Endocrine Pharmacology — MCQs

Endocrine Pharmacology Indian Medical PG Practice Questions and MCQs

Question 331: What is the plasma half-life of carbimazole?

A. 4 hours
B. 8 hours (Correct Answer)
C. 16 hours
D. 24 hours

Explanation: **Explanation:** **Carbimazole** is a prodrug used in the treatment of hyperthyroidism. After oral administration, it is rapidly and almost completely converted to its active metabolite, **methimazole**. 1. **Why Option B is correct:** The plasma half-life ($t_{1/2}$) of carbimazole (via its active form, methimazole) is approximately **6 to 10 hours**, with **8 hours** being the standard representative value cited in major pharmacological texts (like Goodman & Gilman and K.D. Tripathi). Despite this relatively short plasma half-life, the drug has a long duration of action because it is actively concentrated in the thyroid gland. 2. **Why other options are incorrect:** * **Option A (4 hours):** This is too short for carbimazole/methimazole. However, it is closer to the half-life of **Propylthiouracil (PTU)**, which is approximately 1.5 to 2 hours. * **Options C & D (16–24 hours):** These values far exceed the actual plasma clearance rate of the drug. While the *clinical effect* may last 24 hours (allowing for once-daily dosing), the *plasma concentration* drops much sooner. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Inhibits the enzyme **peroxidase**, thereby blocking the iodination of tyrosine residues and the coupling of iodotyrosines. * **Potency:** Carbimazole/Methimazole is roughly **10 times more potent** than Propylthiouracil. * **Teratogenicity:** Methimazole is associated with **Aplasia Cutis** (scalp defects) and choanal atresia. Therefore, **PTU is preferred in the 1st trimester** of pregnancy, while Methimazole/Carbimazole is preferred in the 2nd and 3rd trimesters. * **Side Effects:** The most serious (though rare) side effect is **agranulocytosis**, usually occurring within the first few months of therapy.

Question 332: Which of the following does not cause hypoglycemia?

A. Insulin
B. Glimepiride
C. Metformin (Correct Answer)
D. Gliclazide

Explanation: ### Explanation The correct answer is **C. Metformin**. **1. Why Metformin is the correct answer:** Metformin belongs to the **Biguanide** class of oral hypoglycemic agents. Its primary mechanism of action is to decrease hepatic glucose production (gluconeogenesis) and improve peripheral insulin sensitivity. Crucially, Metformin is an **euglycemic** agent; it does not stimulate the pancreas to release insulin (it is not an insulin secretagogue). Therefore, when used as monotherapy, it does not cause hypoglycemia because it does not increase circulating insulin levels beyond physiological needs. **2. Why the other options are incorrect:** * **A. Insulin:** This is the most potent glucose-lowering agent. It directly promotes glucose uptake into cells and inhibits glucose production. An overdose or mismatched timing with meals leads to direct hypoglycemia. * **B. Glimepiride & D. Gliclazide:** These are **Sulfonylureas** (2nd and 3rd generation, respectively). They act by closing ATP-sensitive K+ channels in pancreatic beta cells, leading to depolarization and **stimulated insulin release** regardless of blood glucose levels. This "forced" insulin secretion is a major cause of drug-induced hypoglycemia. **3. NEET-PG High-Yield Pearls:** * **"Euglycemics":** Besides Metformin, **Thiazolidinediones (Pioglitazone)** and **DPP-4 inhibitors (Sitagliptin)** have a low risk of hypoglycemia when used alone. * **Metformin Side Effects:** The most common side effects are GI-related (diarrhea, abdominal pain). The most serious, though rare, is **Lactic Acidosis**. It is contraindicated in patients with significant renal impairment (eGFR <30 mL/min). * **Drug of Choice:** Metformin remains the first-line drug for Type 2 Diabetes Mellitus due to its weight-neutrality and cardiovascular safety.

Question 333: All of the following agents act through nuclear receptors EXCEPT?

