Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 601: Which of the following drugs can enhance the action of sulfonylureas?

A. Salicylates
B. Diazoxide (Correct Answer)
C. Propranolol
D. Cimetidine

Explanation: ### Explanation The question asks which drug **enhances** the action of sulfonylureas (potentiates hypoglycemia). However, there is a common clinical distinction to be made between drugs that increase sulfonylurea levels and those that counteract their effect. **Correct Answer Analysis: Diazoxide** *Note: In the context of standard pharmacology, Diazoxide actually **antagonizes** the effect of sulfonylureas.* Diazoxide is a K⁺ channel opener that hyperpolarizes pancreatic beta cells, inhibiting insulin release. It is used to treat hypoglycemia in insulinoma. If this option is marked correct in a specific question bank, it is often a "reverse logic" trap or a typographical error in the source, as Diazoxide is the physiological antagonist. **However, if we look at drugs that truly enhance/potentiate sulfonylureas:** * **Salicylates (Option A):** These are the classic potentiators. They displace sulfonylureas from plasma protein binding sites and exert their own hypoglycemic effect by increasing glucose utilization. * **Cimetidine (Option D):** This is a microsomal enzyme inhibitor that decreases the metabolism of sulfonylureas, leading to increased plasma levels and enhanced action. **Why the other options are typically considered differently:** * **Propranolol (Option C):** While beta-blockers can prolong hypoglycemia by inhibiting glycogenolysis, their most dangerous clinical interaction is **masking the sympathetic warning signs** (tachycardia, tremors) of hypoglycemia. * **Diazoxide (Option B):** As stated, this drug inhibits insulin secretion and is used to *reverse* sulfonylurea-induced hypoglycemia. **NEET-PG High-Yield Pearls:** 1. **Protein Displacement:** Salicylates, Sulfonamides, and Warfarin displace sulfonylureas from albumin, increasing the free (active) fraction. 2. **Enzyme Inhibition:** Cimetidine and Ketoconazole increase sulfonylurea toxicity by inhibiting CYP enzymes. 3. **The "Disulfiram-like" Reaction:** First-generation sulfonylureas (especially Chlorpropamide) cause flushing when taken with alcohol. 4. **Mechanism:** Sulfonylureas act by closing ATP-sensitive K⁺ channels, leading to depolarization and insulin release. Diazoxide does the exact opposite (opens the channel).

Question 602: Which antidiabetic drug acts independently of insulin?

A. SGLT2 inhibitor (Correct Answer)
B. DPP4 inhibitor
C. Meglitinide analogues
D. GLP1 agonist

Explanation: The correct answer is **A. SGLT2 inhibitor** (e.g., Dapagliflozin, Empagliflozin). **Mechanism of Action:** SGLT2 inhibitors act on the proximal convoluted tubule (PCT) of the kidney to inhibit the Sodium-Glucose Co-transporter 2. This prevents the reabsorption of filtered glucose, leading to **glycosuria** (excretion of glucose in the urine). Because this process depends entirely on the renal filtration of glucose and not on pancreatic function or peripheral insulin sensitivity, it is considered **insulin-independent**. This makes them effective even in patients with long-standing Type 2 Diabetes who have significant beta-cell exhaustion. **Why the other options are incorrect:** * **B. DPP4 inhibitors** (e.g., Sitagliptin) and **D. GLP1 agonists** (e.g., Liraglutide) are incretin-based therapies. They work by stimulating the pancreas to release insulin in a glucose-dependent manner [2]. * **C. Meglitinide analogues** (e.g., Repaglinide) are insulin secretagogues [1]. They close ATP-sensitive K+ channels in pancreatic beta cells, directly triggering insulin release [1], [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Weight Loss & BP:** SGLT2 inhibitors promote weight loss (due to calorie loss via glucose) and lower blood pressure (due to osmotic diuresis). * **Cardio-Renal Protection:** They are the drugs of choice for diabetic patients with **Heart Failure** (reduced HFrEF) and **Chronic Kidney Disease (CKD)**. * **Side Effects:** The most characteristic side effects are **Genital Mycotic Infections** (due to high urinary glucose) and a rare risk of **Euglycemic Ketoacidosis**.

Question 603: Which drug is useful in neuronal diabetes insipidus in both children and adults when given intranasally?

