Endocrine Pharmacology Practice Questions

Q: What is the advantage of desmopressin over vasopressin in the treatment of diabetes insipidus?

Is more selective for V2 receptor subtype. **Explanation:** **1. Why Option C is Correct:** Vasopressin (ADH) acts on two primary receptors: **V1** (located on vascular smooth muscle, causing vasoconstriction) and **V2** (located in the renal collecting ducts, causing water reabsorption). **Desmopressin (dDAVP)** is a synthetic analogue of vasopressin designed to be highly selective for the **V2 receptor**. By minimizing V1 activity, desmopressin effectively treats Diabetes Insipidus (DI) by concentrating urine without causing the unwanted systemic vasoconstriction (hypertension, angina, or abdominal cramps) associated with native vasopressin. It also has a significantly longer duration of action (6–20 hours) compared to vasopressin (2–8 hours). **2. Why Other Options are Wrong:** * **Option A:** Desmopressin actually **increases** the release of Factor VIII and von Willebrand factor from endothelial cells (via V2-like receptors). This makes it a treatment for Hemophilia A and von Willebrand Disease, not a disadvantage. * **Option B:** Both drugs treat DI, which helps correct hypernatremia. However, the primary risk of overdose with both is **hyponatremia** (due to excessive water retention), not hypernatremia. * **Option D:** While both drugs reduce polyuria and secondary thirst, desmopressin is preferred due to its **selectivity and duration**, not because it has a superior direct effect on the thirst center. **3. NEET-PG High-Yield Pearls:** * **Route of Choice:** Intranasal is common, but oral and IV/SC routes are available. * **Drug of Choice (DOC):** Desmopressin is the DOC for **Central Diabetes Insipidus** and **Nocturnal Enuresis**. * **V1 vs. V2:** Remember **V1 = Vascular** (Constriction); **V2 = Volume/Valves** (Water reabsorption and Factor VIII/vWF release). * **Terlipressin:** A V1-selective analogue used in esophageal varices.

Q: Bisphosphonates are used for which of the following conditions, EXCEPT?

Osteosclerosis. **Explanation:** **Bisphosphonates** (e.g., Alendronate, Zoledronate) are structural analogs of pyrophosphate that primarily act by inhibiting **osteoclasts**, the cells responsible for bone resorption. **Why Osteosclerosis is the Correct Answer:** **Osteosclerosis** is a condition characterized by an abnormal increase in bone density (hardening of bone). Since bisphosphonates inhibit bone breakdown and further increase bone mineral density, they would potentially worsen the condition or provide no therapeutic benefit. Therefore, they are not indicated here. **Analysis of Incorrect Options:** * **Osteoporosis (Option B):** This is the most common indication. Bisphosphonates are first-line drugs that decrease bone resorption, thereby increasing bone mass and reducing the risk of fractures. * **Osteolytic Bone Metastases (Option A):** Cancers (like breast or multiple myeloma) often cause "punched-out" lytic lesions by activating osteoclasts. Bisphosphonates (especially IV Zoledronate) inhibit this process, reducing bone pain and pathological fractures. * **Paget’s Disease (Option D):** This involves disordered, excessive bone remodeling. Bisphosphonates are the treatment of choice to suppress the overactive osteoclasts and normalize bone turnover. **NEET-PG High-Yield Pearls:** * **Mechanism:** They bind to hydroxyapatite crystals and inhibit the enzyme **FPPS (Farnesyl Pyrophosphate Synthase)** in the mevalonate pathway of osteoclasts. * **Administration:** Oral bisphosphonates must be taken on an empty stomach with a full glass of water, and the patient must remain upright for 30 minutes to prevent **erosive esophagitis**. * **Side Effects:** Osteonecrosis of the Jaw (ONJ) and atypical subtrochanteric fractures (with long-term use). * **Drug of Choice:** Zoledronate is the most potent bisphosphonate and is the drug of choice for **Hypercalcemia of Malignancy**.

