Antihistamines in Dermatological Conditions — MCQs
Second-generation cephalosporin that can be used orally is:
Which antiemetic phenothiazine has labyrinthine suppressant activity and is used for vertigo?
The non-sedative antihistamines are all EXCEPT one:
Which of the following drugs can cause hypotension by releasing histamine from mast cells?
A 30-year-old woman is diagnosed with gonorrhea and reports a penicillin allergy (rash). Which alternative treatment regimen is most appropriate?
How do antihistamines help in allergic rhinitis?
Ichthyosis is a side effect of -
A 56-year-old woman has nausea due to chemotherapy for breast cancer. Droperidol is effective in reducing nausea because it blocks which of the following?
What is the optimal wavelength of light emitted by a Wood's lamp for dermatological examinations?
All of the following statements are TRUE about second generation antihistaminic agents EXCEPT:
Antihistamines in Dermatological Conditions Indian Medical PG Practice Questions and MCQs
Question 1: Second-generation cephalosporin that can be used orally is:
- A. Cefepime
- B. Cefalothin
- C. Cefaclor (Correct Answer)
- D. Cefadroxil
Explanation: ***Cefaclor*** - **Cefaclor** is a commonly used **second-generation cephalosporin** that is available in an **oral formulation**, making it suitable for outpatient treatment of various bacterial infections. - Its spectrum of activity includes many Gram-positive and Gram-negative bacteria, often used for **respiratory tract infections** and **otitis media**. *Cefepime* - **Cefepime** is a **fourth-generation cephalosporin**, not a second-generation one, and is primarily administered **intravenously** for severe infections. - It has a broader spectrum against both Gram-positive and Gram-negative bacteria, including **Pseudomonas aeruginosa**. *Cefalothin* - **Cefalothin** (also known as cephalothin) is a **first-generation cephalosporin** that is typically administered **parenterally** (intravenously or intramuscularly). - It is not available in an oral formulation, limiting its use to hospital settings for moderate to severe infections. *Cefadroxil* - **Cefadroxil** is a **first-generation cephalosporin** and is available for oral administration. - While it is an oral cephalosporin, it belongs to the first generation, not the second generation as requested by the question.
Question 2: Which antiemetic phenothiazine has labyrinthine suppressant activity and is used for vertigo?
- A. Prochlorperazine
- B. Promethazine (Correct Answer)
- C. Cinnarizine
- D. Hyoscine
Explanation: ***Promethazine*** - Promethazine is a **phenothiazine derivative** with strong **antihistaminic (H1)** properties, making it highly effective for **labyrinthine suppression** and treatment of vertigo. - It is widely used for **motion sickness, vertigo, and nausea** associated with vestibular disturbances. - Its mechanism combines **dopamine D2 receptor antagonism** (phenothiazine effect) with potent **antihistaminic** and **anticholinergic** actions that specifically suppress vestibular function. - The antihistaminic component is particularly important for labyrinthine suppressant activity. *Prochlorperazine* - While prochlorperazine is a **phenothiazine antiemetic**, it is primarily used for severe nausea and vomiting (migraine, postoperative, chemotherapy-induced). - It has predominantly **dopamine D2 antagonist** activity at the chemoreceptor trigger zone (CTZ) but weaker antihistaminic properties compared to promethazine. - Less commonly used specifically for vertigo compared to promethazine due to weaker vestibular suppressant effects. *Cinnarizine* - While effective for vertigo, cinnarizine is an **antihistamine** and **calcium channel blocker**, not a phenothiazine. - It acts on the **vestibular system** by inhibiting calcium influx into vestibular sensory cells. *Hyoscine* - Hyoscine (**scopolamine**) is an **anticholinergic drug** (not a phenothiazine) effective for motion sickness and some forms of vertigo. - Works by blocking **muscarinic acetylcholine receptors** in the vestibular nuclei.
