For which of the following patients would you recommend prophylaxis against mycobacterium avium-intracellulare?

30-year old HIV positive male with CD4 count of 20 cells/microliter and a viral load of < 50 copies/mL

22-year old HIV positive female with CD4 count of 750 cells/microliter and a viral load of 500,000 copies/mL

45-year old HIV positive female with CD4 count of 250 cells/microliter and a viral load of 100,000 copies/mL

50-year old HIV positive female with CD4 count of 150 cells/microliter and a viral load of < 50 copies/mL

36-year old HIV positive male with CD4 count of 75 cells/microliter and an undetectable viral load

A 65-year-old man presents to his primary care physician for a rash. He states that for the past several days he has felt burning and itching around his eye. Yesterday, he noticed that a rash had formed. Review of systems is notable for mild diarrhea for the past week. The patient has a past medical history of diabetes, asthma, seasonal allergies, and hypertension. He is not currently taking any medications. Physical exam is notable for a vesicular rash surrounding the orbit. Which of the following is the best next step in management?

Removal of gluten containing products from the diet

A 24-year-old woman, gravida 1, para 0, at 39 weeks' gestation, is admitted to the hospital in active labor. She currently has contractions occurring every 3–5 minutes. For the past 3 days, she has had burning pain in the vulvar area associated with intense itching. Her pregnancy has been uneventful. She has a history of genital herpes at the age of 16, which was treated with acyclovir. Her vital signs are within normal limits. Genital examination shows grouped vesicles on an erythematous base over the vulvar region. Pelvic examination shows rupture of membranes and that the cervix is 3 cm dilated. Which of the following is the most appropriate next step in management?

Oral acyclovir therapy and cesarean delivery

Tocolytic therapy until lesions are crusted

Oral acyclovir therapy and vaginal delivery

Topical acyclovir and vaginal delivery

Topical acyclovir and cesarean delivery

A 53-year-old woman comes to the physician in February because of a 1-day history of fever, chills, headache, and dry cough. She also reports malaise and generalized muscle aches. She works as a teacher at a local high school, where there was recently an outbreak of influenza. She has a history of intermittent asthma, for which she takes albuterol as needed. She declined the influenza vaccine offered in the fall because her sister told her that a friend developed a flulike illness after receiving the vaccine. She is worried about possibly becoming ill and cannot afford to miss work. Her temperature is 37.9°C (100.3°F), heart rate is 58/min, and her respirations are 12/min. Physical examination is unremarkable. Her hemoglobin concentration is 14.5 g/dL, leukocyte count is 9,400/mm3, and platelet count is 280,000/mm3. In addition to analgesia, which of the following is the most appropriate next step in management?

Live attenuated influenza vaccine

A 2-month-old girl is admitted to the hospital because of a 1-day history of fever and difficulty breathing. She has also had nasal congestion for 2 days. She was born at 28 weeks' gestation and weighed 1105 g (2 lb 7 oz); she currently weighs 2118 g (4 lb 11 oz). Her neonatal course was complicated by respiratory distress syndrome. She required supplemental oxygen for 36 days following birth. She was diagnosed with bronchopulmonary dysplasia 3 weeks ago. The infant missed an appointment with the pediatrician 2 weeks ago. Her only medication is vitamin D drops. She appears lethargic. Her temperature is 38.6°C (101.4°F), pulse is 160/min, respirations are 55/min, and blood pressure is 80/45 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 87%. Physical examination shows moderate subcostal retractions. Wheezing is heard on auscultation of the chest. Her hemoglobin concentration is 10.5 g/dL, leukocyte count is 13,000/mm3, and platelet count is 345,000/mm3. Mechanic ventilatory support is initiated. After 4 days in the pediatric intensive care unit, the patient dies. Administration of which of the following is most likely to have prevented this patient's outcome?

Respiratory syncytial virus immune globulin

A 26-year-old female medical student presents to occupational health after sustaining a needlestick injury. She reports that she was drawing blood from an HIV-positive patient when she stuck herself percutaneously while capping the needle. She immediately washed the puncture wound with betadine. The medical student has a negative HIV serology from the beginning of medical school two years ago. She is monogamous with one male partner and denies any intravenous drug use. The source patient was recently diagnosed with HIV, and has a CD4 count of 550 cells/µL. His most recent viral load is 1,800,000 copies/mL, and he was started on HAART three days ago. Which of the following is the best next step to manage the female medical student’s exposure?

Draw her repeat HIV serology and immediately initiate three-drug antiretroviral therapy

Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if positive

Perform genotype testing on source patient and initiate antiretroviral therapy tailored to results

Immediately initiate three-drug antiretroviral therapy

Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if negative

A 28-year-old woman G1P0 presents at 38 weeks of gestation for a standard prenatal visit. She endorses occasional mild lower back pain but otherwise remains asymptomatic. Her past medical history is significant for HIV for which she is treated with azidothymidine (AZT). Her vital signs and physical exam are unremarkable. Her current HIV viral titer level is 1,400 copies. If she were to go into labor today, what would be the next and most important step for the prevention of vertical HIV transmission to the newborn?