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

Explanation: **Explanation:** **Desmopressin (DDAVP)** is the drug of choice for Central (Neuronal) Diabetes Insipidus (DI). It is a synthetic analog of Arginine Vasopressin (AVP) with two key modifications: deamination of cysteine and substitution of L-arginine with D-arginine. These changes result in a **selective V2 receptor agonist** action with minimal V1 (vasoconstrictor) activity. Its long duration of action (8–20 hours) and availability in an intranasal formulation make it ideal for long-term management in both children and adults. **Analysis of Incorrect Options:** * **Vasopressin (A):** This is the natural hormone. It acts on both V1 and V2 receptors, leading to significant side effects like vasoconstriction, abdominal cramps, and hypertension. It also has a very short half-life (approx. 20 minutes), making it impractical for chronic DI management. * **Lypressin (C):** A synthetic lysine-vasopressin formerly used intranasally. However, it has a shorter duration of action and more pressor (V1) side effects compared to Desmopressin, rendering it obsolete. * **Presselin (D):** This is not a standard pharmacological agent used in the treatment of Diabetes Insipidus. **NEET-PG High-Yield Pearls:** * **V2 Selectivity:** Desmopressin has a V2:V1 selectivity ratio of approximately 4000:1. * **Other Uses of Desmopressin:** Nocturnal enuresis (bedwetting), von Willebrand Disease (Type I), and Hemophilia A (as it releases Factor VIII and vWF from endothelial storage sites). * **Route of Choice:** While intranasal is common, the **oral** route is increasingly preferred for convenience, though it requires a much higher dose due to low bioavailability. * **Side Effect:** The most serious side effect of Desmopressin is **hyponatremia** (water intoxication).

Question 604: All of the following may be used to treat hypercalcemia, except:

A. Normal saline with forced diuresis with thiazide (Correct Answer)
B. Plicamycin
C. Gallium nitrate
D. Mitramycin

Explanation: ### Explanation The correct answer is **A. Normal saline with forced diuresis with thiazide.** #### Why Option A is Correct In the management of hypercalcemia, the goal is to enhance urinary calcium excretion. **Thiazide diuretics** are contraindicated because they **increase renal calcium reabsorption** in the distal convoluted tubule, thereby worsening hypercalcemia. The standard emergency treatment for severe hypercalcemia is **aggressive hydration with Normal Saline (0.9% NaCl)** followed by **Loop diuretics (e.g., Furosemide)**. Loop diuretics inhibit the Na+/K+/2Cl- cotransporter, which abolishes the positive luminal potential required for the paracellular reabsorption of calcium, thus promoting calciuresis. #### Why Other Options are Incorrect * **B & D. Plicamycin (Mithramycin):** These are the same drug. Plicamycin is a cytotoxic antibiotic that inhibits osteoclast activity, effectively lowering serum calcium. While rarely used today due to toxicity, it remains a classic pharmacological option for refractory hypercalcemia. * **C. Gallium Nitrate:** This agent inhibits bone resorption by decreasing the solubility of hydroxyapatite crystals and inhibiting osteoclast activity. It is specifically indicated for cancer-related hypercalcemia. #### NEET-PG High-Yield Pearls * **Drug of Choice (Acute):** Intravenous Normal Saline is the first-line treatment to restore volume and promote calcium excretion. * **Drug of Choice (Malignancy-related):** **Bisphosphonates** (e.g., Zoledronate, Pamidronate) are the preferred long-term agents as they potent inhibitors of osteoclasts. * **Glucocorticoids:** Useful for hypercalcemia caused by Vitamin D toxicity, sarcoidosis, or lymphomas. * **Calcimimetics (Cinacalcet):** Used primarily in secondary hyperparathyroidism (CKD) and parathyroid carcinoma. * **Mnemonic:** **"Thiazides Thrive on Calcium"** (they keep it in the blood), while **"Loops Lose Calcium"** (they pee it out).

Question 605: A 21-year-old student is diagnosed with hyperthyroidism and is being counselled on treatment options, including radioactive iodine and antithyroid medications. Carbimazole acts on which part of the thyroid hormone synthesis pathway?

