Biliary excretion US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Biliary excretion. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Biliary excretion US Medical PG Question 1: A 72-year-old man presents to the emergency department with a 1 hour history of bruising and bleeding. He says that he fell and scraped his knee on the ground. Since then, he has been unable to stop the bleeding and has developed extensive bruising around the area. He has a history of gastroesophageal reflux disease, hypertension, and atrial fibrillation for which he is taking an oral medication. He says that he recently started taking omeprazole for reflux. Which of the following processes is most likely inhibited in this patient?
- A. Sulfation
- B. Oxidation (Correct Answer)
- C. Filtration
- D. Acetylation
- E. Glucuronidation
Biliary excretion Explanation: ***Oxidation***
- The patient is taking **omeprazole**, a proton pump inhibitor, which is a known **CYP450 inhibitor**.
- Since the patient is also on an **oral anticoagulant** for atrial fibrillation, inhibition of CYP450 enzymes can reduce the metabolism of the anticoagulant, leading to **increased anticoagulant effect** and subsequent bleeding and bruising.
*Sulfation*
- **Sulfation** is a phase II metabolic reaction that converts compounds into more polar and excretable forms, but omeprazole primarily affects phase I metabolism involving CYP450 enzymes.
- While sulfation can be important for the metabolism of some drugs, it is not the primary process inhibited by omeprazole to cause increased bleeding with oral anticoagulants.
*Filtration*
- **Filtration** is a renal process and not a metabolic enzyme pathway affected by omeprazole.
- Omeprazole's interaction with anticoagulants mainly occurs through hepatic metabolism, not renal filtration.
*Acetylation*
- **Acetylation** is a phase II metabolic reaction, primarily carried out by **N-acetyltransferases**.
- Omeprazole is primarily known to interact with **CYP450 enzymes** (phase I metabolism) rather than N-acetyltransferases.
*Glucuronidation*
- **Glucuronidation** is a phase II metabolic reaction involving **UGT enzymes** that typically inactivates and increases the excretion of drugs.
- While important for drug metabolism, omeprazole's primary drug interactions leading to increased anticoagulant effects are via **CYP450 inhibition** (phase I metabolism), not directly through glucuronidation.
Biliary excretion US Medical PG Question 2: What is the primary mechanism for iron absorption in the duodenum?
- A. Simple diffusion
- B. Passive paracellular transport
- C. Endocytosis
- D. DMT1 transporter (Correct Answer)
Biliary excretion Explanation: ***DMT1 transporter***
- The **divalent metal transporter 1 (DMT1)** is the primary mechanism for absorbing **non-heme iron (ferrous iron, Fe2+)** into duodenal enterocytes.
- This active transport process is pH-dependent and drives iron uptake against a concentration gradient.
*Simple diffusion*
- Applies to the movement of substances down their concentration gradient without the aid of membrane proteins, which is not the main mechanism for iron due to its ionic nature.
- While some highly lipid-soluble substances can cross membranes this way, metal ions like iron require specific transporters.
*Passive paracellular transport*
- Involves substances moving *between* cells, rather than *through* them, often occurring in leaky epithelia.
- While some fluid and electrolytes may use this route, it is not the primary or regulated pathway for iron absorption.
*Endocytosis*
- A process where cells engulf substances by forming vesicles from the plasma membrane.
- While some macromolecules are absorbed via endocytosis, it is not the major mechanism for absorbing dietary iron in the duodenum.
Biliary excretion US Medical PG Question 3: A 42-year-old woman is brought to the emergency department because of intermittent sharp right upper quadrant abdominal pain and nausea for the past 10 hours. She has vomited 3 times. There is no associated fever, chills, diarrhea, or urinary symptoms. She has 2 children who both attend high school. She appears uncomfortable. She is 165 cm (5 ft 5 in) tall and weighs 86 kg (190 lb). Her BMI is 32 kg/m2. Her temperature is 37.0°C (98.6°F), pulse is 100/min, and blood pressure is 140/90 mm Hg. She has mild scleral icterus. On physical examination, her abdomen is soft and nondistended, with tenderness to palpation of the right upper quadrant without guarding or rebound. Bowel sounds are normal. Laboratory studies show the following:
Blood
Hemoglobin count 14 g/dL
Leukocyte count 9,000 mm3
Platelet count 160,000 mm3
Serum
Alkaline phosphatase 238 U/L
Aspartate aminotransferase 60 U/L
Bilirubin
Total 2.8 mg/dL
Direct 2.1 mg/dL
Which of the following is the most appropriate next step in diagnosis?
