Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 101: Conversion of T4 to T3 inhibition is associated with which of the following drugs?

A. Propylthiouracil (Correct Answer)
B. Ampicillin
C. Lithium
D. Carbimazole

Explanation: ### Explanation **Correct Option: A (Propylthiouracil)** The synthesis of thyroid hormones involves multiple steps. While both **Propylthiouracil (PTU)** and Carbimazole/Methimazole inhibit the enzyme **thyroid peroxidase**, preventing the iodination of tyrosine residues and the coupling of iodotyrosines, PTU has a unique additional mechanism. It inhibits the enzyme **5’-deiodinase** (Type 1) in peripheral tissues. This enzyme is responsible for converting the less active prohormone **T4 (Thyroxine)** into the more potent **T3 (Triiodothyronine)**. This dual action makes PTU particularly useful in managing severe thyrotoxicosis. **Analysis of Incorrect Options:** * **B. Ampicillin:** An antibiotic that inhibits cell wall synthesis; it has no known effect on thyroid hormone metabolism. * **C. Lithium:** Used in bipolar disorder, Lithium inhibits the **release** of preformed thyroid hormones from the colloid by interfering with thyroglobulin proteolysis. It does not inhibit peripheral conversion. * **D. Carbimazole:** A prodrug converted to Methimazole. While it is more potent than PTU in inhibiting thyroid peroxidase, it **does not** inhibit the peripheral conversion of T4 to T3. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice in Thyroid Storm:** PTU is preferred over Methimazole because it rapidly lowers T3 levels by blocking peripheral conversion. * **Pregnancy:** PTU is the drug of choice in the **1st trimester** (due to lower teratogenic risk/aplasia cutis associated with Methimazole). Methimazole is preferred in the 2nd and 3rd trimesters to avoid PTU-induced hepatotoxicity. * **Other drugs inhibiting T4 to T3 conversion:** Propranolol (high doses), Glucocorticoids (e.g., Dexamethasone), Amiodarone, and Oral Cholecystographic agents (Ipodate).

Question 102: Which of the following has the least mineralocorticoid activity?

A. Aldosterone
B. Cortisol
C. Dexamethasone (Correct Answer)
D. Fludrocortisone

Explanation: **Explanation:** The correct answer is **Dexamethasone**. In pharmacology, corticosteroids are classified based on their relative **glucocorticoid** (anti-inflammatory/metabolic) and **mineralocorticoid** (salt-retaining) potencies. **Dexamethasone** is a long-acting, highly potent synthetic glucocorticoid. It is specifically designed to have maximal anti-inflammatory effects with **zero to negligible mineralocorticoid activity**. This makes it the drug of choice in conditions where fluid retention must be avoided, such as cerebral edema. **Analysis of Incorrect Options:** * **Aldosterone (A):** The primary endogenous mineralocorticoid. It has maximal salt-retaining activity and negligible glucocorticoid effects. * **Cortisol (B):** The primary endogenous glucocorticoid. While it acts on glucocorticoid receptors, it also has significant mineralocorticoid activity (Ratio 1:1). In high concentrations, it can cause significant sodium retention and potassium loss. * **Fludrocortisone (D):** A synthetic steroid with very high mineralocorticoid potency. It is the drug of choice for replacement therapy in Addison’s disease to provide the necessary salt-retaining effect. **NEET-PG High-Yield Pearls:** 1. **Potency Comparison:** Dexamethasone is ~25–30 times more potent than Hydrocortisone (Cortisol) as an anti-inflammatory agent but has **0** mineralocorticoid potency. 2. **Drug of Choice:** For **Congenital Adrenal Hyperplasia (CAH)** in utero, Dexamethasone is used because it is not inactivated by placental 11β-HSD2, allowing it to reach the fetus. 3. **Topical/Inhaled:** Beclomethasone and Budesonide also have negligible systemic mineralocorticoid effects due to high first-pass metabolism or local action. 4. **Shortest Acting:** Hydrocortisone; **Longest Acting:** Dexamethasone/Betamethasone.

Question 103: True about sulfonylureas?

A. Chlorpropamide is a second-generation agent.
B. The most common side effect is hypoglycemia. (Correct Answer)
C. Effective even after pancreatectomy.
D. Safe in pregnancy.

