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🎓 MUHS Pharmacology — Autacoids: Exam Answers in Easy Language

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1. What are Autacoids?

• Histamine
• Serotonin (5-HT)
• Prostaglandins (PGs)
• Leukotrienes
• Bradykinin
• Angiotensin
• Platelet-Activating Factor (PAF)
• Kallidin

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2. Histamine — All Important Points

What is Histamine?

• Histamine is a biogenic amine found in animal and plant tissues.
• Mainly stored in mast cell granules in: skin, lungs, liver, gastric mucosa, and placenta.
• It is a key mediator in inflammation and allergic/hypersensitivity reactions.

Histamine Receptors (easy table):

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3. H₁ Antagonists (Antihistaminics)

Mechanism of Action:

Classification:

1st Generation — by sedation level:

2nd Generation (No sedation):

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4. Uses of H₁ Antihistamines (1st Generation)

1. Allergic diseases — urticaria, pruritus, rhinitis, angioedema, conjunctivitis
2. Common cold — symptomatic relief (anticholinergic drying effect)
3. Pre-anaesthetic medication — Promethazine used for sedation + anticholinergic effect
4. Antiemetic (vomiting) — Promethazine, Diphenhydramine, Dimenhydrinate — useful in:
   • Motion sickness
   • Drug-induced vomiting
   • Post-operative vomiting
   • Cancer chemotherapy + radiation vomiting
5. Parkinsonism — Promethazine, Diphenhydramine, Orphenadrine reduce tremor, rigidity, sialorrhoea (anticholinergic + sedative)
6. Blood transfusion reactions — control chills and rigors
7. Sedative/hypnotic — Promethazine, Diphenhydramine → induce sleep in children for minor surgeries

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5. Serotonin (5-HT) — All Important Points

What is Serotonin?

• Full name: 5-hydroxytryptamine (5-HT)
• Made from the amino acid tryptophan (by hydroxylation → decarboxylation, similar to catecholamine synthesis)
• Stored in vesicles; action terminated by reuptake

Serotonin Receptors:

5-HT Antagonists:

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6. Ergot Alkaloids

• Naturally found in the fungus Claviceps purpurea
• Act on multiple receptors (alpha-adrenergic, serotonin, dopamine)
• Used in: migraine, post-partum hemorrhage (oxytocic), Parkinson's

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7. Migraine Treatment

Acute Attack:

• Triptans (sumatriptan, naratriptan) — 5-HT₁B/D agonists → vasoconstriction
• NSAIDs, Ergotamine

Prophylaxis (Prevention):

• Beta-blockers (propranolol) — most used
• Calcium channel blockers (flunarizine — selective for cerebral vessels; also blocks Na channels)
• TCAs (amitriptyline) — reduce attack frequency (exact mechanism unclear)
• Note: CCBs + beta-blockers should NOT be given together

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8. Prostaglandins (PGs)

Key Facts:

• PGs are products of long-chain fatty acids
• Arachidonic acid is the precursor for all PGs
• Enzyme: Cyclooxygenase (COX) converts arachidonic acid → PGs
• Main PGs: PGE₂, PGF₂α, PGI₂ (prostacyclin), TXA₂ (thromboxane)

COX-1 vs COX-2:

Arachidonic Acid Pathway:

Membrane phospholipids
        ↓ (Phospholipase A₂)
Arachidonic acid
   ↓ (COX)               ↓ (Lipoxygenase)
Prostaglandins         Leukotrienes

Effects of PGs:

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

Mechanism: Block COX → reduce PG synthesis

4 Key Actions:

Aspirin Doses:

• Low dose (75–300 mg): Antiplatelet
• 2–3 g/day: Analgesic + Antipyretic
• 4–6 g/day: Anti-inflammatory
• High dose (2–3 g/day): Inhibits both PGI₂ and TXA₂ → antiplatelet effect is lost

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10. Adverse Effects of Aspirin

1. GIT — Nausea, vomiting, dyspepsia (irritates gastric mucosa; also stimulates CTZ)
2. CVS — Sodium + water retention; can worsen heart failure; reduces effect of antihypertensives
3. Renal/Urate — Low doses: inhibit urate secretion → raise uric acid → worsen gout
4. Salicylism (mild toxicity) — tinnitus, headache, dizziness
5. Aspirin toxicity — Respiratory changes:
   • Early: Respiratory alkalosis (stimulates respiratory centre)
   • Compensated: Bicarbonate excretion
   • Toxic doses: Respiratory depression → Respiratory acidosis + Metabolic acidosis (uncompensated)
6. Reye's syndrome — Avoid aspirin in children with viral fever (liver + brain damage)
7. Pre-surgery: Withdraw aspirin 1 week before surgery (bleeding risk)

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11. Quick Recall Mnemonics

"Highly Sedative: Di-Di-Pro (Diphenhydramine, Dimenhydrinate, Promethazine)" "Second Gen: Lo-Ce-Levo-Aze-Fex (Loratadine, Cetirizine, Levocetirizine, Azelastine, Fexofenadine)"

"Ondansetron, Granisetron, Tropisetron, Palonosetron, Ramosetron" — all end in "-setron"

All end in "-triptan" → Sumatriptan, Naratriptan, Zolmitriptan

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12. Important One-Liners for Exams

• Autacoids = local hormones
• Histamine stored in → mast cell granules
• H₁ receptor → Ca²⁺ pathway; H₂ receptor → cAMP pathway
• 2nd gen antihistamines → no sedation because they don't cross BBB
• Serotonin made from → tryptophan
• PG precursor → arachidonic acid; enzyme → COX
• COX-1 = protective (stomach); COX-2 = inflammatory
• Aspirin (low dose) → antiplatelet; effect lasts 8–10 days (platelet lifetime)
• Ondansetron → 5-HT₃ blocker → used in chemo-induced vomiting
• Flunarizine → calcium channel blocker → migraine prophylaxis
• Promethazine → most versatile antihistamine: sedative, antiemetic, anti-Parkinson, pre-anaesthetic

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