- A. Endoscopic retrograde cholangiopancreatography (ERCP)
- B. Supine and erect X-rays of the abdomen
- C. Computed tomography (CT) scan of the abdomen
- D. Hepatobiliary iminodiacetic acid (HIDA) scan of the biliary tract
- E. Transabdominal ultrasonography (Correct Answer)
Biliary excretion Explanation: ***Transabdominal ultrasonography***
- This is the **initial diagnostic test of choice** for suspected **gallstones** or other biliary pathology due to its non-invasive nature, accessibility, and high sensitivity for detecting stones.
- The patient's presentation with **RUQ pain**, nausea, vomiting, obesity, and mild **scleral icterus** with elevated **alkaline phosphatase** and **direct bilirubin** is highly suggestive of **choledocholithiasis** or **cholecystitis**.
*Endoscopic retrograde cholangiopancreatography (ERCP)*
- **ERCP** is a **therapeutic procedure** used to remove stones from the common bile duct, rather than a primary diagnostic tool.
- It is an **invasive procedure** with risks such as pancreatitis and is reserved for cases where obstruction is confirmed and needs intervention.
*Supine and erect X-rays of the abdomen*
- **Plain X-rays** are not effective for diagnosing gallstones as only about **10-20% of gallstones are radiopaque**.
- While they can rule out other causes of abdominal pain like bowel obstruction or perforation, they are **not the primary imaging modality** for biliary issues.
*Computed tomography (CT) scan of the abdomen*
- A **CT scan** is less sensitive than ultrasound for detecting gallstones and is associated with **radiation exposure**.
- It might be used if ultrasound findings are inconclusive or if there is concern for other intra-abdominal pathology, but it is **not the initial test of choice** for suspected cholelithiasis.
*Hepatobiliary iminodiacetic acid (HIDA) scan of the biliary tract*
- A **HIDA scan** is primarily used to diagnose **acute cholecystitis** (inflammation of the gallbladder) by assessing gallbladder emptying or obstruction of the cystic duct.
- While useful for acute cholecystitis, it is **not the first-line diagnostic test** for simply detecting gallstones or common bile duct stones, for which ultrasound is superior.
Biliary excretion US Medical PG Question 4: A patient is receiving daily administrations of Compound X. Compound X is freely filtered in the glomeruli and undergoes net secretion in the renal tubules. The majority of this tubular secretion occurs in the proximal tubule. Additional information regarding this patient's renal function and the renal processing of Compound X is included below:
Inulin clearance: 120 mL/min
Plasma concentration of Inulin: 1 mg/mL
PAH clearance: 600 mL/min
Plasma concentration of PAH: 0.2 mg/mL
Total Tubular Secretion of Compound X: 60 mg/min
Net Renal Excretion of Compound X: 300 mg/min
Which of the following is the best estimate of the plasma concentration of Compound X in this patient?
- A. 2 mg/mL (Correct Answer)
- B. 3 mg/mL
- C. There is insufficient information available to estimate the plasma concentration of Compound X
- D. 1 mg/mL
- E. 0.5 mg/mL
Biliary excretion Explanation: ***2 mg/mL***
* The **net renal excretion of Compound X (300 mg/min)** is the sum of the filtered load and the net tubular secretion.
* Given that Compound X is **freely filtered** and undergoes **net secretion (60 mg/min)**, we can calculate the filtered load and subsequently its plasma concentration.
* **Net excretion = Filtered load + Net tubular secretion**
* **300 mg/min = Filtered load + 60 mg/min**
* **Filtered load = 300 mg/min - 60 mg/min = 240 mg/min**
* Since **Filtered load = Glomerular Filtration Rate (GFR) * Plasma concentration (P_X)**, and GFR is estimated by **inulin clearance (120 mL/min)**:
* **240 mg/min = 120 mL/min * P_X**
* **P_X = 240 mg/min / 120 mL/min = 2 mg/mL**.
*3 mg/mL*
* This value would imply a significantly higher filtered load or a different contribution from tubular secretion.
* Calculations using this plasma concentration would not align with the provided excretion and secretion rates.
