AIM STEP 10 • 3rd Year MBBS
Student Memory Support
Topic 20 — Eicosanoids, Dermatologic Pharmacotherapy and Selected Herbal Medicines
High-yield memory reinforcement for rapid KMU examination revision. :contentReference[oaicite:0]{index=0}
1. High-Yield Flashcards
Tap each question to reveal the answer.
Which precursor gives rise to most eicosanoids?
Arachidonic acid released from cell-membrane phospholipids.
Which eicosanoids are formed mainly through the cyclooxygenase pathway?
Prostaglandins, prostacyclin and thromboxanes.
How do most prostaglandins produce their cellular effects?
By binding to specific G-protein-coupled prostanoid receptors.
What are the main vascular and platelet effects of prostacyclin?
Vasodilation and inhibition of platelet aggregation.
What are the major pharmacological effects of thromboxane A₂?
Platelet aggregation, vasoconstriction and bronchial smooth-muscle contraction.
How do prostaglandin analogues lower intraocular pressure in glaucoma?
They increase aqueous humor outflow, especially through the uveoscleral pathway.
Which vehicle is preferred for a dry, thick and scaly skin lesion?
An ointment because it is greasy, occlusive and retains moisture.
Which formulation is particularly suitable for a hairy or oily area?
A gel because it is non-greasy, spreads easily and dries quickly.
What is the key application principle for topical treatment of scabies?
Apply the scabicide adequately over the relevant body surface, not only to visible lesions.
How does benzoyl peroxide help acne vulgaris?
It generates reactive oxygen species that reduce Cutibacterium acnes and also has mild comedolytic activity.
What is the main action of topical tretinoin in acne?
It normalizes follicular keratinization and reduces microcomedone formation.
What is the major therapeutic action of isotretinoin in severe acne?
Marked suppression of sebaceous gland activity and sebum production.
Which serious safety issue is shared by isotretinoin and acitretin?
Both are highly teratogenic retinoids.
Which important interaction occurs when garlic is combined with aspirin or warfarin?
Bleeding tendency may increase because garlic can reduce platelet aggregation.
What clinically important interaction may occur between ginseng and glucose-lowering medication?
An additive glucose-lowering effect may increase the risk of hypoglycemia.
What is the important interaction between Coenzyme Q10 and warfarin?
Coenzyme Q10 may reduce the anticoagulant effect of warfarin.
2. Mnemonics
Mnemonic Title: Major COX Products
PPT
Meaning: Prostaglandins • Prostacyclin • Thromboxanes
Mnemonic Title: Acne Treatment Targets
SBKI
Meaning: Sebum • Bacteria • Keratinization • Inflammation — the main treatment targets in acne.
Mnemonic Title: Herbal Interaction Pairing
GGQ
Meaning: Garlic → bleeding • Ginseng → glucose/CNS effects • Coenzyme Q10 → reduced warfarin effect
3. Memory Tables
PGI₂ vs TXA₂
| Feature | PGI₂ | TXA₂ |
|---|---|---|
| Main source emphasis | Vascular endothelium | Activated platelets |
| Platelets | Inhibits aggregation | Promotes aggregation |
| Vessels | Vasodilation | Vasoconstriction |
Topical Vehicle Selection
| Skin Situation | Preferred Formulation | Memory Logic |
|---|---|---|
| Dry, thick, scaly | Ointment | Occlusive and hydrating |
| Mildly moist | Cream | Less greasy semisolid |
| Hairy or oily | Gel | Spreads and dries quickly |
| Large surface | Lotion | Fluid and easy to spread |
| Weeping or exudative | Wet dressing | Cools and removes exudate |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Cyclooxygenase produces prostaglandins, prostacyclin and thromboxanes; lipoxygenase produces leukotrienes.
- PGE₂ contributes to inflammatory pain and fever.
- Misoprostol is a PGE₁ analogue associated with gastric mucosal protection and uterine effects.
- Latanoprost, travoprost, tafluprost and bimatoprost reduce intraocular pressure by increasing aqueous outflow.
- Permethrin is an important preferred topical drug for uncomplicated scabies.
- Crotamiton combines scabicidal and antipruritic activity but is less reliable than permethrin.
- Benzyl benzoate can cause marked local irritation, especially on excoriated skin.
- Tretinoin commonly causes local erythema, peeling, burning and photosensitivity.
- Isotretinoin commonly causes mucocutaneous dryness and may raise serum lipids.
- Acitretin is a systemic retinoid for psoriasis with prolonged teratogenic concern.
KMU Trap: Do not reverse PGI₂ and TXA₂: prostacyclin inhibits platelet aggregation, whereas thromboxane A₂ promotes it.
5. Clinical Memory Hooks
Glaucoma + gradual iris darkening and longer eyelashes → think prostaglandin-related ocular therapy such as bimatoprost or latanoprost.
Dry, thick, scaly skin lesion → choose an occlusive ointment to improve hydration.
Severe acne + marked reduction in sebum + dry lips → isotretinoin effect with important teratogenic risk.
Warfarin user starting Coenzyme Q10 → anticoagulant effect may decrease, so the interaction must be recognized.
6. Starred High-Yield Exam Points
- ⭐ PGI₂ → vasodilation + inhibition of platelet aggregation; TXA₂ → vasoconstriction + platelet aggregation.
- ⭐ Prostaglandin analogues used in glaucoma lower intraocular pressure mainly by increasing aqueous humor outflow.
- ⭐ Permethrin is an important preferred topical scabicide and requires adequate body-surface application.
- ⭐ Isotretinoin is highly teratogenic and markedly suppresses sebaceous gland activity.
- ⭐ Acitretin is a systemic retinoid used in psoriasis and has prolonged teratogenic risk.
- ⭐ Garlic may increase bleeding with aspirin or warfarin; Coenzyme Q10 may reduce warfarin’s anticoagulant effect.