Pharmacology MCQ Questions with Answers

Pharmacokinetics is the study of...

• How a drug acts on the body and its mechanism
• The absorption, distribution, metabolism and excretion of a drug
• Poisons and their antidotes
• The discovery and design of new drugs

Answer: The absorption, distribution, metabolism and excretion of a drug. Pharmacokinetics is what the body does to a drug (ADME). Pharmacodynamics is the reverse, what the drug does to the body, and toxicology deals with poisons.

What is the bioavailability of a drug given by intravenous injection?

• 50%
• 75%
• 100%
• It depends on first-pass metabolism

Answer: 100%. An IV dose goes straight into the circulation, so its bioavailability is 100% by definition. Oral doses are often lower because of incomplete absorption and first-pass metabolism.

Naloxone is used in emergencies to reverse an overdose of which group of drugs?

• Opioids
• Benzodiazepines
• Barbiturates
• Tricyclic antidepressants

Answer: Opioids. Naloxone is an opioid receptor antagonist that quickly reverses the breathing depression caused by opioids such as morphine and heroin. Benzodiazepine overdose is reversed with flumazenil instead.

Salbutamol relieves an asthma attack because it is a...

• Selective beta-2 agonist
• Beta-1 blocker
• Muscarinic agonist
• Leukotriene receptor antagonist

Answer: Selective beta-2 agonist. Salbutamol stimulates beta-2 receptors in the smooth muscle of the airways, which relaxes it and widens the airways. A fine tremor of the hands is a common side effect.

Glyceryl trinitrate (nitroglycerin) for angina is placed under the tongue mainly to...

• Hide its bitter taste
• Slow down its absorption
• Make one dose last 24 hours
• Avoid first-pass metabolism in the liver

Answer: Avoid first-pass metabolism in the liver. Drugs absorbed under the tongue enter the systemic circulation directly and skip the liver on their first pass. Swallowed GTN is largely destroyed by the liver before it can act.

How does low-dose aspirin reduce platelet clumping?

• It blocks the recycling of vitamin K
• It irreversibly inhibits cyclooxygenase, cutting thromboxane A2
• It breaks down fibrin in clots
• It directly inhibits thrombin

Answer: It irreversibly inhibits cyclooxygenase, cutting thromboxane A2. Aspirin acetylates and permanently blocks COX-1 in platelets, so they make less thromboxane A2. Platelets cannot make new enzyme, so the effect lasts for the platelet's lifespan of about 7 to 10 days.

Penicillins kill bacteria by...

• Blocking protein synthesis at the 30S ribosome
• Inhibiting DNA gyrase
• Inhibiting cell wall synthesis
• Blocking folic acid synthesis

Answer: Inhibiting cell wall synthesis. Penicillins bind penicillin-binding proteins and stop the cross-linking of peptidoglycan, so the cell wall weakens and the bacterium bursts. DNA gyrase is the target of fluoroquinolones, and folate synthesis of sulphonamides.

Omeprazole reduces stomach acid by inhibiting...

• Histamine H2 receptors
• The H+/K+ ATPase (proton pump)
• Muscarinic M1 receptors
• Gastrin release

Answer: The H+/K+ ATPase (proton pump). Omeprazole is a proton pump inhibitor. It blocks the H+/K+ ATPase, the final step of acid secretion in the parietal cells. Ranitidine and famotidine are the H2 blockers.

A patient started on enalapril develops a persistent dry cough. What is the usual explanation?

• Build-up of bradykinin
• Beta-2 blockade in the airways
• Fluid collecting in the lungs
• Allergy to the tablet coating

Answer: Build-up of bradykinin. Enalapril is an ACE inhibitor, and ACE also breaks down bradykinin. Blocking it lets bradykinin build up in the airways and set off a cough. Angiotensin receptor blockers do not do this, so they are the usual switch.

What is the first-line drug for anaphylactic shock?

