Antibiotic Prophylaxis — MCQs
A patient develops an infection of methicillin resistant Staphylococcus aureus. All of the following can be used to treat this infection except
A patient with a non-obstructing carcinoma of the sigmoid colon is being prepared for elective resection. To minimize the risk of postoperative infectious complications, what should be included in your planning?
Which of the following drugs need not be stopped before surgery?
Which of the following is the drug of choice for preoperative antibiotic prophylaxis in a patient undergoing cardiac surgery?
Which of the following is a first-generation cephalosporin used for surgical prophylaxis?
Which of the following steps has proven benefit in decreasing puerperal infection following cesarean section?
A person is bitten by a dog. The dog and the person are fully immunized. There is a small abrasion mark on the site of bite. What would you advise to the person?
A 37-year-old G2P1 woman at 38 weeks' gestation presents to the obstetrics clinic for a prenatal visit. The patient had difficulty becoming pregnant but was successful after using in vitro fertilization. She has a history of recurrent herpes outbreaks and is currently experiencing genital pain and tingling. Her first pregnancy was complicated by failure to progress, which resulted in a cesarean birth. Routine rectovaginal culture at 36 weeks was positive for Group B streptococci. Which of the following would be an absolute indication for delivering the child by LSCS (Lower Segment Cesarean Section):
To prevent acute rheumatic fever, acute pharyngitis due to group A streptococci should be treated with antibiotics before:
What is the optimal timing for administering antibiotic prophylaxis before surgery?
Antibiotic Prophylaxis Indian Medical PG Practice Questions and MCQs
Question 1: A patient develops an infection of methicillin resistant Staphylococcus aureus. All of the following can be used to treat this infection except
- A. Cotrimoxazole
- B. Ciprofloxacin
- C. Cefaclor (Correct Answer)
- D. Vancomycin
Explanation: ***Cefaclor*** - **Cefaclor** is a second-generation **cephalosporin**, which, like all beta-lactam antibiotics, is ineffective against **MRSA** because **MRSA** produces an altered penicillin-binding protein (PBP2a) encoded by the **mecA** gene. - This altered **PBP2a** has a low affinity for **beta-lactam antibiotics**, rendering them inactive. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) is a commonly used and effective oral antibiotic for treating **MRSA** infections, particularly in outpatient settings. - It inhibits **folate synthesis** in bacteria, an essential pathway for their growth and replication. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** that can be used to treat certain **MRSA** infections, although resistance can be an issue. [2] - It works by inhibiting bacterial **DNA gyrase** and **topoisomerase IV**, crucial enzymes for DNA replication. [2] *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that is a first-line treatment for serious **MRSA** infections, especially in hospitalized patients. [1] - It works by inhibiting **bacterial cell wall synthesis** at a different site than beta-lactams, making it effective against **MRSA**. [1]
Question 2: A patient with a non-obstructing carcinoma of the sigmoid colon is being prepared for elective resection. To minimize the risk of postoperative infectious complications, what should be included in your planning?
- A. Postoperative administration for 5 to 7 days of parenteral antibiotics effective against aerobes and anaerobes
- B. A single preoperative parenteral dose of antibiotic effective against aerobes and anaerobes may provide initial coverage. (Correct Answer)
- C. Postoperative administration for 2 to 4 days of parenteral antibiotics effective against aerobes and anaerobes
- D. Avoidance of oral antibiotics to prevent emergence of Clostridioides difficile
Explanation: ***Single preoperative parenteral dose of antibiotic effective against aerobes and anaerobes*** - For **elective colorectal surgery**, a single dose of a **broad-spectrum parenteral antibiotic** administered within 60 minutes prior to incision is the standard of care to reduce surgical site infections. - This approach ensures adequate drug levels in the tissues during the period of potential bacterial contamination and is a cornerstone of modern surgical prophylaxis. - Current guidelines (WHO, SCIP) recommend a single preoperative dose, which may be redosed intraoperatively if the procedure is prolonged beyond 3-4 hours. *Avoidance of oral antibiotics to prevent emergence of Clostridioides difficile* - This is **incorrect**. **Oral antibiotics** (such as neomycin and metronidazole) are routinely used preoperatively in conjunction with mechanical bowel preparation for colorectal surgery to reduce intraluminal bacterial load. - The concern for *Clostridioides difficile* infection is generally low with short-term, targeted prophylactic antibiotic regimens compared to broad-spectrum, prolonged use. - The combination of oral and parenteral antibiotics has been shown to further reduce surgical site infections. *Postoperative administration for 5 to 7 days of parenteral antibiotics* - **Prolonged postoperative antibiotic administration** beyond 24 hours in uncomplicated cases is not recommended as it increases the risk of **antibiotic resistance**, *C. difficile* infection, and adverse drug reactions without additional benefit. - The goal of prophylactic antibiotics is to cover the period of contamination during surgery, not to treat presumed ongoing infection postoperatively. *Postoperative administration for 2 to 4 days of parenteral antibiotics* - While administration for up to 24 hours post-operatively may be considered in some high-risk cases, routine **prolonged postoperative antibiotics** (2-4 days) are unnecessary for most elective colorectal resections. - Evidence suggests that continuing antibiotics beyond the immediate perioperative period does not further reduce the incidence of **surgical site infections** in clean-contaminated surgeries.
