Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 381: Bisphosphonate-induced osteomalacia is commonly seen with which of the following drugs?

A. Alendronate
B. Pamidronate
C. Zolendronate
D. Etidronate (Correct Answer)

Explanation: **Explanation:** **1. Why Etidronate is the Correct Answer:** Etidronate is a **first-generation (non-nitrogenous)** bisphosphonate. Unlike newer agents, it lacks a nitrogen side chain and has a unique pharmacological profile. Its primary drawback is that it **non-selectively inhibits the mineralization of osteoid** (bone matrix) at therapeutic doses used to inhibit bone resorption. When mineralization is impaired while the organic matrix continues to form, it leads to **osteomalacia**. To minimize this risk clinically, Etidronate is often administered in a "cyclic" manner (e.g., 2 weeks on, 10-12 weeks off). **2. Why Other Options are Incorrect:** * **Alendronate (Option A), Pamidronate (Option B), and Zoledronate (Option C):** These are **second and third-generation (nitrogen-containing)** bisphosphonates. They are significantly more potent (100 to 10,000 times) in inhibiting osteoclast-mediated bone resorption compared to Etidronate. Crucially, at clinical doses, they do not interfere with bone mineralization. Therefore, they do not cause osteomalacia. **3. NEET-PG High-Yield Pearls:** * **Mechanism of Action:** Nitrogenous bisphosphonates (Alendronate, Zoledronate) inhibit the enzyme **Farnesyl Pyrophosphate (FPP) Synthase** in the mevalonate pathway, leading to osteoclast apoptosis. * **Osteonecrosis of the Jaw (ONJ):** This is a more common side effect of high-dose intravenous bisphosphonates (like Zoledronate) rather than Etidronate. * **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**. * **Drug of Choice:** Zoledronate is the most potent bisphosphonate and the drug of choice for malignancy-associated hypercalcemia.

Question 382: All of the following reduce T4 absorption except:

A. Metformin (Correct Answer)
B. Iron salts
C. Raloxifene
D. Colesevelam

Explanation: **Explanation:** The absorption of **Levothyroxine (T4)** occurs primarily in the duodenum and jejunum and is highly sensitive to the presence of food, gastric pH, and concomitant medications. **Why Metformin is the correct answer:** Metformin does **not** interfere with the gastrointestinal absorption of T4. Instead, Metformin is known for a unique pharmacodynamic effect: it can cause **suppression of TSH levels** in hypothyroid patients without altering free T4 or T3 levels. The mechanism is thought to involve enhanced central dopaminergic tone or direct effects on the thyrotrophs in the pituitary, but it does not reduce the bioavailability of exogenous thyroxine. **Why the other options are incorrect:** * **Iron salts (B):** Ferrous sulfate and other iron supplements form insoluble complexes with thyroxine in the gut, significantly reducing its absorption. * **Raloxifene (C):** This Selective Estrogen Receptor Modulator (SERM) has been shown to malabsorb T4, likely through competitive binding or interference with the intestinal transport mechanism. * **Colesevelam (D):** As a bile acid sequestrant, it binds to thyroxine in the gastrointestinal tract, preventing its absorption. Other resins like Cholestyramine act similarly. **High-Yield Clinical Pearls for NEET-PG:** * **Administration Rule:** T4 should be taken on an **empty stomach** (30–60 minutes before breakfast) to ensure maximum absorption. * **Other drugs reducing T4 absorption:** Calcium carbonate, Proton Pump Inhibitors (PPIs - due to increased gastric pH), Aluminum hydroxide, and Sucralfate. * **Estrogen Effect:** Oral estrogens increase **Thyroxine-Binding Globulin (TBG)**, necessitating an increase in the T4 dose in hypothyroid women starting HRT or OCPs.

Question 383: What is the mechanism of action of sulfonylureas?

A. Stimulation of insulin release (Correct Answer)
B. Alpha-glucosidase inhibition
C. PPAR-gamma inhibition
D. Insulin sensitization

