Which of the following adverse drug reactions best explains the patient's disorder?

Correct Answer: C

Rationale: The adverse drug reaction that best explains the patient's disorder is an idiosyncratic reaction. Idiosyncratic reactions are unpredictable and occur rarely in response to a drug. In this case, the baby's presentation of microcephaly, broad nasal bridge, short nose, cleft palate, and hypoplasia of the distal phalanges are consistent with a teratogenic effect of a drug taken by the mother during pregnancy. The use of phenytoin for seizures during pregnancy is known to be associated with such birth defects, indicating an idiosyncratic reaction.

Correct Answer: C

Rationale: The most likely cause of the patient's disorder is a genetic polymorphism of CYP2C9. Genetic polymorphisms can affect the metabolism of drugs, including warfarin, leading to variations in drug response and potential adverse effects. In this case, the patient's red urine may be a result of altered metabolism of warfarin due to genetic variations in the CYP2C9 isozyme, which plays a key role in the biotransformation of the drug. This can result in increased levels of unmetabolized warfarin in the body, potentially leading to adverse effects such as red urine.

Correct Answer: D

Rationale: A noncompetitive antagonist best defines a beta-blocker that binds reversibly to beta receptors because it binds to a site on the receptor that is not the same as the agonist binding site, thereby preventing the receptor from being activated by the agonist. This type of antagonist does not compete with the agonist for binding to the receptor, making it an effective blocker of receptor activation. In this case, the drug had no intrinsic activity and only bound reversibly to beta receptors, indicating its role as a noncompetitive antagonist.

Correct Answer: B

Rationale: In this question, the correct answer is B) Tachyphylaxis. Tachyphylaxis refers to a rapid decrease in response to a drug after its administration, leading to a diminished effect upon repeated dosing. In the context of the first cigarette of the day causing tachycardia, this pattern represents tachyphylaxis as the body rapidly develops a decreased response to the stimulant effects of nicotine with repeated exposure. Now, let's analyze why the other options are incorrect: A) Cross-tolerance: Cross-tolerance occurs when the development of tolerance to one drug results in a reduced response to another drug. This does not directly apply to the scenario of the first cigarette causing tachycardia. C) Pharmacokinetic tolerance: This type of tolerance occurs when the body becomes more efficient at metabolizing a drug, leading to reduced drug levels in the bloodstream and decreased effects over time. It does not explain the specific scenario presented in the question. D) Innate tolerance: This term refers to a natural, inherent reduced response to a drug. It does not account for the acquired tolerance seen in the described situation. In an educational context, understanding different types of drug tolerance is crucial for healthcare professionals to optimize drug therapy and address issues such as diminishing drug efficacy over time. Recognizing specific tolerance patterns helps in adjusting treatment plans to achieve desired therapeutic outcomes. This question highlights the importance of recognizing tachyphylaxis in the context of pharmacological responses to substances like nicotine.

Correct Answer: B

Rationale: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is associated with hemolytic anemia triggered by certain drugs like chloroquine. The patient's presentation with hemolytic anemia after chloroquine treatment suggests a G6PD deficiency, making it the most likely enzyme involved in this patient's disease.