Tell me all about analgesic used in basic opd bases commonly n how which work at wht severity

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Loading Image

I now have rich, authoritative content from multiple textbooks. Let me compile the full answer.

Analgesics Used in Basic OPD Practice: What They Are, How They Work, and When to Use Them

The WHO Analgesic Ladder - The Framework

The World Health Organization developed the analgesic ladder as the cornerstone of pain management. It guides drug selection based on pain severity (mild, moderate, severe), not a "try everything weak first" approach.

Step	Pain Severity	Drug Class	Examples
Step 1	Mild (NRS 1-3)	Non-opioids + adjuvants	Paracetamol, NSAIDs, Aspirin
Step 2	Moderate (NRS 4-6)	Weak opioids + non-opioids + adjuvants	Tramadol, Codeine, Hydrocodone
Step 3	Severe (NRS 7-10)	Strong opioids + non-opioids + adjuvants	Morphine, Oxycodone, Hydromorphone

Adjuvants (e.g. tricyclic antidepressants, anticonvulsants) can be added at any step.

STEP 1 - Mild Pain (NRS 1-3)

1. Paracetamol (Acetaminophen / APAP)

The #1 first-line OPD analgesic.

Mechanism:

Inhibits prostaglandin synthesis in the CNS, producing antipyretic and analgesic effects
Has minimal peripheral COX inhibition (peripherally inactivated), so it has weak anti-inflammatory activity
Does NOT affect platelet function or cause GI bleeding
Is NOT classified as an NSAID

Uses in OPD: Headache, fever, mild musculoskeletal pain, post-procedure pain, toothache, pain in children (drug of choice for viral illness in kids - avoids Reye syndrome risk)

Dose: 500-1000 mg every 4-6 hours; max 4 g/day (3 g/day in liver disease)

Key side effect: Hepatotoxicity in overdose - NAPQI (toxic metabolite) accumulates when glutathione is depleted, causing hepatic necrosis. Antidote = N-acetylcysteine.

Avoid in: Severe hepatic impairment, alcoholism, chronic malnutrition.

2. NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)

This is the most commonly used drug class for mild-to-moderate OPD pain.

Mechanism: NSAIDs inhibit cyclooxygenase (COX-1 and/or COX-2), which blocks prostaglandin synthesis:

Analgesic effect: PGE2 sensitizes nerve endings to bradykinin and histamine. By reducing PGE2, pain sensation drops. COX-2 inhibition is primarily responsible for analgesia.
Anti-inflammatory effect: Reduced prostaglandin formation dampens inflammation
Antipyretic effect: Blocks PGE2 synthesis in the anterior hypothalamus, resetting the thermostat to normal

Common OPD NSAIDs:

Drug	Notes
Ibuprofen	Most commonly used; 400-600 mg TDS with food; good safety profile
Diclofenac	Commonly used in musculoskeletal pain; available as tablet, injection, gel
Naproxen	Longer acting (twice daily); good for dysmenorrhea, arthritis
Aspirin	Analgesic at low-moderate dose; anti-inflammatory at high dose; antiplatelet at 75-100 mg
Ketorolac	One exception - effective for severe pain (renal/biliary colic); short-term use only
Celecoxib	COX-2 selective; less GI side effects; for patients at GI risk
Mefenamic acid	Widely used for dysmenorrhea

Uses in OPD: Headache, dysmenorrhea, arthralgia, myalgia, dental pain, soft tissue injuries, osteoarthritis, gout

No single NSAID has superior analgesic efficacy over another - they are considered equivalent.

Key side effects:

GI: Gastric irritation, peptic ulcer (COX-1 inhibition reduces protective gastric mucus)
Renal: Reduced renal blood flow, fluid retention
Cardiovascular: Increased risk of MI and stroke (except aspirin)
Platelet: Reduced aggregation, increased bleeding time
Aspirin in children < 19 years with viral infections - risk of Reye syndrome (avoid it)

Protect the stomach: Co-prescribe a PPI (omeprazole) if long-term NSAIDs are needed.