Explanation: **Explanation:** **Mechanism of Action (Option A):** Sulfonylureas (e.g., Glibenclamide, Glimepiride) are **insulin secretagogues**. They act by binding to the **Sulfonylurea Receptor-1 (SUR1)** subunit of the ATP-sensitive potassium ($K_{ATP}$) channels located on the pancreatic $\beta$-cell membrane. This binding leads to: 1. **Closure of $K_{ATP}$ channels**, preventing potassium efflux. 2. **Depolarization** of the $\beta$-cell membrane. 3. Opening of **voltage-gated $Ca^{2+}$ channels**, leading to calcium influx. 4. **Exocytosis** of insulin-containing granules into the bloodstream. **Analysis of Incorrect Options:** * **B. Alpha-glucosidase inhibition:** This is the mechanism of **Acarbose and Miglitol**, which delay carbohydrate absorption in the gut. * **C. PPAR-gamma inhibition:** This is incorrect. Thiazolidinediones (TZDs) are actually **PPAR-gamma agonists** (activators), not inhibitors. * **D. Insulin sensitization:** This describes the primary action of **Metformin** (Biguanides) and **Pioglitazone** (TZDs), which improve peripheral glucose uptake rather than stimulating insulin secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Prerequisite:** Sulfonylureas require functional $\beta$-cells to work; they are ineffective in Type 1 Diabetes. * **Side Effects:** The most common and serious side effect is **hypoglycemia**. Weight gain is also frequently observed. * **First-generation vs. Second-generation:** First-gen drugs (e.g., Tolbutamide) are rarely used now due to lower potency and higher side effects. * **Disulfiram-like reaction:** Classically associated with **Chlorpropamide**. * **Safety:** **Glipizide** is preferred in patients with mild-to-moderate renal impairment as it is primarily metabolized by the liver.

Question 384: Epalrestat is an?

A. Aldolasereductase inhibitor (Correct Answer)
B. Fructose cogener
C. Glucose receptor blocker
D. Glucose reuptake activator

Explanation: **Explanation:** **Epalrestat** is a specific, reversible inhibitor of the enzyme **Aldose Reductase**. **Mechanism of Action:** In states of chronic hyperglycemia (Diabetes Mellitus), the normal glycolytic pathway becomes saturated. Excess glucose is then shunted to the **Polyol Pathway**, where Aldose Reductase converts glucose into **sorbitol**. Sorbitol is polar, does not easily cross cell membranes, and accumulates intracellularly. This leads to osmotic stress, oxidative damage, and decreased nerve conduction velocity. By inhibiting Aldose Reductase, Epalrestat prevents sorbitol accumulation, thereby delaying the progression of **diabetic peripheral neuropathy**. **Analysis of Incorrect Options:** * **Option B (Fructose congener):** Fructose is the end-product of the polyol pathway (sorbitol is converted to fructose by sorbitol dehydrogenase). Epalrestat does not mimic fructose; it prevents its precursor's formation. * **Option C & D (Glucose receptor/reuptake):** Epalrestat does not significantly affect systemic blood glucose levels, insulin receptors, or SGLT transporters. Its action is localized to preventing end-organ damage rather than glycemic control. **Clinical Pearls for NEET-PG:** * **Indication:** Primarily used for the improvement of subjective neuropathy symptoms (numbness, pain) and abnormal vibratory sensation. * **Metabolism:** It is primarily metabolized by the liver; hence, caution is advised in patients with hepatic impairment. * **Side Effects:** Common side effects include elevation of liver enzymes (ALT/AST), nausea, and abdominal pain. * **High-Yield Fact:** While many Aldose Reductase Inhibitors (like Alrestatin or Sorbinil) failed clinical trials due to toxicity, Epalrestat is clinically approved and widely used in countries like India and Japan.

Question 385: What is the most common side effect of Dapagliflozin?

A. Glycosuria
B. Weight loss
C. Fatigue
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Dapagliflozin** is a selective inhibitor of the **Sodium-Glucose Co-transporter 2 (SGLT2)** located in the proximal convoluted tubule of the kidney. By inhibiting this transporter, the drug prevents the reabsorption of filtered glucose, leading to its excretion in the urine. **Why "All of the above" is correct:** The mechanism of action directly leads to the clinical effects listed: 1. **Glycosuria:** This is the primary pharmacodynamic effect. By blocking glucose reabsorption, Dapagliflozin induces significant glucose excretion in the urine. 2. **Weight Loss:** Since glucose is a source of calories (4 kcal/g), the chronic loss of glucose through urine results in a net caloric deficit, leading to modest but consistent weight loss in diabetic patients. 3. **Fatigue:** This can occur as a side effect due to mild volume depletion (osmotic diuresis caused by glycosuria) or as a result of the shift in metabolic substrate utilization. **Clinical Pearls for NEET-PG:** * **Genitourinary Infections:** The most clinically significant side effect to remember is an increased risk of **vulvovaginal candidiasis** and urinary tract infections (UTIs) due to the glucose-rich environment in the urinary tract. * **Euglycemic Ketoacidosis:** A rare but high-yield side effect where patients present with ketoacidosis despite near-normal blood glucose levels. * **Cardiorenal Benefits:** SGLT2 inhibitors are now first-line for patients with Heart Failure (reduced Ejection Fraction) and Chronic Kidney Disease, regardless of diabetic status. * **Contraindication:** They are generally not initiated if the eGFR is <30 mL/min/1.73 m².

Question 386: Which is the longest-acting insulin?

