Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 141: Diazoxide acts by which of the following mechanisms?

A. Increasing insulin release
B. Inhibiting insulin release (Correct Answer)
C. Inhibiting insulin release
D. Inhibiting glucagon release

Explanation: **Explanation:** **Mechanism of Action:** Diazoxide is a potent **K⁺ channel opener** (specifically the ATP-sensitive K⁺ channels) located in the beta cells of the pancreas. By keeping these channels open, it causes K⁺ efflux, leading to **hyperpolarization** of the beta-cell membrane. This hyperpolarization prevents the opening of voltage-gated calcium channels, thereby **inhibiting the exocytosis of insulin**. Consequently, blood glucose levels rise. **Analysis of Options:** * **Option B & C (Correct):** Diazoxide directly inhibits insulin secretion via K⁺ channel activation. It is primarily used to treat hypoglycemia caused by hyperinsulinism (e.g., insulinoma or leucine-sensitive hypoglycemia). * **Option A:** This is the mechanism of **Sulfonylureas** (e.g., Glibenclamide), which *close* ATP-sensitive K⁺ channels to stimulate insulin release. * **Option D:** Diazoxide does not significantly inhibit glucagon; its primary glycemic effect is mediated through the suppression of insulin. **High-Yield Clinical Pearls for NEET-PG:** 1. **Dual Action:** Besides its pancreatic effects, Diazoxide also opens K⁺ channels in vascular smooth muscle, causing vasodilation. It was historically used as an IV bolus for hypertensive emergencies. 2. **Side Effects:** A classic side effect is **Hypertrichosis** (excessive hair growth), similar to Minoxidil (another K⁺ channel opener). It can also cause salt and water retention. 3. **Contraindication:** It should be used cautiously in patients with congestive heart failure due to fluid retention. 4. **Drug of Choice:** It is a key medical management option for **Insulinoma** patients who are not candidates for surgery.

Question 142: Metformin is used as an antihyperglycemic agent in Diabetes Mellitus. Which of the following are considered off-label or additional uses of Metformin, EXCEPT?

A. Polycystic Ovarian Disease (PCOD)
B. Non-alcoholic fatty liver disease
C. Alcoholic fatty liver disease (Correct Answer)
D. Metabolic abnormalities associated with HIV disease

Explanation: **Explanation:** Metformin, a biguanide, is the first-line drug for Type 2 Diabetes Mellitus. Its primary mechanism involves activating **AMP-activated protein kinase (AMPK)**, which leads to decreased hepatic gluconeogenesis and improved peripheral insulin sensitivity. **Why Option C is the Correct Answer:** Metformin has **no proven clinical benefit** in treating **Alcoholic Fatty Liver Disease (AFLD)**. The pathogenesis of AFLD is driven by ethanol metabolism and oxidative stress rather than primary insulin resistance. Furthermore, chronic alcohol consumption is a major risk factor for **lactic acidosis** (a rare but fatal side effect of Metformin) because both alcohol and Metformin increase the lactate-to-pyruvate ratio. Therefore, Metformin is generally avoided or used with extreme caution in patients with significant alcohol intake. **Analysis of Other Options (Off-label/Additional Uses):** * **A. Polycystic Ovarian Disease (PCOD):** Metformin is widely used to improve insulin sensitivity, which reduces hyperinsulinemia. This helps restore ovulation and reduces androgen levels. * **B. Non-alcoholic Fatty Liver Disease (NAFLD):** Since NAFLD is the hepatic manifestation of metabolic syndrome and insulin resistance, Metformin is often used to improve biochemical markers (though its effect on liver histology is limited). * **D. HIV-associated Metabolic Abnormalities:** Metformin is used to manage lipodystrophy and insulin resistance associated with Highly Active Antiretroviral Therapy (HAART). **High-Yield NEET-PG Pearls:** * **DOC:** Metformin is the drug of choice for obese diabetics. * **Weight Neutral/Loss:** Unlike sulfonylureas or insulin, Metformin does not cause weight gain. * **Vitamin Deficiency:** Long-term use can lead to **Vitamin B12 deficiency** (megaloblastic anemia). * **Contraindication:** Avoid if eGFR is **<30 mL/min/1.73 m²** due to the risk of lactic acidosis.

