Tetracyclines — MCQs
Which of the following is NOT a mechanism of antibiotic resistance?
Which of the following conditions is not treated by penicillin G?
Pseudotumor Cerebri in Infants is seen with?
Antibiotic treatment of choice for treating cholera in an adult is a single dose of:
Which of the following combinations does not show synergistic action?
A woman presenting with symptoms of urinary tract infection was prescribed a drug that causes tendon rupture and arthropathy. What is the mechanism of action of the drug?
Which one of the following drugs cannot cause Pseudotumor Cerebri ?
23 years old woman complains of recurrent acne over her face. History revealed that she had taken topical antibiotics for her acne without any significant improvement. Which one of the following tetracyclines is most preferred for her acne?
What is the primary purpose of xenobiotic metabolism?
Tetracycline is used in prophylaxis of which of the following diseases?
Tetracyclines Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is NOT a mechanism of antibiotic resistance?
- A. Efflux pump activity
- B. Inactivation by enzymes such as beta-lactamase
- C. Modification of drug target sites
- D. Increased drug absorption (Correct Answer)
Explanation: ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].
Question 2: Which of the following conditions is not treated by penicillin G?
- A. Bacterial meningitis
- B. Syphilis
- C. Anthrax
- D. Rickettsial infection (Correct Answer)
Explanation: ***Rickettsial infection*** - **Rickettsial infections**, such as Rocky Mountain spotted fever or typhus, are caused by **obligate intracellular bacteria** that are not susceptible to penicillin G. - The primary treatment for rickettsial infections is **doxycycline**, due to its ability to penetrate host cells and inhibit bacterial protein synthesis. *Bacterial meningitis* - **Bacterial meningitis**, particularly caused by susceptible strains of *Neisseria meningitidis*, *Streptococcus pneumoniae*, and *Haemophilus influenzae*, can be effectively treated with **high-dose intravenous penicillin G** [1]. - Penicillin G's ability to cross the **blood-brain barrier** in inflamed meninges makes it a suitable option, though ceftriaxone is now more commonly used empirically due to resistance concerns [2]. *Syphilis* - **Penicillin G** remains the **drug of choice** for all stages of syphilis, caused by *Treponema pallidum*. - For primary, secondary, and early latent syphilis, a **single intramuscular dose of benzathine penicillin G** is curative. *Anthrax* - While **ciprofloxacin** and **doxycycline** are often considered first-line for anthrax, **penicillin G** can also be an effective treatment for susceptible strains of *Bacillus anthracis*. - It is particularly used in cases of less severe cutaneous anthrax or to de-escalate treatment once susceptibility is confirmed.
Question 3: Pseudotumor Cerebri in Infants is seen with?
- A. Aminoglycosides
- B. Tetracyclines (Correct Answer)
- C. Macrolides
- D. NSAIDs
Explanation: ***Tetracyclines***- **Tetracyclines**, particularly in infants, are a known cause of **pseudotumor cerebri**, also known as **idiopathic intracranial hypertension (IIH)**. - This condition involves increased **intracranial pressure (ICP)**, leading to symptoms like **headache**, **visual disturbances**, and **papilledema**. *Aminoglycosides*- **Aminoglycosides** are primarily associated with **ototoxicity** (hearing loss) and **nephrotoxicity** (kidney damage) [1]. - They are not typically linked to the development of **pseudotumor cerebri**. *NSAIDS*- **NSAIDs** (Nonsteroidal Anti-inflammatory Drugs) are more commonly associated with **gastrointestinal ulcers** and **renal impairment**. - While they can have neurological side effects in some cases, **pseudotumor cerebri** is not a characteristic or common adverse effect. *Macrolides*- **Macrolides** like erythromycin or azithromycin are generally well-tolerated and are primarily associated with **gastrointestinal upset** and **QT prolongation**. - There is no significant evidence linking **macrolide use** to the development of **pseudotumor cerebri**.
Question 4: Antibiotic treatment of choice for treating cholera in an adult is a single dose of:
- A. Co-trimoxazole
- B. Doxycycline (Correct Answer)
- C. Furazolidone
- D. Tetracycline
Explanation: ***Doxycycline***- **Doxycycline** is the recommended first-line antibiotic for cholera in adults due to its effectiveness in reducing stool volume and duration of diarrhea, and it is often given as a **single oral dose**.- Its broad-spectrum activity and good oral bioavailability make it a practical choice for treating **Vibrio cholerae** infections, especially in outbreak settings.*Co-trimoxazole*- While **co-trimoxazole (trimethoprim-sulfamethoxazole)** can be effective against some strains of Vibrio cholerae, resistance has become more common, limiting its use as a first-line agent.- Its efficacy as a single-dose treatment for cholera is generally less established compared to doxycycline.*Furazolidone*- **Furazolidone** has been used in the past for cholera treatment, but its use has declined due to concerns about side effects and the development of resistance.- It is not typically recommended as the first-line treatment for cholera in adults, particularly as a single dose.*Tetracycline*- **Tetracycline** is historically effective against cholera, but modern guidelines often prefer doxycycline due to its improved tolerability, once-daily dosing, and similar efficacy profile.- The older tetracyclines often require multiple doses per day, which can impact patient compliance compared to a single-dose regimen of doxycycline.