Question 3: Which of the following drugs need not be stopped before surgery?
- A. High Dose Aspirin
- B. Metformin
- C. Digitalis (Correct Answer)
- D. Warfarin
Explanation: ***Digitalis*** - **Digitalis (digoxin)** is often continued through surgery, especially in patients with **heart failure** or **atrial fibrillation** to maintain cardiac function. - Its cessation could precipitate **cardiac decompensation** or arrhythmias, which are high-risk events during surgery. *High Dose Aspirin* - **High-dose aspirin** should generally be stopped before surgery due to its **antiplatelet effects**, increasing the risk of perioperative bleeding. - The duration of discontinuation depends on the type of surgery and individual patient risk. *Metformin* - **Metformin** should be stopped before surgery due to the risk of **lactic acidosis**, especially in situations involving **renal impairment** or hypoperfusion associated with surgery. - It's typically held on the day of surgery and for 24-48 hours post-operatively, depending on renal function. *Warfarin* - **Warfarin** is a strong oral anticoagulant that must be discontinued before most surgeries to prevent **excessive bleeding**. - It is typically stopped 5 days pre-op, and patients often receive **bridging therapy** with heparin, depending on their risk for thromboembolism.
Question 4: Which of the following is the drug of choice for preoperative antibiotic prophylaxis in a patient undergoing cardiac surgery?
- A. Cefazolin (Correct Answer)
- B. Penicillin
- C. Clindamycin
- D. Vancomycin
Explanation: ***Cefazolin*** - **Cefazolin** is a first-generation cephalosporin that provides excellent coverage against **Staphylococcus aureus** and **Streptococcus species**, which are common pathogens in surgical site infections in cardiac surgery. - It has a favorable safety profile, long half-life allowing for convenient dosing, and good tissue penetration, making it the preferred choice for **preoperative antibiotic prophylaxis** in most cardiac surgery cases. *Penicillin* - **Penicillin** has a narrow spectrum of activity compared to cefazolin and does not adequately cover all potential pathogens in cardiac surgery, particularly **methicillin-susceptible Staphylococcus aureus (MSSA)**. - Due to its limited spectrum, penicillin is generally not recommended for routine **surgical prophylaxis**, especially in complex procedures like cardiac surgery. *Clindamycin* - **Clindamycin** is an alternative for patients with **beta-lactam allergies**, providing coverage against gram-positive organisms and anaerobes. - However, for routine prophylaxis without a specific allergy or high risk of resistant organisms, **clindamycin** is less effective than cefazolin against the most prevalent surgical pathogens. *Vancomycin* - **Vancomycin** is reserved for patients with a known **penicillin allergy** or a high risk of **methicillin-resistant Staphylococcus aureus (MRSA)** colonization or infection. - Its routine use as a primary prophylactic agent in cardiac surgery is discouraged to prevent the development of **vancomycin resistance**.
Question 5: Which of the following is a first-generation cephalosporin used for surgical prophylaxis?
- A. Ceftriaxone
- B. Cefoxitin
- C. Cefazolin (Correct Answer)
- D. Cefepime
Explanation: ***Cefazolin*** - **Cefazolin** is a **first-generation cephalosporin** routinely used for **surgical prophylaxis** due to its effective coverage against common skin flora like *Staphylococcus aureus* and streptococci. - Its **longer half-life** allows for less frequent dosing pre-operatively, making it practical for preventing surgical site infections. *Ceftriaxone* - **Ceftriaxone** is a **third-generation cephalosporin** with a broader spectrum of activity, including good coverage against many gram-negative bacteria, but it is not typically the first choice for routine surgical prophylaxis. - It is more commonly reserved for treating serious infections such as **meningitis**, **gonorrhea**, and complicated intra-abdominal infections. *Cefoxitin* - **Cefoxitin** is a **second-generation cephalosporin** known for its excellent activity against **anaerobic bacteria**, in addition to gram-positive and some gram-negative organisms. - While it can be used for surgical prophylaxis in procedures with **high anaerobic risk** (e.g., colorectal surgery), it is not a first-generation cephalosporin. *Cefepime* - **Cefepime** is a **fourth-generation cephalosporin** with a very broad spectrum of activity, including excellent coverage against **Pseudomonas aeruginosa** and improved activity against gram-positive bacteria compared to third-generation cephalosporins. - It is reserved for severe infections, such as **febrile neutropenia** and hospital-acquired pneumonia, and is not generally used for routine surgical prophylaxis.