A. Degludec (Correct Answer)
B. Aspart
C. Regular insulin
D. Glargine insulin

Explanation: **Explanation:** **Correct Answer: A. Degludec** Insulin Degludec is currently the longest-acting basal insulin analog available. Its prolonged duration of action (over 42 hours) is due to its unique chemical structure: the deletion of threonine at position B30 and the attachment of a 16-carbon fatty acid chain to lysine at B29. Upon subcutaneous injection, it forms **multi-hexamers**, which result in a slow, continuous release into the circulation. This provides a stable, "peakless" profile with significantly less intra-individual variability compared to other insulins. **Incorrect Options:** * **B. Aspart:** This is a **rapid-acting** insulin analog (onset: 10–20 mins; duration: 3–5 hours). It is used for postprandial glucose control. * **C. Regular Insulin:** This is a **short-acting** insulin. It is the only form that can be given intravenously (IV) and is the drug of choice for Diabetic Ketoacidosis (DKA). Its duration is approximately 5–8 hours. * **D. Glargine:** This is a **long-acting** insulin analog. While it was the standard for basal therapy for years, its duration is roughly 24 hours. Degludec has a significantly longer half-life and duration than Glargine U100. **High-Yield Clinical Pearls for NEET-PG:** * **Ultra-long acting:** Degludec (>42h) > Glargine U300 (>36h) > Glargine U100 (24h) > Detemir (~20h). * **Flexibility:** Due to its long half-life, Degludec allows for more flexibility in dosing timing compared to Glargine. * **Safety:** Degludec is associated with a lower risk of **nocturnal hypoglycemia** compared to NPH or Glargine. * **Afrezza:** The only FDA-approved **inhaled** insulin (rapid-acting); contraindicated in smokers and COPD patients.

Question 387: Which type of insulin is most commonly used in emergency situations such as diabetic ketoacidosis?

A. Lispro
B. Regular (Correct Answer)
C. Aspart
D. Glargine

Explanation: **Explanation:** **Regular Insulin (Short-acting)** is the treatment of choice for medical emergencies like Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS) [3]. The primary reason is its **versatility in administration**: Regular insulin is the only conventional insulin that can be administered **intravenously (IV)** [1], [5]. When given IV, it has an immediate onset of action and a short half-life (approx. 5–10 minutes), allowing clinicians to titrate the dose precisely based on hourly blood glucose monitoring. **Analysis of Incorrect Options:** * **Lispro & Aspart (Rapid-acting):** While these can be used in DKA via subcutaneous pumps [2] or in mild cases, they are generally reserved for prandial (mealtime) glucose control [4]. Their primary advantage is a faster onset than subcutaneous Regular insulin, but they are not the standard for IV emergency protocols. * **Glargine (Long-acting):** This is a "basal" insulin designed to provide a peakless, 24-hour effect. It is contraindicated in acute emergencies because its action cannot be quickly reversed or adjusted, which is essential when managing the rapidly shifting metabolic state of DKA. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Choice:** In DKA, Regular insulin is given as a continuous IV infusion (0.1 units/kg/hr) [3]. * **The "Clear" Rule:** Regular insulin is a clear solution, unlike NPH (Intermediate), which is cloudy. * **Potassium Warning:** Always monitor potassium levels before and during insulin therapy in DKA, as insulin shifts potassium into cells, potentially causing life-threatening hypokalemia [3]. * **Other Uses:** Regular insulin is also used in the emergency management of **Hyperkalemia** (given with IV Dextrose).

Question 388: Metyrapone inhibits which enzyme?

A. 11-beta-hydroxylase (Correct Answer)
B. 21-beta-hydroxylase
C. Both enzymes
D. Neither enzyme

Explanation: **Explanation:** **Metyrapone** is a selective inhibitor of the enzyme **11-beta-hydroxylase** (CYP11B1) [1]. This enzyme is responsible for the final step of cortisol synthesis in the adrenal cortex, converting 11-deoxycortisol into cortisol [1]. 1. **Why Option A is correct:** By inhibiting 11-beta-hydroxylase, Metyrapone significantly reduces cortisol production. This leads to a compensatory increase in ACTH secretion (due to loss of negative feedback), which in turn causes an accumulation of the precursor **11-deoxycortisol** [1]. This precursor is excreted in the urine as 17-hydroxycorticosteroids, making the "Metyrapone test" a diagnostic tool for assessing pituitary ACTH reserve [1]. 2. **Why Options B and C are incorrect:** Metyrapone does not inhibit **21-beta-hydroxylase**. 21-beta-hydroxylase is an enzyme involved in the earlier steps of both the glucocorticoid and mineralocorticoid pathways (converting progesterone to DOC and 17-OH progesterone to 11-deoxycortisol). Deficiency or inhibition of this enzyme is the most common cause of Congenital Adrenal Hyperplasia (CAH), but it is not the target of Metyrapone. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Use:** Metyrapone is primarily used for the medical management of **Cushing’s Syndrome** (especially in pregnant patients, as it is safer than other options) and for testing the Hypothalamic-Pituitary-Adrenal (HPA) axis [1]. * **Side Effects:** Because it shifts steroid precursors toward the androgen pathway, it can cause **hirsutism** and acne in women. It can also cause hypertension due to the accumulation of 11-deoxycorticosterone (DOC), which has mineralocorticoid activity [1]. * **Comparison:** Unlike Ketoconazole (which inhibits multiple CYP enzymes), Metyrapone is relatively selective for the 11-beta-hydroxylation step [1].