Question 143: Which of the following drugs does not cause hypoglycemia?

A. Tolbutamide
B. Glibenclamide
C. Metformin (Correct Answer)
D. Chlorpropamide

Explanation: The key to answering this question lies in distinguishing between **insulin secretagogues** and **euglycemic agents (insulin sensitizers).** **1. Why Metformin is the Correct Answer:** Metformin belongs to the **Biguanide** class. Its primary mechanism of action is to decrease hepatic glucose production (gluconeogenesis) and improve peripheral insulin sensitivity. Crucially, Metformin **does not stimulate insulin release** from the pancreatic beta cells. Because it does not increase circulating insulin levels beyond physiological needs, it does not cause hypoglycemia when used as monotherapy. It is therefore classified as a "euglycemic" agent. **2. Why the Other Options are Incorrect:** * **Tolbutamide (Option A), Glibenclamide (Option B), and Chlorpropamide (Option D)** are all **Sulfonylureas** [1]. * **Mechanism:** They act by blocking ATP-sensitive K⁺ channels in the pancreatic beta-cell membrane [2]. This leads to depolarization, Ca²⁺ influx, and the **forced release of insulin**, regardless of the prevailing blood glucose level [2]. * Because they trigger insulin secretion even when blood sugar is normal, **hypoglycemia** is their most common and significant side effect [3]. **3. NEET-PG High-Yield Clinical Pearls:** * **Drug of Choice:** Metformin is the first-line drug for Type 2 Diabetes Mellitus and is weight-neutral or leads to weight loss. * **Side Effects:** The most serious (though rare) side effect of Metformin is **Lactic Acidosis**; it is contraindicated in renal failure (CrCl <30 ml/min). * **Long-acting Sulfonylureas:** Chlorpropamide has the longest half-life and is most notorious for causing prolonged hypoglycemia and a disulfiram-like reaction with alcohol. * **Other Euglycemic classes:** Pioglitazone (Thiazolidinediones) and DPP-4 inhibitors (Gliptins) also have a low risk of hypoglycemia.

Question 144: Which of the following drugs inhibits 5'-deiodinase?

A. Propylthiouracil (Correct Answer)
B. Methimazole
C. Lugol's iodine
D. Radioactive iodine

Explanation: ### Explanation The conversion of the prohormone **Thyroxine (T4)** to the more potent **Triiodothyronine (T3)** occurs in peripheral tissues via the enzyme **5'-deiodinase** [1]. Inhibiting this enzyme is a crucial therapeutic strategy in managing severe thyrotoxicosis. **1. Why Propylthiouracil (PTU) is correct:** PTU is a thioamide with a dual mechanism of action. Like other thioamides, it inhibits **Thyroid Peroxidase (TPO)**, preventing iodine organification and coupling within the thyroid gland. However, PTU is unique because it also **inhibits peripheral 5'-deiodinase**, rapidly decreasing the conversion of T4 to T3. This makes it the preferred thioamide in treating **Thyroid Storm**. **2. Why the other options are incorrect:** * **B. Methimazole:** While it also inhibits TPO and is more potent/longer-acting than PTU, it **does not** inhibit peripheral 5'-deiodinase. * **C. Lugol's Iodine:** This is a solution of potassium iodide. It works primarily via the **Wolff-Chaikoff effect**, which acutely inhibits thyroid hormone release by "stunning" the gland with high iodine concentrations [2]. It does not affect peripheral conversion. * **D. Radioactive Iodine (I-131):** This works by emitting beta particles that cause follicular destruction (permanent ablation). It has no immediate effect on enzymatic conversion. **Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Methimazole is generally preferred for hyperthyroidism due to once-daily dosing and lower hepatotoxicity [3]. * **Pregnancy:** PTU is the DOC in the **1st trimester** (lower teratogenicity/aplasia cutis risk); Methimazole is preferred in the 2nd and 3rd trimesters. * **Other 5'-deiodinase inhibitors:** Propranolol (high doses) [1], Glucocorticoids (e.g., Dexamethasone), and Amiodarone also inhibit this enzyme.

