Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 161: Finasteride acts by blocking which of the following?

A. α-receptors
B. 5–α reductase enzyme (Correct Answer)
C. Androgen receptors
D. β–receptors

Explanation: **Explanation:** **Mechanism of Action:** Finasteride is a competitive and specific inhibitor of the **Type II 5-α reductase enzyme**. This enzyme is responsible for the intracellular conversion of Testosterone into **Dihydrotestosterone (DHT)**, primarily in the prostate gland and hair follicles. DHT is a more potent androgen than testosterone; by blocking its production, Finasteride reduces the size of the prostate and prevents hair follicle miniaturization. **Analysis of Options:** * **Option A (α-receptors):** Drugs like Tamsulosin and Prazosin block α1-receptors. While used for BPH, they act by relaxing smooth muscles in the bladder neck rather than altering hormone levels. * **Option C (Androgen receptors):** Drugs that block androgen receptors are called anti-androgens (e.g., **Flutamide, Bicalutamide, Spironolactone**). Finasteride does not block the receptor; it reduces the concentration of the ligand (DHT). * **Option D (β-receptors):** β-blockers (e.g., Propranolol) are used in cardiovascular conditions and have no role in androgen metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Uses:** Finasteride is FDA-approved for **Benign Prostatic Hyperplasia (BPH)** and **Male Pattern Baldness (Androgenetic Alopecia)**. * **Dosing:** 5 mg/day for BPH; 1 mg/day for Alopecia. * **Dutasteride:** A related drug that inhibits both Type I and Type II 5-α reductase. * **Teratogenicity:** Finasteride is highly teratogenic (Category X). Pregnant women should not even handle crushed tablets, as it can cause hypospadias in a male fetus. * **Side Effects:** Decreased libido, erectile dysfunction, and gynecomastia.

Question 162: Which of the following is NOT a mechanism of action of an oral contraceptive containing a combination of oestrogen-progestin?

A. Inhibition of ovulation
B. A change in the cervical mucus (Correct Answer)
C. Inhibition of motility of the uterine tubes
D. Inhibition of motility of sperm

Explanation: ### Explanation The question asks for the mechanism that is **NOT** a primary action of Combined Oral Contraceptive Pills (COCPs). **Why the correct answer is Option B:** Actually, there is a slight nuance in the question framing. In standard pharmacology (K.D. Tripathi), **all four options** are technically mechanisms of COCPs. However, in the context of NEET-PG and standard MCQ patterns, **Option B (A change in cervical mucus)** and **Option C** are considered the *primary* mechanisms of **Progestin-only pills (POPs)**. If we must select the "least" applicable or the one that doesn't fit the "combination" profile as uniquely as the others: The primary, most potent mechanism of the **Combination** pill is the **Inhibition of Ovulation** via negative feedback on the HPO axis. While COCPs *do* change cervical mucus (making it thick and hostile), this is the secondary mechanism. *Note: If this question is from a specific recall where B is marked correct, it implies that the examiner considers cervical mucus changes as the hallmark of Progestin-only methods rather than the synergistic effect of the combination.* **Analysis of Options:** * **A. Inhibition of Ovulation:** This is the **main** mechanism of COCPs. Estrogen inhibits FSH (preventing follicular development), and Progestin inhibits the LH surge (preventing ovulation). * **C. Inhibition of motility of the uterine tubes:** Progestins decrease the rhythmic contractions and ciliary activity of the fallopian tubes, hindering the transport of the ovum/zygote. * **D. Inhibition of motility of sperm:** The progestin component renders the endometrium out of sync and the tubal environment hostile, indirectly affecting sperm migration and capacitation. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Mechanism of COCP:** Inhibition of Ovulation (Negative feedback on FSH/LH). * **Primary Mechanism of POP (Mini-pill):** Making cervical mucus thick and viscous (preventing sperm penetration). * **Primary Mechanism of IUCD (Copper-T):** Creating a sterile inflammatory response in the endometrium (spermicidal). * **Primary Mechanism of LNG-IUD (Mirena):** Endometrial atrophy and cervical mucus thickening. * **Estrogen Component:** Usually Ethinylestradiol (20–35 µg). * **Non-contraceptive benefits of COCPs:** Reduced risk of Ovarian and Endometrial cancers (Protective effect).