*There is insufficient information available to estimate the plasma concentration of Compound X*
* The problem provides all necessary values: **Inulin clearance (GFR)**, **net tubular secretion of Compound X**, and **net renal excretion of Compound X**.
* These parameters are sufficient to determine the filtered load and thus the plasma concentration of Compound X.
*1 mg/mL*
* A plasma concentration of 1 mg/mL would result in a lower filtered load than calculated and would not account for the observed net renal excretion.
* **Filtered load = 120 mL/min * 1 mg/mL = 120 mg/min**. Total excretion would then be 120 mg/min + 60 mg/min = 180 mg/min, which contradicts the given 300 mg/min.
*0.5 mg/mL*
* This plasma concentration would lead to an even lower filtered load, making it impossible to achieve the *net renal excretion of Compound X* given the tubular secretion.
* **Filtered load = 120 mL/min * 0.5 mg/mL = 60 mg/min**. Total excretion would be 60 mg/min + 60 mg/min = 120 mg/min, which is much lower than the given 300 mg/min.
Biliary excretion US Medical PG Question 5: A 46-year-old man comes to the physician for a follow-up examination. Two weeks ago, he underwent laparoscopic herniorrhaphy for an indirect inguinal hernia. During the procedure, a black liver was noted. He has a history of intermittent scleral icterus that resolved without treatment. Serum studies show:
Aspartate aminotransferase 30 IU/L
Alanine aminotransferase 35 IU/L
Alkaline phosphatase 47 mg/dL
Total bilirubin 1.7 mg/dL
Direct bilirubin 1.1 mg/dL
Which of the following is the most likely diagnosis?
- A. Gilbert syndrome
- B. Dubin-Johnson syndrome (Correct Answer)
- C. Type II Crigler-Najjar syndrome
- D. Type I Crigler-Najjar syndrome
- E. Rotor syndrome
Biliary excretion Explanation: ***Dubin-Johnson syndrome***
- The presence of a **black liver** during surgery is pathognomonic for Dubin-Johnson syndrome, due to the accumulation of **melanin-like pigment** from impaired hepatocyte excretion.
- This syndrome is characterized by **intermittent conjugated hyperbilirubinemia** (direct bilirubin 1.1 mg/dL, total bilirubin 1.7 mg/dL) and **normal liver enzymes**, consistent with the patient's presentation of scleral icterus that resolved spontaneously.
*Gilbert syndrome*
- Gilbert syndrome is characterized by **unconjugated hyperbilirubinemia** due to reduced UDP-glucuronosyltransferase activity, while this patient has elevated direct bilirubin.
- It does **not cause a black liver**, nor does it typically present with such a significant elevation in direct bilirubin.
*Type II Crigler-Najjar syndrome*
- This syndrome involves **unconjugated hyperbilirubinemia** (due to a defect in UDP-glucuronosyltransferase) and would not present with a black liver.
- While less severe than Type I, it still primarily affects **unconjugated bilirubin metabolism**.
*Type I Crigler-Najjar syndrome*
- This is a severe form of **unconjugated hyperbilirubinemia**, often leading to **kernicterus** in infancy, and is not consistent with an adult presenting with intermittent mild icterus and normal liver enzymes.
- It is not associated with a **black liver**.
*Rotor syndrome*
- Rotor syndrome also causes **conjugated hyperbilirubinemia** with normal liver enzymes but is distinguished from Dubin-Johnson by the **absence of a black liver**.
- It is usually less severe than Dubin-Johnson and has a slightly different pattern of urinary coproporphyrin excretion.
Biliary excretion US Medical PG Question 6: A 20-year-old girl presents to a physician following unprotected coitus with her boyfriend about 10 hours ago. She tells the doctor that although they usually use a barrier method of contraception, this time they forgot. She does not want to become pregnant. She also mentions that she has major depression and does not want to take an estrogen-containing pill. After necessary counseling, the physician prescribes an enteric-coated pill containing 1.5 mg of levonorgestrel. Which of the following is the primary mechanism of action of this drug?
- A. Atrophy of the endometrium
- B. Reduction in motility of cilia in the fallopian tubes
- C. Mucosal hypertrophy and polyp formation in cervix
- D. Thickening of the cervical mucus
- E. Delayed ovulation through inhibition of follicular development (Correct Answer)
Biliary excretion Explanation: ***Delayed ovulation through inhibition of follicular development***
- The primary mechanism of action of **levonorgestrel** as emergency contraception is to **inhibit or delay ovulation** by suppressing the luteinizing hormone (LH) surge.