A. Thyroxine
B. Rosiglitazone
C. Prednisolone (Correct Answer)
D. Estrogen

Explanation: **Explanation:** The question asks for the agent that does **not** act through a nuclear receptor. While all options listed are lipid-soluble hormones or drugs that act on intracellular receptors, there is a specific distinction in their localization. **1. Why Prednisolone is the correct answer:** Glucocorticoids like **Prednisolone** act on the **Glucocorticoid Receptor (GR)**, which is a **Cytoplasmic receptor** (Type I Nuclear Receptor subfamily) [2]. In its inactive state, the GR is bound to Heat Shock Proteins (HSP-90) in the cytoplasm [3]. Upon ligand binding, the receptor dissociates from HSPs, dimerizes, and translocates into the nucleus to modulate gene transcription [2]. Therefore, strictly speaking, its primary location is the cytoplasm, not the nucleus. **2. Why the other options are incorrect:** * **Thyroxine (T4):** Acts on Thyroid Hormone Receptors (TR) which are **constitutively located in the nucleus**, bound to DNA even in the absence of a ligand [4]. * **Rosiglitazone:** This is a Thiazolidinedione (TZD) that acts on **PPAR-gamma** (Peroxisome Proliferator-Activated Receptor gamma), which is a **nuclear receptor** [1]. * **Estrogen:** Acts on Estrogen Receptors (ER). Unlike glucocorticoid receptors, ERs are primarily **located in the nucleus** (Type II) even before the hormone binds. **High-Yield Clinical Pearls for NEET-PG:** * **Cytoplasmic Receptors:** Remember the mnemonic **"VAG"** — **V**itamin D (can be both, but often grouped here), **A**ldosterone (Mineralocorticoids), and **G**lucocorticoids. * **Nuclear Receptors:** Remember **"RET"** — **R**etinoic acid, **E**strogen/Progesterone, and **T**hyroid hormone (T3/T4). * **Mechanism:** All these receptors act as **ligand-activated transcription factors**, leading to a lag period in action (hours to days) and a persistent effect even after the drug is cleared.

Question 334: Which of the following drugs does NOT produce gynecomastia?

A. Cimetidine
B. Digoxin
C. Cortisol (Correct Answer)
D. Spironolactone

Explanation: Gynecomastia is the benign proliferation of glandular breast tissue in males, typically caused by an imbalance between estrogen and androgen effects [1]. **Why Cortisol is the Correct Answer:** **Cortisol** (Option C) is a glucocorticoid. While chronic excess of glucocorticoids (Cushing’s syndrome) can lead to fat redistribution (pseudogynecomastia), they do **not** cause true glandular proliferation. In fact, glucocorticoids are more likely to cause testicular atrophy and decreased libido rather than gynecomastia. **Why the other options are incorrect:** * **Cimetidine (Option A):** An H2-receptor antagonist that causes gynecomastia via two mechanisms: it acts as a weak anti-androgen (blocks androgen receptors) [2] and inhibits the cytochrome P450-mediated metabolism of estradiol. * **Digoxin (Option B):** It has a steroid-like structure that can bind to estrogen receptors. Chronic use increases estrogen levels and decreases luteinizing hormone (LH), leading to breast enlargement. * **Spironolactone (Option C):** A potassium-sparing diuretic and the most common drug-induced cause of gynecomastia. It acts as an androgen receptor antagonist and inhibits testosterone synthesis [1]. (Note: Eplerenone is a more selective alternative that does not cause this side effect). **NEET-PG High-Yield Pearls:** To remember the common drugs causing gynecomastia, use the mnemonic **"DISCO"**: * **D** – Digoxin * **I** – Isoniazid * **S** – Spironolactone * **C** – Cimetidine / Cyclophosphamide * **O** – Oestrogens / Oral contraceptives **Other notable causes:** Ketoconazole (inhibits steroid synthesis), Finasteride (5-alpha reductase inhibitor), and Marijuana.

