Which of the following medications is used to treat hypothyroidism by replacing thyroid hormone?

Correct Answer: A

Rationale: The correct answer is A: Levothyroxine. Levothyroxine is a synthetic form of the thyroid hormone T4, used to treat hypothyroidism by supplementing the deficient thyroid hormone levels in the body. It helps regulate metabolism, energy levels, and overall bodily functions. Methimazole (B) is used to treat hyperthyroidism by reducing the production of thyroid hormones. Fluoxetine (C) is an antidepressant, not used for thyroid conditions. Lithium (D) is used for bipolar disorder, not for hypothyroidism. In summary, Levothyroxine is the correct choice as it directly replaces the deficient thyroid hormone, while the other options are not indicated for treating hypothyroidism.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Atorvastatin, simvastatin, and lovastatin are all statin medications that lower cholesterol by inhibiting the HMG-CoA reductase enzyme. This enzyme is crucial in the production of cholesterol in the liver. By inhibiting this enzyme, statins help reduce the amount of cholesterol synthesized in the body, leading to lower overall cholesterol levels. Therefore, all three medications listed are effective in lowering cholesterol levels. The other choices (A, B, C) are incorrect as they do not fully address the question and fail to acknowledge that all three medications listed are part of the same drug class with the same mechanism of action.

Correct Answer: B

Rationale: The correct answer is B because celecoxib selectively inhibits COX-2 enzymes, which are responsible for producing prostaglandins involved in pain and inflammation. By targeting COX-2 specifically, celecoxib reduces pain and inflammation without affecting COX-1, which is important for maintaining gastrointestinal mucosa and platelet function. Therefore, choice A is incorrect as celecoxib does not inhibit both COX-1 and COX-2. Choices C and D are also incorrect as celecoxib does not increase prostaglandin synthesis or bind to opioid receptors.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Isoniazid is a first-line medication for tuberculosis due to its efficacy in killing the bacteria. 2. It works by inhibiting the synthesis of mycolic acids in the bacterial cell wall. 3. This disrupts the cell wall formation, leading to bacterial death. 4. Amoxicillin, ceftriaxone, and doxycycline are not typically used as first-line treatments for tuberculosis. Summary: Isoniazid is the correct choice for treating tuberculosis as it specifically targets the bacteria causing the infection. Amoxicillin, ceftriaxone, and doxycycline are not effective against tuberculosis bacteria.

Correct Answer: C

Rationale: The correct answer is C because gabapentin binds to calcium channels in the central nervous system. This action reduces the release of excitatory neurotransmitters, such as glutamate, which helps in reducing pain signals sent to the brain. Option A is incorrect as gabapentin does not directly affect serotonin levels. Option B is incorrect as gabapentin does not inhibit norepinephrine reuptake. Option D is incorrect as gabapentin does not increase dopamine release. Therefore, the correct mechanism of action for gabapentin is binding to calcium channels to modulate pain signaling.