The house officer considers prescribing nadolol for a 53-year-old patient. Which of the following preexisting conditions (co-morbidities) would most likely contraindicate safe use of this drug?

Correct Answer: B

Rationale: The correct answer is B: Asthma. Nadolol is a non-selective beta-blocker, which can lead to bronchoconstriction and worsen asthma symptoms due to its effect on beta-2 receptors in the lungs. This can be dangerous for patients with asthma as it can exacerbate respiratory distress. Choices A, C, and D are not contraindications for nadolol as it can actually be beneficial in these conditions by reducing heart rate and blood pressure.

Correct Answer: B

Rationale: The correct answer is B: Glaucoma. Pilocarpine is a cholinergic agonist that works by causing constriction of the pupil and increasing the outflow of aqueous humor in the eye, thereby reducing intraocular pressure in glaucoma. Increased salivary secretion (A) is a side effect of pilocarpine use. Pilocarpine is not indicated for treating intestinal colic (C) or cardiac arrhythmias (D).

Correct Answer: A

Rationale: The correct answer is A: Amphetamine. Amphetamine is a central nervous system stimulant that helps manage narcolepsy symptoms by promoting wakefulness. It increases levels of neurotransmitters like dopamine and norepinephrine, enhancing alertness. Adrenaline (B), Isoprenaline (C), and Salbutamol (D) are not typically used to treat narcolepsy as they do not directly target the underlying cause of excessive daytime sleepiness. Adrenaline and Isoprenaline are more commonly used for acute situations like anaphylaxis or cardiac arrest. Salbutamol is a bronchodilator used for conditions like asthma.

Correct Answer: D

Rationale: The correct answer is D. Bethanechol is a parasympathomimetic drug that primarily acts on muscarinic receptors in the bladder and gastrointestinal tract, causing increased smooth muscle contraction and promoting urination and improved GI motility. It does not affect intraocular pressure. A, B, and C are incorrect: A: Methacholine - acts as a muscarinic agonist causing bronchoconstriction, not vasodilation. B: Neostigmine - inhibits acetylcholinesterase leading to increased acetylcholine levels, enhancing neuromuscular transmission, not directly stimulating skeletal muscles. C: Pilocarpine - acts on muscarinic receptors in the eye, causing miosis and increased aqueous humor outflow, not increased sweat secretion.

Correct Answer: D

Rationale: The correct answer is D: Guanethidine. Guanethidine is a quaternary amine, which prevents it from passing the blood-brain barrier due to its charge. The blood-brain barrier is selective and only allows certain molecules to pass through. In contrast, choices A, B, and C (Ephedrine, Propranolol, Clonidine) are all capable of crossing the blood-brain barrier to some extent due to their chemical properties. Ephedrine is a weak base, Propranolol is lipophilic, and Clonidine is relatively small in size, allowing them to penetrate the blood-brain barrier.