Drugs Used in Skin Disorders — MCQs

Drugs Used in Skin Disorders Indian Medical PG Practice Questions and MCQs

Question 51: Which mechanism best explains the therapeutic effect of coal tar in psoriasis?

A. DNA synthesis inhibition
B. Immunosuppression
C. Keratolysis
D. Anti-inflammatory (Correct Answer)

Explanation: ***Anti-inflammatory*** - Coal tar exerts significant **anti-inflammatory effects**, reducing erythema, scaling, and pruritus in psoriatic plaques. - It also has important **antiproliferative effects** on keratinocytes, normalizing the accelerated epidermal turnover characteristic of psoriasis. - Both anti-inflammatory and antiproliferative mechanisms contribute to its therapeutic efficacy. - The exact molecular mechanisms remain incompletely understood but likely involve effects on cytokine production and cell signaling pathways. *DNA synthesis inhibition* - While coal tar does have **antiproliferative properties** that reduce keratinocyte proliferation, this is considered part of its overall mechanism rather than the singular best explanation. - The question asks for the mechanism that "best explains" the effect, and anti-inflammatory action is more broadly recognized as the primary characterization. - Other agents like **methotrexate** work more specifically through direct DNA synthesis inhibition. *Immunosuppression* - Coal tar is **not a systemic immunosuppressant** like cyclosporine or biologics (anti-TNF agents, IL-17 inhibitors). - Its effects are primarily local and topical, targeting skin inflammation rather than systemic immune modulation. - It does not suppress T-cell function or other immune pathways to the degree of true immunosuppressive agents. *Keratolysis* - Coal tar has **mild keratolytic properties** (helps remove scales), but this is a secondary benefit rather than its primary therapeutic mechanism. - **Salicylic acid** is the prototypical keratolytic agent and is often combined with coal tar in psoriasis treatment. - The descaling effect aids in allowing the active anti-inflammatory and antiproliferative components to penetrate better.

Question 52: A 30-year-old man presents with multiple small red papules on his face and chest that appeared after starting a new medication. Which medication is most likely the cause?

A. Amoxicillin
B. Hydrochlorothiazide
C. Prednisone
D. Phenytoin (Correct Answer)

Explanation: ***Phenytoin*** - **Phenytoin** is well-known for causing **drug-induced hypersensitivity reactions** presenting as **morbilliform (measles-like) or exanthematous eruptions** with small, red papules - These reactions typically appear within **1-3 weeks** of starting therapy and commonly affect the **face, trunk, and upper extremities** - Phenytoin can also cause more severe reactions like **DRESS syndrome** and **SJS/TEN**, making recognition of early cutaneous signs clinically important - In the context of pharmacology testing, phenytoin's dermatological side effects are **high-yield** and frequently examined *Amoxicillin* - While **amoxicillin** is a common cause of drug rashes overall (affecting 5-10% of patients), these rashes are often **delayed** (appearing 4-14 days after treatment) and frequently **non-allergic** in nature - The classic "**amoxicillin rash**" often occurs in the context of **viral infections** (especially EBV) rather than as a true drug hypersensitivity - Without additional context suggesting concurrent viral illness, other medications should be considered first *Hydrochlorothiazide* - **Hydrochlorothiazide** primarily causes **photosensitivity reactions** that require sun exposure, presenting as sunburn-like eruptions in sun-exposed areas - Can also rarely cause **lichenoid eruptions** or **vasculitis**, but generalized small red papules are not its characteristic presentation *Prednisone* - **Prednisone** is a corticosteroid with **anti-inflammatory and immunosuppressive** properties that typically **suppress rash formation** - Chronic use may cause **steroid acne** or skin atrophy, but acute papular eruptions after starting the medication are highly unlikely - Prednisone is often used to **treat** drug-induced rashes, not cause them

Question 53: Which drug is used as a single oral dose agent for the treatment of scabies?

A. Permethrin
B. Retinoids
C. Ivermectin (Correct Answer)
D. Co-trimoxazole

Explanation: ***Ivermectin*** - **Ivermectin** is the only **oral agent** that can be given as a **single dose** for scabies treatment. - Its mechanism involves targeting **gamma-aminobutyric acid (GABA)**-gated chloride channels in the parasite, causing paralysis and death. *Permethrin* - **Permethrin** is a topical cream and not an oral agent; it is applied to the skin, typically for 8-14 hours. - It works by disrupting the **sodium channels** in the parasite's nervous system, leading to paralysis and death. *Retinoids* - **Retinoids** are primarily used for conditions like **acne** and **psoriasis**, and they are not effective against parasitic infections like scabies. - They function by modulating **gene expression** and influencing cell growth and differentiation. *Co-trimoxazole* - **Co-trimoxazole** is an **antibiotic** used to treat bacterial infections and has no efficacy against the scabies mite. - It is a combination of **sulfamethoxazole** and **trimethoprim**, both of which inhibit bacterial folic acid synthesis.

Question 54: Which of the following is a melanising agent?