Question 5: Which of the following combinations does not show synergistic action?
- A. Streptomycin plus penicillin
- B. Rifampicin plus dapsone
- C. Penicillin plus tetracycline (Correct Answer)
- D. Penicillin plus sulfonamide
Explanation: ***Penicillin plus tetracycline*** - This combination is generally **antagonistic** or **indifferent**, not synergistic. Penicillin is a cell wall synthesis inhibitor that works best on actively growing bacteria, while tetracycline is a bacteriostatic protein synthesis inhibitor that can reduce bacterial growth, thereby diminishing penicillin's effect. - The combination is usually avoided as the **bacteriostatic action of tetracycline** can counteract the **bactericidal action of penicillin**, leading to reduced efficacy, especially in infections requiring rapid bacterial clearance. *Penicillin plus sulfonamide* - This combination can show synergism in some contexts, particularly as sulfonamides inhibit **folate synthesis**, while penicillin inhibits **cell wall synthesis**. - While not a classic synergistic pair for all infections, their mechanisms of action are distinct, and they can sometimes be used together, although specific synergistic effects are more limited compared to other pairs. *Streptomycin plus penicillin* - This is a classic example of **synergistic action**, particularly in conditions like **enterococcal endocarditis**. - Penicillin damages the bacterial cell wall, allowing **streptomycin** (an aminoglycoside) to more easily penetrate the cell and act on ribosomal targets, leading to enhanced bactericidal effect. *Rifampicin plus dapsone* - This combination is a cornerstone of **multi-drug therapy for leprosy**, demonstrating clear synergy against *Mycobacterium leprae*. - **Rifampicin** inhibits bacterial RNA synthesis, and **dapsone** inhibits folate synthesis, attacking different essential bacterial pathways which, when combined, are more effective and reduce the development of resistance.
Question 6: A woman presenting with symptoms of urinary tract infection was prescribed a drug that causes tendon rupture and arthropathy. What is the mechanism of action of the drug?
- A. Ribosomal inhibition
- B. Cell wall synthesis
- C. Inhibition of folic acid synthesis
- D. DNA gyrase inhibition (Correct Answer)
Explanation: ***DNA gyrase inhibition*** - The description of a drug causing **tendon rupture** and **arthropathy** in the context of a urinary tract infection (UTI) suggests a **fluoroquinolone**. - Fluoroquinolones exert their bactericidal effect by inhibiting **bacterial DNA gyrase** (also known as topoisomerase II) and **topoisomerase IV**, thereby preventing DNA replication and repair. *Ribosomal inhibition* - This mechanism is characteristic of antibiotics like **aminoglycosides**, **tetracyclines**, and **macrolides**. - While some of these can treat UTIs, they are not typically associated with **tendon rupture** or **arthropathy** as major side effects. *Cell wall synthesis* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillins, cephalosporins) and **vancomycin**. - These drugs are common for UTIs but do not cause **tendon rupture** or **arthropathy**. *Inhibition of folic acid synthesis* - This mechanism is used by **sulfonamides** and **trimethoprim**, often combined as trimethoprim-sulfamethoxazole. - While effective for UTIs, these drugs are not known to cause **tendon rupture** or **arthropathy**.
Question 7: Which one of the following drugs cannot cause Pseudotumor Cerebri ?
- A. Nitrofurantoin
- B. Metformin (Correct Answer)
- C. Tetracycline
- D. Nalidixic acid
Explanation: ***Metformin*** - **Metformin** is an oral hypoglycemic agent used for **type 2 diabetes** and is not associated with pseudotumor cerebri. - There is no known mechanism by which metformin would increase **intracranial pressure**. *Nitrofurantoin* - **Nitrofurantoin**, an antibiotic used for urinary tract infections, has been rarely implicated in drug-induced **pseudotumor cerebri**. - It works by interfering with **bacterial enzyme systems**, not typically affecting host intracranial fluid dynamics directly, but can cause idiosyncratic reactions. *Tetracycline* - **Tetracycline-class antibiotics** are well-known causes of **pseudotumor cerebri** (idiopathic intracranial hypertension). - This effect is thought to be dose-dependent and related to interference with **cerebrospinal fluid (CSF) absorption** or production. *Nalidixic acid* - **Nalidixic acid**, a quinolone antibiotic, is also recognized as a cause of **pseudotumor cerebri**, particularly in children. - Its mechanism is not fully understood but is believed to involve disturbances in **CSF dynamics**.
