8th January 2024

Cautions

Renal impairment

There is little evidence for opioid choice in renal impairment. Practice is mainly guided by clinical experience, but there are some important considerations with certain drugs:

• Morphine metabolites are renally excreted. Renal impairment can, therefore, increase the half-life and cause accumulation and an increased side effect burden. At an eGFR of 20-50ml/min, it is used at 75% of the normal dose. Below that, alternative opioids are recommended.
• Oxycodone is preferred in renal impairment to morphine in some hospital trusts, but there is still the risk of accumulation. Modified-release oxycodone should be avoided in stage 4-5 CKD, but immediate release can be used.
• Alfentanil is safe in renal failure and is the drug of choice in stage 4 & 5 CKD if a syringe driver is needed. There is also a sublingual option.

Across all drugs, the dose should be slowly and carefully titrated, as rapid changes can cause accumulation.

Hepatic impairment

Unlike renal impairment, there is no figure by which to grade hepatic impairment, meaning there are no cut-offs for dose changes. Most opioids are metabolised in the liver, so there is an increased risk of toxicity. Drugs should be started at lower doses and titrations slower as a result. With regard to specific drugs:

• Oral morphine bioavailability can be increased to 100% in hepatic impairment. It can be used safely with cautious use but should be avoided if there is both liver and kidney failure, e.g., hepato-renal syndrome.
• Oxycodone effectiveness and onset can be impacted, as can clearance. It should be avoided in moderate to severe hepatic impairment.
• Fentanyl is metabolised to non-active metabolites, so can be safely used in hepatic failure. It is particularly useful where there is both hepatic and renal failure.

Driving

Driving rules are a favourite question in the exam. Taking strong opioids is not a reason to stop driving or inform the DVLA. Although drug driving is an offence, a medical defence can be raised where the drug is legally prescribed and taken in accordance with the advice of the prescriber. Patients who do not follow this advice may be liable to prosecution. It is therefore important to be aware of and alert patients to the following rules:

• Patients should carry evidence of their legal prescription for the drug.
• Drivers should not drive if they are impaired by the drug. To drive if they are drowsy, for instance, is an offence.
• Patients should be advised not to drive when starting or titrating the dose of opioids, as this increases the risk of sedation.