STEP 2 - Moderate Pain (NRS 4-6)

3. Tramadol (Weak Opioid - Most Common OPD Opioid)

Mechanism (dual mechanism):

Acts on mu-opioid receptors (partial agonism) - spinal and supraspinal analgesia
Inhibits norepinephrine and serotonin reuptake - modulates descending pain pathways

Uses in OPD: Post-procedure pain, moderate musculoskeletal pain, neuropathic pain component, cancer pain (step 2)

Dose: 50-100 mg every 4-8 hours; max 400 mg/day

Key side effects: Nausea, vomiting, dizziness, constipation, risk of seizures (especially with SSRIs - serotonin syndrome risk), dependence with long-term use

Advantage: Less respiratory depression than pure opioids; available orally in OPD setting

4. Codeine

Mechanism: Prodrug - converted to morphine by CYP2D6 in the liver; activates mu-opioid receptors

Uses: Mild-moderate pain, cough suppression

Note: ~10% of people are "poor metabolizers" (CYP2D6 deficiency) and get no analgesia; ~1-2% are "ultra-rapid metabolizers" and can have toxicity

STEP 3 - Severe Pain (NRS 7-10)

Typically not initiated in a basic OPD - these require controlled prescriptions and close monitoring.

5. Opioids (Strong) - Morphine, Oxycodone, Hydromorphone, Fentanyl, Pethidine

Mechanism:

Activate mu-opioid receptors (OP3)
- Subtype I (supraspinal): Peripheral analgesia, euphoria, prolactin release
- Subtype II (spinal): Spinal analgesia, respiratory depression, dependence, GI dysmotility, miosis
Also act on kappa (K) receptors:
- K1: Spinal analgesia and miosis
- K2: Psychotomimesis and dysphoria
- K3: Supraspinal analgesia

Classification:

Natural: Morphine, Codeine
Semisynthetic: Heroin, Hydrocodone, Oxymorphone, Hydromorphone
Synthetic: Tramadol, Fentanyl, Pethidine, Methadone

Duration of action:

Minutes-to-hours: Fentanyl, Alfentanil, Sufentanil
2-4 hours: Pethidine, Pentazocine
4-8 hours: Morphine, Codeine
8+ hours: Methadone, Buprenorphine

Adverse effects: Respiratory depression, nausea, vomiting, miosis, hypotension, urinary retention, constipation, pruritus, dependence

Drug interactions: Enhanced CNS depression with alcohol, barbiturates, phenothiazines, tricyclic antidepressants

Adjuvant Analgesics (Added at Any Step)

These drugs are not primary analgesics but enhance pain relief, especially for neuropathic pain:

Drug Class	Examples	Used For
Anticonvulsants	Gabapentin, Pregabalin	Neuropathic pain, nerve compression
Tricyclic antidepressants	Amitriptyline	Neuropathic/chronic pain
SNRIs	Duloxetine	Diabetic neuropathy, fibromyalgia
Topical agents	Lidocaine gel, Diclofenac gel	Local musculoskeletal, post-herpetic neuralgia
Muscle relaxants	Cyclobenzaprine, Baclofen	Muscle spasm component of pain

Quick Summary: Which Drug at Which Severity?

NRS 1-3 (Mild):     Paracetamol 500-1000 mg ± Ibuprofen 400 mg
NRS 4-6 (Moderate): Tramadol 50-100 mg ± Paracetamol ± NSAID
NRS 7-10 (Severe):  Morphine/Oxycodone (hospital/specialist level)
                     + Ketorolac IV/IM (severe colic in ED)
Neuropathic pain:   Add Pregabalin/Amitriptyline at any step

Key OPD Prescribing Principles (WHO "5 Rights")

Per WHO Cancer Pain Guidelines:

By mouth - oral route preferred when feasible
By the clock - regular scheduled dosing (not just "as needed") for continuous relief
By the ladder - match drug to pain severity
For the individual - titrate to each patient
Attention to detail - reassess regularly, watch for adverse effects

Sources: Lippincott Illustrated Reviews: Pharmacology; Cummings Otolaryngology Head & Neck Surgery; Tintinalli's Emergency Medicine; Forensic Medicine and Toxicology 36th ed.

This is a shared conversation. Sign in to Orris to start your own chat.