- This prevents the release of an egg, thereby averting fertilization if intercourse has recently occurred.
*Atrophy of the endometrium*
- While progestins can cause endometrial changes, **atrophy** is not the primary mechanism of action for high-dose levonorgestrel in emergency contraception.
- Significant endometrial changes that would prevent implantation typically require longer-term exposure or different formulations.
*Reduction in motility of cilia in the fallopian tubes*
- This is not a primary mechanism of action for **levonorgestrel** as an emergency contraceptive.
- While hormonal changes can influence fallopian tube function, the main contraceptive effect is pre-fertilization.
*Mucosal hypertrophy and polyp formation in cervix*
- **Levonorgestrel** typically causes changes like **thickening of cervical mucus**, not hypertrophy or polyp formation, to impede sperm.
- Mucosal hypertrophy and polyp formation are not considered mechanisms of contraception.
*Thickening of the cervical mucus*
- While **levonorgestrel** does **thicken cervical mucus**, making it harder for sperm to reach the egg, this is a secondary mechanism.
- The primary and most effective action for emergency contraception is the delay of ovulation.
Biliary excretion US Medical PG Question 7: A 53-year-old woman presents to her primary care doctor due to discolored, itchy skin, joint pain, and a feeling of abdominal fullness for the past week. Her medical history includes anxiety and depression. She also experiences occasional headaches and dizziness. Of note, the patient recently returned from an expedition to Alaska, where she and her group ate polar bear liver. Physical examination shows dry skin with evidence of excoriation and mild hepatosplenomegaly. Lab investigations reveal an alkaline phosphatase level of 35 U/L and total bilirubin of 0.4 mg/dL. Which of the following tests is most likely to uncover the etiology of her condition?
- A. Jejunal biopsy
- B. Plasma retinol levels (Correct Answer)
- C. BRCA2 gene mutation
- D. Antimitochondrial antibodies
- E. Elevated hepatic venous pressure gradient
Biliary excretion Explanation: ***Plasma retinol levels***
- The patient's history of consuming **polar bear liver**, combined with symptoms like **discolored, itchy skin**, **joint pain**, and **hepatosplenomegaly**, strongly suggests **vitamin A toxicity (hypervitaminosis A)**.
- Measuring **plasma retinol levels** directly assesses vitamin A status and would confirm dangerously high levels.
*Jejunal biopsy*
- A jejunal biopsy is typically used to diagnose malabsorption syndromes or inflammatory bowel diseases affecting the small intestine.
- The symptoms and the recent dietary history do not point towards a primary intestinal pathology requiring a biopsy for diagnosis.
*BRCA2 gene mutation*
- The BRCA2 gene mutation is associated with an increased risk of certain cancers, particularly breast and ovarian cancers.
- This genetic test is irrelevant to the acute presentation of symptoms or the suspected etiology of vitamin A toxicity.
*Antimitochondrial antibodies*
- **Antimitochondrial antibodies (AMA)** are a hallmark of **primary biliary cholangitis (PBC)**, an autoimmune liver disease.
- While PBC can cause pruritus and liver abnormalities, the patient's acute onset of symptoms after consuming polar bear liver makes vitamin A toxicity a more plausible diagnosis.
*Elevated hepatic venous pressure gradient*
- An **elevated hepatic venous pressure gradient (HVPG)** is a measure of portal hypertension and is used to assess the severity of liver cirrhosis.
- While hepatomegaly is present, there is no indication of advanced liver disease or portal hypertension in the initial presentation; the liver enzyme levels (ALP, bilirubin) are normal, which contradicts severe liver damage leading to portal hypertension.
Biliary excretion US Medical PG Question 8: A 55-year-old woman presents to the physician because of a fever 4 days after discharge from the hospital following induction chemotherapy for acute myeloid leukemia (AML). She has no other complaints and feels well otherwise. Other than the recent diagnosis of AML, she has no history of a serious illness. The temperature is 38.8°C (101.8°F), the blood pressure is 110/65 mm Hg, the pulse is 82/min, and the respirations are 14/min. Examination of the catheter site, skin, head and neck, heart, lungs, abdomen, and perirectal area shows no abnormalities. The results of the laboratory studies show:
Hemoglobin 9 g/dL
Leukocyte count 800/mm3
Percent segmented neutrophils 40%
Platelet count 85,000/mm3
Which of the following is the most appropriate pharmacotherapy at this time?
