Sulfonamides and Trimethoprim — MCQs
HIV patient presented with diarrhea. On stool examination, acid-fast organisms (Isospora belli) were seen. What is the drug of choice in this patient?
The combination of trimethoprim and sulfamethoxazole is effective against which of the following opportunistic infections in the AIDS patient?
Which drug is metabolized by glutathionation?
Toxic focal myopathy is an adverse effect of:
Which of the following drugs does not inhibit bacterial protein synthesis?
When treating urinary tract infection (UTI) in the third trimester, what is the antibiotic of choice?
A pediatrician was called for attending a new born baby in the labour ward. The serum unconjugated bilirubin of this baby was 33 mg/dL. Which of the following drug taken by mother in late 3rd trimester may have led to this problem?
On chronic use, linezolid leads to which of the following?
Drug Induced Lupus is caused by all except
Thymidine is responsible for resistance to which antibiotic ?
Sulfonamides and Trimethoprim Indian Medical PG Practice Questions and MCQs
Question 1: HIV patient presented with diarrhea. On stool examination, acid-fast organisms (Isospora belli) were seen. What is the drug of choice in this patient?
- A. Niclosamide
- B. Nitazoxanide
- C. Primaquine
- D. TMP-SMX (Correct Answer)
Explanation: ***TMP-SMX*** - **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the primary treatment for **Isospora belli** infections, especially in HIV-positive patients [1]. - It is highly effective in eradicating the parasite and preventing relapses in immunocompromised individuals [1]. *Niclosamide* - **Niclosamide** is an antihelminthic drug primarily used for treating **tapeworm infections** [2]. - It is not effective against protozoal parasites like *Isospora belli*. *Nitazoxanide* - **Nitazoxanide** is an antiparasitic drug that can be used for various protozoal and helminthic infections, including *Cryptosporidium* and *Giardia*. - While it has some efficacy against *Isospora belli*, it is generally considered a second-line agent, with **TMP-SMX** being the drug of choice [1]. *Primaquine* - **Primaquine** is an antimalarial drug specifically used to prevent relapse of **Plasmodium vivax** and **Plasmodium ovale** malaria by targeting hypnozoites. - It has no role in the treatment of **Isospora belli** infection.
Question 2: The combination of trimethoprim and sulfamethoxazole is effective against which of the following opportunistic infections in the AIDS patient?
- A. Disseminated Herpes simplex infection
- B. Cryptococcal meningitis infection
- C. Tuberculosis infection
- D. Pneumocystis jirovecii (Correct Answer)
Explanation: ***Pneumocystis jiroveci*** - **Pneumocystis pneumonia (PCP)**, caused by *Pneumocystis jirovecii*, is a common and severe opportunistic infection in AIDS patients. - ** Trimethoprim-sulfamethoxazole (TMP-SMX)**, also known as Bactrim, is the **drug of choice** for both treatment and prophylaxis of PCP [1], [2]. *Disseminated Herpes simplex infection* - **Herpes simplex virus (HSV)** infections are typically treated with antiviral medications like **acyclovir, valacyclovir, or famciclovir**. - TMP-SMX has **no antiviral activity** and is ineffective against HSV. *Cryptococcal meningitis infection* - **Cryptococcal meningitis** is a fungal infection primarily treated with **amphotericin B** in combination with **flucytosine**, followed by fluconazole for maintenance. - TMP-SMX is **not active** against *Cryptococcus neoformans*. *Tuberculosis infection* - **Tuberculosis (TB)**, caused by *Mycobacterium tuberculosis*, requires a **multi-drug regimen** typically including isoniazid, rifampin, pyrazinamide, and ethambutol [3]. - While TMP-SMX has some activity against *Nocardia spp.* and some atypical mycobacteria, it is **not effective** for the treatment of *Mycobacterium tuberculosis*.
Question 3: Which drug is metabolized by glutathionation?
- A. Nicotinic acid
- B. Fosfomycin
- C. Benzodiazepines
- D. Dapsone (Correct Answer)
Explanation: ***Dapsone***- **Dapsone** undergoes hepatic metabolism via **N-hydroxylation** by CYP450 enzymes (particularly CYP2E1 and CYP3A4), forming reactive **hydroxylamine metabolites**.- These reactive metabolites are toxic and can cause **methemoglobinemia** and **hemolysis**.- **Glutathione conjugation (glutathionation)** serves as an important **detoxification pathway** for these reactive dapsone metabolites [1].- Individuals with **glutathione deficiency** (such as G6PD deficiency) are at increased risk of dapsone-induced hemolytic anemia [2].*Fosfomycin*- **Fosfomycin** is primarily eliminated by the kidneys as an **unchanged drug** (up to 90% excreted unchanged in urine).- It undergoes **minimal hepatic metabolism** and does NOT undergo significant glutathionation.- Its primary route of elimination is **renal excretion** via glomerular filtration.*Benzodiazepines*- **Benzodiazepines** are primarily metabolized in the liver via **CYP450 enzymes** (Phase I oxidation) followed by **glucuronidation** (Phase II conjugation).- They do NOT undergo glutathionation as a significant metabolic pathway.*Nicotinic acid*- **Nicotinic acid** (niacin) undergoes conjugation with **glycine** to form nicotinuric acid and **methylation** to form N-methylnicotinamide.- It does NOT undergo glutathione conjugation.