A. Dapsone
B. Kojic acid
C. Methoxsalen (Correct Answer)
D. Minocycline

Explanation: ***Methoxsalen*** - **Methoxsalen** is a **psoralen** derivative used in combination with ultraviolet A (UVA) light therapy (**PUVA**) to treat skin conditions like **vitiligo** and **psoriasis**. - It works by intercalating into DNA and forming adducts, which, when exposed to UVA light, stimulate **melanocyte proliferation** and melanin production. *Dapsone* - **Dapsone** is an **antibiotic** and **anti-inflammatory** agent primarily used to treat leprosy, dermatitis herpetiformis, and certain other dermatoses. - It works by inhibiting folic acid synthesis in bacteria and suppressing neutrophil function, and it **does not stimulate melanin production**. *Kojic acid* - **Kojic acid** is a common ingredient in cosmetic products used to **lighten skin** by inhibiting the enzyme **tyrosinase**, which is essential for melanin synthesis. - Therefore, it is a **depigmenting agent**, not a melanizing agent. *Minocycline* - **Minocycline** is a **tetracycline antibiotic** used to treat various bacterial infections, including acne and Lyme disease. - A known side effect of minocycline is **hyperpigmentation** of the skin, nails, and teeth, but this pigmentation is due to deposition of breakdown products of the drug and not due to stimulation of melanin production by melanocytes.

Question 55: Which of the following was historically used as an adjunctive systemic treatment for genital warts but is now rarely employed due to limited efficacy and significant side effects?

A. Acyclovir
B. Minocycline
C. Podophyllin
D. Interferon alpha (Correct Answer)

Explanation: ***Interferon alpha*** - **Interferon alpha** was historically used as an adjunctive treatment for **genital warts**, primarily due to its **antiviral** and **immunomodulatory properties**, though its efficacy was limited and it caused significant side effects. - It works by stimulating the host immune response against the **human papillomavirus (HPV)**, which causes genital warts. *Acyclovir* - **Acyclovir** is an **antiviral medication** used predominantly for **herpes simplex virus (HSV)** infections, such as genital herpes, and not for genital warts caused by HPV. - Its mechanism of action involves inhibiting viral DNA replication, which is specific to herpesviruses. *Podophyllin* - **Podophyllin** is a **topical cytotoxic agent** that induces necrosis in genital warts and is still used today. - While effective, it is applied directly to the warts and is not administered systemically like **interferon alpha** was. *Minocycline* - **Minocycline** is a **tetracycline antibiotic** used to treat bacterial infections, such as those caused by *Acne vulgaris* or *Chlamydia*. - It has no antiviral activity against **HPV** and therefore is not used for genital warts.

Question 56: What is the Drug of Choice (DOC) for Onychomycosis?

A. Terbinafine (Correct Answer)
B. Fluconazole
C. Itraconazole
D. Nystatin

Explanation: ***Terbinafine*** - **Terbinafine** is considered the **drug of choice** for **onychomycosis** due to its potent fungicidal activity against **dermatophytes**, which are the most common cause of nail infections [1]. - It accumulates in the nail plate at therapeutic levels, leading to high cure rates and a relatively good safety profile [2]. *Fluconazole* - While effective against some fungi, **fluconazole** is primarily fungistatic and generally less effective against dermatophytes compared to terbinafine for onychomycosis, resulting in lower cure rates [1]. - It is often preferred for **mucocutaneous candidiasis** and other systemic fungal infections [1]. *Itraconazole* - **Itraconazole** is an alternative for onychomycosis, often administered in pulse doses, but it can have more significant drug interactions and a higher risk of hepatic toxicity compared to terbinafine [1]. - Its efficacy against dermatophytes is comparable to terbinafine, but its side effect profile makes it a second-line option [1]. *Nystatin* - **Nystatin** is a topical antifungal effective primarily against **Candida species**, and is not effective against **dermatophytes**, which are the main pathogens in onychomycosis. - It is typically used for mucocutaneous candidiasis, such as oral thrush or vaginal yeast infections, and is not absorbed systemically.

Question 57: Which of the following is the most potent topical corticosteroid?

A. Triamcinolone acetonide
B. Hydrocortisone acetate
C. Clobetasol propionate (Correct Answer)
D. Betamethasone valerate

Explanation: ***Clobetasol propionate*** - **Clobetasol propionate** is recognized as one of the most potent **Class I topical corticosteroids**, used for severe inflammatory skin conditions. - Its high potency allows for effective suppression of severe inflammation and pruritus, but also carries a greater risk of **adverse effects** with prolonged use. *Triamcinolone acetonide* - **Triamcinolone acetonide** is a **medium-potency** topical corticosteroid (Class IV-V), less potent than clobetasol propionate. - It is commonly used for moderate inflammatory skin conditions, such as eczema and psoriasis, but not for severe cases requiring maximum potency. *Hydrocortisone acetate* - **Hydrocortisone acetate** is a **low-potency** topical corticosteroid (Class VII), making it the least potent option listed. - It's often used for mild inflammatory conditions, sensitive areas like the face, or for less severe conditions requiring minimal corticosteroid strength. *Betamethasone valerate* - **Betamethasone valerate** is a **medium-to-high potency** topical corticosteroid (Class III-V), placing it among stronger corticosteroids but still less potent than clobetasol propionate. - It is effective for moderate to severe inflammatory skin conditions but does not reach the highest level of potency demonstrated by clobetasol.

