7.3 Opioid Adverse Effects, Neurotoxicity, and Rotation

Complications are Domain 2 Task D

HPCC Task D asks you to assess for and respond to complications (side effects, interactions) and efficacy. On a 150-item CHPN exam this is high-yield because almost every hospice patient on an opioid will have a bowel problem, and a smaller but dangerous subset will declare opioid-induced neurotoxicity (OIN). Generic names appear throughout: morphine, hydromorphone, oxycodone, fentanyl, methadone, senna, docusate, polyethylene glycol, methylnaltrexone, naloxegol, metoclopramide, naloxone.

Sort effects into three buckets:

• Expected, little or no tolerance: constipation, miosis.
• Common early, often transient: nausea, sedation in the first 48–72 hours after start or a significant increase.
• Uncommon at titrated palliative doses, or a toxicity syndrome: clinically important respiratory depression in the opioid-tolerant dying patient; OIN (myoclonus, hyperalgesia, delirium); urinary retention; severe pruritus.

Constipation — start the bowel regimen with the opioid

Opioid-induced constipation (OIC) is expected. Tolerance to it essentially does not develop. Waiting until the patient has gone four days without a stool is the classic fail. Start a stimulant plus a softener (for example senna plus docusate) or polyethylene glycol (PEG) when the opioid is started. The working piece is the stimulant or the PEG; docusate alone is a weak plan. Push oral fluids and fiber only if the gut still works and that matches goals; in dying ileus, fiber can worsen obstruction physiology.

If OIC is refractory after an adequate laxative trial, a peripherally acting mu-opioid receptor antagonist (PAMORA) may be appropriate: methylnaltrexone (typically subcutaneous in palliative care) or naloxegol (oral). These spare central analgesia if the blood-brain barrier stays intact. Do not give a PAMORA when mechanical bowel obstruction is present or suspected — perforation is the feared complication. Match to prognosis and goals: a patient dying in hours may be better served by a rectal suppository, a comfort-focused exam, and not another injection. A patient with weeks of life and bloating misery may gain a great deal from methylnaltrexone.

Nausea

Opioid nausea is often transient over several days as tolerance develops. It is not automatically an allergy. Constipation itself causes nausea — fix the bowel. Gastroparesis physiology responds to metoclopramide if that is not contraindicated. Chemoreceptor-trigger-zone nausea may respond to an antidopaminergic agent. Ondansetron helps serotonergic nausea but can worsen constipation. If nausea persists, rotate the opioid rather than stacking every antiemetic forever.

Sedation versus dying

New or increased opioid doses commonly cause sleepiness for one to three days. If the patient is arousable, breathing adequately, and more comfortable, observe, protect from falls, and teach the family that this is often temporary. Persistent sedation after that window is a reason to reduce the dose, add a stimulant such as methylphenidate if goals include alertness, or rotate.

Dying looks different: mottling, cooling, Cheyne-Stokes or irregular breathing, loss of swallow, and a trajectory of hours to days. Families often beg you to reverse that breathing pattern with naloxone. That is reversing dying, not reversing an overdose. Teach the difference out loud and, when needed, write an order not to give naloxone for expected terminal breathing.

Pruritus and urinary retention

Pruritus is not always histamine-driven; morphine is sometimes more pruritogenic than fentanyl. Rotation, a small mixed agonist-antagonist strategy in selected settings, or ondansetron may help more than a sedating antihistamine. Scratching until skin breaks is a quality-of-life problem worth treating; mild itch that the patient barely notices is not a reason to stop analgesia.

Urinary retention clusters with spinal or epidural opioids, older men with prostatic hypertrophy, and anticholinergic stacks. Bladder scan or straight catheterization relieves pain that looks like abdominal agony. Review the med list; rotating or reducing the opioid is sometimes required.

Respiratory depression — the myth that withholds morphine

In opioid-tolerant palliative patients, doses titrated to pain or dyspnea rarely cause life-threatening respiratory depression. Pain and dyspnea themselves drive ventilation. The CHPN error is withholding morphine for breathlessness because a family or a covering clinician fears the last breath. Treat the dyspnea. Monitor. Do not confuse a dying respiratory pattern with iatrogenic overdose.

True iatrogenic overdose looks like a sudden change after a dosing error or a new route: difficult to arouse or unarousable (not merely asleep and waking to voice), shallow respirations or a rate under about 8/minute with hypoventilation (hypoxemia, not just a sleepy rate of 10 while saturating well). Sleeping on opioids with a rate of 8 and pink, arousable patients are often sleeping, not overdosed.

Naloxone — dilute, cautious, not reverse dying

Naloxone is indicated for life-threatening opioid-induced CNS and respiratory depression in a patient whose goals still include recovery of ventilation — typically a still-recoverable person after an iatrogenic bolus, a pump programming error, or an accidental extra dose. It is not indicated for the expected course of dying.

Palliative technique (Fast Fact teaching that matches CHPN judgment):

1. Confirm goals and that this is overdose, not dying.
2. Stop further opioid until the patient is safe.
3. Dilute 0.4 mg naloxone to 10 mL with saline (0.04 mg/mL).
4. Give 1 mL every 1–2 minutes until the patient is breathing more deeply and arousable enough to protect the airway — not until they are wide awake and in screaming pain.
5. If about 0.8 mg produces no response, look for other causes (benzodiazepines, stroke, sepsis).

A full undiluted ampule in a tolerant palliative patient can precipitate acute withdrawal, pulmonary edema, and a pain crisis. Community 2 mg or 4 mg spray technique is for unwitnessed street overdose, not routine hospice dying.

Opioid-induced neurotoxicity

OIN is a metabolite and dose-accumulation syndrome, more common with morphine and hydromorphone in renal impairment, dehydration, rapid escalation, and poor performance status. Hallmarks:

• Myoclonus (multifocal jerks)
• Hyperalgesia (pain worsening as the dose rises) and allodynia (light touch hurts)
• Delirium, hallucinations, agitation
• In severe cases, seizures

This is not a reason to double the same opioid. The pain is being amplified by the drug. Management aligned with goals:

• Hydrate (oral, IV, or subcutaneous) if dehydration is contributing and hydration is acceptable.
• Lower the dose of the offending opioid.
• Rotate to a structurally different opioid, often one with fewer offending metabolites (fentanyl or specialist-managed methadone).
• Treat myoclonus as a bridge with a benzodiazepine if jerks themselves cause distress, while you rotate — benzodiazepines are not the whole plan.
• For patients imminently dying whose myoclonus is mild and not bothersome, explanation and observation may be kinder than a chaotic rotation.

Rotation indications and incomplete cross-tolerance

Rotate when any of these are true:

• Pain remains uncontrolled despite adequate titration and adherence
• Adverse effects are intolerable (persistent sedation, nausea, pruritus, OIN)
• Route must change (nothing by mouth, malabsorption, need for a patch or infusion)
• Renal failure makes morphine, codeine, or meperidine poor choices
• Formulary, shortage, or cost barriers that actually interrupt analgesia

Because cross-tolerance is incomplete, the new opioid is usually started at a reduced equianalgesic dose (often about 25–50% less, more reduction when rotating for toxicity, less reduction when pain is raging). Methadone conversion is specialist territory. After rotation, reassess within hours for oral drugs and sooner for parenteral.

Rotation — indications to memorize

1. Uncontrolled pain despite titration
2. Intolerable side effects or OIN
3. Need for a new route
4. Organ failure that makes the current opioid a metabolite trap
5. Access (shortage, cost) that is actually interrupting doses