Question 6: Which of the following steps has proven benefit in decreasing puerperal infection following cesarean section?
- A. Administration of single dose of ampicillin or 1st generation cephalosporin at the time of cesarean (Correct Answer)
- B. Non closure of peritoneum
- C. Single layer uterine closure
- D. Skin closure with staples than with suture
Explanation: ***Administration of single dose of ampicillin or 1st generation cephalosporin at the time of cesarean*** - Prophylactic **antibiotics** administered prior to skin incision significantly reduce the risk of **puerperal infection** (e.g., endometritis, wound infection) following cesarean section. - The timing of administration (within 60 minutes of skin incision) is crucial for optimal effectiveness, typically using a **first-generation cephalosporin** or **ampicillin** for broad-spectrum coverage. *Non closure of peritoneum* - Studies have shown that **non-closure of the visceral and parietal peritoneum** during cesarean section has no significant impact on the rate of puerperal infection. - While it may shorten operative time and reduce pain, it does not offer a demonstrable benefit in reducing postoperative infections. *Single layer uterine closure* - **Single-layer uterine closure** has been found to be comparable to double-layer closure in terms of postoperative infection rates and uterine healing. - There is no strong evidence to suggest that single-layer closure specifically decreases the incidence of puerperal infection more effectively than double-layer closure. *Skin closure with staples than with suture* - The choice between **staples and sutures** for skin closure after cesarean section does not show a consistent difference in the incidence of **wound infection**. - While staples may be faster and might reduce suture-related complications, they do not inherently decrease the overall risk of puerperal infection compared to traditional suturing.
Question 7: A person is bitten by a dog. The dog and the person are fully immunized. There is a small abrasion mark on the site of bite. What would you advise to the person?
- A. Amoxiclav
- B. Metronidazole
- C. Ciprofloxacin
- D. Observation (Correct Answer)
Explanation: ***Observation*** - This is a **Category II exposure** (minor abrasion/scratch) according to **WHO rabies classification**. With both the dog and person **fully immunized**, the recommended management is **immediate wound washing** with soap and water followed by **observation of the dog for 10 days**. - If the dog remains healthy during the 10-day observation period, no further rabies post-exposure prophylaxis is needed. The person's prior vaccination provides adequate protection. - **Prophylactic antibiotics are NOT routinely indicated** for minor abrasions in immunized individuals when the wound can be properly cleaned. The risk of significant bacterial infection in superficial wounds is low with proper wound care. - This approach follows **WHO and IAPSM guidelines** for rational dog bite management, avoiding unnecessary antibiotic use. *Amoxiclav* - Prophylactic antibiotics like **amoxicillin-clavulanate** are reserved for **high-risk wounds**: deep puncture wounds (Category III), wounds near bones/joints, hand/face wounds, delayed presentation (>8 hours), or immunocompromised patients. - A **small abrasion** in an immunized person does not meet criteria for routine antibiotic prophylaxis. Over-prescription contributes to **antimicrobial resistance**. - The primary concern in dog bite management is **rabies prevention**, not routine bacterial prophylaxis for minor wounds. *Metronidazole* - **Metronidazole** alone has limited coverage against common bite wound pathogens and would not be appropriate even if antibiotics were indicated. - It lacks activity against aerobic organisms like *Pasteurella* and *Staphylococcus* species commonly found in dog bites. *Ciprofloxacin* - **Ciprofloxacin** is not the first-line antibiotic for dog bites even when prophylaxis is indicated, due to limited anaerobic and Gram-positive coverage. - More importantly, antibiotics are **not routinely needed** for this Category II exposure with proper wound care and observation.