Question 58: What is the maximum cumulative dose of isotretinoin for acne treatment?

A. 30-60 mg/kg
B. 60-90 mg/kg
C. 90-120 mg/kg
D. 120-150 mg/kg (Correct Answer)

Explanation: ***120-150 mg/kg*** - The goal of **isotretinoin cumulative dosing** is to achieve long-term remission and reduce the risk of relapse. - A cumulative dose in the range of **120-150 mg/kg** has been shown to optimize treatment outcomes for severe or recalcitrant acne. *30-60 mg/kg* - This range is typically considered too low to achieve the optimal **cumulative dose** for sustained remission in severe acne. - Doses within this range might be used in some cases for milder forms of acne or in patients with significant side effects, but not as the standard maximum. *60-90 mg/kg* - While this is closer to an effective cumulative dose, it still often falls short of the recommended range for maximizing the long-term efficacy and reducing relapse rates in patients with severe forms of acne. - Studies suggest that higher cumulative doses correlate with better treatment success and fewer recurrences. *90-120 mg/kg* - This range is often considered a minimal target for a **cumulative dose**, especially at the higher end of the range (120 mg/kg). - While effective for many patients, aiming for the upper end (120-150 mg/kg) often provides a more robust and durable response, particularly in more severe or nodular acne.

Question 59: Which drug would treat both dermatophytosis and candidal infection?

A. Ketoconazole (Correct Answer)
B. Nystatin
C. Griseofulvin
D. Tolnaftate

Explanation: ***Ketoconazole*** - **Ketoconazole** is an **imidazole antifungal** that inhibits the synthesis of ergosterol, a crucial component of fungal cell membranes. - It has a broad spectrum of activity, effectively treating both **dermatophytes** (causing dermatophytosis) and **Candida species** (causing candidal infections). *Griseofulvin* - **Griseofulvin** works by inhibiting **fungal cell division** and is primarily used for **dermatophyte infections** of the skin, hair, and nails. - It is **ineffective against Candida species** because Candida cells do not take up the drug. *Nystatin* - **Nystatin** is a **polyene antifungal** agent that disrupts the fungal cell membrane by binding to ergosterol. - Its activity is almost exclusively limited to **Candida infections**, and it is not effective against dermatophytes. *Tolnaftate* - **Tolnaftate** is a topical antifungal agent that acts by inhibiting **ergosterol biosynthesis**, specifically targeting **squalene epoxidase**. - It is primarily effective against **dermatophyte infections** but has little or no activity against Candida species.

Question 60: A 32-year-old gay male presented to his community STD clinic with perianal condyloma acuminatum. Physical removal was recommended due to the size of the lesions, along with topical immunomodulatory therapy. Which of the following drugs was most likely selected?

A. Acyclovir (antiviral)
B. 5-Fluorouracil (chemotherapy)
C. Imiquimod (topical immunomodulator) (Correct Answer)
D. Podophyllin (antimitotic agent)

Explanation: ***Imiquimod (topical immunomodulator)*** - **Imiquimod** is a topical immunomodulator that stimulates the production of **cytokines**, such as **interferon-alpha**, thereby enhancing the local immune response against **HPV-infected cells**. - It is a common and effective therapy for external **genital** and **perianal warts (condyloma acuminatum)**, often used in conjunction with other treatments, especially for larger lesions. *Acyclovir (antiviral)* - **Acyclovir** is an antiviral drug primarily used to treat infections caused by the **herpes simplex virus (HSV)** and **varicella-zoster virus (VZV)**, not **human papillomavirus (HPV)**. - While condyloma acuminatum is caused by **HPV**, acyclovir has no therapeutic effect against it. *5-Fluorouracil (chemotherapy)* - **5-Fluorouracil** is a **cytotoxic chemotherapy agent** that inhibits **DNA synthesis** and is sometimes used topically for certain skin cancers and actinic keratoses. - While it can be used for warts, it is generally considered an off-label use and is **less commonly chosen** for perianal condyloma acuminatum due to significant local irritation and potential for ulceration. *Podophyllin (antimitotic agent)* - **Podophyllin** is a **cytotoxic agent** that arrests cell division and is used topically to treat some types of warts by causing **necrosis** of the wart tissue. - While effective, its application has to be carefully performed by a clinician, and it is **contraindicated in pregnancy**; it is also not classified as an immunomodulator.

Practice by Chapter

Topical Corticosteroids

Practice Questions

Topical Antimicrobials

Practice Questions

Antiacne Medications

Practice Questions

Drugs for Psoriasis

Practice Questions

Antihistamines in Dermatological Conditions

Practice Questions

Sunscreens and Photoprotective Agents

Practice Questions

Agents for Pigmentary Disorders

Practice Questions

Drugs for Parasitic Skin Infestations

Practice Questions

Keratolytics and Emollients

Practice Questions

Biological Agents in Dermatology

Practice Questions

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