Drugs Flashcards
Learn the nature, mechanisms of action, uses and side effects of common classes of drugs
List the types of muscarinic receptors and their locations
M1 --> Exocrine glands, CNS M2 --> Heart M3 --> Smooth muscle of blood vessels, lungs M4 --> CNS M5 --> Not well known
What is atropine?
An antimuscarinic drug - antagonist of M2 muscarinic receptors.
List medical uses of atropine.
Heart –> Post MI, bradycardia
Eyes –> Cycloplegic and mydriatic
Poisoning –> Blocks Ach at muscarinic receptors
What are ipratropium and tiotropium?
Antimuscarinic drugs - binds to M3 muscarinic receptors in lungs to relax smooth muscle and open up airway
List some medical uses of ipratropium and tiotropium.
COPD and asthma
What are oxybutynin and tolterodine?
Antimuscarinic drugs used to modify bladder function.
- Tolterodine relative specific to B2 receptors.
How do oxybutynin and tolterodine work?
Increase SNS and decrease PNS activity –> Tightened urinary sphincter
List some medical uses of oxybutynin and tolterodine.
Overactive bladder
Urinary frequency
Incontinence
What is tropicamide?
An antimuscarinic drug - binds to M4 muscarinic receptors in muscles of the eye.
List some clinical uses of tropicamide.
Glaucoma
Dilation of the pupil and relaxation of the lens for examination
List some adverse effects of all antimuscarinic drugs given systematically.
Dry mouth (most common) Erectile dysfunction Bronchodilation Constipation Tightened sphincter - due to decreased detrussor activity leading to increased urinary bladder retention Dry eyes and blurred vision Increased IOP
What is hyoscine and where does it act?
An centrally acting antimuscarinic drug similar to atropine, but more sedating.
Acts on the brain.
What is hyoscine widely used to treat?
Motion sickness and post-op nausea and vomiting.
What is hyoscine also knwon as?
Scopolamine.
What is benzhexol and what is it used for?
A centrally acting antimuscarinic used to treat Parkinson’s disease.
List some medical uses of ACE inhibitors.
Hypertension Heart failure Post MI Diabetic neuropathy Progressive renal insufficiency
List some side effects of ACE inhibitors.
Cough Hypotension Urticaria/ angioedema Hyperkalaemia Foetal injury Renal failure (in patients w/ renal artery stenosis secondary to a fall in BP and reduced renal perfusion)
Why are ACE inhibitors dangerous in patients taking potassium supplements or potassium-sparing drugs?
ACE inhibitors prevent the release of aldosterone, which normally causes K+ excretion –> Increased risk of hyperkalaemia.
Name a few ACE inhibitors.
Enalapril
Lisinopril
Name a few angiotensin receptor blockers (ARBs).
Losartan
Irbesartan
How do ARBs work?
ARBs are antagonists of the Type I receptors (AT1) for angiotensin II –> Block renal and vascular actions of angiotension II.
When are ARBs used?
Hypertension (alternative to ACE inhibitors as they have fewer side effects)
Chronic heart failure
List some side effects of ARBs.
Hypotension
Hyperkalaemia
Foetal injury
Renal failure (in patients w/ renal artery stenonis secondary to a fall in BP and reduced renal perfusion).
Name a direct renin antagonist.
Aliskiren. * These are a new class of agents.
How do direct renin antagonists work?
Inhibit renin’s enzymatic activity –> Prevent the conversion of angiotensinogen into angiotensin I.
Name a phenylalkylamine.
Verapamil
*Verapamil has a larger negative inotropic effect than diltiazem.
What are phenylalkylamines and where do they act?
They are calcium-channel blockers (CCBs) and rate-slowing calcium antagonists acting on cardiac and smooth muscle.
How do phenylalkylamines work?
Reduce Ca2+ entry into cardiac and smooth muscle cells –> Negative inotropic effects –> Reduced contractility
Inhibit AV node conduction
List some medical uses of phenylalkylamines.
Hypertension
Angina
Treatment of paroxysmal supraventricular tachycardia (SVT = tachycardia originating above ventricular tissue)
Atrial fibrillation
List some unwanted effects of phenylalkylamines.
Bradycardia and AV block
Worsening of heart failure
Constipation
Name a benzothiazepine.
Diltiazem.
What are benzothiazepines and where do they act?
They are calcium-channel blockers (CCBs) and rate-slowing calcium antagonists acting on cardiac and smooth muscle.
List some medical uses and unwanted effects of benzothiazepines.
Medical uses: HTN, angina.
Unwanted effects: bradycardia or AV block, worsening of heart failure, constipation.
Name a dihydropyridine.
Amlodipine.
What are dihydropyridines and where do they act?
They are CCBs and non-rate slowing calcium antagonists acting on smooth muscle actions only.
How do dihydropyridines work?
Inhibit Ca2+ entry into vascular smooth muscle cells.
List some medical uses of dihydropyridines.
HTN
Angina (preferred here)
List some unwanted effects of dihydropyridines.
Ankle oedema
Headache/flushing
Palpitations (reflex tachycardia)
Name some organic nitrates.
Glyceryl trinitrate (GTN) Nicorandil
How do organic nitrates work?
Stimulate NO release in smooth muscle cells (nitrate-based drugs) and guanylate cyclase (nicorandil) –> Vasodilation
List some medical uses of organic nitrates.
Angina
Acute and chronic heart failure
BP control during anaesthesia.
What effects do organic nitrates have on vascular circulation?
Reduce preload, i.e venous return
Reduce afterload, i.e peripheral resistance
*Minor effects: antiplatelet, coronary artery vasodilation.
List some unwanted effects of organic nitrates.
