Symptoms and signs of opioid toxicity and opioid induced hyperalgesia

Presentation

Opioid toxicity presents with a recognisable clinical triad - sedation/reduced consciousness, respiratory depression, and pupillary miosis - alongside other features (myoclonus, hallucinations, nausea) that clinicians must actively distinguish from disease progression or another cause of deterioration
A common, important clinical scenario given the ubiquity of opioid use in palliative care - toxicity can arise from dose escalation, accumulation (renal impairment, particularly with morphine's active metabolites), drug interaction, or a switch/conversion error

Sedation typically precedes clinically significant respiratory depression - increasing drowsiness is usually the earliest and most reliable warning sign, and should prompt dose review before respiratory rate has already fallen
Myoclonus (involuntary muscle jerking) is a recognised sign of opioid accumulation/toxicity, particularly with morphine in renal impairment (from accumulated active metabolites), and can progress to more significant neuroexcitatory effects including seizures if unaddressed

Clinical assessment (level of consciousness/sedation score, respiratory rate, pupil size) rather than a single measure alone - sedation trending down is often the earliest and most actionable warning sign, appearing before respiratory rate has significantly fallen
Distinguish opioid toxicity from disease progression/approaching death, which can produce overlapping features (reduced consciousness, altered breathing pattern) - a trial dose reduction/reversal can help clarify the cause when genuinely uncertain

Reduce or withhold the opioid dose and reassess; for significant toxicity, consider naloxone, titrated carefully in a patient on chronic opioids to reverse toxicity without precipitating a severe, distressing withdrawal/pain crisis (small incremental doses, not a full reversal bolus, unless the situation is immediately life-threatening)
Review and correct the underlying cause (renal function, recent dose change, drug interaction, or a conversion calculation error) to prevent recurrence, not just treat the acute episode

Renal impairment (morphine metabolite accumulation), opioid conversion calculation errors, terminal sedation vs opioid toxicity differentiation

In a patient on long-term opioids, full-dose naloxone reversal risks precipitating severe pain and a distressing withdrawal syndrome - cautious, titrated reversal (aiming to restore adequate respiratory function while preserving some analgesic effect) is the correct approach in most non-immediately-life-threatening toxicity

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