Explanation: **Explanation:** **1. Why Option B is Correct:** Sulfonylureas (SUs) are "insulin secretagogues." They work by binding to the **SUR1 subunit** of the ATP-sensitive K⁺ channels on pancreatic beta cells. This leads to channel closure, cell depolarization, calcium influx, and the subsequent release of pre-formed insulin. Because this insulin release is **independent of blood glucose levels**, it can persist even when glucose is low, making **hypoglycemia** the most common and clinically significant side effect. **2. Why the Other Options are Incorrect:** * **Option A:** Chlorpropamide, along with Tolbutamide, belongs to the **First-generation** sulfonylureas. Second-generation agents include Glibenclamide (Glyburide), Glipizide, and Gliclazide. * **Option C:** Sulfonylureas require **functional pancreatic beta cells** to work. Since their mechanism involves stimulating the pancreas to release insulin, they are completely ineffective in patients who have undergone a pancreatectomy or those with Type 1 Diabetes. * **Option D:** Sulfonylureas are generally **avoided in pregnancy** as they can cross the placenta and cause fetal hyperinsulinemia and neonatal hypoglycemia. **Insulin** remains the drug of choice for gestational diabetes (though Metformin and Glibenclamide are sometimes used in specific guidelines, they are not the "standard" for safety). **High-Yield Clinical Pearls for NEET-PG:** * **Disulfiram-like reaction:** Most commonly associated with **Chlorpropamide** when taken with alcohol. * **SIADH:** Chlorpropamide can cause water retention and hyponatremia. * **Weight Gain:** A common side effect of SUs (unlike Metformin). * **Glimepiride:** Often classified as a third-generation SU; it has the lowest risk of hypoglycemia among this class.

Question 104: A 26-year-old man with a 10-month history of ileal Crohn's disease, treated with several drugs, now presents with muscle weakness, centripetal obesity, and a plethoric face. These side effects are most likely associated with the long-term use of which of the following medications?

A. Azathioprine
B. Cyclosporine
C. Olsalazine
D. Prednisone (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Prednisone** The patient is presenting with classic features of **Iatrogenic Cushing’s Syndrome** (centripetal obesity, plethoric face, and muscle weakness/proximal myopathy) [1], [2], [3]. Prednisone is a potent glucocorticoid frequently used to induce remission in moderate-to-severe Crohn’s disease [3]. Long-term use leads to: * **Fat Redistribution:** Centripetal obesity, "moon face" (plethora), and "buffalo hump" [1], [3]. * **Protein Catabolism:** Leading to muscle wasting (weakness) and skin thinning [1], [2]. * **Metabolic Effects:** Hyperglycemia and osteoporosis [1]. **Analysis of Incorrect Options:** * **A. Azathioprine:** An immunosuppressant (thiopurine) used for maintaining remission in Crohn’s. Its primary side effects are **bone marrow suppression** (leukopenia) and pancreatitis, not cushingoid features. * **B. Cyclosporine:** A calcineurin inhibitor. While it can cause gingival hyperplasia and hirsutism, it typically presents with **nephrotoxicity, hypertension, and tremors** rather than centripetal obesity. * **C. Olsalazine:** A 5-aminosalicylate (5-ASA) prodrug. It acts locally in the colon and is mainly associated with **secretory diarrhea** and hypersensitivity reactions; it lacks systemic endocrine side effects. **NEET-PG High-Yield Pearls:** * **Steroid-Induced Myopathy:** Characterized by proximal muscle weakness; it is a "painless" myopathy, unlike inflammatory myositis [1], [2]. * **Withdrawal Caution:** Long-term prednisone causes HPA-axis suppression. Abrupt withdrawal can lead to life-threatening **Acute Adrenal Insufficiency** [3]. * **Drug of Choice:** For Crohn’s limited to the ileum/right colon with fewer systemic effects, **Budesonide** is preferred due to high first-pass metabolism.

Question 105: Which of the following is not true regarding carbimazole?

A. Safely used in pregnancy (Correct Answer)
B. More potent than propylthiouracil
C. Single daily dose administration
D. Does not inhibit peripheral conversion of T-4 to T-3

Explanation: **Explanation:** **Carbimazole** is a prodrug rapidly converted to **methimazole** in the body [1]. It belongs to the thioamide class of anti-thyroid drugs used to treat hyperthyroidism. **1. Why Option A is the correct answer (Not True):** Carbimazole is **not** considered safe in the first trimester of pregnancy. It is a known teratogen associated with specific fetal malformations, most notably **Aplasia Cutis** (congenital skin defects, usually on the scalp) and **Choanal Atresia**. Therefore, **Propylthiouracil (PTU)** is the drug of choice during the first trimester because it is more highly protein-bound and crosses the placenta less readily [1], [2]. **2. Analysis of Incorrect Options (True Statements):** * **Option B:** Carbimazole/Methimazole is approximately **10 times more potent** than PTU, requiring a lower milligram dose to achieve the same effect [1]. * **Option C:** It has a longer duration of action (half-life of ~6 hours vs. 1.5 hours for PTU) and accumulates in the thyroid gland, allowing for **once-daily dosing**, which improves patient compliance [1], [2]. * **Option D:** Unlike PTU, carbimazole **does not inhibit the peripheral conversion** of T4 to T3. It primarily acts by inhibiting the enzyme thyroid peroxidase, preventing iodine organification and coupling. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Methimazole/Carbimazole is the DOC for Graves' disease in non-pregnant adults and children due to lower hepatotoxicity and better compliance [1]. * **Thyroid Storm:** PTU is preferred in thyroid storm because it uniquely inhibits peripheral T4 to T3 conversion. * **Adverse Effect:** The most serious (though rare) side effect of thioamides is **agranulocytosis**; patients should be warned to report a sore throat or fever immediately.

