Furthermore, substance use in the inpatient setting is often treated with drugs that may interact with opioids. For instance, alcohol withdrawal is typically treated with benzodiazepines, which we have shown increases the risk of inpatient opioid overdose.
Surprisingly, age and liver failure were not found to be risk factors. There is some precedent for these findings in the literature. Zedler et al, for example, also did not find hepatic dysfunction to be statistically significant to include as a risk factor for their own opioid risk tool (31). Regarding the geriatric population, adverse effects are thought to be due to changes in pharmacokinetics, pharmacodynamics, and drug-drug interactions (32). Our study, however, did not find age to be a risk factor associated with adverse events related to opioid use. While it is known that the elderly population are more likely to suffer from other comorbid conditions – which as noted above have been associated with adverse effects from opioids – all other factors constant, age itself is not the risk factor in question.
Limitations:
Our study was performed with data collected from a single health system in one geographical region; though diverse in terms of populations served, the health system only serves a small portion of the northeast United States. Although a thorough search of the EMR was performed, there is inherent potential for misclassification of diagnostic coding. For example, a diagnosis of heart failure may have been charted, even though the patient may have only had a prior history of reduced ejection fraction or simply a diastolic dysfunction. Thus, there may be variation among different physicians and even among the different admitting services which may lead to biases in how patient admissions are documented. Lastly, it is important to recognize that naloxone is often administered reflexively by rapid response teams as a reaction to alterations in consciousness even when opioids are not the most likely culprit. As such, there were certain cases in which it was unclear whether the naloxone administration was given for reversal of opioids or for ambiguous altered mental status of unknown etiology.