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: Failed to generate a rationale of 500+ characters after 5 retries.

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.