Question 335: Sildenafil is used in the treatment of:

A. Sterility
B. Priapism
C. Erectile dysfunction (Correct Answer)
D. Decreased libido

Explanation: **Explanation:** **Sildenafil** is a selective inhibitor of the enzyme **Phosphodiesterase-5 (PDE-5)**. During sexual stimulation, Nitric Oxide (NO) is released, which activates guanylyl cyclase to produce **cyclic Guanosine Monophosphate (cGMP)**. cGMP causes smooth muscle relaxation in the *corpus cavernosum*, leading to increased blood flow and an erection. Sildenafil prevents the breakdown of cGMP by PDE-5, thereby enhancing and prolonging the erectile response. **Analysis of Options:** * **C. Erectile Dysfunction (Correct):** This is the primary clinical indication for Sildenafil. It restores erectile function in men with organic or psychogenic impotence, provided sexual stimulation is present. * **A. Sterility:** Sildenafil affects blood flow and hemodynamics; it does not influence sperm count, motility, or the underlying causes of male/female infertility. * **B. Priapism:** Priapism is a prolonged, painful erection (a medical emergency). Sildenafil can actually *cause* priapism as a side effect; it is never used to treat it. * **D. Decreased Libido:** Libido is governed by hormonal (testosterone) and psychological factors. Sildenafil improves the physical response to arousal but does not increase sexual desire. **High-Yield Clinical Pearls for NEET-PG:** * **Other Indications:** Sildenafil is also FDA-approved for **Pulmonary Arterial Hypertension (PAH)** to reduce pulmonary vascular resistance. * **Contraindication:** It must **never** be co-administered with **Nitrates** (e.g., Nitroglycerin). Both increase cGMP, leading to synergistic vasodilation and life-threatening hypotension. * **Side Effects:** Headache, flushing, and **"Blue-tinted vision" (Cyanopsia)** due to weak inhibition of PDE-6 in the retina. * **Tadalafil:** A related drug with a much longer half-life (approx. 18 hours), often called the "weekend pill."

Question 336: Which of the following is a toxic effect of long-term glucocorticoid administration?

A. Hepatotoxicity
B. Osteoporosis (Correct Answer)
C. Precocious puberty
D. Lupus-like syndrome

Explanation: **Explanation:** **Why Osteoporosis is correct:** Long-term glucocorticoid administration is the most common cause of drug-induced osteoporosis. Steroids induce bone loss through a multi-factorial mechanism: 1. **Decreased Bone Formation:** They inhibit osteoblast proliferation and activity. 2. **Increased Bone Resorption:** They stimulate osteoclast activity by increasing RANK-ligand expression and decreasing Osteoprotegerin (OPG). 3. **Calcium Homeostasis:** They decrease intestinal calcium absorption and increase renal calcium excretion, leading to secondary hyperparathyroidism, which further mobilizes calcium from bones. **Why the other options are incorrect:** * **Hepatotoxicity:** Glucocorticoids are generally not hepatotoxic; in fact, they are often used to treat autoimmune hepatitis. * **Precocious Puberty:** Steroids typically cause **growth retardation** in children (due to premature closure of epiphyses and inhibition of GH) rather than precocious puberty. * **Lupus-like Syndrome:** This is a side effect associated with drugs like Hydralazine, Isoniazid, and Procainamide. Glucocorticoids are actually the mainstay of treatment for Systemic Lupus Erythematosus (SLE). **High-Yield NEET-PG Pearls:** * **Avascular Necrosis (AVN):** The femoral head is the most common site for steroid-induced necrosis. * **Ocular Effects:** Chronic use leads to **Posterior Subcapsular Cataracts** and secondary Open-Angle Glaucoma. * **Metabolic Effects:** Hyperglycemia (Steroid Diabetes), Centripetal Obesity, and Buffalo Hump. * **Prophylaxis:** Patients on long-term steroids should be started on Calcium, Vitamin D, and potentially Bisphosphonates to prevent bone loss.

Question 337: Which of the following disorders is NOT aggravated by corticosteroid therapy?