Question 163: All of the following agents are useful in acromegaly EXCEPT:

A. Bromocriptine
B. Somatostatin
C. Octreotide
D. Nafarelin (Correct Answer)

Explanation: **Explanation:** Acromegaly is caused by the excessive secretion of **Growth Hormone (GH)**, usually due to a pituitary adenoma. Management focuses on inhibiting GH release or blocking its action. **Why Nafarelin is the correct answer:** Nafarelin is a **GnRH (Gonadotropin-Releasing Hormone) agonist**. While continuous administration of GnRH agonists suppresses the pituitary-gonadal axis (useful in precocious puberty, endometriosis, and prostate cancer), it has **no therapeutic role** in suppressing Growth Hormone. Therefore, it is ineffective in treating acromegaly. **Analysis of Incorrect Options:** * **Bromocriptine:** This is a **Dopamine (D2) agonist**. While dopamine normally stimulates GH in healthy individuals, it paradoxically inhibits GH release from the pituitary tumor in patients with acromegaly [2]. * **Somatostatin:** This is the endogenous **Growth Hormone Inhibiting Hormone (GHIH)**. It directly inhibits the secretion of GH from the anterior pituitary [1]. * **Octreotide:** This is a potent, long-acting **synthetic analog of Somatostatin** [1]. It is the preferred medical treatment for acromegaly because it has a longer half-life and is more effective than natural somatostatin [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (Medical):** Somatostatin analogs like **Octreotide** or **Lanreotide** [1]. * **GH Receptor Antagonist:** **Pegvisomant** is used for resistant cases; it blocks the peripheral action of GH rather than its secretion [2]. * **Dopamine Agonists:** **Cabergoline** is generally preferred over Bromocriptine due to better efficacy and fewer side effects [2]. * **Side Effects of Octreotide:** Steatorrhea and **cholelithiasis** (gallstones) due to inhibition of cholecystokinin (CCK) and gallbladder contractility [3].

Question 164: Which oral hypoglycemic agent is known to cause cholestatic jaundice?

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

Explanation: **Explanation:** **Chlorpropamide**, a first-generation sulfonylurea, is the correct answer. While all sulfonylureas can potentially cause hepatic dysfunction, Chlorpropamide is classically associated with **cholestatic jaundice** as an idiosyncratic reaction. This occurs due to hypersensitivity leading to bile stasis within the canaliculi. **Why Chlorpropamide is the correct choice:** Chlorpropamide has a long half-life (approx. 32 hours) and is notorious for specific side effects not commonly seen with newer generations. Beyond cholestatic jaundice, it is famous for causing a **Disulfiram-like reaction** with alcohol and **SIADH** (Syndrome of Inappropriate Antidiuretic Hormone), leading to dilutional hyponatremia. **Analysis of Incorrect Options:** * **A. Tolbutamide:** A first-generation sulfonylurea with a very short half-life. While it can cause skin rashes or GI upset, it is significantly less associated with cholestatic jaundice compared to Chlorpropamide. * **B & C. Glibenclamide and Glipizide:** These are second-generation sulfonylureas. They are more potent and generally have a better safety profile regarding idiosyncratic hepatic reactions. Their primary side effect is hypoglycemia (especially Glibenclamide due to active metabolites). **NEET-PG High-Yield Pearls:** 1. **Chlorpropamide Mnemonic (The 3 Cs):** **C**holestatic jaundice, **C**hlorpropamide-alcohol flush (Disulfiram-like), and **C**oncentrated urine (SIADH). 2. **Safety in Elderly:** Chlorpropamide is generally avoided in the elderly due to the prolonged risk of hypoglycemia and hyponatremia. 3. **Renal Failure:** Most sulfonylureas are avoided in renal impairment; however, **Gliquidone** is primarily excreted in bile and is safer, while **Glipizide** is also preferred over Glibenclamide.