- A. Valacyclovir
- B. Vancomycin
- C. Imipenem (Correct Answer)
- D. Caspofungin
- E. Ciprofloxacin
Biliary excretion Explanation: ***Imipenem***
- This patient presents with **febrile neutropenia** (fever >38.3°C and absolute neutrophil count <500/mm³ or expected to fall below 500/mm³). This is a **medical emergency** requiring prompt empiric **broad-spectrum antibiotic** therapy covering **Gram-positive** and **Gram-negative** organisms.
- **Imipenem** is a carbapenem antibiotic with broad-spectrum activity, making it an appropriate choice for empiric treatment of febrile neutropenia, especially in high-risk patients like those undergoing induction chemotherapy for AML.
*Valacyclovir*
- **Valacyclovir** is an antiviral medication used primarily for **herpes simplex** and **varicella-zoster virus** infections.
- While immunocompromised patients are susceptible to viral infections, there is no clinical evidence at this time to suggest a viral etiology, and **febrile neutropenia** takes precedence for immediate broad-spectrum antibacterial coverage.
*Vancomycin*
- **Vancomycin** is an antibiotic that specifically targets **Gram-positive bacteria**, particularly **methicillin-resistant Staphylococcus aureus (MRSA)**.
- Empiric vancomycin is not typically recommended as initial sole therapy for febrile neutropenia unless there is strong suspicion of a Gram-positive infection (e.g., catheter-related infection, mucositis, skin and soft tissue infection, or known colonization with MRSA), which is not present here.
*Caspofungin*
- **Caspofungin** is an **antifungal** medication used to treat invasive fungal infections, including candidiasis and aspergillosis.
- Initial management of febrile neutropenia focuses on bacterial infections; empiric antifungal therapy is usually initiated if fever persists despite broad-spectrum antibiotics for several days.
*Ciprofloxacin*
- **Ciprofloxacin** is a fluoroquinolone antibiotic with good activity against many **Gram-negative bacteria** but limited activity against **Gram-positive organisms** and anaerobes.
- While it can be used for prophylaxis or as part of a combination regimen, it is not considered sufficient as a single agent for empiric treatment of **high-risk febrile neutropenia** due to its limited spectrum and increasing resistance patterns.
Biliary excretion US Medical PG Question 9: Five days after being admitted to the hospital for a scald wound, a 2-year-old boy is found to have a temperature of 40.2°C (104.4°F). He does not have difficulty breathing, cough, or painful urination. He initially presented one hour after spilling a pot of boiling water on his torso while his mother was cooking dinner. He was admitted for fluid resuscitation, nutritional support, pain management, and wound care, and he was progressing well until today. He has no other medical conditions. Other than analgesia during this hospital stay, he does not take any medications. He appears uncomfortable but not in acute distress. His pulse is 150/min, respirations are 41/min, and blood pressure is 90/50 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 99%. Examination shows uneven, asymmetrical scalding covering his anterior torso in arrow-like patterns with surrounding erythema and purulent discharge. The remainder of the examination shows no abnormalities. His hemoglobin is 13.4 g/dL, platelet count is 200,000/mm3, and leukocyte count is 13,900/mm3. Which of the following is the most appropriate initial pharmacological treatment for this patient?
- A. Vancomycin and metronidazole
- B. Amoxicillin/clavulanic acid and ceftriaxone
- C. Ampicillin/sulbactam and daptomycin
- D. Vancomycin and cefepime (Correct Answer)
- E. Piperacillin/tazobactam and cefepime
Biliary excretion Explanation: ***Vancomycin and cefepime***
- The patient presents with classic signs of **burn wound infection**, including fever, purulent discharge, and a rapid pulse, necessitating broad-spectrum antibiotic coverage.
- **Vancomycin** provides excellent coverage against **MRSA (methicillin-resistant *Staphylococcus aureus*)**, a common pathogen in burn infections, while **cefepime** covers **gram-negative bacteria**, including *Pseudomonas aeruginosa*, which is also frequently implicated.
