[Opioids for Cancer Pain and its Use under Particular Conditions: A Narrative Review]

All health professionals should be aware of the importance of evaluating pain - fifth vital sign- in cancer patients. Peripheral and central acting analgesics are widely used to treat moderate to severe pain, particularly cancer pain. Many guidelines have addressed this issue. However, real life patients' have other problems and comorbidities that may raise doubts when prescribing.

Authors made a literature search, trying to clarify same specific situations: loss of oral route, renal impairment (hemodialysis), hepatic impairment, frequent opiod interactions and the availability of short-acting formulations.

The following medicines were included in this analysis: the natural opiates (morphine and codeine), their synthetic and semisynthetic derivatives (hydromorphone, oxycodone, and fentanyl), the partial agonist buprenorphine and finally tramadol and tapentadol. Transdermal systems are only available for buprenorphine and fentanyl. In hepatic impairment, fentanyl is safe, but with the exception of codeine and tramadol; other opioids should be used with caution. In renal failure: fentanyl, hydromorphone, and tapentadol are safe. Morphine should be avoided; other opioids should be used with caution. In hemodialysis, buprenorphine, fentanyl, hydromorphone and tramadol (at doses up to 200 mg/day) may be used.

Failure to recognize the impact of various situations described throughout this work, including the bioavailability due to loss of oral route, due to pharmacokinetics and pharmacodynamics of the various drugs, either in the context of the impaired metabolism or excretion, or in due to pharmacological interactions, conditions a serious risk of subtreatment of pain and consequent impact in terms of quality of life.

Opioid prescription is safe and effective, even in moderate to severe comorbidities such as renal and hepatic impairment and in patients with no oral route available. In this case, as when considering pharmacological interactions, an individualized therapeutic plan is the best solution and the patient should be assessed regularly. Unadjusted doses may relate to bad pain control and a higher prevalence of adverse events.