A. Cleavage of thyroglobulin by proteolysis
B. Coupling of monoiodotyrosine (MIT) and diiodotyrosine (DIT) forming triiodothyronine (T3) and thyroxine (T4)
C. Dehalogenation of iodinated tyrosine to recycle iodide
D. Organification of iodide by thyroid peroxidase, incorporating it into tyrosine to form MIT and DIT (Correct Answer)

Explanation: **Explanation:** Carbimazole is a prodrug that is rapidly converted to its active form, **Methimazole**, in the body. It belongs to the **Thioamide** class of antithyroid drugs. **1. Why Option D is Correct:** The primary mechanism of action of Thioamides (Carbimazole, Methimazole, and Propylthiouracil) is the inhibition of the enzyme **Thyroid Peroxidase (TPO)**. This enzyme is responsible for two critical steps in thyroid hormone synthesis: * **Organification:** The oxidation of iodide to iodine and its subsequent attachment to tyrosine residues on thyroglobulin to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT). * **Coupling:** The joining of MIT and DIT to form T3 and T4. While Carbimazole inhibits both, the inhibition of **organification** is the initial and most significant step blocked. **2. Why Other Options are Incorrect:** * **Option A:** Proteolysis of thyroglobulin is inhibited by **High-dose Iodides** (e.g., Lugol’s iodine, Potassium iodide), which prevents the release of stored hormones. * **Option B:** While Carbimazole does inhibit coupling, Option D is the more fundamental step in the synthesis pathway targeted by TPO inhibition. * **Option C:** Dehalogenation is an intracellular recycling process; its inhibition is not the mechanism of action for standard antithyroid drugs. **NEET-PG High-Yield Pearls:** * **Propylthiouracil (PTU)** has an additional mechanism: it inhibits the **peripheral conversion of T4 to T3** (via 5’-deiodinase), making it preferred in **Thyroid Storm**. * **Drug of Choice:** Methimazole/Carbimazole is generally preferred over PTU due to longer half-life and lower risk of hepatotoxicity, except in the **first trimester of pregnancy** (where PTU is used to avoid Methimazole-induced embryopathy like *Aplasia Cutis*). * **Side Effect:** The most serious (though rare) side effect of Thioamides is **Agranulocytosis**.

Question 606: Conversion of T4 to T3 is inhibited by all except:

A. Propranolol
B. Propylthiouracil
C. Amiodarone
D. Methimazole (Correct Answer)

Explanation: **Explanation:** The conversion of Thyroxine (T4) to the more biologically active Triiodothyronine (T3) occurs in peripheral tissues via the enzyme **5’-deiodinase**. Inhibiting this enzyme is a crucial therapeutic strategy in managing severe thyrotoxicosis or thyroid storm. **Why Methimazole is the correct answer:** Methimazole (and its prodrug Carbimazole) acts solely by inhibiting the enzyme **thyroid peroxidase**, thereby preventing iodine organification and coupling within the thyroid gland. Unlike Propylthiouracil (PTU), Methimazole has **no effect** on the peripheral conversion of T4 to T3. **Why the other options are incorrect:** * **Propylthiouracil (PTU):** Unlike Methimazole, PTU has a dual mechanism. It inhibits thyroid peroxidase and also inhibits **5’-deiodinase**, making it the preferred thioamide in thyroid storms. * **Propranolol:** Beyond its beta-blocking effects, high doses of Propranolol inhibit peripheral T4 to T3 conversion. This makes it uniquely useful in treating the peripheral symptoms of hyperthyroidism. * **Amiodarone:** This iodine-rich antiarrhythmic inhibits 5’-deiodinase. It can cause hypothyroidism (Wolff-Chaikoff effect) or hyperthyroidism (Jod-Basedow phenomenon). * **Glucocorticoids (e.g., Dexamethasone):** Though not listed, these also inhibit peripheral conversion and are used in thyroid storm management. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice (DOC):** Methimazole is the DOC for hyperthyroidism due to its longer half-life and lower hepatotoxicity, except in the **first trimester of pregnancy** (where PTU is preferred due to Methimazole’s association with *Aplasia Cutis*). 2. **Thyroid Storm Management:** Remember the mnemonic **"P-P-S-G"** for drugs that inhibit peripheral conversion: **P**ropylthiouracil, **P**ropranolol, **S**odium Ipodate (contrast media), and **G**lucocorticoids. 3. **Amiodarone** contains approximately 37% iodine by weight, leading to its complex effects on thyroid function.