*Vancomycin and metronidazole*
- While vancomycin covers gram-positive bacteria like **MRSA**, **metronidazole** primarily targets **anaerobic bacteria**, which are less common as primary pathogens in burn wound infections.
- This combination lacks adequate coverage for crucial gram-negative bacteria such as *Pseudomonas aeruginosa*.
*Amoxicillin/clavulanic acid and ceftriaxone*
- This combination provides coverage against some common community-acquired pathogens but is insufficient for the broad-spectrum needs of a severe **hospital-acquired burn infection**.
- It lacks reliable coverage for **MRSA** and *Pseudomonas aeruginosa*, which are critical in this setting.
*Ampicillin/sulbactam and daptomycin*
- **Ampicillin/sulbactam** covers some gram-positive and gram-negative bacteria but would not reliably cover **MRSA** or *Pseudomonas aeruginosa*.
- **Daptomycin** is effective against gram-positive bacteria, including **MRSA**, but does not cover gram-negative pathogens, leaving a significant gap in treatment.
*Piperacillin/tazobactam and cefepime*
- Both **piperacillin/tazobactam** and **cefepime** are excellent broad-spectrum antibiotics covering gram-negative pathogens, including *Pseudomonas aeruginosa*, but are largely redundant in this combination.
- This regimen lacks specific coverage for **MRSA**, which is a significant concern in nosocomial burn wound infections.
Biliary excretion US Medical PG Question 10: A 57-year-old HIV-positive male with a history of intravenous drug abuse presents to the emergency room complaining of arm swelling. He reports that he developed progressively worsening swelling and tenderness over the right antecubital fossa three days prior. He recently returned from a trip to Nicaragua. His past medical history is notable for an anaphylactoid reaction to vancomycin. His temperature is 101.4°F (38.6°C), blood pressure is 140/70 mmHg, pulse is 110/min, and respirations are 20/min. Physical examination reveals an erythematous, fluctuant, and tender mass overlying the right antecubital fossa. Multiple injection marks are noted across both upper extremities. He undergoes incision and drainage and is started on an antibiotic that targets the 50S ribosome. He is discharged with plans to follow up in one week. However, five days later he presents to the same emergency room complaining of abdominal cramps and watery diarrhea. Which of the following classes of pathogens is most likely responsible for this patient’s current symptoms?
- A. Gram-negative curved bacillus
- B. Gram-negative bacillus
- C. Anaerobic flagellated protozoan
- D. Gram-positive bacillus (Correct Answer)
- E. Gram-positive coccus
Biliary excretion Explanation: ***Gram-positive bacillus***
- The patient was administered an antibiotic targeting the **50S ribosomal subunit** following incision and drainage for a suspected skin infection (likely **MRSA** given IV drug abuse). This strongly suggests **clindamycin** was used.
- **Clindamycin** is a known risk factor for developing **Clostridioides (formerly Clostridium) difficile infection (CDI)**, which is caused by a **Gram-positive, spore-forming bacillus** and manifests with **abdominal cramps and watery diarrhea**.
*Gram-negative curved bacillus*
- This class of pathogens includes organisms like **Vibrio cholerae** or **Campylobacter jejuni**, which can cause diarrhea.
- However, the patient's presentation with **colitis** after antibiotic use is more consistent with **Clostridioides difficile**, not typically a curved Gram-negative bacillus.
*Gram-negative bacillus*
- While some Gram-negative bacilli (e.g., E. coli, Salmonella) can cause diarrhea, their association with **antibiotic-induced colitis** following treatment for a skin abscess is less direct than that of *Clostridioides difficile*.
- The initial skin infection in IV drug users is most commonly staphylococcal (Gram-positive coccus), for which a 50S targeting antibiotic would be prescribed.
*Anaerobic flagellated protozoan*
- This description often refers to pathogens like **Giardia lamblia** or **Trichomonas vaginalis**, which are not bacteria.
- While *Giardia* can cause diarrhea, it typically causes **malabsorption** and **greasy stools**, and wouldn't be triggered by recent antibiotic use for a skin infection.
*Gram-positive coccus*
- **Gram-positive cocci** (e.g., Staphylococcus aureus) are the likely cause of the initial skin infection/abscess.
- However, they do not typically cause **antibiotic-associated colitis** with watery diarrhea; rather, the *antibiotic treatment itself* for these organisms can predispose to *Clostridioides difficile*.
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