Urge the patient to have a cesarean section delivery

Add nevirapine to the patient’s AZT

Treat the newborn with AZT following delivery

A 25-year-old man presents with jaw discomfort and the inability to open his mouth fully for about 3 days. About a week ago, he says he cut himself while preparing a chicken dinner but did not seek medical assistance. Five days after the original injury, he started noticing jaw discomfort and an inability to open his mouth completely. He has no history of a serious illness or allergies and takes no medications. The patient says he had received his primary tetanus series in childhood, and that his last booster was more than 10 years ago. His blood pressure is 125/70 mm Hg and temperature is 36.9℃ (98.5°F). On physical examination, the patient is unable to open his jaw wider than 2.5 cm. Head and neck examinations are otherwise unremarkable. There is a 5 cm linear shallow laceration with some granulation tissue on the right index finger without necrosis, erythema, or pus. After wound care and initiation of metronidazole, which of the following is the next best step in the management of this patient?

No further treatment is required

Antiviral prophylaxis strategies for USMLE Step 3: High-Yield Pharmacology Lessons

Influenza & RSV Prophylaxis - Flu & Baby Shields

Influenza Prophylaxis
- Agent: Oseltamivir, Zanamivir (Neuraminidase Inhibitors).
- Indication: High-risk individuals (e.g., nursing home residents) post-exposure, typically within 48 hours.
- Used for both treatment and prophylaxis.
RSV Prophylaxis
- Agent: Palivizumab (monoclonal antibody).
- Indication: High-risk infants: premature (<29 wks), chronic lung disease of prematurity, hemodynamically significant congenital heart disease.
- Given monthly during RSV season (typically winter).

⭐ Pearl: Palivizumab is passive immunization via a monoclonal antibody against the RSV F protein; it is NOT a vaccine.

Palivizumab mechanism of action on RSV F protein

Herpesvirus Prophylaxis - Herpes Hide & Seek

Goal: Prevent reactivation and disease in high-risk individuals, particularly the immunocompromised.
Key Scenarios & Agents:
- Neonatal HSV: For mothers with active genital lesions, give maternal acyclovir starting at 36 weeks gestation.
- Transplant Recipients (CMV): Valganciclovir is a common choice. Letermovir is used for allogeneic stem cell transplant recipients.
- HIV Patients:
  - HSV/VZV: Acyclovir for frequent/severe recurrences.
  - CMV: Prophylaxis with valganciclovir if CD4 count is < 50 cells/μL.

⭐ Letermovir uniquely inhibits the CMV terminase complex, avoiding the myelosuppression often seen with ganciclovir/valganciclovir.

Anti-herpesvirus drug mechanisms

📌 All Viruses Gone: Acyclovir, Valacyclovir, Ganciclovir.

HIV Prophylaxis (PrEP & PEP) - Risky Business Reversal

PrEP (Pre-Exposure Prophylaxis): For ongoing high-risk individuals before potential exposure.
- Regimen: Daily oral Tenofovir/Emtricitabine (TDF/FTC or TAF/FTC).
- 📌 PrEP Prevents HIV.
PEP (Post-Exposure Prophylaxis): Emergency use after a single high-risk event.
- Must start within 72 hours of exposure.
- Regimen: 28-day course of a 3-drug antiretroviral therapy (ART).
  - e.g., TDF/FTC + Dolutegravir or Raltegravir.

⭐ For PEP, efficacy is highest when initiated immediately. The 72-hour window is an absolute maximum; effectiveness declines with every passing hour.

Perinatal & Special Cases - Newborn & Bite Guards

HIV: Zidovudine (ZDV) to mother & neonate.
HBV: Infants of HBsAg(+) mothers get HBV vaccine + HBIG within 12 hours of birth.
VZV: VZIG to neonates if maternal varicella occurs 5 days before to 2 days after delivery.
Rabies (Bite): Post-exposure prophylaxis (PEP) includes Rabies Immune Globulin (RIG) and vaccine.

⭐ In rabies PEP, infiltrate RIG around the wound; give the remainder IM at a site distant from the vaccine.

High‑Yield Points - ⚡ Biggest Takeaways

Influenza prophylaxis often involves oseltamivir for close contacts of infected individuals, especially in high-risk settings like nursing homes.

Acyclovir/valacyclovir are used for continuous suppression of recurrent genital herpes and for VZV prophylaxis in the immunocompromised.

CMV prophylaxis with valganciclovir is crucial for solid organ transplant recipients.

HIV PrEP uses tenofovir-based regimens in high-risk individuals, while PEP requires a 3-drug ART regimen post-exposure.

RSV prevention in high-risk infants relies on palivizumab.

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