Respiratory

Updated COVID-19 outpatient antiviral therapy

Clinical Overview and When to Suspect COVID-19 Requiring Outpatient Antivirals

— Risk factors (NIH/IDSA): age ≥50 (especially ≥65), unvaccinated or incomplete primary series, immunocompromise, obesity (BMI ≥25–30), diabetes, CKD, CVD, chronic lung disease (COPD, asthma, ILD), active cancer, sickle cell, pregnancy, disability, smoking.

— Age alone ≥65 is a sufficient indication, even if otherwise healthy.

— Confirm with antigen or NAAT — either is acceptable for treatment initiation; do not delay treatment waiting for PCR if antigen positive and pretest probability high.

— A negative single antigen with high clinical suspicion → repeat antigen in 48 hr or send NAAT; treat empirically only if presentation is classic and high-risk.

— Nirmatrelvir/ritonavir: within 5 days of symptom onset.

— Remdesivir (3-day outpatient IV course): within 7 days.

— Molnupiravir: within 5 days (alternative only).

Step 3 management: In an ambulatory clinic, the decision tree is symptom onset date → confirmed/likely COVID → risk factor present → antiviral choice driven by drug–drug interactions and renal function, not vaccination status.

Scope of the problem: SARS-CoV-2 remains endemic with seasonal surges; most infections are now mild/moderate and managed outpatient, but high-risk patients still progress to hospitalization or death without timely antiviral therapy.

Who needs antivirals? Symptomatic, non-hospitalized adults and adolescents (≥12 yrs, ≥40 kg for nirmatrelvir/ritonavir) with mild–moderate COVID-19 AND at least one risk factor for severe disease, within a defined symptom window.

When to suspect/test: Acute respiratory or systemic symptoms (fever, cough, sore throat, congestion, fatigue, myalgia, anosmia, GI symptoms) in the setting of community transmission or known exposure.

Symptom-onset window matters:

Goal of therapy: Reduce progression to hospitalization/death; not for symptom relief in low-risk patients.

Presentation Patterns and Key History

— Exact date of symptom onset (Day 0 = first symptom) — drives the 5- vs 7-day antiviral window.

— Vaccination/booster history — does not exclude treatment but informs counseling; do not withhold antivirals from vaccinated high-risk patients.

— Prior COVID infections and prior antiviral use (relevant for rebound counseling).

— Comorbidities: cardiopulmonary, renal (eGFR), hepatic, immunosuppression (transplant, chemo, biologics, HIV with low CD4).

— Pregnancy/lactation status in any patient of reproductive potential.

— Specifically ask about: statins, anticoagulants (DOACs, warfarin), antiarrhythmics (amiodarone, flecainide), immunosuppressants (tacrolimus, cyclosporine, sirolimus), antiseizure drugs (carbamazepine, phenytoin), rifampin, HIV/HCV regimens, ergots, sildenafil for PAH, fentanyl, methadone, hormonal contraception.

— Include herbals: St. John's wort is a contraindication.

Board pearl: A high-risk patient on simvastatin or lovastatin needs the statin held during and 5 days after nirmatrelvir/ritonavir; atorvastatin/rosuvastatin require dose reduction. Failing to address this is a common stem trap.

Key distinction: "Mild" (symptoms, no dyspnea/abnormal imaging) vs "moderate" (LRT disease but SpO₂ ≥94%) — both are outpatient antiviral candidates; "severe" (SpO₂ <94%) requires hospitalization and IV remdesivir ± dexamethasone.

Typical mild–moderate outpatient COVID-19: low-grade fever, dry cough, sore throat, rhinorrhea, fatigue, myalgia, headache; SpO₂ ≥94% on room air and no signs of lower respiratory tract disease on exam/imaging defines outpatient candidacy.

History elements that change management:

Comprehensive medication reconciliation is mandatory before prescribing nirmatrelvir/ritonavir — this is the single highest-yield Step 3 step.

Red-flag symptoms to screen for (would push toward ED, not oral antiviral): dyspnea at rest, chest pain, confusion, cyanosis, inability to maintain hydration, SpO₂ <94%, RR >24.

Physical Exam Findings and Hemodynamic Assessment

— SpO₂ <94% or a drop ≥3% with ambulation → reclassify as severe; arrange ED evaluation, not outpatient oral antiviral.

— Tachypnea (RR >20–24) or accessory muscle use → escalate.

— HR persistently >110 not explained by fever.

— Orthostasis or SBP <100 in a non-baseline-hypotensive patient.

— Cap refill >3 sec, cool extremities.

— These warrant ED transfer, not oral antivirals.

CCS pearl: On a CCS-style outpatient case, orders should include "pulse oximetry, room air" and "ambulatory pulse oximetry" before deciding on disposition. A vitals-only encounter that skips ambulatory SpO₂ is a missed step.

Vital signs first: temperature, HR, BP, RR, SpO₂ on room air at rest AND with ambulation (a 6-minute or even 1-minute walk pulse-ox can unmask exertional hypoxia missed at rest).