Question 106: Which of the following is an amylin analog?

A. Sitagliptin
B. Liraglutide
C. Nateglinide
D. Pramlintide (Correct Answer)

Explanation: **Explanation:** **Pramlintide** is the correct answer as it is a synthetic analog of **Amylin** (Islet Amyloid Polypeptide). Amylin is a hormone co-secreted with insulin from pancreatic beta cells. It works by slowing gastric emptying, suppressing postprandial glucagon secretion, and increasing satiety. Pramlintide is unique because it is the only non-insulin antidiabetic drug approved for use in both **Type 1 and Type 2 Diabetes Mellitus**, typically administered via subcutaneous injection before meals. **Analysis of Incorrect Options:** * **A. Sitagliptin:** This is a **DPP-4 inhibitor** (Gliptin) [1]. It works by preventing the breakdown of endogenous incretins (GLP-1 and GIP), thereby increasing insulin secretion and decreasing glucagon levels in a glucose-dependent manner [1]. * **B. Liraglutide:** This is a **GLP-1 Receptor Agonist** (Incretin mimetic) [2]. While it shares some effects with amylin (like slowed gastric emptying), it acts specifically on the GLP-1 receptor [2]. * **C. Nateglinide:** This is a **Meglitinide** (Glinide) [3]. It is a short-acting insulin secretagogue that closes ATP-sensitive potassium channels in pancreatic beta cells, similar to sulfonylureas but with a faster onset [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Pramlintide reduces postprandial glucose excursions without causing hypoglycemia (unless used with insulin). * **Side Effects:** The most common side effect is **nausea**. * **Contraindication:** It is contraindicated in patients with **gastroparesis** due to its effect on slowing gastric motility. * **Dosing Tip:** When starting pramlintide, the dose of rapid-acting or premixed insulin should be reduced by 50% to avoid severe hypoglycemia.

Question 107: Which of the following is a human insulin analog?

A. Lispro (Correct Answer)
B. Regular
C. NPH insulin
D. Lente insulin

Explanation: **Explanation:** Insulin analogs are modified forms of human insulin created using recombinant DNA technology. By altering the amino acid sequence, the pharmacokinetic profile (onset and duration of action) is changed to better mimic physiological insulin secretion. **1. Why Lispro is correct:** **Insulin Lispro** is a **rapid-acting insulin analog**. It is created by reversing the penultimate amino acids on the B-chain (Proline at B28 and Lysine at B27). This modification prevents the formation of hexamers, allowing the insulin to dissociate rapidly into monomers upon subcutaneous injection. This results in a very quick onset (5–15 mins) and a short duration of action, making it ideal for postprandial glucose control. **2. Why the other options are incorrect:** * **Regular Insulin:** This is short-acting **human insulin** (not an analog). It exists as hexamers in solution, requiring 30–60 minutes to dissociate into absorbable monomers. * **NPH (Neutral Protamine Hagedorn):** This is an **intermediate-acting human insulin**. It is a suspension of regular insulin complexed with protamine and zinc to delay absorption. * **Lente Insulin:** This is an intermediate-acting **bovine or porcine insulin** (now largely obsolete). It is a mixture of amorphous and crystalline insulin with zinc. **High-Yield NEET-PG Pearls:** * **Rapid-acting analogs:** Lispro, Aspart, Glulisine (Mnemonic: **L**ive **A**s **G**od). * **Long-acting (Basal) analogs:** Glargine (peakless), Detemir, Degludec (longest half-life). * **Clinical Use:** Rapid-acting analogs have a lower risk of postprandial hypoglycemia compared to Regular insulin because their action profile more closely matches the glucose spike from a meal.

Question 108: Which of the following is a selective estrogen receptor modulator (SERM)?