Q: Which antiprogestin is used for emergency contraception?

Mifepristone. **Explanation:** **Mifepristone (Option A)** is a potent competitive progesterone receptor antagonist (antiprogestin). In the context of emergency contraception (EC), it works primarily by inhibiting or delaying ovulation. If taken post-ovulation, it may also alter the endometrium to prevent implantation. A single low dose (10 mg or 25 mg) is highly effective as an EC if taken within 120 hours (5 days) of unprotected intercourse. **Analysis of Incorrect Options:** * **Misoprostol (Option B):** A synthetic Prostaglandin E1 (PGE1) analog. It is used for medical abortion (in combination with Mifepristone), induction of labor, and management of PPH, but it has no role as an emergency contraceptive. * **Methotrexate (Option C):** A folate antagonist and cytotoxic drug. It is the medical treatment of choice for unruptured ectopic pregnancy and is used in some regimens for early medical abortion, but not for EC. * **Norethisterone (Option D):** A first-generation synthetic progestin. While progestins like **Levonorgestrel (LNG)** are used for EC, Norethisterone is typically used for cycle regulation, dysfunctional uterine bleeding, or as a daily oral contraceptive pill. **High-Yield NEET-PG Pearls:** * **Ulipristal Acetate:** A Selective Progesterone Receptor Modulator (SPRM) and currently the most effective oral EC, effective up to 120 hours. * **Levonorgestrel (LNG):** The most commonly used EC (1.5 mg single dose); most effective when taken within 72 hours. * **Copper T 380A:** The **most effective** method of emergency contraception overall if inserted within 5 days of unprotected intercourse. * **Yuzpe Regimen:** An older method using combined oral contraceptive pills (Ethinylestradiol + LNG); it is less effective and has more side effects (nausea/vomiting) than LNG-only pills.

Q: Meglitinide analogues act by which mechanism?

Increasing insulin release. Meglitinide analogues (e.g., **Repaglinide, Nateglinide**) are known as **"Prandial Glucose Regulators."** [1], [2], [3] Like Sulfonylureas, they act as insulin secretagogues. [1], [2] They bind to a specific site on the **ATP-sensitive K⁺ channels** in the pancreatic β-cell membrane (distinct from the Sulfonylurea receptor site). [1], [2], [3] This binding causes the channels to close, leading to cell depolarization, an influx of Calcium (Ca²⁺), and subsequent exocytosis of insulin. [2] Their rapid onset and short duration of action make them ideal for controlling postprandial hyperglycemia. [1], [2], [3] **Analysis of Incorrect Options:** * **B (Decreasing glucagon release):** This is a secondary effect of GLP-1 agonists and DPP-4 inhibitors, but not the primary mechanism of Meglitinides. * **C (Decreasing intestinal absorption):** This describes the mechanism of **Alpha-glucosidase inhibitors** (e.g., Acarbose, Voglibose), which delay carbohydrate digestion. * **D (Promoting peripheral utilization):** This is the primary mechanism of **Biguanides (Metformin)** and **Thiazolidinediones (Pioglitazone)**, which act as insulin sensitizers in muscle and adipose tissue. **High-Yield Clinical Pearls for NEET-PG:** * **Rapid Onset:** Meglitinides should be taken **15–30 minutes before meals** ("Skip a meal, skip a dose"). [1], [3] * **Safety in Renal Impairment:** Repaglinide is primarily excreted via bile, making it safer for patients with **renal insufficiency** compared to most Sulfonylureas. * **Side Effects:** The most common side effect is hypoglycemia (though less frequent than with long-acting Sulfonylureas) and weight gain. [3] * **Nateglinide** is a D-phenylalanine derivative [1], [2], whereas **Repaglinide** is a benzoic acid derivative.

Q: Which of the following statements regarding the mechanism of action of sulfonylureas is true?

