Autonomic, dopamine, serotonin & antiemetic drugs flashcards
22 high-yield MRCP Part 1 cards from the Intellect Medicos Clinical Pharmacology & Toxicology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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Alpha-1 adrenoceptors are coupled to ______ (raising IP3/calcium), whereas alpha-2 adrenoceptors are coupled to Gi (lowering cAMP).
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Gq
Why? Alpha-1 contracts smooth muscle (vessels, radial iris muscle, bladder neck, prostate). Alpha-2 is mainly presynaptic and inhibitory. All beta receptors are Gs.
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Alpha-1 adrenoceptors are coupled to Gq (raising IP3/calcium), whereas alpha-2 adrenoceptors are coupled to ______ (lowering cAMP).
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Gi
Why? Alpha-1 contracts smooth muscle (vessels, radial iris muscle, bladder neck, prostate). Alpha-2 is mainly presynaptic and inhibitory. All beta receptors are Gs.
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How do clonidine and methyldopa lower blood pressure?
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They are central alpha-2 agonists that reduce noradrenaline release and sympathetic outflow.
Why? Presynaptic alpha-2 receptors provide negative feedback on noradrenaline release.
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Which receptor does mirabegron stimulate, and what is it used for?
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Beta-3 adrenoceptor agonist — used for overactive bladder.
Why? Beta-3 stimulation relaxes the detrusor muscle during filling, increasing bladder capacity.
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What is the main effect of adrenaline at low dose compared with high dose?
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Low dose: beta effects dominate (vasodilatation, raised heart rate). High dose: alpha-1 effects dominate (vasoconstriction, raised BP).
Why? Adrenaline acts on alpha-1, alpha-2, beta-1 and beta-2 receptors; beta receptors are more sensitive at low concentrations.
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Which inotrope is a selective beta-1 agonist used in cardiogenic shock and acute heart failure?
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Dobutamine.
Why? Beta-1 stimulation increases contractility and cardiac output.
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Which alpha-blocker is used first in the pre-operative preparation of a phaeochromocytoma?
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Phenoxybenzamine (an irreversible, non-selective alpha-blocker).
Why? It blocks the vasoconstrictor effects of the catecholamine surge, controlling blood pressure.
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Name the two commonly used beta-blockers that also block alpha-1 receptors.
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Labetalol and carvedilol.
Why? Alpha-1 blockade adds vasodilatation to the beta-blocking effect.
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Name three adverse effects of beta-2 agonists such as salbutamol.
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Tremor, tachycardia and hypokalaemia.
Why? Beta-2 stimulation drives potassium into cells and acts on skeletal muscle; some beta-1 cross-stimulation raises heart rate.
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Which investigation is needed before and during treatment with an ergot-derived dopamine agonist such as cabergoline?
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Echocardiography (to look for fibrotic cardiac valve disease).
Why? Ergot-derived dopamine agonists can cause cardiac valvular, pulmonary and retroperitoneal fibrosis.
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Which behavioural adverse effect must patients starting pramipexole or ropinirole be warned about?
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Impulse control disorders, e.g. pathological gambling, hypersexuality, compulsive shopping.
Why? These non-ergot dopamine agonists stimulate reward pathways; family members should also be warned.
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What is the mechanism of action of triptans such as sumatriptan?
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5-HT1B/1D receptor agonists.
Why? They constrict cranial blood vessels and reduce release of inflammatory neuropeptides in migraine.
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Which 5-HT2 antagonist can be used as a specific treatment for serotonin syndrome?
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Cyproheptadine.
Why? It blocks 5-HT2A receptors; it is used when supportive care and benzodiazepines are not enough.
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Milrinone (used short-term in acute heart failure) inhibits phosphodiesterase-______, whereas roflumilast (used in severe COPD) inhibits phosphodiesterase-4.
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3
Why? PDE3 in heart and vessels: raised cAMP gives inotropy plus vasodilatation. PDE4 in inflammatory cells: anti-inflammatory. PDE5: sildenafil/tadalafil.
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Milrinone (used short-term in acute heart failure) inhibits phosphodiesterase-3, whereas roflumilast (used in severe COPD) inhibits phosphodiesterase-______.
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4
Why? PDE3 in heart and vessels: raised cAMP gives inotropy plus vasodilatation. PDE4 in inflammatory cells: anti-inflammatory. PDE5: sildenafil/tadalafil.
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Which drug class is an absolute contraindication with sildenafil?
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Nitrates (and other nitric oxide donors such as nicorandil).
Why? Both raise cGMP and cause vasodilatation; together they can cause profound hypotension.
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Which antiemetic is most effective for preventing motion sickness?
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Hyoscine hydrobromide (an antimuscarinic), e.g. as a transdermal patch.
Why? Motion sickness comes from vestibular input; antimuscarinics and H1 antihistamines (cyclizine, cinnarizine, promethazine) act at the vestibular nuclei and vomiting centre.
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Which class of antiemetic is aprepitant, and what is its main use?
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NK1 (substance P) receptor antagonist — chemotherapy-induced nausea and vomiting.
Why? It blocks neurokinin-1 receptors in the CTZ and vomiting centre; it is used with a 5-HT3 antagonist and dexamethasone.
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What are the two mechanisms of action of metoclopramide?
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Central D2 antagonism at the chemoreceptor trigger zone, plus a peripheral 5-HT4 agonist (prokinetic) effect on the gut.
Why? The prokinetic effect speeds gastric emptying, so it is useful in gastroparesis and migraine-related nausea.
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Which antiemetic is preferred in a patient with Parkinson's disease?
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Domperidone (a peripheral D2 antagonist that hardly crosses the blood–brain barrier).
Why? Centrally acting D2 antagonists such as metoclopramide, prochlorperazine and haloperidol worsen parkinsonism.
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A 22-year-old woman is given IV metoclopramide for vomiting. Two hours later her eyes are fixed in an upward gaze and her neck is twisted. What is the treatment?
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An IV or IM antimuscarinic such as procyclidine.
Why? This is an acute dystonic reaction (oculogyric crisis) from D2 blockade; it is commonest in young women.
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Which opioid receptor mediates analgesia, respiratory depression and euphoria?
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The mu (μ) receptor.
Why? Kappa receptors give analgesia with dysphoria; delta receptors play a minor role.
More Clinical Pharmacology & Toxicology topics
- Pharmacokinetics, receptors & pharmacogenetics
- CYP450 & drug interactions
- Drug & therapeutic level monitoring
- Pregnancy, breastfeeding & contraception
- Antimicrobial mechanisms & toxicity
- Cardiovascular, immunosuppressant & anaesthetic drugs
- Overdose of common drugs
- Poisons, antidotes & recreational drugs
- Adverse drug reactions: drugs causing X