Question 165: All of the following are rare but life-threatening adverse effects of thioamide group of anti-thyroid drugs except?

A. Agranulocytosis
B. Aplastic anemia
C. Liver toxicity
D. Lung fibrosis (Correct Answer)

Explanation: **Explanation:** Thioamides (Propylthiouracil and Methimazole/Carbimazole) are the mainstay of medical management for hyperthyroidism. While generally well-tolerated, they are associated with specific rare but severe idiosyncratic reactions. **Why Lung Fibrosis is the Correct Answer:** **Lung fibrosis** is not an adverse effect associated with thioamides. It is a classic high-yield side effect of other drugs like **Amiodarone** (an anti-arrhythmic that can cause thyroid dysfunction), **Bleomycin**, and **Busulfan**. **Analysis of Incorrect Options:** * **Agranulocytosis (A):** This is the most feared life-threatening complication (incidence 0.1–0.5%). It usually occurs within the first 3 months of therapy. Patients are strictly advised to report immediately if they develop a sore throat or fever. * **Aplastic Anemia (B):** Though extremely rare, thioamides can cause bone marrow suppression leading to pancytopenia/aplastic anemia. * **Liver Toxicity (C):** Both drugs are hepatotoxic but manifest differently. **Propylthiouracil (PTU)** is associated with severe **fulminant hepatic failure** (Black Box Warning), whereas **Methimazole** more commonly causes **cholestatic jaundice**. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Methimazole is preferred due to its longer half-life and lower risk of liver failure, except in specific scenarios. * **Pregnancy:** **PTU** is the drug of choice in the **1st trimester** (less teratogenic; Methimazole causes *Aplasia Cutis*). **Methimazole** is preferred in the **2nd and 3rd trimesters** to avoid PTU-induced maternal hepatotoxicity. * **Thyroid Storm:** PTU is preferred because it also inhibits the peripheral conversion of T4 to T3. * **ANCA-associated vasculitis** is another rare, life-threatening side effect specifically linked to PTU.

Question 166: Which of the following drugs does NOT cause thyroid dysfunction?

A. Amiodarone
B. Lithium
C. Cholestyramine
D. Paracetamol (Correct Answer)

Explanation: **Explanation:** **Paracetamol (Acetaminophen)** is the correct answer because it is a centrally acting analgesic and antipyretic that has no significant interaction with the hypothalamic-pituitary-thyroid axis or thyroid hormone metabolism. It does not interfere with iodine uptake, hormone synthesis, or peripheral conversion. **Why the other options are incorrect:** * **Amiodarone:** This iodine-rich antiarrhythmic frequently causes thyroid dysfunction. It can lead to **hypothyroidism** (Wolff-Chaikoff effect) or **hyperthyroidism** (Jod-Basedow phenomenon or destructive thyroiditis). It also inhibits the peripheral conversion of T4 to T3. * **Lithium:** Used in bipolar disorder, lithium inhibits the release of thyroid hormones from the gland. It is a well-known cause of **drug-induced hypothyroidism** and goiter. * **Cholestyramine:** This bile acid sequestrant binds to thyroid hormones in the gastrointestinal tract, interfering with their enterohepatic circulation and significantly **reducing the absorption** of oral levothyroxine. **High-Yield Clinical Pearls for NEET-PG:** * **Wolff-Chaikoff Effect:** Autoregulation where high iodine levels (e.g., from Amiodarone) inhibit thyroid hormone synthesis. * **Drugs inhibiting T4 to T3 conversion:** Propranolol, Glucocorticoids, Amiodarone, and Propylthiouracil (PTU). * **Phenytoin/Carbamazepine:** These induce hepatic enzymes (CYP450), increasing the metabolism of T4 and potentially necessitating higher doses of levothyroxine. * **Amiodarone Content:** Each 200mg tablet contains approximately 75mg of organic iodine.

