Pharmacology Autonomic Nervous System Agents Questions and Answers 1 — Questions and Answers
Question 1: A 68-year-old male with open-angle glaucoma is prescribed pilocarpine eye drops. What is the primary mechanism by which this medication lowers intraocular pressure?
- Decreasing the production of aqueous humor by acting on beta-receptors in the ciliary body.
- Increasing the outflow of aqueous humor by causing contraction of the ciliary muscle. (Correct answer)
- Relaxing the iris sphincter muscle to widen the trabecular meshwork.
- Blocking alpha-adrenergic receptors in the uveoscleral pathway.
Correct answer: Increasing the outflow of aqueous humor by causing contraction of the ciliary muscle.
Pilocarpine is a direct-acting muscarinic agonist. When administered topically to the eye, it stimulates muscarinic receptors on the ciliary muscle, causing it to contract. This contraction increases tension on the trabecular meshwork, which facilitates the outflow of aqueous humor from the anterior chamber, thereby reducing intraocular pressure.
Question 2: A patient with asthma requires a rescue inhaler for acute bronchospasm. Which of the following agents is most appropriate due to its selective action on bronchial smooth muscle?
- Phenylephrine
- Norepinephrine
- Albuterol (Correct answer)
- Dobutamine
Correct answer: Albuterol
Albuterol is a selective beta-2 adrenergic agonist. Beta-2 receptors are predominantly located in the smooth muscle of the bronchioles. Stimulation of these receptors leads to smooth muscle relaxation and bronchodilation, making it an effective treatment for acute asthma symptoms. Phenylephrine is an alpha-1 agonist, norepinephrine acts on alpha-1, alpha-2, and beta-1 receptors, and dobutamine is primarily a beta-1 agonist.
Question 3: A patient is being treated with a medication that has significant anticholinergic properties. Which of the following side effects is most consistent with this drug's profile?
- Excessive salivation
- Bradycardia
- Pupillary constriction (miosis)
- Urinary retention (Correct answer)
Correct answer: Urinary retention
Anticholinergic agents block the action of acetylcholine at muscarinic receptors. This blockade of the parasympathetic nervous system leads to a classic set of side effects, often remembered by the mnemonic 'can't see, can't pee, can't spit, can't s***'. Urinary retention ('can't pee') is a common side effect due to the relaxation of the bladder detrusor muscle. The other options are characteristic of cholinergic stimulation.
Question 4: A surgeon administers neostigmine to a patient at the end of a procedure to reverse the effects of a non-depolarizing neuromuscular blocker. What is the mechanism of action for neostigmine?
- It directly stimulates nicotinic receptors at the neuromuscular junction.
- It inhibits the breakdown of acetylcholine by acetylcholinesterase. (Correct answer)
- It acts as a competitive antagonist at the same receptor as the neuromuscular blocker.
- It blocks the reuptake of acetylcholine into the presynaptic terminal.
Correct answer: It inhibits the breakdown of acetylcholine by acetylcholinesterase.
Neostigmine is a reversible acetylcholinesterase inhibitor. By inhibiting the enzyme acetylcholinesterase, it prevents the breakdown of acetylcholine in the synaptic cleft. This increases the concentration and duration of action of acetylcholine at the neuromuscular junction, allowing it to outcompete the non-depolarizing blocker and restore neuromuscular transmission.
Question 5: A 72-year-old male treated for benign prostatic hyperplasia (BPH) with tamsulosin, an alpha-1A selective antagonist, reports feeling dizzy, especially when standing up from a seated position. This side effect is best explained by which of the following effects of the drug?
- Negative inotropic effect on the heart.
- Relaxation of vascular smooth muscle. (Correct answer)
- Bronchoconstriction leading to hypoxia.
- Central nervous system depression.
Correct answer: Relaxation of vascular smooth muscle.
Alpha-1 adrenergic antagonists, including tamsulosin, block alpha-1 receptors on vascular smooth muscle. This leads to vasodilation and a decrease in peripheral resistance. A common side effect is orthostatic hypotension, which is a drop in blood pressure upon standing that causes dizziness or lightheadedness.
Question 6: When comparing the primary hemodynamic effects of intravenous epinephrine and norepinephrine at typical clinical doses, which statement is most accurate?
- Norepinephrine causes a greater increase in heart rate than epinephrine.
- Epinephrine primarily increases systolic blood pressure, while norepinephrine primarily increases diastolic blood pressure.
- Epinephrine has a more potent effect on beta-2 receptors, leading to vasodilation in certain vascular beds. (Correct answer)
- Norepinephrine is a potent bronchodilator, while epinephrine has minimal effect on the airways.
Correct answer: Epinephrine has a more potent effect on beta-2 receptors, leading to vasodilation in certain vascular beds.
Epinephrine is a potent agonist at both alpha and beta adrenergic receptors. Its stimulation of beta-2 receptors causes vasodilation in skeletal muscle vascular beds, which can lower or maintain diastolic pressure. Norepinephrine has strong alpha-1 and beta-1 activity but weak beta-2 activity, leading to potent vasoconstriction and a significant increase in both systolic and diastolic blood pressure. Therefore, epinephrine's beta-2 effects are a key differentiating factor.
Pharmacology Autonomic Nervous System Agents Questions and Answers 1
A 68-year-old male with open-angle glaucoma is prescribed pilocarpine eye drops.
What is the primary mechanism by which this medication lowers intraocular pressure?