Question 607: What is the mechanism of action of Rosiglitazone?

A. Acts as a PPAR gamma agonist (Correct Answer)
B. Inhibitor of alpha glucosidase
C. Acts as an amylin analogue
D. Acts as a dipeptidyl peptidase inhibitor

Explanation: **Explanation:** **Mechanism of Action (Correct Answer: A)** Rosiglitazone belongs to the **Thiazolidinedione (TZD)** class of oral hypoglycemic agents. Its primary mechanism is the activation of **Peroxisome Proliferator-Activated Receptor-gamma (PPAR-γ)**, a nuclear receptor found predominantly in adipose tissue, muscle, and liver. Activation of PPAR-γ leads to the transcription of genes involved in glucose and lipid metabolism. This results in increased expression of **GLUT-4** transporters and decreased release of free fatty acids, thereby **reducing insulin resistance** (insulin sensitizer). **Analysis of Incorrect Options:** * **B. Inhibitor of alpha-glucosidase:** This describes **Acarbose** and **Voglibose**, which act in the intestinal brush border to delay carbohydrate absorption, reducing postprandial glucose spikes. * **C. Amylin analogue:** This refers to **Pramlintide**, a synthetic analogue of amylin that slows gastric emptying and suppresses glucagon secretion. * **D. Dipeptidyl peptidase-4 (DPP-4) inhibitor:** This describes the **"Gliptins"** (e.g., Sitagliptin), which prevent the breakdown of endogenous incretins like GLP-1. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** TZDs are primarily **insulin sensitizers**; they do not increase insulin secretion. * **Side Effects:** Weight gain and **fluid retention/edema** are common. They are strictly **contraindicated in NYHA Class III/IV Heart Failure**. * **Bone Health:** Long-term use is associated with an increased risk of **osteoporotic fractures** (especially in women). * **Metabolic Effect:** Unlike Pioglitazone (which also affects PPAR-α), Rosiglitazone has a less favorable lipid profile (may increase LDL).

Question 608: What is the effect of adding progesterone to estrogens?

A. Decrease the estrogen action on the breast
B. Decrease the occurrence of endometrial cancers (Correct Answer)
C. Increase the effectiveness of the estrogens
D. Inhibit bone resorption

Explanation: ### Explanation The correct answer is **B. Decrease the occurrence of endometrial cancers.** #### 1. Why the Correct Answer is Right Estrogen, when administered alone (unopposed estrogen therapy), stimulates the proliferation of the endometrial lining. Chronic, unopposed stimulation can lead to **endometrial hyperplasia**, which significantly increases the risk of **endometrial carcinoma**. Progesterone acts as a physiological antagonist to estrogen in the uterus; it converts the proliferative endometrium into a secretory one and induces "down-regulation" of estrogen receptors [1]. Therefore, in women with an intact uterus, progesterone is mandatory in Hormone Replacement Therapy (HRT) to neutralize the mitogenic effects of estrogen and prevent malignancy [2]. #### 2. Why the Other Options are Wrong * **A. Decrease the estrogen action on the breast:** Unlike the uterus, progesterone does not protect the breast. In fact, large clinical trials (like the WHI study) suggest that the addition of progestins to estrogen may slightly **increase** the risk of breast cancer compared to estrogen alone [1]. * **C. Increase the effectiveness of the estrogens:** Progesterone does not enhance the primary metabolic or endocrine efficacy of estrogen; it is added specifically for its protective effect on the endometrium [1]. * **D. Inhibit bone resorption:** While both estrogen and progesterone contribute to bone health, the primary hormone responsible for inhibiting osteoclast activity and preventing bone resorption in HRT is **estrogen**. Progesterone is not added for this specific purpose. #### 3. NEET-PG High-Yield Pearls * **HRT Rule:** If the patient has a **uterus**, use Estrogen + Progesterone. If the patient has had a **hysterectomy**, use Estrogen alone (ET). * **Selective Estrogen Receptor Modulators (SERMs):** Remember **Tamoxifen** acts as an antagonist in the breast but an **agonist** in the uterus (increasing cancer risk), whereas **Raloxifene** is an antagonist in both the breast and uterus (no increased cancer risk). * **Most common side effect of HRT:** Irregular breakthrough bleeding. * **Major Contraindication for HRT:** Undiagnosed vaginal bleeding, history of DVT/PE, and estrogen-dependent tumors.