Question 167: Which type of insulin is used to manage a case of diabetic ketoacidosis?

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

Explanation: **Explanation:** In the management of **Diabetic Ketoacidosis (DKA)**, the primary goal is to suppress ketogenesis and normalize blood glucose levels. **Regular (Soluble) Insulin** is the gold standard and the only insulin formulation recommended for **intravenous (IV) administration** in DKA. **Why Regular Insulin is Correct:** Regular insulin is a short-acting insulin that, when given intravenously, has an immediate onset of action and a very short half-life (approx. 5–10 minutes). This allows for precise, minute-to-minute titration via a continuous infusion pump, which is essential to prevent rapid shifts in osmolarity and to manage the dynamic metabolic state of a DKA patient. **Why Other Options are Incorrect:** * **Lispro and Aspart (Options B & D):** These are ultra-short-acting insulin analogs. While they can be used subcutaneously in mild DKA, they are not the standard for IV management in acute, severe cases. They are more expensive than Regular insulin without providing additional benefits in an IV setting. * **Glargine (Option C):** This is a long-acting, peakless insulin analog used for basal coverage. It has a slow onset and is never used for the acute management of DKA because its effects cannot be quickly reversed if hypoglycemia occurs. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Choice:** IV bolus followed by continuous IV infusion (0.1 units/kg/hr) is the preferred protocol. * **The "Switch":** Transition from IV Regular insulin to subcutaneous insulin only when the **anion gap has closed**, the patient is conscious, and is able to tolerate oral intake. * **Potassium Warning:** Always check potassium levels before starting insulin; insulin shifts $K^+$ into cells, potentially worsening hypokalemia. * **Bicarbonate:** Not routinely used unless pH is < 6.9.

Question 168: All of the following drugs are useful in nephrogenic diabetes insipidus, except?

A. Amiloride
B. Indomethacin
C. Chlorpropamide (Correct Answer)
D. Thiazide diuretics

Explanation: **Explanation:** **Nephrogenic Diabetes Insipidus (NDI)** occurs when the kidneys are unresponsive to Antidiuretic Hormone (ADH). Therefore, drugs that work by enhancing ADH action or mimicking it are ineffective. **Why Chlorpropamide is the Correct Answer:** Chlorpropamide is a first-generation sulfonylurea used in **Central Diabetes Insipidus**. It works by sensitizing the renal tubules to the action of ADH and increasing ADH release from the posterior pituitary. Since the fundamental defect in NDI is renal resistance to ADH, chlorpropamide has no therapeutic effect in this condition. **Analysis of Incorrect Options:** * **Thiazide Diuretics (e.g., Hydrochlorothiazide):** Paradoxically used in NDI. They cause mild hypovolemia, leading to increased proximal tubule reabsorption of salt and water, which reduces the volume of filtrate delivered to the distal nephron, thereby decreasing urine output. * **Amiloride:** This is the **drug of choice for Lithium-induced NDI**. It blocks the Epithelial Sodium Channels (ENaC) in the collecting duct, preventing lithium from entering the cells and exerting its toxic effects. * **Indomethacin:** NSAIDs inhibit prostaglandin synthesis. Since prostaglandins (PGE2) normally antagonize ADH action, inhibiting them enhances water reabsorption and reduces renal blood flow, decreasing urine volume. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Central DI:** Desmopressin (dDAVP). * **Drug of Choice for NDI (General):** Thiazides. * **Drug of Choice for Lithium-induced NDI:** Amiloride. * **Most common cause of NDI in adults:** Lithium therapy. * **Most common cause of NDI in children:** X-linked recessive mutation in the V2 receptor.

Question 169: Use of Ergotamine is contraindicated in which of the following conditions?

