Opioid toxicity and renal impairment

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Opioid toxicity exists on a spectrum. Early drowsiness, slowed thinking and unsteadiness can progress to hallucinations, myoclonus, hyperalgesia and respiratory depression. Ask what changed: dose, formulation, route, patch number, infusion, rescue frequency, renal function, hydration, infection or another sedative. A stable dose can become toxic during sepsis or dehydration because clearance changes faster than the prescription.

Clinically important respiratory depression is recognised by ventilation, not oxygen saturation alone. Count respiratory rate for a full minute, assess depth, effort, airway patency, arousability and carbon-dioxide retention when available. Supplemental oxygen may preserve saturation while ventilation continues to fall. Support the airway and breathing immediately and do not wait for naloxone or a complete medication history.

Naloxone dosing depends on context. In coma or major overdose, follow the emergency or toxicology protocol. For an opioid-dependent patient who is breathing inadequately but has a pulse, experienced teams may use smaller intravenous increments, for example 100 to 200 micrograms at intervals of 2 to 3 minutes, aiming for safe ventilation rather than complete analgesic reversal. Some specialist palliative protocols use still smaller diluted increments. Verify the locally approved concentration and regimen and obtain resuscitation support.

Renal impairment changes opioid selection. Morphine-3- and morphine-6-glucuronide accumulate, and codeine generates morphine-related active metabolites. Diamorphine is rapidly converted to morphine and shares the metabolite problem. Oxycodone parent drug and metabolites can accumulate and requires caution. Fentanyl may suit stable transdermal requirements, while alfentanil is sometimes chosen for continuous subcutaneous use in severe renal impairment; both require high-potency conversion checks and specialist oversight.

Do not confuse reduced consciousness in the last days with opioid poisoning automatically. Examine timing, respiratory pattern, dose change, pupils, myoclonus and other causes. If ventilation is adequate and the person is comfortably dying on a previously tolerated dose, routine naloxone can precipitate pain without benefit. If opioid toxicity is causing dangerous respiratory depression, goals of care do not justify leaving it untreated; provide proportionate reversal and then restore a safer comfort regimen.

After stabilisation, treat dehydration, infection, retention, constipation or biochemical disturbance if consistent with goals. Hold, reduce or rotate the opioid with palliative and pharmacy input. Account for residual patches and long-acting formulations, recalculate breakthrough medication in the new drug and route, and remove superseded supplies. Explain the event and new safety plan to the patient and caregivers without implying blame.

Key points

Increasing sedation, impaired attention and slowed breathing are more important toxicity signals than pinpoint pupils alone.
First-line emergency care is airway and ventilation support plus stopping further opioid; naloxone supplements rather than replaces resuscitation.
In opioid-dependent palliative patients, titrate naloxone to adequate breathing when possible because complete abrupt reversal can cause severe pain and withdrawal.
Observe beyond the antagonist's action and anticipate repeat doses or infusion for modified-release, patch, methadone or renally accumulated exposure.
Check the last 72 hours of regular, rescue, patch and pump doses, all recent conversions, renal trend, hydration and concurrent sedatives.
Morphine, diamorphine and codeine rely on renal elimination of active metabolites and are commonly avoided or used only with expert adjustment in severe renal impairment.
Fentanyl and alfentanil have no clinically important active renally cleared metabolites, but potency, route and conversion still require specialist or pharmacy governance.
Oxycodone can also accumulate in renal dysfunction and is not a risk-free default; use reduced dosing and close review only under the relevant formulary.
The gold-standard recovery plan treats the precipitant, reduces or rotates the opioid, recalculates rescue, cancels old prescriptions and monitors through both drugs' pharmacological tails.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Excess exposure

Rapid titration, duplicate formulations, multiple patches, infusion error, misunderstood rescue instructions or an incorrect conversion can raise opioid concentration beyond tolerance.

Reduced clearance

Acute or chronic renal failure, hepatic dysfunction, dehydration and frailty prolong parent-drug or metabolite exposure even when the prescription has not changed.

Interacting depressants

Benzodiazepines, gabapentinoids, sedating antipsychotics, alcohol, antihistamines and other central depressants compound impaired arousal, airway protection and ventilation.