Question 3: The non-sedative antihistamines are all EXCEPT one:
- A. Cinnarizine (Correct Answer)
- B. Fexofenadine
- C. Levocetirizine
- D. Desloratidine
Explanation: ***Cinnarizine*** - **Cinnarizine** is a first-generation antihistamine with notable **sedative effects** due to its ability to cross the blood-brain barrier. - It is primarily used for **motion sickness** and vestibular disorders, where its sedative properties can be a significant side effect. *Fexofenadine* - **Fexofenadine** is a second-generation antihistamine known for being **non-sedating**. - It has a high affinity for peripheral H1-receptors and does not readily cross the **blood-brain barrier**. *Levocetirizine* - **Levocetirizine** is the active enantiomer of cetirizine, also a **second-generation non-sedating** antihistamine. - It is effective in treating allergy symptoms with minimal central nervous system effects. *Desloratidine* - **Desloratidine** is the active metabolite of loratadine and is classified as a **non-sedating second-generation** antihistamine. - It has a long duration of action and low potential for causing drowsiness.
Question 4: Which of the following drugs can cause hypotension by releasing histamine from mast cells?
- A. Morphine (Correct Answer)
- B. Sulfadiazine
- C. Procaine
- D. Aspirin
Explanation: ***Correct Option - Morphine*** **Morphine** and other opioids can cause **non-immunologic histamine release** from mast cells, leading to **vasodilation**, bronchoconstriction, and systemic hypotension. - The release of histamine directly causes a decrease in **peripheral vascular resistance**, contributing to a drop in blood pressure - This is a **direct pharmacological effect**, not an allergic reaction - Other opioids with similar effects include **codeine** and **meperidine** *Incorrect Option - Procaine* **Procaine** is a local anesthetic that can cause hypotension primarily due to its **direct vasodilatory effect** and cardiovascular depression, rather than histamine release. - While allergic reactions to procaine (which involve histamine) can occur, hypotension in this context is usually related to **systemic absorption** and cardiovascular depression - The mechanism is NOT direct mast cell degranulation *Incorrect Option - Sulfadiazine* **Sulfadiazine** is an antibiotic that may cause hypotension as part of an **allergic reaction** (e.g., anaphylaxis), which would involve histamine. - However, it does not typically cause **direct, non-immunologic histamine release** from mast cells as a primary mechanism - Any histamine release would be **immunologic** (allergic), not direct pharmacological mast cell degranulation *Incorrect Option - Aspirin* **Aspirin** (acetylsalicylic acid) can cause significant hypotension in cases of **overdose** or severe intolerance. - Primary mechanism involves **prostaglandin synthesis inhibition**, which can influence vascular tone - May cause cardiovascular depression in overdose - Does NOT cause direct histamine release from mast cells
Question 5: A 30-year-old woman is diagnosed with gonorrhea and reports a penicillin allergy (rash). Which alternative treatment regimen is most appropriate?
- A. Azithromycin 2g orally single dose
- B. Cefixime 400mg orally single dose
- C. Ciprofloxacin 500mg orally single dose
- D. Spectinomycin 2g IM single dose (Correct Answer)
Explanation: ***Spectinomycin 2g IM single dose*** - **Spectinomycin** is a safe and effective alternative for treating uncomplicated gonorrhea in patients with a history of severe penicillin or cephalosporin allergy. - It provides bactericidal activity against *Neisseria gonorrhoeae* and is administered as a **single intramuscular injection**. *Azithromycin 2g orally single dose* - While azithromycin is part of the dual therapy for gonorrhea (with ceftriaxone), using it as a **monotherapy** is not recommended due to increasing rates of resistance. - The CDC no longer recommends 2g azithromycin monotherapy for gonorrhea due to concerns about **macrolide resistance**. *Cefixime 400mg orally single dose* - **Cefixime** is a third-generation cephalosporin, and a penicillin allergy (especially a rash) may indicate a risk of **cross-reactivity** with cephalosporins. - While it's an alternative, it's generally avoided in significant penicillin allergy due to the potential for hypersensitivity reactions [1] and may have **lower efficacy** than ceftriaxone [2]. *Ciprofloxacin 500mg orally single dose* - **Ciprofloxacin** is a fluoroquinolone, and its use for gonorrhea is no longer recommended due to widespread and increasing **quinolone resistance** of *Neisseria gonorrhoeae* [2]. - Treatment with ciprofloxacin is associated with unacceptably high rates of **treatment failure** in many regions.