Question 145: What is the drug of choice for central diabetes insipidus?

A. Vasopressin
B. Desmopressin (Correct Answer)
C. Lypressin
D. Presselin

Explanation: **Explanation:** **Desmopressin (dDAVP)** is the drug of choice for **Central Diabetes Insipidus (CDI)**. CDI is characterized by a deficiency of Antidiuretic Hormone (ADH) from the posterior pituitary. Desmopressin is a synthetic analogue of vasopressin with two key modifications: it has a longer half-life and is a **selective V2 receptor agonist**. By acting on V2 receptors in the renal collecting ducts, it increases water reabsorption without causing the significant vasoconstriction associated with V1 receptor activation. It can be administered intranasally, orally, or parenterally. **Analysis of Incorrect Options:** * **Vasopressin (ADH):** While it is the endogenous hormone, it is not the drug of choice because it acts non-selectively on both V1 (vasoconstriction) and V2 receptors. It has a very short duration of action (15–20 minutes), requiring frequent dosing, and carries a risk of hypertension and myocardial ischemia. * **Lypressin:** This is a synthetic analogue (8-lysine vasopressin) formerly used for CDI. However, it has a shorter duration of action and less potency compared to Desmopressin, making it obsolete in modern practice. * **Presselin:** This is not a standard pharmacological agent used in the treatment of Diabetes Insipidus. **High-Yield Clinical Pearls for NEET-PG:** * **V2 Selectivity:** Desmopressin has a V2:V1 selectivity ratio of approximately 2000:1. * **Other Uses of Desmopressin:** It is also the drug of choice for **Nocturnal Enuresis** and is used in **Von Willebrand Disease (Type 1)** and **Hemophilia A** because it stimulates the release of Factor VIII and vWF from endothelial cells. * **Diagnosis:** To differentiate Central from Nephrogenic DI, a **Water Deprivation Test** followed by Desmopressin administration is used; a significant increase in urine osmolality indicates Central DI.

Question 146: Which of the following drugs is NOT used for the treatment of osteoporosis?

A. Bisphosphonates
B. Steroids (Correct Answer)
C. Denosumab
D. Calcium

Explanation: **Explanation:** The correct answer is **Steroids**. In fact, long-term use of glucocorticoids (steroids) is one of the most common causes of **secondary osteoporosis**. **Why Steroids are the correct answer:** Steroids induce bone loss through multiple mechanisms: 1. **Decreased Bone Formation:** They inhibit osteoblast activity and promote osteocyte apoptosis. 2. **Increased Bone Resorption:** They increase the expression of RANK-L and decrease Osteoprotegerin (OPG), leading to osteoclast activation. 3. **Calcium Imbalance:** They decrease intestinal calcium absorption and increase renal calcium excretion, leading to secondary hyperparathyroidism. **Why the other options are incorrect:** * **Bisphosphonates (e.g., Alendronate, Zoledronate):** These are the **first-line drugs** for osteoporosis. They inhibit osteoclast-mediated bone resorption by binding to hydroxyapatite crystals. * **Denosumab:** This is a monoclonal antibody against **RANK-L**. By inhibiting RANK-L, it prevents the maturation of osteoclasts, thereby increasing bone mineral density. * **Calcium:** Adequate calcium intake (often combined with Vitamin D) is a fundamental component of both prevention and treatment of osteoporosis to maintain bone mineralization. **High-Yield Clinical Pearls for NEET-PG:** * **Teriparatide:** A recombinant PTH analogue; it is the only **anabolic agent** (builds bone) mentioned frequently in exams. * **Raloxifene:** A Selective Estrogen Receptor Modulator (SERM) used for postmenopausal osteoporosis; it has the added benefit of reducing the risk of breast cancer. * **Drug of Choice:** Bisphosphonates remain the DOC for most patients with osteoporosis. * **Side Effect:** A classic side effect of Bisphosphonates is **esophagitis** (patients must stay upright for 30 minutes) and the rare **Osteonecrosis of the Jaw (ONJ)**.