Changing sensitivity

Opioid-naive status, older age, sleep-disordered breathing, hypercapnic respiratory disease and neurological impairment increase susceptibility at lower circulating concentrations.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Ventilatory drive suppression
Mu-receptor activation reduces brainstem response to carbon dioxide, slowing rate and tidal volume before hypoxia and arrest develop.
2
Active metabolite accumulation
Morphine glucuronides and codeine-derived metabolites are renally cleared and can accumulate, causing prolonged analgesia, sedation, respiratory depression and neuroexcitation.
3
Neuroexcitatory toxicity
High exposure and metabolites can promote myoclonus, hallucinations, delirium, seizures, allodynia and paradoxical hyperalgesia despite continuing opioid receptor effects.
4
Carbon-dioxide narcosis
Hypoventilation raises arterial carbon dioxide, worsening cerebral depression and acidosis in a self-reinforcing cycle that oxygen alone cannot correct.
5
Antagonist offset
Naloxone often has shorter effect than the causative opioid, especially modified-release, transdermal or renally accumulated exposure, so toxicity can recur after apparent recovery.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Early sedation

Longer sleep, slurred speech, reduced attention, unsteady gait or difficulty completing usual tasks after a dose change warrants immediate review.

Respiratory toxicityRed flag

Slow shallow ventilation, difficult rousing, cyanosis or hypercapnia with compatible exposure is a life-threatening opioid pattern.

Neuroexcitation

Myoclonus, vivid dreams, hallucinations, delirium, allodynia or seizures can reflect metabolite accumulation rather than insufficient analgesia.

Renal accumulation

Symptoms developing after dehydration, infection, urinary obstruction or falling eGFR on an unchanged morphine dose strongly suggest impaired elimination.

Patch excess

Duplicate patches, external heating, fever or failure to remove the previous strength can produce delayed and prolonged fentanyl exposure.

Mixed toxicity

Incomplete response to naloxone or disproportionate coma suggests another sedative, metabolic, infectious or intracranial contributor alongside opioid effect.

Red flags requiring action

Progressive drowsiness usually precedes major respiratory depression and must not be dismissed as normal sleep after a dose increase.
Respiratory rate below 8, cyanosis, apnoea, inability to rouse or carbon-dioxide retention needs airway support and proportionate naloxone.
New myoclonus, hallucinations, delirium, allodynia or diffuse hyperalgesia indicates opioid neurotoxicity, often before severe respiratory signs.
Acute kidney injury, eGFR below 30 mL/min/1.73 m², dehydration or sepsis can rapidly turn a previously tolerated morphine regimen toxic.
Multiple patches, an infusion-programming error, recent conversion or concurrent benzodiazepine, gabapentinoid or alcohol exposure demands immediate dose reconstruction.
Reduced consciousness at end of life may have several causes; naloxone is for clinically important opioid respiratory depression, not routine reversal of expected dying.
A response to naloxone does not exclude intracranial disease, sepsis, hypoglycaemia or mixed toxicity and does not end observation.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line ABCDE and ventilation assessmentFirst stepFirst line
Why
Measure arousability, respiratory rate and depth, airway, oxygenation, circulation, temperature, pupils and capillary glucose.
Interpretation and limitations
Inadequate ventilation requires immediate support and antidote consideration; a normal saturation on oxygen does not establish respiratory safety.
02
Chronological opioid reconstruction
Why
List every administered regular and rescue dose, patch, infusion and recent switch over enough time to capture long-acting exposure.
Interpretation and limitations
Look for duplicate formulations, route or decimal error, unexpected rescue use and old patches; preserve pumps and charts for medication-safety review.
03
Renal, hepatic and metabolic profile
Why
Check creatinine and eGFR trend, liver tests, calcium, sodium, glucose and other results guided by the clinical presentation.
Interpretation and limitations
Acute change, dehydration or severe impairment can explain accumulation and determines whether the opioid must be withheld, reduced or changed.
04
Concurrent depressant review
Why
Identify benzodiazepines, gabapentinoids, sedating antipsychotics, antihistamines, alcohol, illicit drugs and anaesthetic exposure.
Interpretation and limitations
Mixed effects raise monitoring needs and explain incomplete naloxone response; do not reverse one drug and overlook the rest.
05
Focused cause assessment
Why
Evaluate sepsis, retention, impaction, intracranial disease, hypercapnia, seizure, terminal decline and uncontrolled pain mechanisms.
Interpretation and limitations
Toxicity can coexist with a precipitating illness and genuine pain; treatment must address all clinically relevant causes.
06
Post-reversal observation plan
Why
Match continuous monitoring and review duration to the causative opioid, route, renal clearance, co-ingestants and naloxone requirement.
Interpretation and limitations
Recurrent sedation or slowing indicates continuing opioid effect and may require repeat naloxone or infusion with higher-acuity care.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Expected terminal decline

Reduced interaction and irregular breathing may accompany dying, but recent opioid change, pinpoint pupils, slow shallow ventilation and temporal association support toxicity.

