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?

Endoscopic retrograde cholangiopancreatography (ERCP)

Supine and erect X-rays of the abdomen

Computed tomography (CT) scan of the abdomen

Hepatobiliary iminodiacetic acid (HIDA) scan of the biliary tract

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?

There is insufficient information available to estimate the plasma concentration of Compound X

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?

Type II Crigler-Najjar syndrome

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?

Delayed ovulation through inhibition of follicular development

Reduction in motility of cilia in the fallopian tubes

Mucosal hypertrophy and polyp formation in cervix

Thickening of the cervical mucus

A 55-year-old woman presents to the emergency room with severe abdominal pain for the past 24 hours. She has also noticed blood in her urine. She does not have any significant past medical history. Family history is significant for her mother having cholecystitis status post cholecystectomy at age 45. Her vital signs include: temperature 36.8°C (98.2°F), pulse 103/min, respiratory rate 15/min, blood pressure 105/85 mm Hg. Physical examination is significant for a woman continuously moving on the exam table in an attempt to get comfortable. Laboratory findings are significant for the following: Serum electrolytes Na 138 mEq/L N: 135–145 mEq/L K 4.0 mEq/L N: 3.5–5.0 mEq/L Cl 102 mEq/L N: 98–108 mEq/L CO2 27 mEq/L N: 22–32 mEq/L Ca 9.2 mEq/dL N: 8.4–10.2 mEq/dL PO4 3.5 mg/dL N: 3.0–4.5 mg/dL A 24-hour urine collection is performed and reveals a urinary calcium of 345 mg/day (ref: < 300 mg/day in men; < 250 mg/day in women). A non-contrast CT of the abdomen is performed and is shown in the exhibit. The patient’s symptoms pass within the next 12 hours with hydration and acetaminophen for pain management. She is prescribed a medication to prevent subsequent episodes. At which of the following parts of the nephron does this medication most likely work?

Descending limb of the loop of Henle

Thick ascending limb of the loop of Henle

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?

Elevated hepatic venous pressure gradient

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?

Amoxicillin/clavulanic acid and ceftriaxone

Ampicillin/sulbactam and daptomycin

Piperacillin/tazobactam and cefepime

Biliary excretion for USMLE Step 1: High-Yield Pharmacology Lessons

Biliary Excretion - The Liver's VIP Lane

A key elimination pathway for large, polar drugs and metabolites, especially those with a molecular weight >500 Da.
Involves active transport systems that can be saturated and are potential sites of drug-drug interactions.
Phase II conjugation reactions (e.g., glucuronidation, sulfation) increase polarity, preparing drugs for biliary excretion.

Uptake (Basolateral): Transporters like OATP and OCT1 move drugs from blood into hepatocytes.
Excretion (Canalicular): ATP-dependent transporters like MRP2, BCRP, and MDR1 (P-glycoprotein) pump drugs into bile.

⭐ Dubin-Johnson syndrome is a genetic defect in the MRP2 transporter, leading to impaired excretion of conjugated bilirubin and other drugs.

Hepatocyte transporters in biliary excretion

Drug Properties - The Entry Ticket

For a drug to be excreted in bile, it needs the right "ticket." This primarily depends on its physicochemical properties, contrasting sharply with drugs cleared by the kidneys.

Feature	Favors Biliary Excretion	Favors Renal Excretion
Molecular Wt.	High (> 500 Da)	Lower (< 500 Da)
Polarity	Amphipathic	Water-soluble
Metabolism	Requires conjugation (e.g., glucuronidation) to add a polar group	Often excreted unchanged or with minimal metabolism

Enterohepatic Circulation - The Comeback Tour

Certain drugs, after being conjugated (e.g., glucuronidation) in the liver and excreted into the bile, can get a "second chance" at life.
Mechanism: In the gut, intestinal bacteria produce the enzyme β-glucuronidase.
- This enzyme cleaves the glucuronide conjugate from the drug (deconjugation).
- The now free, more lipid-soluble drug is reabsorbed back into the portal circulation.
Clinical Significance: This recycling process ↑ the drug's half-life ($t_{1/2}$) and its duration of action.
Key Examples:
- Oral Contraceptives
- Warfarin
- Digoxin
- Morphine

Drug transport and metabolism in a hepatocyte

⭐ Exam Favorite: Broad-spectrum antibiotics can kill gut flora, disrupting enterohepatic circulation of oral contraceptives and potentially leading to contraceptive failure.

High‑Yield Points - ⚡ Biggest Takeaways

Biliary excretion is a primary elimination route for large MW (>500 Da), polar, and amphipathic compounds.

Hepatocytes use active transport (e.g., MRP2, OATPs) to secrete drugs from blood into bile against a concentration gradient.

Enterohepatic circulation-reabsorption of the drug from the intestine-can significantly prolong its half-life and duration of action.

Key examples include ceftriaxone, rifampin, digoxin, and steroid hormones.

Liver disease or biliary obstruction can impair this pathway, leading to ↑ drug toxicity.

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