Question 6: How do antihistamines help in allergic rhinitis?
- A. inhibit prostaglandin synthesis to relieve itching.
- B. block histamine receptors to reduce symptoms. (Correct Answer)
- C. reduce inflammation by blocking leukotrienes.
- D. prevent the release of mast cell mediators.
Explanation: **Correct Answer: Block histamine receptors to reduce symptoms.** - Antihistamines work by competitively binding to **histamine H1 receptors**, preventing histamine from exerting its effects. - This action directly reduces symptoms such as **sneezing**, **itching**, and **rhinorrhea** (runny nose) associated with allergic reactions. - They act after histamine has been released by blocking its receptors on target tissues. *Incorrect: Inhibit prostaglandin synthesis to relieve itching.* - This mechanism of action is characteristic of **NSAIDs (non-steroidal anti-inflammatory drugs)**, which primarily target pain and inflammation, not the histamine-mediated symptoms of allergic rhinitis. - While prostaglandins can contribute to inflammation, antihistamines do not act on their synthesis. *Incorrect: Reduce inflammation by blocking leukotrienes.* - This mechanism describes the action of **leukotriene receptor antagonists** (e.g., Montelukast), which are used in asthma and allergic rhinitis but are distinct from antihistamines. - Leukotrienes are potent inflammatory mediators, and blocking them helps reduce inflammation and bronchoconstriction. *Incorrect: Prevent the release of mast cell mediators.* - This is the mechanism of **mast cell stabilizers** (e.g., cromolyn sodium), which prevent the degranulation of mast cells and the subsequent release of histamine and other inflammatory mediators. - Antihistamines act after histamine has already been released, not before.
Question 7: Ichthyosis is a side effect of -
- A. Capreomycin
- B. Letrozole
- C. Clofazimine (Correct Answer)
- D. Cephalosporin
Explanation: ***Clofazamine*** - **Clofazimine** is an antimycobacterial drug used to treat **leprosy**, and one of its characteristic skin-related side effects is **ichthyosis**, presenting as dry, scaly skin. - It accumulates in fatty tissues and the reticuloendothelial system, causing a range of skin pigmentation changes from red-brown to black, often associated with generalized dryness and scaling. *Capreomycin* - **Capreomycin** is an injectable antibiotic primarily used for **multi-drug resistant tuberculosis (MDR-TB)**. - Its main side effects involve **nephrotoxicity** and **ototoxicity**, not ichthyosis. *Letrozole* - **Letrozole** is an **aromatase inhibitor** used in the treatment of **hormone-receptor-positive breast cancer** in postmenopausal women. - Common side effects include **hot flashes**, **arthralgia**, and **fatigue**, but not ichthyosis. *Cephalosporin* - **Cephalosporins** are a class of **beta-lactam antibiotics** widely used for bacterial infections. - While they can cause various side effects like **allergic reactions** (rash, anaphylaxis), **gastrointestinal upset**, and **nephrotoxicity** at high doses, ichthyosis is not a recognized side effect.
Question 8: A 56-year-old woman has nausea due to chemotherapy for breast cancer. Droperidol is effective in reducing nausea because it blocks which of the following?