Act on SUR1 receptors on the pancreatic beta cell membrane. **Explanation:** **Mechanism of Action (The Correct Answer):** Sulfonylureas (e.g., Glibenclamide, Glimepiride) are **insulin secretagogues**. They act by binding to the **Sulfonylurea Receptor 1 (SUR1)**, which is a subunit of the ATP-sensitive potassium ($K_{ATP}$) channel located on the pancreatic beta-cell membrane. 1. Binding leads to the **closure of $K_{ATP}$ channels**, preventing potassium efflux. 2. This causes **depolarization** of the cell membrane. 3. Depolarization opens **voltage-gated $Ca^{2+}$ channels**, leading to calcium influx. 4. Increased intracellular calcium triggers the **exocytosis of insulin** granules. **Analysis of Incorrect Options:** * **Option A & B:** These are the primary mechanisms of **Biguanides (Metformin)**. Metformin activates AMPK, which decreases hepatic gluconeogenesis (output) and improves insulin sensitivity in peripheral tissues (skeletal muscle). Sulfonylureas primarily focus on insulin release, not sensitivity. * **Option D:** This describes the mechanism of **Thiazolidinediones (TZDs)** like Pioglitazone. TZDs act as ligands for the **PPAR-$\gamma$** nuclear receptor, which modulates the transcription of genes involved in lipid and glucose metabolism. **High-Yield NEET-PG Pearls:** * **Site of Action:** Sulfonylureas require functional beta cells; hence, they are ineffective in Type 1 Diabetes. * **Side Effects:** The most common side effect is **hypoglycemia**, and the most notorious for causing prolonged hypoglycemia is **Chlorpropamide** (1st Gen). **Weight gain** is also a significant side effect. * **Safety:** **Glipizide** is preferred in patients with renal impairment as it is primarily metabolized by the liver. * **Disulfiram-like reaction:** Classically associated with first-generation sulfonylureas (Chlorpropamide).

Q: Which of the following decreases thyroid hormone on a long-term basis?

I131. **Explanation:** The correct answer is **I131 (Radioactive Iodine)**. **Mechanism of Action:** I131 is the isotope of choice for treating hyperthyroidism (Graves' disease) and thyroid carcinoma. It is orally administered and rapidly trapped by the thyroid gland. It emits **beta particles**, which have a short penetration range (0.5–2 mm). This results in the selective pyknosis and necrosis of follicular cells, followed by fibrosis. Unlike antithyroid drugs (like Carbimazole), which only inhibit hormone synthesis, I131 causes **permanent destruction** of the thyroid parenchyma, leading to a long-term, irreversible decrease in thyroid hormone levels. **Analysis of Incorrect Options:** * **A. T4 (Levothyroxine):** This is exogenous thyroid hormone used for replacement therapy. Administering T4 increases systemic thyroid hormone levels; it does not decrease them. * **C. Calcitriol:** This is the active form of Vitamin D (1,25-dihydroxyvitamin D3). It regulates calcium and phosphate homeostasis but has no direct inhibitory effect on the synthesis or release of thyroid hormones (T3/T4). * **D. Fluorouracil (5-FU):** This is a pyrimidine analogue used as a cytotoxic chemotherapy agent. While it affects rapidly dividing cells, it is not used to modulate thyroid function. **High-Yield Clinical Pearls for NEET-PG:** * **Wolff-Chaikoff Effect:** A transient decrease in thyroid hormone levels caused by high doses of *stable* iodine (Lugol's iodine), usually lasting only 10–14 days. * **Contraindication:** I131 is strictly **contraindicated in pregnancy** (crosses the placenta and destroys the fetal thyroid) and during breastfeeding. * **Side Effect:** The most common long-term complication of I131 therapy is **hypothyroidism**, requiring lifelong T4 supplementation. * **Monitoring:** The clinical response to I131 is slow, taking 2–3 months for full effect.

Q: Administration of all the following will provide uterine relaxation, except?

