Pharmacological Pain Management: Essential Knowledge 

Pain management is multimodal, especially in ICU settings. The choice of medication depends on pain type (nociceptive vs neuropathic), severity, patient comorbidities, and route of administration. 

1. Opioid Analgesics 

Indication: Moderate to severe pain (nociceptive pain, post-operative, trauma, cancer pain). 

Common Opioids: 

Morphine (IV, PO, SC) 
Fentanyl (IV, transdermal patch)  
Remifentanil (IV, ultra-short acting) 

Mechanism: Mu-opioid receptor agonists → inhibit pain transmission in CNS. 

Effects: 
Analgesia 
Sedation 
Euphoria (may contribute to dependence with longer term use) 
Cough suppression 

Side Effects: 
Respiratory depression (monitor patients closely) 
Hypotension (especially morphine) 
Nausea, vomiting, constipation 
Pruritus 
Tolerance and dependence with prolonged use 

Advantages: 

Highly effective for severe pain 
Can be administered IV in ICU/emergency department environment for rapid onset 
Can be titrated using Patient-Controlled Analgesia (PCA) 

2. Non-Opioid Analgesics (NSAIDs, Paracetamol) 

Indication: Mild to moderate pain, inflammatory pain, fever. Can reduce opioid requirements. 

Common drugs: 

Paracetamol (Acetaminophen) – IV, PO 
NSAIDs: Ibuprofen, Ketorolac (IV), Diclofenac 

Mechanism: Inhibit prostaglandin synthesis → reduce inflammation and pain. 

Effects: 

Analgesia 
Anti-pyretic
Anti-inflammatory (NSAIDs only) 

Side Effects: 

Paracetamol: hepatotoxicity in overdose (check dose in adult patients under 40kg)
NSAIDs: gastrointestinal bleeding, renal impairment, platelet dysfunction, increased risk of cardiovascular events 

Advantages: 

Opioid-sparing (reduce dose and side effects) 
Useful for multimodal analgesia 

3. Adjunct Medications (Co-analgesics) 

These enhance pain control, particularly for neuropathic pain or chronic pain. 

A. Tricyclic Antidepressants (TCAs) 

Example: Amitriptyline 
Mechanism: Inhibits norepinephrine and serotonin reuptake → modulates pain 
Indication: Neuropathic pain, chronic pain syndromes 
Side Effects: Sedation, anticholinergic effects (dry mouth, constipation, urinary retention), orthostatic hypotension 

B. Anticonvulsants 
Examples: Gabapentin, Carbamazepine 
Mechanism: Modulate calcium channels in neurons → reduce neuropathic pain 
Indication: Neuropathic pain, post-herpetic neuralgia, diabetic neuropathy 
Side Effects: Dizziness, sedation, ataxia, hyponatremia (carbamazepine), diplopia 

C. Analgesic Skin Patches 
Examples: Fentanyl patch, Lidocaine patch 
Mechanism: Localized or systemic opioid effect (fentanyl) or sodium channel blockade (lidocaine) 
Indication: Chronic pain, localized neuropathic pain 
Side Effects: Skin irritation, systemic opioid effects with fentanyl 

4. PCA (Patient-Controlled Analgesia) 

Typically used for post-operative or severe pain 
Staff MUST be competent to care for patients with PCA
Patient self-administers small, pre-set opioid doses IV 

Advantages: 
Better pain control 
Reduced nursing workload 
Lower risk of overdose with pre-set limits 
Common drugs: Morphine, Fentanyl

5. Epidural Analgesia 

Delivery of opioids ± local anaesthetics directly to epidural space 

Indications: Post-operative pain, trauma, abdominal/pelvic surgery 

Advantages: 
Superior analgesia 
Reduced systemic opioid use 

Side Effects: 
Hypotension, urinary retention, infection, epidural haematoma (rare) 

6. Multimodal Analgesia: Combining Drugs 

Rationale: Combining drugs with different mechanisms enhances analgesia and reduces opioid-related side effects. 

Examples: 

Opioid + Paracetamol/NSAID: Lower opioid dose, reduced sedation, fewer GI/renal issues 
Opioid + Gabapentin/Amitriptyline: Better neuropathic pain control 
PCA + Epidural + NSAID: Maximal pain control in ICU/post-op patients 




Key Points: 
Always assess pain type (nociceptive vs neuropathic) before choosing drugs. 
Monitor respiratory rate, sedation score, haemodynamics, renal and liver function. 
Adjust doses in elderly, renal/hepatic impairment, critical illness. 
Multimodal therapy reduces opioid side effects and improves patient comfort. 
Consider route of administration: IV for ICU, PO for step-down care, patches for chronic pain.