Initial assessment
In a patient with pain, the first step is to accurately characterize the type of pain (acute vs chronic; nociceptive vs neuropathic), its intensity, functional impact and clinical context. It is essential from the outset to distinguish baseline pain, which is continuous, from episodes of breakthrough pain, which are sudden and transient, as this distinction guides the choice of drug, formulation and route of administration. Risk factors should also be assessed, including advanced age, respiratory, renal or hepatic comorbidities, polypharmacy and history of substance misuse.
Clinical framework
Analgesic selection should take into account the care setting. In primary care, a more conservative approach is favoured, starting with paracetamol and, when necessary, weak or intermediate-potency opioids. In hospital and palliative care settings, pain is often more intense or complex, and the use of strong opioids, parenteral routes or transdermal systems is common, requiring closer clinical monitoring.
Baseline pain versus breakthrough pain
The distinction between baseline pain and breakthrough pain is central to opioid prescribing. Baseline pain should be treated with drugs administered at regular intervals, often in prolonged-release formulations, with the aim of maintaining stable analgesic levels. Breakthrough pain, on the other hand, requires rapid-onset formulations, used as rescue medication and adjusted according to individual response and patient tolerance. Prolonged-release formulations should not be used as rescue medication.
Choice of opioid and route of administration
Opioid selection should be based on pain intensity, previous response to other analgesics and patient characteristics. Drugs such as morphine, oxycodone or hydromorphone may be used through different routes, whereas transdermal systems, such as fentanyl or buprenorphine, are intended for patients with stable pain and continuous analgesic requirements. These systems have a slow onset of action and are not suitable for acute or unstable pain, and should be accompanied by a rescue strategy during the first hours.
Safety and monitoring
All opioids carry a risk of sedation and respiratory depression, particularly after initiation or dose escalation. Clinical monitoring is essential, especially in older adults, patients with COPD, obesity, renal or hepatic impairment, or when opioids are combined with other sedative drugs. The therapeutic goal should always be to achieve adequate pain relief with the lowest effective dose, avoiding rapid titration without reassessment.
Rotation and therapeutic adjustment
Whenever switching from one opioid to another is considered, cross-tolerance should be assumed to be incomplete. The initial dose of the new drug should be reduced cautiously, followed by progressive titration according to clinical response. Additional adjustments are often required in renal impairment or liver disease, due to the risk of accumulation and toxicity.
Special situations
Some opioids require additional precautions. Transmucosal fentanyl is reserved for opioid-tolerant patients and for cancer-related breakthrough pain. Methadone has complex pharmacokinetics, risk of QT prolongation and delayed accumulation, and should only be used by experienced teams. Identifying these situations is essential to prevent serious adverse events.
Follow-up and reassessment
Opioid therapy should be accompanied by regular clinical reassessment, evaluating analgesic efficacy, adverse effects, functionality and adherence. Pain management is a dynamic process that requires continuous adjustment and an individualized approach, integrating clinical context, therapeutic goals and patient safety.