Delirium from illness

Sepsis, hypercalcaemia, urinary retention, constipation, hypoxia and organ failure produce cognitive fluctuation and may also precipitate opioid accumulation.

Intracranial pathology

Brain metastasis, haemorrhage, seizure and raised intracranial pressure can cause coma or pupillary change and require focused neurological assessment.

Other sedative toxicity

Benzodiazepines, alcohol, gabapentinoids, antipsychotics and mixed overdose can mimic or worsen opioid effects and may not fully respond to naloxone.

Uncontrolled pain behaviour

Agitation and vocalisation can reflect pain, but neurotoxicity, withdrawal, delirium and akathisia should be considered before additional opioid is given.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Respiratory emergencyVentilate, reverse proportionately and observeFirst stepThe patient is difficult to rouse and has clinically important hypoventilation after possible opioid exposure.

1Stop opioid, call emergency help, support airway and ventilation, give oxygen as indicated, check glucose and attach appropriate continuous monitoring.
2EscalationGive intravenous naloxone under the local emergency protocol, titrating to adequate ventilation when opioid dependence permits and escalating doses for apnoea or severe overdose as directed.
3Observe for recurrent depression, repeat or infuse naloxone if necessary and investigate long-acting exposure, renal accumulation and mixed causes.

02NeurotoxicityReduce exposure and treat the precipitantMyoclonus, hallucination, delirium, hyperalgesia or sedation develops without current respiratory collapse.

1EscalationWithhold routine escalation, assess recent dosing, hydration, renal function, infection, constipation, retention and interacting medicines.
2Reduce or temporarily stop the causative opioid as clinically required, treat reversible contributors and obtain palliative or pharmacy advice for rotation.
3Provide a renal-appropriate rescue plan, monitor cognition and breathing closely and remove superseded medicines once the new regimen is verified.

03Renal analgesiaSelect by clearance and pain stabilityeGFR is below 30, renal function is deteriorating or dialysis and end-stage kidney disease complicate opioid treatment.

1Reassess pain mechanism, total exposure, toxicity, trajectory and whether requirements are stable enough for a patch or need titratable subcutaneous treatment.
2Avoid unreviewed morphine, diamorphine and codeine accumulation and select the opioid, dose and route with the current renal palliative formulary, pharmacy and specialist team.
3Write a coherent maintenance and rescue plan, monitor after every renal or dose change and coordinate dosing with dialysis or other relevant treatment.

04After incidentRebuild analgesia and system safetyThe patient has recovered from toxicity or a near-miss conversion, patch or pump error is identified.

1Map the causal sequence across prescribing, dispensing, administration, renal change and communication and disclose the event through the local safety process.
2Create a lower or rotated regimen with independent calculation, bowel and symptom support and explicit old-drug stop and new-drug start instructions.
3Educate patient and carers, reconcile every care setting and monitor until residual long-acting exposure and the new opioid have reached a stable safe relationship.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Reverses opioid-mediated hypoventilation while airway support, exposure reconstruction and assessment of alternative or mixed causes continue.

Naloxone for opioid respiratory depression

Follow the local emergency or toxicology protocol. In an opioid-dependent patient with inadequate ventilation but a pulse, experienced clinicians may titrate 100 to 200 micrograms intravenously every 2 to 3 minutes to adequate breathing; severe apnoea or overdose requires the protocol's larger initial regimen and resuscitation support.

It can precipitate severe pain, vomiting and acute withdrawal and may wear off before the opioid; repeat dosing, infusion and prolonged observation may be required.

Provides maintenance analgesia without clinically important active renally cleared metabolites when oral treatment is unsuitable and pain is stable.

