Analgesics, Opioids, and Gastrointestinal Drugs – Mechanisms, Uses

Pain and gastrointestinal (GI) disorders are among the most common health issues worldwide. Pain may arise from acute injury, surgery, or chronic illnesses, while GI conditions such as acid reflux, ulcers, constipation, and gastritis affect millions globally.

To manage these conditions, medications including analgesics (pain relievers), opioids, NSAIDs, acetaminophen, and gastrointestinal drugs (PPIs, H2 blockers, laxatives) are widely used in both outpatient and inpatient care.

Analgesics and Opioids

Analgesics are drugs that relieve pain without necessarily affecting consciousness. They include opioids, NSAIDs, salicylates, and acetaminophen.

1. Opioids

Opioids are the strongest painkillers, acting on the central nervous system (CNS) to reduce pain perception.

Suffixes: -done, -one

Examples:

• -done: Methadone, Oxycodone, Hydrocodone
• -one: Morphine, Hydromorphone, Oxymorphone

Mechanism: Bind to μ-opioid receptors in the CNS → inhibit pain signaling → analgesia, sedation, euphoria.

Uses: Severe acute and chronic pain (post-surgery, cancer, trauma).

Side Effects: Respiratory depression, constipation, tolerance, dependence, addiction.

Clinical Note: Opioids must be used cautiously due to the risk of opioid use disorder (OUD) and overdose.

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

Suffixes: -olac, -profen

Examples: Ketorolac, Ibuprofen, Naproxen

Mechanism: Inhibit COX-1 and COX-2 enzymes, reducing prostaglandin synthesis → ↓ inflammation, pain, and fever.

Uses: Mild-to-moderate pain, inflammation (arthritis, gout), fever.

Side Effects: Gastric irritation, peptic ulcers, renal toxicity, bleeding risk.

Clinical Note: NSAIDs should be avoided in patients with peptic ulcer disease and kidney disease.

3. Salicylates

Example: Aspirin (ASA)

Mechanism: Irreversibly inhibits COX enzymes → reduces prostaglandins and thromboxane → analgesic, anti-inflammatory, antipyretic, and antiplatelet effect.

Uses: Mild pain, fever, inflammation, cardiovascular prevention (low-dose aspirin for clot prevention).

Side Effects: Gastric bleeding, Reye’s syndrome in children, hypersensitivity.

4. Nonsalicylates

Example: Acetaminophen (Paracetamol)

Mechanism: Inhibits COX enzymes in the CNS (weak anti-inflammatory action, strong antipyretic).

Uses: Headache, fever, mild pain, preferred in children and patients with ulcers.

Side Effects: Liver toxicity (in overdose).

Clinical Note: Acetaminophen is the first-line drug for fever in children.

Gastrointestinal Drugs

GI drugs are widely prescribed for acid-related disorders and bowel regulation.

1. Histamine H2 Receptor Antagonists (H2 Blockers)

Suffixes: -tidine, -dine

Examples: Ranitidine, Famotidine, Nizatidine

Mechanism: Block H2 receptors in gastric parietal cells → reduce gastric acid secretion.

Uses: GERD, peptic ulcer disease, gastritis, Zollinger-Ellison syndrome.

Side Effects: Headache, diarrhea, rare CNS effects (confusion in elderly).

Clinical Note: Ranitidine has been withdrawn in many countries due to safety concerns (NDMA contamination).

2. Proton Pump Inhibitors (PPIs)

Suffix: -prazole

Examples: Omeprazole, Pantoprazole, Esomeprazole

Mechanism: Irreversibly inhibit H+/K+ ATPase (proton pump) in gastric parietal cells → suppress acid production.

Uses: GERD, erosive esophagitis, peptic ulcers, H. pylori eradication.

Side Effects: Long-term use → hypomagnesemia, B12 deficiency, osteoporosis, kidney disease.

Clinical Note: PPIs are more effective than H2 blockers but should be used at the lowest effective dose.

3. Laxatives

Suffix: -lax

Examples: Bisacodyl (Dulcolax), Polyethylene glycol, Lactulose

Mechanism: Increase bowel motility, soften stool, or retain water in intestines.

Uses: Constipation, bowel prep before colonoscopy, hepatic encephalopathy (lactulose).

Side Effects: Diarrhea, electrolyte imbalance, dependency with prolonged use.

Clinical Applications

1. Pain Management:

• Severe pain → Opioids (morphine, oxycodone).
• Mild-to-moderate pain → NSAIDs, acetaminophen.
• Cardiovascular protection → Low-dose aspirin.

2. Fever Treatment:

• First-line: Acetaminophen.
• Alternatives: NSAIDs (ibuprofen).

3. Acid Reflux and Peptic Ulcers:

• First-line: PPIs (-prazole).
• Alternative: H2 blockers (-tidine).

4. Constipation Relief:

• Laxatives (lactulose for hepatic encephalopathy, polyethylene glycol for chronic constipation).

Quick Reference Table

Drug Class	Suffix/Example	Mechanism	Main Uses
Opioids	-done, -one	μ-opioid receptor agonists	Severe pain, post-surgery, cancer pain
NSAIDs	-olac, -profen	COX inhibition → ↓ prostaglandins	Pain, inflammation, fever
Salicylates	Aspirin (ASA)	COX inhibition (irreversible)	Pain, fever, clot prevention
Nonsalicylates	Acetaminophen	CNS COX inhibition	Fever, mild pain
H2 Blockers	-tidine, -dine	Block H2 gastric receptors	GERD, ulcers
Proton Pump Inhibitors	-prazole	Block proton pump (H+/K+ ATPase)	GERD, ulcers, H. pylori
Laxatives	-lax	Increase bowel motility/soften stool	Constipation, bowel prep

Frequently Asked Questions (FAQs)

Q1. What is the difference between NSAIDs and acetaminophen?

NSAIDs have anti-inflammatory properties and work peripherally, while acetaminophen mainly works in the CNS, reducing fever and pain but with minimal anti-inflammatory action.

Q2. Why is aspirin not given to children?

It may cause Reye’s syndrome, a rare but serious condition affecting the liver and brain.

Q3. Are opioids safe for long-term use?

Opioids can cause tolerance, dependence, and addiction. They are generally reserved for short-term severe pain or chronic pain in cancer.

Q4. Which is safer for stomach ulcers: H2 blockers or PPIs?

PPIs (-prazole) are more effective and preferred, but H2 blockers (-tidine) may be used for milder cases.

Q5. Can laxatives be used daily?

Occasional use is safe, but long-term overuse can cause dependency and electrolyte imbalance. Lifestyle changes (hydration, fiber intake) are preferred.

Q6. Why should PPIs not be used indefinitely?

Chronic PPI use may lead to nutrient deficiencies (B12, magnesium), osteoporosis, and kidney disease. They should be tapered or reassessed regularly.