A. Diabetes mellitus
B. Anemia
C. Ischaemic heart disease (Correct Answer)
D. Postpartum hemorrhage

Explanation: ### Explanation **Correct Answer: C. Ischaemic heart disease** **Mechanism and Rationale:** Ergotamine is an ergot alkaloid that acts as a partial agonist at **α-adrenergic** and **5-HT (serotonin)** receptors [3]. Its primary therapeutic effect in migraines is mediated through **potent vasoconstriction** of cranial blood vessels [4]. However, this vasoconstriction is non-selective and systemic. In patients with **Ischaemic Heart Disease (IHD)** or peripheral vascular disease, ergotamine can cause significant coronary artery vasospasm, worsening myocardial ischemia and potentially triggering a myocardial infarction [2]. Therefore, it is strictly contraindicated in IHD, uncontrolled hypertension, and Raynaud’s disease [2]. **Analysis of Incorrect Options:** * **A. Diabetes mellitus:** While diabetics often have underlying vascular complications, diabetes itself is not an absolute contraindication unless the patient has documented coronary artery disease or severe peripheral vascular disease. * **B. Anemia:** There is no direct pharmacological interaction or contraindication between ergotamine use and low hemoglobin levels. * **C. Postpartum hemorrhage (PPH):** This is actually an **indication** for certain ergot alkaloids (specifically **Methylergometrine**). Ergot derivatives cause forceful uterine contractions and vasoconstriction, which helps control bleeding after delivery [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Ergotism (St. Anthony’s Fire):** Chronic toxicity characterized by severe peripheral ischemia, gangrene, and hallucinations [3]. * **Drug Interaction:** Ergotamine metabolism is inhibited by **CYP3A4 inhibitors** (e.g., Ritonavir, Erythromycin), which can lead to "Ergotism" even with standard doses. * **Triptans vs. Ergots:** Both are contraindicated in IHD due to coronary vasoconstriction. * **Uterine Effect:** Ergotamine is never used for induction of labor because it causes sustained (tetanic) contractions, which can lead to fetal hypoxia or uterine rupture [1].

Question 170: Which thyroid inhibitor produces the fastest response?

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

Explanation: **Explanation:** The speed of response in treating hyperthyroidism depends on whether the drug inhibits the **synthesis** of new hormones or the **release** of pre-formed hormones. **1. Why Lugol’s Iodine is Correct:** Lugol’s iodine (potassium iodide) acts by inhibiting the **release** of thyroid hormones from the colloid into the circulation. This occurs via the **Wolff-Chaikoff effect**, where high concentrations of iodine acutely suppress thyroid peroxidase and endocytosis of thyroglobulin. Because it acts on pre-formed hormones already stored in the gland, the clinical response is seen within **1–2 days**, making it the fastest-acting agent. **2. Why the Other Options are Incorrect:** * **Propylthiouracil (PTU):** This is an antithyroid drug (thioamide) that inhibits the **synthesis** of new hormones by blocking thyroid peroxidase. It does not affect stored hormones; therefore, it takes **1–3 weeks** to show clinical effects as the existing stores must first be depleted. * **Radioactive Iodine (I-131):** This works by emitting beta particles that destroy thyroid tissue. The process of follicular destruction is slow, usually taking **2–3 months** for full effect. * **Lithium Carbonate:** While lithium can inhibit hormone release (similar to iodine), it is significantly less potent and slower than Lugol's iodine. It is rarely used clinically for this purpose due to its narrow therapeutic index. **NEET-PG High-Yield Pearls:** * **Pre-operative use:** Lugol’s iodine is given 10 days before thyroidectomy to decrease the **vascularity and size** of the gland, making it firm and easier to operate on. * **Escape Phenomenon:** The effect of iodine lasts only for 10–14 days, after which the thyroid "escapes" the inhibition and thyrotoxicosis may worsen. * **Drug of Choice in Pregnancy:** PTU is preferred in the **1st trimester** (due to less teratogenicity), while Methimazole is preferred in the 2nd and 3rd trimesters.

Practice by Chapter

Hypothalamic and Pituitary Hormones

Practice Questions

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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