Question 389: Which of the following is not used in the management of thyrotoxic crisis?

A. Propranolol
B. Hydrocortisone
C. Oral potassium iodide
D. Levothyroxine (Correct Answer)

Explanation: **Explanation** **Thyrotoxic crisis (Thyroid Storm)** is a life-threatening medical emergency characterized by an extreme hypermetabolic state due to excessive thyroid hormones ($T_3$ and $T_4$). **Why Levothyroxine is the correct answer:** Levothyroxine is **synthetic $T_4$** used for the treatment of hypothyroidism. Administering it during a thyroid storm would be catastrophic, as it would further increase thyroid hormone levels, worsening the tachycardia, hyperthermia, and heart failure associated with the crisis. **Why the other options are used (Management Protocol):** * **Propranolol (Option A):** A non-selective beta-blocker used to control sympathetic overactivity (tachycardia, palpitations, tremors). It also uniquely inhibits the peripheral conversion of $T_4$ to the more active $T_3$. * **Hydrocortisone (Option B):** Corticosteroids are used to treat relative adrenal insufficiency occurring during the stress of a storm and to further inhibit the peripheral conversion of $T_4$ to $T_3$. * **Oral Potassium Iodide (Option C):** Administered to inhibit the release of preformed thyroid hormones from the gland (**Wolff-Chaikoff effect**). *Note: It must be given at least 1 hour after starting antithyroid drugs like Propylthiouracil (PTU) to prevent the iodide from being used as a substrate for new hormone synthesis.* **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Propylthiouracil (PTU)** is preferred over Methimazole in thyroid storm because it inhibits both hormone synthesis and the peripheral conversion of $T_4$ to $T_3$. * **Sequence of Treatment:** Always give PTU/Methimazole *before* Iodine to avoid the "Jod-Basedow" phenomenon. * **Supportive Care:** Aggressive cooling (avoid aspirin as it displaces $T_4$ from binding proteins) and IV fluids are essential.

Question 390: Which of the following antifungal drugs can be used in the treatment of Cushing syndrome?

A. Ketoconazole (Correct Answer)
B. Fluconazole
C. Itraconazole
D. Miconazole

Explanation: **Explanation:** **Ketoconazole** is the correct answer because of its unique ability to inhibit steroidogenesis. While primarily an antifungal, at high doses, it non-selectively inhibits several cytochrome P450 enzymes, most notably **11β-hydroxylase** and **17α-hydroxylase (CYP17)**. This inhibition blocks the synthesis of cortisol in the adrenal cortex, making it a first-line medical therapy for controlling hypercortisolism in patients with Cushing syndrome (especially those awaiting surgery or with ectopic ACTH production). **Why other options are incorrect:** * **Fluconazole, Itraconazole, and Miconazole:** These are newer-generation azoles designed to be more selective for fungal CYP450 enzymes (lanosterol 14α-demethylase). They lack the potent inhibitory effect on human adrenal steroidogenic enzymes seen with Ketoconazole. Therefore, they do not significantly lower systemic cortisol levels and have no role in treating Cushing syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Ketoconazole inhibits the first step of steroid synthesis (cholesterol side-chain cleavage) and subsequent hydroxylase steps. * **Adverse Effects:** Due to its non-selective nature, it also inhibits testosterone synthesis, leading to **gynecomastia** and decreased libido in males. * **Hepatotoxicity:** It is associated with a risk of severe liver injury; hence, LFTs must be monitored. * **Other Adrenal Inhibitors:** Other drugs used in Cushing include **Metyrapone** (selective 11β-hydroxylase inhibitor), **Mitotane** (adrenolytic), and **Pasireotide** (somatostatin analog).

Practice by Chapter

Hypothalamic and Pituitary Hormones

Practice Questions

Thyroid Drugs and Antithyroid Agents

Practice Questions

Insulin and Oral Hypoglycemic Agents

Practice Questions

Adrenocorticosteroids

Practice Questions

Sex Hormones: Estrogens and Progestins

Practice Questions

Androgens and Anabolic Steroids

Practice Questions

Hormonal Contraceptives

Practice Questions

Drugs Affecting Calcium Metabolism

Practice Questions

Drugs for Osteoporosis

Practice Questions

Pharmacological Management of Obesity

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free