Question 8: 23 years old woman complains of recurrent acne over her face. History revealed that she had taken topical antibiotics for her acne without any significant improvement. Which one of the following tetracyclines is most preferred for her acne?
- A. Doxycycline (Correct Answer)
- B. Oxytetracycline
- C. Minocycline
- D. Demeclocycline
Explanation: ***Doxycycline*** - **Doxycycline** is a commonly preferred tetracycline for acne due to its **anti-inflammatory properties** and efficacy against *P. acnes* at sub-antimicrobial doses. - Its **longer half-life** allows for once-daily dosing, improving patient adherence compared to other tetracyclines. *Oxytetracycline* - While effective against *P. acnes*, **oxytetracycline** generally requires higher doses and more frequent administration, which can lead to poorer patient compliance. - It often causes **gastric irritation**, making it less favorable for long-term acne management. *Minocycline* - **Minocycline** is also effective for acne but is associated with a higher risk of **side effects** like dizziness, headache, and hyperpigmentation (e.g., skin, teeth). - Its potential for **drug-induced lupus-like syndrome** and **hepatotoxicity** makes it less preferred compared to doxycycline, especially for prolonged use. *Demeclocycline* - **Demeclocycline** is primarily used as an **ADH antagonist** for treating syndrome of inappropriate antidiuretic hormone (SIADH) and is not a first-line treatment for acne. - It has a higher incidence of **photosensitivity** and overall greater renal toxicity compared to other tetracyclines, making it unsuitable for acne.
Question 9: What is the primary purpose of xenobiotic metabolism?
- A. Increase water solubility (Correct Answer)
- B. Increase lipid solubility
- C. Make them nonpolar
- D. None of the above
Explanation: ***Increase water solubility*** - The primary goal of xenobiotic metabolism is to make these foreign compounds more **hydrophilic** (water-soluble). - This increased water solubility facilitates their **excretion** from the body via urine or bile. *Increase lipid solubility* - Increasing **lipid solubility** would make xenobiotics more likely to accumulate in **adipose tissue** and pass through cell membranes, hindering their excretion. - This is the opposite of the desired outcome for xenobiotic elimination. *Make them nonpolar* - Making xenobiotics **nonpolar** would be equivalent to increasing their lipid solubility, as nonpolar molecules tend to be lipid-soluble. - This would impede excretion and potentially lead to **bioaccumulation**, which is harmful. *None of the options* - This option is incorrect because xenobiotic metabolism specifically aims to increase **water solubility** for elimination.
Question 10: Tetracycline is used in prophylaxis of which of the following diseases?
- A. Meningitis
- B. Leptospirosis (Correct Answer)
- C. Brucellosis
- D. Cholera
Explanation: ***Leptospirosis (Correct Answer)*** - **Doxycycline**, a tetracycline antibiotic, is the **standard prophylactic agent** for **leptospirosis**, especially for individuals with high exposure risk (travelers to endemic areas, military personnel, occupational exposure). - **Prophylactic regimen**: 200 mg once weekly during exposure and for 2 weeks after last exposure. - It helps prevent the disease by inhibiting bacterial growth before infection becomes established. *Cholera (Incorrect)* - While tetracyclines like doxycycline can be used to **treat cholera** to reduce fluid loss and duration of diarrhea, they are **not used for prophylaxis** in healthy individuals. - Prophylaxis relies on **safe water and sanitation practices**, **oral cholera vaccine**, and proper food handling—not routine antibiotic administration. *Brucellosis (Incorrect)* - **Tetracyclines** (doxycycline) are essential for the **treatment** of **brucellosis**, typically in combination with rifampicin or streptomycin for 6 weeks, due to its intracellular nature and risk of relapse. - However, they are **not routinely used for prophylaxis** against brucellosis, even in high-risk individuals. *Meningitis (Incorrect)* - **Tetracyclines are not recommended for prophylaxis of bacterial meningitis**. - Prophylaxis for close contacts of meningococcal meningitis typically involves **rifampin**, **ceftriaxone**, or **ciprofloxacin**—not tetracyclines.
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