Question 4: Toxic focal myopathy is an adverse effect of:
- A. Penicillin
- B. Aminoglycosides
- C. Insulin
- D. Narcotics (Correct Answer)
Explanation: ***Narcotics*** - **Narcotics**, particularly **pentazocine**, when injected repeatedly into the same muscle group, can lead to **toxic focal myopathy**. - This condition involves localized muscle damage, necrosis, and woody fibrosis at the injection site due to the direct toxic effect of the drug on muscle tissue. - Pentazocine-induced myopathy is a well-documented adverse effect in patients with chronic intramuscular injections. *Penicillin* - **Penicillin** is generally associated with **hypersensitivity reactions** like rash, anaphylaxis, or interstitial nephritis. - It is not typically known to cause focal myopathy as a direct adverse effect. *Aminoglycosides* - **Aminoglycosides** are primarily associated with **nephrotoxicity** and **ototoxicity**. - They can also cause **neuromuscular blockade**, but not focal muscle damage through direct toxicity to muscle tissue. *Insulin* - **Insulin** administration can cause **lipohypertrophy** or **lipoatrophy** at injection sites due to fat tissue changes. - However, it does not directly lead to **toxic focal myopathy** involving muscle tissue damage.
Question 5: Which of the following drugs does not inhibit bacterial protein synthesis?
- A. Aminoglycosides
- B. Chloramphenicol
- C. Clindamycin
- D. Sulfonamides (Correct Answer)
Explanation: ***Sulfonamides*** - Sulfonamides do **NOT** inhibit bacterial protein synthesis; instead, they inhibit **folic acid synthesis**. - They act as **competitive inhibitors** of dihydropteroate synthase, an enzyme involved in the synthesis of dihydrofolic acid. - Folic acid is essential for nucleotide synthesis and DNA replication, making sulfonamides bacteriostatic agents that work through a completely different mechanism than protein synthesis inhibitors. *Aminoglycosides* - Aminoglycosides bind to the **30S ribosomal subunit**, causing misreading of mRNA and premature termination of protein synthesis. - This leads to the production of **abnormal and non-functional proteins**, ultimately killing the bacterial cell. *Chloramphenicol* - Chloramphenicol binds to the **50S ribosomal subunit**, thereby inhibiting the peptidyl transferase enzyme. - This prevents the formation of **peptide bonds** between amino acids, effectively blocking protein elongation. *Clindamycin* - Clindamycin also binds to the **50S ribosomal subunit**, specifically at the P-site. - It interferes with the **translocation step** of protein synthesis, preventing ribosomal movement along the mRNA.
Question 6: When treating urinary tract infection (UTI) in the third trimester, what is the antibiotic of choice?
- A. Tetracycline
- B. Sulfonamide
- C. Nitrofurantoin
- D. Cephalosporin (Correct Answer)
Explanation: ***Cephalosporin*** - **Cephalosporins** are generally considered safe and effective for treating UTIs during all trimesters of pregnancy, including the third trimester. - They have **low teratogenic risk** and broad-spectrum activity against common UTI pathogens. *Tetracycline* - **Tetracyclines** are contraindicated in the third trimester due to the risk of permanent **discoloration of fetal teeth** and inhibition of bone growth. - They readily cross the **placenta** and accumulate in the fetal skeletal system. *Sulfonamide* - **Sulfonamides** like trimethoprim-sulfamethoxazole should be avoided in the third trimester, especially near term, due to the risk of **kernicterus** in the neonate. - Sulfonamides compete with **bilirubin** for binding sites on albumin, potentially leading to elevated unconjugated bilirubin. *Nitrofurantoin* - **Nitrofurantoin** should be avoided in the third trimester (after 36 weeks of gestation) in pregnant patients with G6PD deficiency due to the risk of **hemolytic anemia** in the neonate. - It's generally considered safe in the first and second trimesters, but caution is advised in the late third trimester.
Question 7: A pediatrician was called for attending a new born baby in the labour ward. The serum unconjugated bilirubin of this baby was 33 mg/dL. Which of the following drug taken by mother in late 3rd trimester may have led to this problem?