Transdermal fentanyl in selected renal impairment

Only for a patient already opioid tolerant with a stable requirement; choose patch strength through the current renal and palliative conversion table, product information and pharmacy or specialist check rather than a generic starting dose.

Not for rapid titration or an opioid-naive patient; heat, fever, skin, cachexia and delayed offset affect exposure, and separate renal-appropriate rescue is required.

A short-acting opioid option for titratable subcutaneous analgesia in severe renal impairment because clinically important active renal metabolites are absent.

Alfentanil under specialist renal prescribing

Use only a patient-specific microgram-dose subcutaneous rescue and 24-hour infusion regimen calculated and independently checked by specialist palliative care or pharmacy under the local severe-renal-impairment protocol.

Very high potency creates fatal unit-error risk; CYP3A4 interactions, respiratory depression and rapid dose changes require expert oversight and clear microgram notation.

May be used in some mild-to-moderate renal impairment when morphine is poorly tolerated, but it is not free from accumulation.

Oxycodone with renal caution

If the renal palliative formulary selects oxycodone, use a reduced immediate-release starting dose and extended interval specified for the measured function, with specialist or pharmacy review before every titration or conversion.

Parent drug and metabolites can rise as renal function falls; monitor sedation, hallucinations, myoclonus and breathing and switch strategy during acute kidney injury.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Respiratory arrest

Progressive hypoventilation causes hypercapnia, hypoxia, aspiration, cardiac arrest and hypoxic brain injury without prompt airway and ventilation support.

Withdrawal and pain crisis

Excessive naloxone can abruptly reverse analgesia and precipitate vomiting, agitation, hypertension and severe withdrawal in an opioid-dependent patient.

Recurrent toxicity

Apparent recovery may be followed by renewed depression when naloxone wears off while long-acting opioid or accumulated metabolites remain active.

Falls and aspiration

Less severe sedation and delirium cause falls, inability to swallow, aspiration and loss of safe medicine self-administration.

Persistent uncontrolled pain

Abruptly stopping analgesia without rebuilding a renal-appropriate plan leaves severe pain and may discourage future reporting of toxicity symptoms.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

During acute toxicity continuously monitor airway, respiratory rate and depth, oxygenation, circulation and arousability at the required care level.
After naloxone, observe beyond its duration according to opioid formulation, renal function, co-ingestants and toxicology or critical-care advice.
Trend renal function, hydration and urine output during sepsis, obstruction or decline and review opioid after every material change.
Record myoclonus, hallucinations, delirium, allodynia, pain and rescue response to distinguish neurotoxicity from undertreatment.
Check the body, chart and home supply for all patches and reconcile pump settings, concentrations and administration records.
Monitor the replacement regimen for both withdrawal and renewed toxicity and adjust only through the named coordinated prescriber.
Review sedatives, alcohol, gabapentinoids, falls risk and caregiver administration before discharge or return home.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Oxygen can hide hypoventilation

A satisfactory saturation on supplemental oxygen does not exclude worsening carbon-dioxide retention and falling tidal volume.

Neurotoxicity can look painful

Allodynia, agitation and myoclonus may provoke more opioid prescribing unless accumulation is actively considered.

Naloxone target is ventilation

In opioid dependence, restoring breathing while preserving some analgesia can avoid a dangerous withdrawal and pain surge.

Unchanged dose can become excessive

Acute kidney injury, dehydration and drug interaction alter exposure without any prescribing change.

Renal safe is not dose free

Fentanyl and alfentanil avoid active renal metabolites but retain potent respiratory and interaction risks requiring calculation and monitoring.

Toxicity and pain coexist

Stopping the harmful opioid is only half the task; the team must provide another route to humane analgesia.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for pinpoint pupils before recognising opioid respiratory depression.
02
Using oxygen saturation alone to judge ventilation safety.
03
Giving naloxone before opening and supporting the airway.
04
Reversing an opioid-dependent patient to full wakefulness when smaller titration could restore breathing.
05
Ending observation immediately after a brief naloxone response.
06
Calling hallucinations and myoclonus uncontrolled pain and increasing morphine.
07
Continuing a stable morphine dose unchanged through acute kidney injury.
08
Assuming oxycodone is completely safe in severe renal impairment.
09
Choosing alfentanil without microgram-level specialist and pharmacy checks.
10
Withdrawing all analgesia after toxicity without a replacement plan.