What is a recommended intravenous (IV) pain management regimen?

Intravenous Pain Management Regimen

For IV pain management, use continuous IV opioid infusions (morphine or fentanyl) with round-the-clock dosing plus breakthrough doses of 10-15% of the total daily dose, combined with scheduled IV acetaminophen 1000 mg every 6 hours (maximum 4-6 g/day). 1

Primary IV Opioid Selection and Dosing

Morphine IV

• Starting dose for opioid-naïve patients: 5-10 mg IV, with no upper limit during titration to symptoms 2
• Breakthrough dosing: Administer bolus doses every 15 minutes as needed 2
• Dose escalation rule: If patient requires two bolus doses within one hour, double the regular dose 2
• For patients on continuous infusions: Give bolus dose equal to twice the hourly infusion rate for breakthrough pain 2
• IV morphine is 3 times more potent than oral morphine 3, 4
• Peak effect occurs at 15 minutes IV versus 60 minutes oral 1

Fentanyl IV

• Alternative to morphine, particularly useful for patients with renal impairment 1
• Faster onset than morphine with shorter duration 1
• Preferred when rapid titration is needed 1

Route Considerations

• IV route is preferred over intramuscular (IM) because IM injections are painful and offer no pharmacokinetic advantage 1
• Continuous IV infusion is recommended for patients who cannot swallow or absorb opioids enterally 1
• Subcutaneous route has slower onset (30 minutes) compared to IV (15 minutes) 1

Non-Opioid IV Adjuncts

IV Acetaminophen (Paracetamol)

• Dose: 1000 mg IV every 6 hours 1
• Maximum daily dose: 4-6 grams 1
• Must be used as baseline treatment for all pain intensities to decrease supplementary analgesic requirements 1
• Time to onset: 15-30 minutes 1
• Higher initial dosing (2 g loading dose followed by 1 g every 6 hours for total of 5 g in first 24 hours) is safe and achieves plasma concentrations below toxic threshold 5
• Caution: Monitor for hepatotoxicity 1

IV Ketamine (for Refractory Pain)

• Indicated for opioid-refractory cancer pain or resistant neuropathic pain 1
• Dosing: Start with bolus of 1-3 mg/kg IV over 20-30 minutes 1
• If tolerated and effective, continue with continuous infusion at 0.5-2 mg/kg/hr (maximum 100 mg/hour) 1
• Use lowest dose that controls pain 1
• Side effects (tinnitus, perioral numbness, sedation, lightheadedness, headache) are self-limiting 1

IV Lidocaine (for Neuropathic Pain)

• Particularly useful for cancer-related neuropathic pain or opioid-refractory pain 1
• Dosing: Bolus of 1-3 mg/kg IV over 20-30 minutes 1
• If effective, start continuous infusion at 0.5-2 mg/kg/hr (maximum 100 mg/hour) 1
• Side effects are self-limiting and rarely require discontinuation 1

Scheduling and Titration Algorithm

Step 1: Establish Baseline Regimen

• Provide round-the-clock dosing with continuous IV infusion 1
• Titrate opioid doses to take effect as rapidly as possible 1
• Add scheduled IV acetaminophen 1000 mg every 6 hours 1

Step 2: Breakthrough Pain Management

• Provide breakthrough doses equivalent to 10-15% of total daily opioid dose 1
• Use opioids with rapid onset and short duration for breakthrough doses 1
• If more than four breakthrough doses per day are necessary, increase the baseline continuous infusion rate 1

Step 3: Dose Adjustment

• If two bolus doses needed within one hour, double the regular continuous infusion rate 2
• For patients on continuous infusions developing pain, give bolus equal to twice the hourly rate 2
• No maximum daily dose limit when titrating to symptoms 2

Alternative IV Opioid: Tramadol

IV Tramadol Dosing

• IV tramadol 50 mg at hours 0,2, and 4, then every 4 hours thereafter 6
• This regimen reaches initial peak concentration more rapidly than oral while maintaining similar steady-state levels 6
• Alternative: 75 mg IV at hours 0,3, and 6, then every 6 hours (results in higher peak concentrations) 6
• Maximum daily dose: 400 mg 1
• Caution: May reduce seizure threshold; contraindicated in patients with seizure history 1

Opioid Conversion for IV Route

Converting to IV Morphine

• From IV oxycodone: Multiply oxycodone dose by 1.5 (e.g., 5 mg IV oxycodone = 7.5 mg IV morphine) 3
• From oral morphine: Divide oral dose by 3 (IV morphine is 3 times more potent than oral) 3, 4
• Reduce calculated dose by 25-50% to account for incomplete cross-tolerance between opioids 3

Side Effect Management

Common Opioid Side Effects

• Constipation: Use prophylactic laxatives routinely 1
• Nausea/vomiting: Continue antiemetics as needed 1
• CNS toxicity (drowsiness, confusion, hallucinations, myoclonic jerks): Consider opioid rotation 1
• Opioid-induced hyperalgesia/allodynia: Switch to alternative opioid agonist 1

Reversal of Severe Overdose

• Naloxone 0.04-0.4 mg IV or IM for severe opioid toxicity 2
• Naloxone is short-acting; may require repeated doses 1

Special Population Considerations

Elderly or Debilitated Patients

• Reduce initial doses due to altered pharmacokinetics from poor fat stores, muscle wasting, or altered clearance 4, 7
• Use morphine with caution in renal impairment due to accumulation of toxic metabolites 2, 3
• Avoid NSAIDs in elderly trauma patients; if used, co-prescribe proton pump inhibitor 1

Patients with Renal Dysfunction

• Prefer fentanyl over morphine 1
• Morphine metabolites accumulate and can cause neurotoxicity 2, 3

Critical Pitfalls to Avoid

• Never use meperidine for chronic pain, especially with renal impairment (metabolite accumulation causes seizures and arrhythmias) 1
• Never use IM route when IV is available (IM is painful with no pharmacokinetic advantage) 1
• Never use placebo in pain treatment (unethical) 1
• Avoid opioid agonist-antagonists in patients on pure agonists (precipitates withdrawal) 1
• Monitor for respiratory depression, particularly in opioid-naïve patients 2