- A. Glucocorticoid receptors in the vomiting center
- B. Dopamine receptors in the CTZ (Correct Answer)
- C. ACh receptors in the periphery
- D. 5-HT3 receptors in the CTZ
Explanation: **Dopamine receptors in the CTZ** - Droperidol is a **butyrophenone antipsychotic** that acts as an **antidopaminergic agent**, primarily targeting **D2 dopamine receptors**. - Its antiemetic effect is mainly due to blocking these **dopamine receptors in the chemoreceptor trigger zone (CTZ)**, which is involved in initiating the vomiting reflex. *Glucocorticoid receptors in the vomiting center* - **Glucocorticoids** like dexamethasone are used as antiemetics, but they act via **glucocorticoid receptors**, not through dopamine receptor blockade. - Their mechanism involves inhibiting prostaglandin synthesis and inflammation, reducing the release of serotonin. *ACh receptors in the periphery* - Drugs that block **acetylcholine (ACh) receptors** (e.g., scopolamine) are used for motion sickness, but they are not the primary mechanism of action for droperidol. - **Anticholinergics** typically exert their effects on the vestibular system and peripheral muscarinic receptors. *5-HT 2 receptors in the CTZ* - While some antiemetics (e.g., **ondansetron**) block **serotonin (5-HT3) receptors**, droperidol's primary action is not on **5-HT2 receptors**. - **Serotonin antagonists** are particularly effective for chemotherapy-induced nausea and vomiting as chemotherapy often releases serotonin from enterochromaffin cells.
Question 9: What is the optimal wavelength of light emitted by a Wood's lamp for dermatological examinations?
- A. 365 nm (Correct Answer)
- B. 400 nm
- C. 320 nm
- D. 200 nm
Explanation: **365 nm** - A Wood's lamp primarily emits **long-wave UVA light** in the 320 to 400 nm range, with an optimal peak around **365 nm**. - This specific wavelength is ideal for inducing **fluorescence** in various dermatological conditions, making them visible. *400 nm* - While within the UVA range, **400 nm** is at the higher end and may not provide the optimal fluorescence yield for all diagnostic purposes compared to 365 nm. - Light at 400 nm is closer to the visible light spectrum and might offer less distinction for subtle fluorescence. *320 nm* - **320 nm** is at the lower end of the UVA spectrum, bordering on UVB. - While still capable of inducing some fluorescence, it is generally less effective than 365 nm for the conditions typically examined with a Wood's lamp. *200 nm* - **200 nm** falls into the **UVC range** (100-280 nm), which is harmful and not used for diagnostic purposes in a Wood's lamp. - This wavelength is absorbed by the atmosphere and epidermis and can cause significant **DNA damage**, making it unsafe for routine dermatological examination.
Question 10: All of the following statements are TRUE about second generation antihistaminic agents EXCEPT:
- A. These may possess additional antiallergic mechanisms
- B. These do not impair psychomotor performance
- C. These lack anticholinergic actions
- D. These possess high anti-motion sickness activity (Correct Answer)
Explanation: ***These possess high anti-motion sickness activity*** - Second-generation antihistamines have **poor penetration** into the central nervous system (CNS), making them ineffective for treating **motion sickness**. - **First-generation antihistamines**, which readily cross the blood-brain barrier and have **anticholinergic activity**, are typically used for motion sickness. *These may possess additional antiallergic mechanisms* - Many second-generation antihistamines, such as **cetirizine** and **loratadine**, have additional anti-inflammatory and **antiallergic properties** beyond H1 receptor blockade. - These mechanisms can include inhibiting the release of inflammatory mediators and **stabilizing mast cells**. *These do not impair psychomotor performance* - Second-generation antihistamines are **non-sedating** because they have limited ability to cross the **blood-brain barrier** and thus do not significantly affect CNS function. - This characteristic makes them suitable for use without causing **drowsiness** or impairing activities like driving. *These lack anticholinergic actions* - Unlike first-generation antihistamines, second-generation agents have **minimal to no affinity** for muscarinic acetylcholine receptors. - This lack of **anticholinergic activity** means they do not cause side effects such as **dry mouth**, blurred vision, or urinary retention.
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