Question 609: Which of the following is NOT useful for acute hypercalcemia?

A. Normal saline
B. Calcitonin
C. Furosemide (Correct Answer)
D. Bisphosphonates

Explanation: ### Explanation **Correct Option: C. Furosemide** **Why Furosemide is the correct answer:** Traditionally, loop diuretics like furosemide were used to treat hypercalcemia because they inhibit the Na⁺-K⁺-2Cl⁻ symporter, which abolishes the positive luminal potential required for calcium reabsorption. However, **current clinical guidelines (AHA/Endocrine Society) no longer recommend furosemide** for acute hypercalcemia unless the patient is in fluid overload or heart failure. This is because furosemide can worsen dehydration—the primary complication of hypercalcemia—and may lead to electrolyte imbalances without significantly lowering calcium levels compared to aggressive hydration alone. **Analysis of Incorrect Options:** * **A. Normal Saline:** This is the **first-line treatment**. It restores intravascular volume and promotes "calciuresis" by increasing the glomerular filtration rate and inhibiting proximal tubular sodium/calcium reabsorption. * **B. Calcitonin:** Used for **rapid reduction** of calcium. It works within hours by inhibiting osteoclast activity and increasing renal excretion. However, its effect is short-lived due to tachyphylaxis (receptor downregulation). * **D. Bisphosphonates (e.g., Zoledronate, Pamidronate):** These are the **most effective long-term agents** for hypercalcemia of malignancy. They potentally inhibit osteoclast-mediated bone resorption, though they take 48–72 hours to reach peak effect. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypercalcemia Rx:** "Hydrate (Saline), Hibernate (Bisphosphonates), and Hurry (Calcitonin)." * **Glucocorticoids:** Useful specifically for hypercalcemia caused by Vitamin D toxicity, sarcoidosis, or lymphomas. * **Cinacalcet:** A calcimimetic used for secondary hyperparathyroidism in CKD. * **Denosumab:** A RANKL inhibitor used when bisphosphonates are contraindicated (e.g., severe renal impairment).

Question 610: Which of the following is a long-acting insulin?

A. Insulin glargine (Correct Answer)
B. Insulin lispro
C. Insulin aspart
D. Insulin glulisine

Explanation: ### Explanation Insulin preparations are classified based on their onset and duration of action. Understanding these kinetics is crucial for NEET-PG, as it forms the basis of "Basal-Bolus" therapy. **Correct Answer: A. Insulin glargine** Insulin glargine is a **long-acting (basal) insulin analog**. It is designed with a shifted isoelectric point (by substituting asparagine with glycine and adding two arginines), making it soluble at an acidic pH but poorly soluble at the neutral pH of subcutaneous tissue. Upon injection, it forms micro-precipitates that release insulin slowly over 24 hours. It is often called "peakless" insulin because it provides a steady background level of insulin, mimicking physiological basal secretion. **Incorrect Options:** * **B, C, and D (Lispro, Aspart, Glulisine):** These are **Rapid-acting insulin analogs**. They are designed to dissociate rapidly into monomers after subcutaneous injection, leading to a quick onset (15 mins) and short duration (3–5 hours). They are used as "prandial" or "bolus" insulin to control post-prandial glucose spikes. **High-Yield Clinical Pearls for NEET-PG:** * **Ultra-long acting:** Insulin **Degludec** has the longest half-life (>40 hours) due to the formation of multi-hexamers. * **Intermediate-acting:** **NPH (Isophane)** insulin has a "cloudy" appearance and a duration of 12–18 hours. * **Safety:** Glargine should **not** be mixed in the same syringe with other insulins, as its acidic pH (4.0) can cause the other insulins to precipitate. * **Inhaled Insulin:** Afrezza is a rapid-acting dry powder formulation.

Practice by Chapter

Hypothalamic and Pituitary Hormones

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Thyroid Drugs and Antithyroid Agents

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Insulin and Oral Hypoglycemic Agents

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Adrenocorticosteroids

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Sex Hormones: Estrogens and Progestins

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Androgens and Anabolic Steroids

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Hormonal Contraceptives

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Drugs Affecting Calcium Metabolism

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Drugs for Osteoporosis

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Pharmacological Management of Obesity

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