Question 147: Teriparatide can be used for the treatment of:

A. Osteoporosis (Correct Answer)
B. Hormone responsive breast carcinoma
C. Polycystic ovarian disease
D. Hyperparathyroidism

Explanation: **Explanation:** **Teriparatide** is a recombinant form of human parathyroid hormone (PTH 1-34). Its primary clinical indication is the treatment of **Osteoporosis** (both postmenopausal and idiopathic/hypogonadal in men), particularly in patients at high risk for fractures. 1. **Why Option A is Correct:** While continuous high levels of endogenous PTH (as seen in hyperparathyroidism) cause bone resorption, **intermittent (once-daily) subcutaneous administration** of Teriparatide has a paradoxical **anabolic effect**. It stimulates osteoblastic activity more than osteoclastic activity, leading to increased bone mineral density (BMD) and improved bone architecture. 2. **Why Other Options are Incorrect:** * **B (Breast Carcinoma):** Teriparatide is not used here. In fact, it is contraindicated in patients with a history of skeletal malignancies or bone metastases due to the theoretical risk of osteosarcoma. * **C (PCOD):** PCOD is managed with lifestyle changes, OCPs, metformin, or clomiphene. Teriparatide has no role in androgen or insulin regulation. * **D (Hyperparathyroidism):** Teriparatide is an exogenous PTH analogue. Administering it in hyperparathyroidism would worsen the hypercalcemia and bone loss associated with the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Intermittent administration → "Anabolic Window" (Bone formation > Resorption). * **Black Box Warning:** Risk of **Osteosarcoma** (observed in rat studies); hence, it is usually restricted to a maximum lifetime use of 2 years. * **Contraindications:** Paget’s disease of bone, unexplained elevation of alkaline phosphatase, prior radiation therapy to the skeleton, and skeletal malignancies. * **Side Effects:** Hypercalcemia (transient), leg cramps, and dizziness.

Question 148: Denosumab is used in which of the following conditions?

A. Osteomalacia
B. Osteoarthritis
C. Osteoporosis (Correct Answer)
D. Osteosarcoma

Explanation: **Explanation:** **Denosumab** is a fully human monoclonal antibody that targets and inhibits **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand). Under normal physiological conditions, RANKL binds to RANK receptors on the surface of osteoclast precursors, promoting their maturation and activation. By binding to RANKL, Denosumab mimics the natural action of Osteoprotegerin (OPG), thereby inhibiting osteoclast-mediated bone resorption and increasing bone mineral density. **Why Option C is Correct:** * **Osteoporosis:** Denosumab is FDA-approved for postmenopausal osteoporosis and osteoporosis in men at high risk of fractures. It effectively reduces the risk of vertebral, non-vertebral, and hip fractures. **Why Other Options are Incorrect:** * **A. Osteomalacia:** This is a defect in bone mineralization (often due to Vitamin D deficiency). Treatment involves Vitamin D and Calcium supplementation, not anti-resorptive therapy. * **B. Osteoarthritis:** This is a degenerative joint disease involving cartilage loss. Denosumab does not address the underlying pathophysiology of cartilage degradation. * **D. Osteosarcoma:** This is a primary malignant bone tumor. While Denosumab is used in **Giant Cell Tumor of Bone**, it is not a standard treatment for osteosarcoma. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** RANKL Inhibitor (mimics Osteoprotegerin). * **Administration:** Subcutaneous injection every 6 months (improves compliance). * **Adverse Effects:** Hypocalcemia (most common), skin infections (cellulitis), and Osteonecrosis of the Jaw (ONJ). * **Other Indications:** Bone metastases from solid tumors and Giant Cell Tumor of Bone. * **Key Distinction:** Unlike Bisphosphonates, Denosumab can be used in patients with **renal impairment** as it is not cleared by the kidneys.

Question 149: Which of the following agents is not used in the management of Cushing syndrome?