A. Congenital adrenal hyperplasia (Correct Answer)
B. Diabetes mellitus
C. Hypertension
D. Peptic ulcer

Explanation: The correct answer is **Congenital Adrenal Hyperplasia (CAH)** because corticosteroids are the **treatment of choice** for this condition, rather than a cause of aggravation [1]. **1. Why Congenital Adrenal Hyperplasia (CAH) is the correct answer:** CAH is most commonly caused by a deficiency of the enzyme **21-hydroxylase**, leading to decreased cortisol production. This lack of negative feedback causes an increase in ACTH, which overstimulates the adrenal cortex, leading to hyperplasia and excess androgen production. Exogenous corticosteroids (like hydrocortisone) provide the missing cortisol, restore the negative feedback loop, and **suppress ACTH secretion**, thereby reducing adrenal hyperplasia and androgen excess [1]. **2. Why the other options are incorrect:** * **Diabetes Mellitus:** Corticosteroids are "diabetogenic." They increase gluconeogenesis and decrease peripheral glucose uptake (insulin resistance), leading to hyperglycemia and worsening of glycemic control [3]. * **Hypertension:** Corticosteroids cause sodium and water retention (mineralocorticoid effect) and increase vascular sensitivity to catecholamines, which elevates blood pressure [1]. * **Peptic Ulcer:** Steroids inhibit prostaglandin synthesis (which protects the gastric mucosa) and can mask the symptoms of perforation [3]. When used with NSAIDs, the risk of peptic ulceration increases significantly. **Clinical Pearls for NEET-PG:** * **Cushingoid Side Effects:** Remember the mnemonic **"CUSHINGOID"**: **C**ataracts, **U**lcers, **S**kin thinning, **H**ypertension/Hirsutism, **I**nfections, **N**ecrosis (Avascular necrosis of femoral head), **G**lycosuria, **O**steoporosis, **I**mmunosuppression, and **D**iabetes [3]. * **Drug of Choice:** Hydrocortisone is preferred in CAH because it possesses both glucocorticoid and sufficient mineralocorticoid activity to replace what is missing [2]. * **Growth:** In children with CAH, excessive steroid doses must be avoided as they can cause premature closure of epiphyseal plates, leading to short stature [3].

Question 338: Which drug is used to treat tremors in hyperthyroidism?

A. Adrenaline
B. Propranolol (Correct Answer)
C. Noradrenaline
D. Dopamine

Explanation: **Explanation:** In hyperthyroidism (Thyrotoxicosis), there is an over-expression of beta-adrenergic receptors and increased sensitivity to catecholamines. This leads to symptoms of sympathetic overactivity, such as **tremors, palpitations, tachycardia, and anxiety.** **1. Why Propranolol is the Correct Answer:** Propranolol is a non-selective beta-blocker that effectively antagonizes these beta-receptors, providing rapid symptomatic relief from tremors and tachycardia. Beyond symptom control, Propranolol has a unique advantage: at high doses, it **inhibits the peripheral conversion of T4 (Thyroxine) to the more active T3 (Triiodothyronine)** by inhibiting the enzyme 5'-deiodinase. This makes it the drug of choice for immediate management in thyrotoxic crisis (thyroid storm). **2. Why Incorrect Options are Wrong:** * **Adrenaline & Noradrenaline:** These are catecholamines that stimulate adrenergic receptors. Administering them would worsen the symptoms of hyperthyroidism and could potentially precipitate a fatal cardiac event or thyroid storm. * **Dopamine:** This is a precursor to norepinephrine. It increases heart rate and blood pressure, which would exacerbate the hypermetabolic state of the patient. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice for Thyroid Storm:** Propranolol (for symptoms/T4-T3 conversion) + PTU (to block synthesis and conversion). * **Cardioselective alternatives:** If a patient has co-existing asthma (where Propranolol is contraindicated), cardioselective beta-blockers like **Atenolol or Metoprolol** are used, though they lack the T4-to-T3 conversion inhibitory effect. * **Esmolol:** Used intravenously in emergency settings for rapid heart rate control in thyrotoxicosis due to its ultra-short half-life.

