The efficacy of oxycodone/naloxone PR in the management of severe cancer pain has been extensively studied. Oxycodone is a full opioid receptor agonist with an affinity for endogenous mu, kappa and delta opiate receptors in the brain, spinal cord, and peripheral organs. Binding of oxycodone to endogenous opioid receptors in the central nervous system results in pain relief. Other pharmacological actions of oxycodone include respiratory depression, constipation, and cardiovascular system via histamine release and peripheral vasodilation [
2]. Compared with morphine, which has an absolute bioavailability of approximately 30%, oxycodone has a high bioavailability of up to 87% following oral administration. Following absorption, oxycodone is distributed throughout the body. Approximately 45% is bound to plasma protein. Naloxone reduces bowel function disorders such as constipation that typically arise during opioid analgesic treatment due to its local competitive antagonism of the opioid receptor-mediated oxycodone effect in the gut. Diarrhea may be a possible effect of naloxone, especially at the beginning of treatment, and tends to be transient. Oral administration of naloxone is unlikely to result in a clinically relevant systemic effect due to a pronounced first-pass effect and its very low oral bioavailability upon oral administration. A recent metanalysis including thirteen studies, indicated that naloxone could significantly reduce the occurrence of nausea, and vomiting induced by opioids, without relieving pain and somnolence [
17]. Clinical trials comparing oxycodone/naloxone to traditional opioid regimens have consistently demonstrated comparable analgesic efficacy. Among randomized controlled study on the efficacy and improved bowel function of oxycodone/naloxone PR, improvement in bowel function, analgesic efficacy, and safety profile in patients with non-malignant or malignant pain were confirmed in a phase III clinical trial [
18]. A randomized, double-blind, active-controlled, study investigated the efficacy of receiving up to 120 mg/day of oxycodone/naloxone PR in patients affected by moderate to severe cancer pain as compared to oxycodone alone or shifted from other opioids [
19]. The authors showed how patients who were switched directly from other opioids to oxycodone/naloxone PR experienced a similar analgesic effect, with a mean Brief Pain Inventory Short-Form (BPI-SF) scores comparable for the two groups and with a slight rating decrease during the observation period. Furthermore, a comparison between the administration of oral oxycodone/naloxone PR and transdermal fentanyl was proposed in patients with moderate-to-severe cancer pain [
20]. Despite a similar analgesic activity, oxycodone/naloxone PR was characterized by lower daily dosages, less need for drug escalation, and fewer side effects. In patients with chronic cancer pain, oxycodone/naloxone PR provided an analgesic effect that was like oxycodone alone, with early and sustained benefits in tolerability [
21]. The overall incidence of drug-related adverse events was 28.9% in the oxycodone group and 8.2% in the oxycodone/naloxone group, with a quality of life improved to a significantly greater extent in this group. Studies have also shown that oxycodone/naloxone maintains pain control without compromising the opioid’s analgesic effect. The analgesic response was assessed in 176 cancer patients experiencing moderate to severe pain and receiving oxycodone/naloxone PR [
22]. The results demonstrated a reduction in both average and worst pain intensity over time, along with a decrease in the prevalence of breakthrough pain. Furthermore, 81.3% of patients exhibited a positive response to the treatment. In an open-label extension of a randomized, double-blind study 128 patients with moderate-to-severe cancer pain were randomized to receive oxycodone/naloxone PR or oxycodone alone [
23]. Average pain scores based on the modified Brief Pain Inventory-Short Form were low and stable over the study period. In cancer-pain patients randomized, double-blind treatment a comparison between oxycodone/naloxone PR with controlled-release oxycodone or controlled-release morphine showed how a stable analgesia was achieved by 83% of controlled-release oxycodone and 81% of controlled-release morphine patients [
24]. The findings from RCTs are supported by open-label studies, including 60-day observational study patients who required oxycodone/naloxone PR at high daily doses. The results showed how compared with baseline oxycodone/naloxone PR reduced pain intensity, the impact of pain on quality of life, and the number of breakthrough pain episodes [
25]. In an observational study of patients affected by lung cancer associated with neuropathic pain, more than 80% of patients significantly reduced the average pain intensity improving health-related patient-reported outcomes [
26]. A significant improvement in pain intensity was showed in exploratory, non-randomized, open-label, mono-center study in which the principal aim was to evaluate whether patients with advanced cancer and moderate to severe cancer pain will benefit from treatment with oxycodone/naloxone PR [
27]. An additional observational study reported significant improvements in pain scores [
28]. Finally, the effectiveness and safety of oxycodone/naloxone PR were evaluated in a subgroup of patients with severe cancer pain coming from a prospective, multicenter non-interventional study [
29]. The results showed clinically relevant improvements in pain intensity both in opioid-naïve patients and in patients pretreated with weak or strong opioids, as reflected by reductions in pain scores of more than 50%. A multi-center, open-label, randomized, phase IV study is still proceeding to evaluate pain difference on Brief Pain Inventory-Short Form (BPI-SF) in cancer pain patients marked by a numerical pain score of ≥4/10 at baseline [
30]. The oxycodone/naloxone’s efficacy is represented also by its potential to reduce the need for additional laxatives. In fact, by mitigating the occurrence of OIC, patients can avoid the use of adjunct medications [
31]. A multicenter study reported the effectiveness of oxycodone/naloxone PR in patients with severe pain who had laxative refractory OIC with their previous opioid [
32]. The results showed how more than 60% of patients reported both an improvement in constipation and in quality of life. In summary, oxycodone/naloxone PR has demonstrated considerable efficacy in providing pain relief for cancer patients experiencing severe pain. The combination’s ability to effectively address opioid-induced constipation while maintaining analgesic potency represents a significant advancement in cancer pain management.
Figure 1.
Mechanisms of cancer pain as a direct or indirect consequence of tumor.
Figure 2.
Schematic diagram of mechanism involved in Oxycodone/naloxone PR.
Conventional opioids typically exert a systemic impact by binding to μ-opioid receptors in both the central nervous system and gastrointestinal tract (GUT). The binding of opioids to the CNS produces analgesic effects, while their interaction with the GUT can lead to complications such as opioid-induced constipation. On the other hand, the 2:1 combination of opioid agonist-antagonist demonstrated effectiveness in alleviating opioid-induced constipation. This is achieved by naloxone binding to μ-opioid receptors in the GUT and displacing oxycodone from the receptor. Consequently, the adverse effects of opioids on the GUT are mitigated, while the analgesic effects of oxycodone remain intact due to naloxone’s low bioavailability and its initial metabolism by the liver.
Table 1.
Principal studies regarding the use of oxycodone/naloxone prolonged relies in severe cancer related pain.