Hypotension
Headaches and flushing (associated w/ vasodilation)
*Xs use associated w/ tolerance.
Name some anti-arrhythmic drugs.
Adenosine Amidoarone Dronedarone Verapamil Flecainide Lidocaine
What are anti-arrhythmic drugs used for?
Treatment of supraventricular arrhythmias, ventricular arrhythmias and complex arrhythmias.
What is the mechanism of action of adenosine?
Acts on adenosine receptor (A1) to hyperpolarise cardiac tissue and slow conduction through AV node.
List some adverse effects of adenosine.
Chest pain
Dyspnoea
Dizziness
Nausea
What are amiodarone and dronedarone used to treat?
Supraventricular and tachyarrhythmias.
List some adverse effects of amiodarone and dronedarone.
Amiodarone - accumulates in body, photosensitive skin rashes, hypo- and hyperthyroidism, PF, corneal deposits, neurological and GI disturbances.
Dronedarone - non-iodinated and less toxic, but less effective
What is the action of digoxin and other cardiac glycosides?
Slows ventricular rate in atrial fibrillation and relieves symptoms of chronic heart failure.
What is the mechanism of action of digoxin?
Inhibits Na-K-ATPase –> Increased accumulation of intracellular Na+ –> Increases intracellular Ca2+ as it cannot be exchanged out of the cell via the Na+-Ca2+ exhanger –> Positive inotropic effect (increased contractility)
Central vagal stimulation –> Reduced rate of conduction through AV node –> Reduced HR
What are some adverse effects of digoxin?
*These are common and severe
Dysrhythmias - e.g AV conduction block, ectopic pacemaker activity
NOTES
- Hypokalaemia and hypomagnaesia lower the threshold for digoxin toxicity
- Digoxin toxicity reversed by Digibind (immune Fab)
What is ivabradine used for?
Treatment of angina in patients with normal sinus rhythm.
What is the mechanism of action of ivabradine?
Blocks If channel in SA node –> Slows heart rate
List some contraindications to ivabradine.
Severe bradycardia Sick Sinus Syndrome 2nd or 3rd degree heart block Cardogenic shock Recent MI
List some adverse effects of ivabradine.
Bradycardia
1st-degree heart block
Ventricular and SV arrhythmias
Name some cardiac inotropes.
Dobutamine - B1 adrenoceptor agonist (little effect on HR)
Milrinone - Phosphodiesterase inhibitor (has inotropic effects by inhibiting breakdown of cAMP in cardiomyocytes)
How do cardiac inotropes affect cardiac contraction?
Increase the force of cardiac contraction.
What are cardiac inotropes used for?
Treatment of acute heart failure, e.g after cardiac surgery or in cardiogenic/septic shock.
Name some alpha blockers (A1 antagonists).
Doxazosin (competitive inhibitor)
Phenoxybenzamine (irreversible)
Name some sympatholytics.
Clonidine (A2 adrenoceptor* agonist)
Moxonidine (Imadazoline agonist)
*RECALL: A2 is an inhibitory adrenoceptor (Gi)
When are alpha blockers used?
Occasionally in combination with antihypertensives in resistant HTN.
NOTE: routine use has declined due to increased risk of chronic heart failure.
How and why may phenoxybenzamine be used?
In combination with a beta blocker to provide long-lasting alpha blockade in catecholamine-secreting tumours (e.g. phaeochromacytoma).
How do sympatholytics work?
They are centrally-acting agents that inhibit sympathetic outflow from the brain, and are thus occasionally used as antihypertensives.
About sumitriptan:
1) What is it?
2) How does it works?
3) What is is used for?
4) What are some contraindications to using sumitriptan?
1) It is a 5HT-1D (serotonin) receptor agonist.
2) It constricts some large arteries and inhibits trigeminal nerve transmission.
3) It is used to treat migraine attacks.
4) It is contraindicated in patients with coronary disease.
What is promethazone?
It is an anti-emetic that acts as a competitive antagonist at histaminergic (H1), muscarinic cholinergic (M) and dopaminergic (D2) receptors centrally (labyrinth, nucleus tractus solitarii (=NTS in medulla oblongata) and vomiting centre) to block activation of the vomiting centre.
Potency: H1 > M > D2.
Administered orally.
How does promethazone work?
Acts centrally (labyrinth, NTS and vomiting centres) to block activation of the vomiting centre.
For which conditions is promethazone used?
Anti-emetic used in:
- Motion sickness (prophylaxis and during onset)
- Disorders of labyrinth (e.g Meniere’s)
- Hyperemesis gravidarium
- Pre- and post-op as a sedative and for its antimuscarinic effects
List some unwanted effects of promethazone.
- Dizziness
- Tinnitus
- Fatigue
- Sedation
- Excitation in excess
- Convulsions (children more susceptible)
- Antimuscarinic side effects
What is metaclopramide?
An anti-emetic, primarily a dopamine receptor antagonist.
Antagonistic potency: D2»_space; H1»_space; Muscarinic receptors
How does metaclopramide work?
Acts centrally, specially at chemoreceptor trigger zone (CTZ) –> Acts in GI tract to:
- Increase smooth muscle motility (oesophagus to SI)
- Accelerate gastric emptying
- Accelerate transit of intestinal contents (duodenum to ileo-coecal valve)
What is metaclopramide used for?
Treatment of nausea and vomiting assoc. w/
- Uraemia (severe RF)
- Radiation sickness
- GI disorders
- Cancer chemotherapy (high doses), e.g cisplatin (intratable vomiting)
List some unwanted effects of metaclopramide.
- Drowsiness
- Dizziness
- Anxiety
- Extrapyramidal rxns - e.g Parkinsonian-like syndrome