A. Mitotane
B. Etomidate
C. Metyrapone
D. Amoxapine (Correct Answer)

Explanation: **Explanation:** The management of Cushing syndrome involves inhibiting the overproduction of cortisol. This is achieved through adrenal steroidogenesis inhibitors, adrenolytic agents, or neuromodulators. **Why Amoxapine is the correct answer:** **Amoxapine** is a **Tricyclic Antidepressant (TCA)** primarily used in the treatment of major depressive disorders. It has no role in the suppression of the hypothalamic-pituitary-adrenal (HPA) axis or the inhibition of steroid enzymes. Therefore, it is not used in the management of Cushing syndrome. **Analysis of incorrect options:** * **Mitotane (Option A):** An adrenolytic agent that causes selective destruction of the adrenal cortex (specifically the zona fasciculata and reticularis). It is used primarily in adrenal carcinoma. * **Etomidate (Option B):** An intravenous anesthetic agent that, even at sub-hypnotic doses, is a potent inhibitor of **11β-hydroxylase**. It is used in the emergency management of severe hypercortisolism. * **Metyrapone (Option C):** A selective inhibitor of **11β-hydroxylase**, which blocks the final step of cortisol synthesis. It is frequently used for diagnostic testing and medical management of Cushing syndrome. **NEET-PG High-Yield Pearls:** * **Ketoconazole:** The most commonly used medical therapy for Cushing syndrome; it inhibits multiple enzymes (CYP17, 11β-hydroxylase, and side-chain cleavage). * **Mifepristone:** A glucocorticoid receptor antagonist used to treat hyperglycemia secondary to Cushing syndrome. * **Pasireotide:** A somatostatin analog used specifically for **Cushing Disease** (pituitary etiology) by inhibiting ACTH secretion. * **Drug of choice for medical management:** Ketoconazole is often preferred due to its efficacy and availability.

Question 150: In diabetes mellitus with increased HbA1c, which of the following is NOT a drug used in treatment?

A. Sulfonylureas
B. Acarbose (Correct Answer)
C. Biguanides
D. Thiazolidinediones

Explanation: **Explanation:** The question asks for the drug **NOT** typically used as a primary treatment for significant hyperglycemia (indicated by increased HbA1c). While all options are technically anti-diabetic agents, **Acarbose** is the correct answer in this clinical context due to its limited efficacy. **1. Why Acarbose is the correct answer:** Acarbose is an **$\alpha$-glucosidase inhibitor** that works locally in the intestine to delay carbohydrate absorption. Its primary effect is on **post-prandial glucose (PPG)** rather than fasting plasma glucose. Clinically, Acarbose is a "weak" anti-diabetic agent, reducing HbA1c by only **0.5–0.8%**. In a patient with significantly increased HbA1c, it is rarely used as a mainstay treatment due to its low potency and significant GI side effects (flatulence, diarrhea). **2. Why the other options are incorrect:** * **Sulfonylureas (e.g., Glipizide):** These are potent insulin secretagogues. They significantly reduce HbA1c (1.0–2.0%) and are standard second-line agents. * **Biguanides (Metformin):** The first-line drug for Type 2 Diabetes. It reduces hepatic glucose production and improves insulin sensitivity, lowering HbA1c by 1.0–2.0%. * **Thiazolidinediones (e.g., Pioglitazone):** These are PPAR-$\gamma$ agonists that improve peripheral insulin sensitivity. They are effective at lowering HbA1c by 0.5–1.4%. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Acarbose:** Inhibits $\alpha$-glucosidase at the brush border of the small intestine. * **Drug of Choice (DOC):** Metformin is the DOC for T2DM unless contraindicated (e.g., Renal failure with eGFR <30). * **Weight Neutrality:** Metformin is weight-neutral/loss-promoting, while Sulfonylureas and TZDs cause weight gain. * **Side Effect Note:** If a patient on Acarbose develops hypoglycemia (due to concurrent Sulfonylurea use), treat with **pure glucose (dextrose)**, not sucrose (cane sugar), as Acarbose prevents the breakdown of sucrose.

Practice by Chapter

Hypothalamic and Pituitary Hormones

Practice Questions

Thyroid Drugs and Antithyroid Agents

Practice Questions

Insulin and Oral Hypoglycemic Agents

Practice Questions

Adrenocorticosteroids

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Sex Hormones: Estrogens and Progestins

Practice Questions

Androgens and Anabolic Steroids

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Hormonal Contraceptives

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Drugs Affecting Calcium Metabolism

Practice Questions

Drugs for Osteoporosis

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Pharmacological Management of Obesity

Practice Questions

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