- A. Ampicillin
- B. Azithromycin
- C. Cotrimoxazole (Correct Answer)
- D. Chloroquine
Explanation: ***Cotrimoxazole*** - **Cotrimoxazole** (trimethoprim-sulfamethoxazole) can displace **bilirubin** from albumin-binding sites in the newborn, leading to increased levels of **unconjugated bilirubin** and a higher risk of kernicterus. - Sulfonamides, a component of cotrimoxazole, are known to interfere with **bilirubin metabolism** and transport in neonates, particularly when taken by the mother late in pregnancy. *Ampicillin* - **Ampicillin** is a penicillin-class antibiotic generally considered safe during pregnancy and is not known to cause significant neonatal **hyperbilirubinemia**. - Its mechanism of action does not involve competition for **albumin-binding sites** with bilirubin. *Azithromycin* - **Azithromycin** is a macrolide antibiotic commonly used in pregnancy and does not have a recognized association with significant **unconjugated hyperbilirubinemia** in newborns. - It does not significantly affect the **bilirubin-albumin binding** in neonates. *Chloroquine* - **Chloroquine** is an antimalarial drug, and while generally avoided in the first trimester, it has not been linked to severe neonatal **hyperbilirubinemia** similar to that caused by sulfonamides. - Its primary **side effects** in newborns are not related to bilirubin displacement.
Question 8: On chronic use, linezolid leads to which of the following?
- A. Thrombocytopenia (Correct Answer)
- B. Deranged LFT
- C. Nephrotoxicity
- D. Ototoxicity
Explanation: ***Thrombocytopenia*** - **Linezolid** is known to cause **myelosuppression**, particularly **thrombocytopenia**, with prolonged use (typically >2 weeks). - This adverse effect is usually **reversible** upon discontinuation of the drug. - This is the **most characteristic** and **dose-limiting** hematologic toxicity of chronic linezolid therapy. *Deranged LFT* - While **linezolid** can occasionally cause **elevated liver enzymes**, this is a **less common** adverse effect compared to myelosuppression. - **Thrombocytopenia** is far more characteristic of **chronic linezolid use** and is the primary concern requiring monitoring. - Hepatotoxicity with linezolid is typically mild and less dose-limiting than hematologic effects. *Nephrotoxicity* - **Linezolid** is generally considered to have a low risk of **nephrotoxicity** and does not typically cause significant kidney damage. - **Aminoglycosides** or **vancomycin** are examples of antibiotics more commonly associated with nephrotoxic effects. *Ototoxicity* - **Ototoxicity**, characterized by hearing loss or tinnitus, is not a common or recognized side effect of **linezolid** therapy. - This adverse effect is more frequently associated with drugs like **aminoglycosides** or high-dose **loop diuretics**.
Question 9: Drug Induced Lupus is caused by all except
- A. Hydralazine
- B. Sulphonamides
- C. Isoniazid
- D. Procaine (Correct Answer)
Explanation: ***Procaine*** - While **procainamide**, a derivative of procaine, is a known cause of **drug-induced lupus (DIL)**, **procaine** itself is not typically implicated. - Procaine is a **local anesthetic** and its mechanism of action does not commonly lead to the immunological reactions seen in DIL. *Hydralazine* - **Hydralazine** is a well-established cause of **drug-induced lupus (DIL)**, particularly with higher doses and prolonged use. - It frequently results in the development of **anti-histone antibodies**, a hallmark of DIL. *Sulphonamides* - Various **sulphonamide antibiotics** (e.g., sulfasalazine, sulfamethoxazole) are known to induce **lupus-like syndromes**. - These drugs can trigger immune responses leading to symptoms characteristic of **systemic lupus erythematosus (SLE)**. *Isoniazid* - **Isoniazid**, an anti-tuberculosis medication, is a recognized cause of **drug-induced lupus (DIL)**. - It often leads to the formation of **anti-histone antibodies** and clinical manifestations resembling spontaneous lupus.
Question 10: Thymidine is responsible for resistance to which antibiotic ?
- A. Erythromycin
- B. Sulfonamide (Correct Answer)
- C. Tetracycline
- D. Nitrofurantoin
Explanation: ***Sulfonamide*** - **Thymidine** can contribute to **sulfonamide resistance** because sulfonamides interfere with **folate metabolism** and the subsequent synthesis of purines and pyrimidines, including thymidine. - An excess of thymidine can bypass the metabolic block caused by sulfonamides, allowing bacteria to continue DNA synthesis and grow. *Erythromycin* - **Erythromycin** resistance is primarily mediated by **methylation of ribosomal RNA**, which prevents the antibiotic from binding to the 50S ribosomal subunit. - It does not directly involve thymidine or the folate synthesis pathway. *Tetracycline* - Resistance to **tetracyclines** is commonly due to **efflux pumps** that actively pump the drug out of the bacterial cell or **ribosomal protection proteins** that prevent tetracycline binding. - Thymidine production or metabolism is not a mechanism of tetracycline resistance. *Nitrofurantoin* - **Nitrofurantoin** resistance typically involves **mutations** in bacterial enzymes (like **nitrofuran reductase**) that are responsible for activating the drug into its active form. - These mutations prevent the drug from becoming bactericidal, and thymidine does not play a role in this mechanism.
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