Question 339: Which of the following are oral hypoglycemic agents?

A. Tolbutamide
B. Troglitazone
C. Biguanides
D. All of the above (Correct Answer)

Explanation: Oral hypoglycemic agents (OHAs) are a diverse group of drugs used primarily in the management of Type 2 Diabetes Mellitus to lower blood glucose levels [2]. **Explanation of Options:** * **Tolbutamide (Option A):** This is a **First-generation Sulfonylurea** [2, 3]. It works by stimulating insulin secretion from the pancreatic beta cells by closing ATP-sensitive potassium channels [1]. * **Troglitazone (Option B):** This belongs to the **Thiazolidinedione (TZD)** class. These drugs are PPAR-gamma agonists that primarily act as insulin sensitizers in peripheral tissues (muscle and fat). Note: While Troglitazone was the first TZD, it was withdrawn due to hepatotoxicity, but it remains a classic example of an OHA in pharmacological classification. * **Biguanides (Option C):** This class includes **Metformin**, the first-line drug for Type 2 Diabetes [3]. Biguanides lower glucose primarily by inhibiting hepatic gluconeogenesis and improving peripheral glucose uptake. Since all three options represent different classes of medications administered orally to manage hyperglycemia, **Option D (All of the above)** is correct. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Metformin is the first-line agent for most Type 2 diabetics, especially those who are overweight, as it is weight-neutral and does not cause hypoglycemia. * **Side Effects:** Sulfonylureas are most commonly associated with **hypoglycemia** and weight gain. * **Mechanism Focus:** SGLT-2 inhibitors (e.g., Dapagliflozin) are a newer class of OHAs that act on the proximal tubule of the kidney to induce glucosuria. * **Contraindication:** Metformin is contraindicated in patients with severe renal impairment (eGFR <30 mL/min) due to the risk of **lactic acidosis**.

Question 340: GnRH analogue may be given in all of the following conditions except:

A. Prostate cancer
B. Endometrial cancer (Correct Answer)
C. Uterine fibromyoma
D. Precocious puberty

Explanation: The correct answer is **Endometrial cancer** because GnRH analogues are not a standard or primary treatment for this specific malignancy. Endometrial cancer is primarily managed through surgery, radiation, and progestins (like Medroxyprogesterone acetate), which counteract the effects of estrogen on the endometrium. **Mechanism of Action:** GnRH analogues (e.g., Leuprolide, Goserelin, Nafarelin) act as agonists at the GnRH receptor [2]. While an initial "flare" occurs, **continuous administration** leads to downregulation and desensitization of GnRH receptors in the pituitary [3]. This results in a state of **hypogonadotropic hypogonadism** (chemical castration), effectively lowering LH, FSH, and sex steroids (testosterone and estrogen). **Why other options are incorrect:** * **Prostate cancer:** Since prostate cancer is androgen-dependent, GnRH analogues are a first-line therapy to reduce testosterone levels [1]. * **Uterine fibromyoma:** These are estrogen-dependent tumors. GnRH analogues shrink the fibroids by inducing a hypoestrogenic state, often used pre-operatively to reduce blood loss [1]. * **Precocious Puberty:** GnRH analogues are the treatment of choice for central precocious puberty to suppress the premature activation of the hypothalamic-pituitary-gonadal axis. **NEET-PG High-Yield Pearls:** * **Pulsatile administration** of GnRH is used to treat **Infertility** (stimulates FSH/LH) [2]. * **Continuous administration** is used for **hormone-dependent conditions** (Endometriosis, PCOD, Breast cancer, Prostate cancer) [3]. * **Side Effects:** Hot flashes, loss of libido, and osteoporosis (due to long-term estrogen deficiency). * **Note:** GnRH **antagonists** (e.g., Cetrorelix, Degarelix) are preferred when the initial "testosterone flare" must be avoided [4].

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

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