• Intravenous hydrocortisone
• Oral antihistamine
• Intramuscular adrenaline (epinephrine)
• Nebulised salbutamol

Answer: Intramuscular adrenaline (epinephrine). Intramuscular adrenaline, usually into the outer thigh, is first-line: it raises blood pressure and opens the airways. Antihistamines and steroids are add-ons and never replace it.

What is the specific antidote for paracetamol (acetaminophen) poisoning?

• Naloxone
• Atropine
• Flumazenil
• N-acetylcysteine

Answer: N-acetylcysteine. N-acetylcysteine restores liver glutathione, which neutralises NAPQI, the toxic metabolite of paracetamol. It protects the liver best when started within about 8 hours.

Too much warfarin causes bleeding. Which vitamin reverses its effect?

• Vitamin K
• Vitamin C
• Vitamin B12
• Vitamin D

Answer: Vitamin K. Warfarin blocks the recycling of vitamin K, which the liver needs to make clotting factors II, VII, IX and X. Giving vitamin K restores them. Heparin, by contrast, is reversed with protamine sulphate.

A patient on TB treatment notices orange-red urine and tears. Which drug is responsible?

• Isoniazid
• Pyrazinamide
• Rifampicin
• Ethambutol

Answer: Rifampicin. Rifampicin is itself a red-orange compound and colours urine, sweat and tears. It is harmless, but patients should be warned because it can stain soft contact lenses.

Pyridoxine (vitamin B6) is given along with which anti-TB drug to prevent peripheral neuropathy?

• Rifampicin
• Isoniazid
• Ethambutol
• Streptomycin

Answer: Isoniazid. Isoniazid depletes pyridoxine, which can cause tingling and numbness in the hands and feet. Ethambutol's best-known side effect is on vision (optic neuritis).

Why is propranolol avoided in a patient with asthma?

• It causes a dry cough by raising bradykinin
• It triggers histamine release
• It raises blood sugar sharply
• It blocks beta-2 receptors and can trigger bronchospasm

Answer: It blocks beta-2 receptors and can trigger bronchospasm. Propranolol is a non-selective beta blocker. Blocking beta-2 receptors in the airways can narrow them and set off a severe attack, so cardioselective beta-1 blockers are preferred if one is needed at all, and even those need caution.

Atropine acts as an antagonist at which receptors?

• Muscarinic
• Nicotinic
• Adrenergic beta-1
• Dopamine D2

Answer: Muscarinic. Atropine blocks muscarinic acetylcholine receptors. That is why it speeds up a slow heart, dries secretions and is used in organophosphate poisoning.

Gum overgrowth (gingival hyperplasia) is a well-known side effect of which antiepileptic drug?

• Valproate
• Carbamazepine
• Phenytoin
• Levetiracetam

Answer: Phenytoin. Phenytoin causes gum overgrowth in up to about half of long-term users, usually starting within the first months of treatment. Good oral hygiene reduces it.

Infusing vancomycin too fast can cause flushing of the face, neck and upper body, sometimes with low blood pressure. What is this reaction traditionally called?

• Stevens-Johnson syndrome
• Serotonin syndrome
• Grey baby syndrome
• Red man syndrome

Answer: Red man syndrome. Rapid infusion makes mast cells release histamine directly, without IgE, so it is not a true allergy. Slowing the infusion usually prevents it; it is now called vancomycin infusion reaction. Grey baby syndrome belongs to chloramphenicol.

With regular dosing at fixed intervals, about how many half-lives does a drug take to reach steady state?

• 1
• 4 to 5
• 2
• 10 to 12

Answer: 4 to 5. Each half-life closes half of the remaining gap: about 94% after 4 half-lives and 97% after 5. A loading dose is used when steady state is needed sooner.

A competitive antagonist is added to an agonist. How does the agonist's dose-response curve change?

• It shifts left and the maximum rises
• The maximum response falls with no shift
• It does not change at all
• It shifts right in parallel and the maximum stays the same

Answer: It shifts right in parallel and the maximum stays the same. A competitive antagonist competes for the same binding site, so a higher agonist dose can still win: the curve moves right but reaches the same maximum. A non-competitive antagonist lowers the maximum instead.