Question 8: A 37-year-old G2P1 woman at 38 weeks' gestation presents to the obstetrics clinic for a prenatal visit. The patient had difficulty becoming pregnant but was successful after using in vitro fertilization. She has a history of recurrent herpes outbreaks and is currently experiencing genital pain and tingling. Her first pregnancy was complicated by failure to progress, which resulted in a cesarean birth. Routine rectovaginal culture at 36 weeks was positive for Group B streptococci. Which of the following would be an absolute indication for delivering the child by LSCS (Lower Segment Cesarean Section):
- A. History of previous cesarean section
- B. Current symptoms of genital pain and tingling (Correct Answer)
- C. Maternal colonization with Group B streptococci
- D. In vitro fertilization
Explanation: ***Current symptoms of genital pain and tingling*** - **Genital pain and tingling** in a patient with a history of recurrent herpes outbreaks strongly suggests a **prodromal or active herpes outbreak**. - An active maternal **genital herpes lesion** at the time of labor is an absolute indication for **cesarean delivery** to prevent neonatal herpes simplex virus (HSV) infection, which can be life-threatening. *History of previous cesarean section* - A **prior cesarean section** is a relative indication for a repeat cesarean, but many women are candidates for a **trial of labor after cesarean (TOLAC)** if certain criteria are met. - It is not an absolute contraindication to vaginal delivery itself, especially if the previous cesarean was for a non-recurrent indication like **failure to progress**. *Maternal colonization with Group B streptococci* - **Group B streptococcus (GBS) colonization** is typically managed with **intrapartum antibiotic prophylaxis (IAP)** to prevent early-onset neonatal GBS disease. - It does not necessitate a cesarean section for delivery; rather, antibiotics are given once labor begins or membranes rupture. *In vitro fertilization* - **In vitro fertilization (IVF)** is a method of conception and does not inherently determine the mode of delivery. - Pregnancy achieved through IVF does not, by itself, increase the risk of complications that would mandate a **cesarean section**, unless there are other associated factors like multiple gestations or specific maternal conditions.
Question 9: To prevent acute rheumatic fever, acute pharyngitis due to group A streptococci should be treated with antibiotics before:
- A. 10 days of illness
- B. 7 days of illness
- C. 8 days of illness
- D. 9 days of illness (Correct Answer)
Explanation: ***9 days of illness*** - Treatment of **Group A Streptococcus (GAS)** pharyngitis with appropriate antibiotics within **9 days** of symptom onset effectively prevents subsequent acute rheumatic fever. - This timeframe is crucial because it allows for clearance of the bacteria before the immune response that triggers **rheumatic fever** becomes fully established. *10 days of illness* - This duration is **beyond** the optimal window for preventing acute rheumatic fever, as the immune response may already be sufficient to initiate the disease process. - While still beneficial for symptom resolution, antibiotic treatment initiated at this point is **less effective** in preventing the sequelae of rheumatic fever. *7 days of illness* - Administering antibiotics within **7 days** of illness is highly effective and falls within the appropriate treatment window for preventing acute rheumatic fever [2]. - However, **9 days provides a slightly longer, yet still effective, cutoff**, making prevention of rheumatic fever still possible within this slightly extended period. *8 days of illness* - Antibiotic treatment at **8 days of illness** is still considered within the therapeutic window for preventing acute rheumatic fever [2]. - The goal is to clear the infection and prevent the immune system from mounting the **autoimmune response** that leads to cardiac damage [1].
Question 10: What is the optimal timing for administering antibiotic prophylaxis before surgery?
- A. Immediately before induction of anesthesia
- B. 30-60 minutes before incision (Correct Answer)
- C. 2-3 hours before surgery
- D. Immediately after surgery
Explanation: ***30-60 minutes before incision*** - This is the **optimal timing** recommended by WHO, CDC, and major surgical guidelines for most commonly used prophylactic antibiotics (cefazolin, cefuroxime). - Ensures **peak tissue and serum concentrations** are achieved at the time of incision, providing maximum protection against surgical site infections. - Based on **pharmacokinetic principles**: the antibiotic must be present at bactericidal concentrations in tissues when bacterial contamination occurs. - Studies show this timing significantly reduces surgical site infection rates compared to other timings. *Immediately before induction of anesthesia* - While acceptable in some protocols, this may be too early if there is a delay between induction and incision. - Could result in **declining antibiotic levels** by the time the incision is made, especially for antibiotics with shorter half-lives. *2-3 hours before surgery* - This is **too early** for most antibiotics. - Tissue levels may have already **declined below therapeutic concentrations** by the time of incision. - Does not provide adequate protection during the critical period of bacterial contamination. *Immediately after surgery* - This is **treatment, not prophylaxis**. - Offers **no preventive benefit** against intraoperative contamination. - By this time, bacteria introduced during surgery have already adhered to tissues and begun forming biofilms.
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