A. Danazol
B. Mifepristone
C. Raloxifene (Correct Answer)
D. Dantrolene

Explanation: **Explanation:** **Raloxifene** is the correct answer because it belongs to the class of **Selective Estrogen Receptor Modulators (SERMs)**. SERMs are unique compounds that exert tissue-specific effects: they act as estrogen agonists in some tissues (e.g., bone) and antagonists in others (e.g., breast and endometrium). Raloxifene specifically increases bone mineral density (agonist) while reducing the risk of breast cancer (antagonist). Unlike Tamoxifen, Raloxifene is an antagonist in the uterus, meaning it does not increase the risk of endometrial carcinoma. **Analysis of Incorrect Options:** * **Danazol (A):** An androgen derivative that inhibits gonadotropin release. It is primarily used in endometriosis and hereditary angioedema. * **Mifepristone (B):** A potent progesterone receptor antagonist (and glucocorticoid antagonist) used for medical abortion and Cushing’s syndrome. * **Dantrolene (D):** A direct-acting skeletal muscle relaxant that inhibits calcium release from the sarcoplasmic reticulum. It is the drug of choice for **Malignant Hyperthermia**. **High-Yield Clinical Pearls for NEET-PG:** * **Raloxifene** is the preferred SERM for the prevention and treatment of **postmenopausal osteoporosis**, especially in women at high risk of breast cancer. * **Tamoxifen** (another SERM) is the drug of choice for ER-positive breast cancer but carries a risk of **endometrial hyperplasia/cancer** (agonist at the uterus). * Common side effects of SERMs include **hot flashes** and an increased risk of **venous thromboembolism (VTE)**.

Question 109: Long-acting insulin preparations are typically administered by which route?

A. Oral route
B. Intramuscular route
C. Intradermal route
D. Subcutaneous route (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Subcutaneous route** **Why it is correct:** Insulin is a polypeptide hormone; if given orally, it would be degraded by gastrointestinal enzymes (proteolysis). The **subcutaneous (SC) route** is the standard for long-acting insulins (e.g., Glargine, Detemir, Degludec) because it allows for the formation of a "depot" in the fatty tissue. From this depot, the insulin is slowly and predictably absorbed into the systemic circulation, providing a basal level of insulin that mimics physiological secretion. **Why incorrect options are wrong:** * **Oral route:** As mentioned, insulin is a protein and is inactivated by gastric acid and digestive enzymes (pepsin/trypsin), making it bioavailably zero. * **Intramuscular (IM) route:** While insulin can be absorbed via IM, it is not preferred for long-acting preparations because muscle blood flow is highly variable (e.g., during exercise), leading to unpredictable absorption rates and a higher risk of sudden hypoglycemia. * **Intradermal route:** This route has a very limited volume capacity and is generally used for sensitivity testing or certain vaccines, not for therapeutic hormone replacement. **High-Yield Clinical Pearls for NEET-PG:** * **IV Route:** Only **Regular (Soluble) Insulin** and rapid-acting analogues (in specific emergencies) are given intravenously. Long-acting insulins are **NEVER** given IV as they are formulated to precipitate or hexamerize, which could cause embolic issues or unpredictable kinetics. * **Site of Absorption:** Absorption is fastest from the **Abdomen**, followed by the arms, thighs, and buttocks. * **Lipodystrophy:** Rotating injection sites is crucial to prevent lipohypertrophy, which can impair insulin absorption. * **Longest Acting:** **Insulin Degludec** has the longest duration of action (>42 hours) due to the formation of multi-hexamers in the SC tissue.

Question 110: All of the following are true regarding chlorpropamide except?

A. It is short-acting (Correct Answer)
B. It can cause hypoglycemia in the elderly
C. Causes weight gain
D. Associated with alcoholic flush

Explanation: **Explanation:** Chlorpropamide is a **first-generation sulfonylurea** used in the management of Type 2 Diabetes Mellitus. **1. Why Option A is the Correct Answer (The Exception):** Chlorpropamide is actually the **longest-acting sulfonylurea**, not short-acting. It has an exceptionally long half-life of approximately **32 to 36 hours**, and its duration of action can extend up to 60 hours. This is due to its high protein binding and slow hepatic metabolism. **2. Analysis of Other Options:** * **Option B (Hypoglycemia in elderly):** Because of its long half-life and renal excretion, chlorpropamide carries a very high risk of **prolonged hypoglycemia**, especially in elderly patients with declining renal function. It is generally avoided in this population. * **Option C (Weight gain):** Like all sulfonylureas, chlorpropamide stimulates insulin release (an anabolic hormone), which typically leads to weight gain as a common side effect. * **Option D (Alcoholic flush):** Chlorpropamide is notorious for causing a **Disulfiram-like reaction** (facial flushing, tachycardia) when consumed with alcohol. It inhibits hepatic aldehyde dehydrogenase, leading to acetaldehyde accumulation. **High-Yield Clinical Pearls for NEET-PG:** * **SIADH:** Chlorpropamide is unique among sulfonylureas because it increases the action of ADH on renal tubules, potentially causing **dilutional hyponatremia** (SIADH-like effect). * **Mechanism:** It acts by closing ATP-sensitive K⁺ channels in pancreatic beta cells, leading to depolarization and insulin release. * **Safety:** Due to the risks of severe hypoglycemia and water retention, it has largely been replaced by second-generation sulfonylureas (e.g., Glipizide, Gliclazide) in modern practice.

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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