Nitrous oxide. **Explanation:** The goal of uterine relaxation (tocolysis) is essential in clinical scenarios such as breech extraction, manual removal of the placenta, or uterine inversion. **Why Nitrous Oxide (N₂O) is the correct answer:** Nitrous oxide is an inhalational analgesic (often used as Entonox, a 50:50 mix with oxygen). Unlike potent volatile anesthetic agents, **Nitrous oxide does not affect uterine muscle tone** or contractility. It provides effective analgesia during labor without causing uterine relaxation or increasing the risk of postpartum hemorrhage (PPH). **Analysis of incorrect options:** * **Sevoflurane:** High concentrations of volatile halogenated inhalational anesthetics (like Sevoflurane, Halothane, and Isoflurane) cause dose-dependent relaxation of the myometrium by inhibiting calcium influx. * **Nitroglycerine (NTG):** A potent smooth muscle relaxant and nitric oxide donor. In obstetrics, IV or sublingual NTG is a first-line agent for rapid, short-acting uterine relaxation (e.g., for retained placenta). * **Terbutaline:** A $\beta_2$-adrenergic agonist that increases intracellular cAMP, leading to the inhibition of myosin light-chain kinase and subsequent uterine relaxation. It is commonly used as a tocolytic to delay preterm labor. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of choice for rapid uterine relaxation:** Nitroglycerine (due to its short half-life and rapid onset). * **Inhalational agents:** Halothane is the most potent uterine relaxant among older gases, but Sevoflurane is more commonly used in modern practice. * **PPH Risk:** Because volatile anesthetics cause uterine atony, they must be discontinued immediately after delivery to allow the uterus to contract and prevent PPH. * **Magnesium Sulfate:** Another common tocolytic that acts as a calcium antagonist.

Question 1

What is the advantage of desmopressin over vasopressin in the treatment of diabetes insipidus?

Accepted Answer

Is more selective for V2 receptor subtype

Answer

Causes less formation of factor VIII

Answer

Causes less hypernatremia

Answer

Provides greater relief of excessive thirst the patient is experiencing

Question 2

Bisphosphonates are used for which of the following conditions, EXCEPT?

Accepted Answer

Osteosclerosis

Answer

Osteolytic bone metastases

Answer

Osteoporosis

Answer

Paget's disease

Question 3

Which antiprogestin is used for emergency contraception?

Accepted Answer

Mifepristone

Answer

Misoprostal

Answer

Methotrexate

Answer

Norethisterone

Question 4

Meglitinide analogues act by which mechanism?

Accepted Answer

Increasing insulin release

Answer

Decreasing glucagon release

Answer

Decreasing intestinal absorption of glucose

Answer

Promoting peripheral utilization of glucose

Question 5

Which of the following statements regarding the mechanism of action of sulfonylureas is true?

Accepted Answer

Act on SUR1 receptors on the pancreatic beta cell membrane

Answer

Increase peripheral utilization of glucose

Answer

Reduce hepatic glucose output

Answer

Increase transcription of genes regulating glucose metabolism

Question 6

Which of the following antibiotic can be used in SIADH?

Accepted Answer

Demeclocycline

Answer

Doxycycline

Answer

Minocycline

Answer

Tigecycline

Question 7

Which of the following decreases thyroid hormone on a long-term basis?

Accepted Answer

I131

Answer

T4

Answer

Calcitriol

Answer

Fluorouracil

Question 8

Which of the following drugs is most likely to cause hypoglycemia when used as a monotherapy in the treatment of type 2 diabetes?

Accepted Answer

Glipizide

Answer

Acarbose

Answer

Metformin

Answer

Rosiglitazone

Question 9

Administration of all the following will provide uterine relaxation, except?

Accepted Answer

Nitrous oxide

Answer

Sevoflurane

Answer

Nitroglycerine

Answer

Terbutaline

Question 10

Which of the following drugs promotes the release of endogenous insulin?

Accepted Answer

Glipizide

Answer

Acarbose

Answer

Metformin

Answer

Pioglitazone

Endocrine Pharmacology — MCQs

Endocrine Pharmacology — MCQs

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