General: assess hydration, mental status, ability to tolerate POs (critical because nirmatrelvir/ritonavir is oral, BID × 5 days; vomiting limits therapy).

HEENT: pharyngeal erythema, conjunctival injection; rule out alternative dx (strep, mononucleosis).

Pulmonary: auscultate for crackles, wheezes, decreased breath sounds. Mild–moderate COVID often has a normal lung exam; abnormal findings warrant CXR.

Cardiac: tachycardia is common with fever; new murmurs or irregular rhythm → consider myocarditis or atrial fibrillation triggered by acute illness.

Extremities: unilateral leg swelling/pain — COVID is prothrombotic; consider outpatient DVT workup if suspected, as this changes anticoagulation decisions that interact with nirmatrelvir/ritonavir.

Skin: rashes (COVID toes, urticaria) are usually benign.

Hemodynamic red flags for outpatient triage:

Documentation for billing/quality: record SpO₂, ambulatory SpO₂ (if obtainable via telehealth pulse ox), respiratory rate, and a brief lung exam — these justify outpatient management and antiviral selection.

Diagnostic Workup — Initial Testing

— Rapid antigen test (Ag-RDT): home or point-of-care; high specificity, moderate sensitivity (60–80%). A positive result in a symptomatic patient is sufficient to start antivirals.

— NAAT (PCR): gold standard; useful when antigen negative but suspicion high, or for immunocompromised patients in whom missed diagnosis is high-cost.

— Sequential antigen testing (Day 0 + Day 2) improves sensitivity if initial test is negative.

— Serum creatinine/eGFR is the single most important lab — required for dosing.

▸ eGFR ≥60: standard dose (300 mg/100 mg BID × 5 d).

▸ eGFR 30–59: reduced (150 mg/100 mg BID × 5 d).

▸ eGFR <30: not recommended.

— LFTs — avoid in severe hepatic impairment (Child-Pugh C).

— HIV status if unknown and starting ritonavir-containing regimen — risk of resistance if undiagnosed HIV exposed to sub-therapeutic ritonavir.

— Obtain CXR if: focal lung findings on exam, SpO₂ <94%, dyspnea, or to evaluate alternative dx (CHF, pneumonia, PE).

— Reserve CT for suspected PE (D-dimer–guided) or unclear CXR.

Board pearl: A high-risk patient with classic symptoms and a positive household contact but no available test → treat with antivirals; do not delay 24–48 hours waiting for PCR results when within the 5-day window.

Confirmatory testing:

Do not require testing to delay treatment if a household contact tested positive and the patient is symptomatic with high pretest probability and high risk — the FDA EUA permits treatment based on clinical diagnosis when testing is unavailable.

Baseline labs before nirmatrelvir/ritonavir:

Pregnancy test in patients of reproductive potential (informs molnupiravir contraindication and counseling on hormonal contraception interaction with ritonavir).

Imaging: not routinely required for outpatient mild–moderate COVID.

ECG: not routinely indicated, but consider if palpitations, chest pain, or starting a QT-prolonging interacting drug.

Diagnostic Workup — Advanced or Confirmatory Studies

— Persistent dyspnea, hypoxia, or symptom worsening after Day 5–7.

— Immunocompromised patient with prolonged or relapsing illness.

— Diagnostic uncertainty (overlapping influenza, RSV, bacterial pneumonia).

— Highly recommended during respiratory virus season — influenza coinfection changes management (add oseltamivir; influenza-specific antivirals do not have the major DDIs of nirmatrelvir/ritonavir).

— RSV positive in older adults with comorbidities warrants supportive care; no specific outpatient antiviral.

— Bilateral peripheral ground-glass opacities suggest COVID pneumonia.

— Lobar consolidation suggests bacterial superinfection — add empiric antibiotics (amoxicillin or doxycycline outpatient) if clinically indicated.

— Lymphopenia and elevated CRP/ferritin correlate with severity but do not change outpatient antiviral choice.

Key distinction: CRP, D-dimer, and ferritin are prognostic biomarkers, not treatment-decision tools, in the outpatient setting — Step 3 traps may offer these as "next best step"; the correct answer is usually start antiviral and arrange follow-up, not order an inflammatory panel.

Board pearl: Always co-test for influenza during flu season — coinfection is real and antiviral choice differs.

When to extend the workup beyond a simple symptomatic outpatient:

Multiplex respiratory PCR (SARS-CoV-2 / influenza A&B / RSV):

CXR or low-dose chest CT:

D-dimer: only if PE suspected; COVID raises baseline D-dimer, so use age-adjusted thresholds and Wells score.

CBC, CMP, CRP: not required for routine outpatient antiviral initiation; obtain if patient appears more ill, has comorbidities being monitored, or to baseline before remdesivir.

HIV testing if status unknown — particularly before ritonavir, and as part of standard preventive care under USPSTF (one-time screening ages 15–65).

Pregnancy testing as above.

Genotypic resistance testing: not routinely available or indicated; persistent infection in immunocompromised patients may warrant ID consultation for prolonged or combination therapy.

Risk Stratification and First-Line Management Logic

— Symptomatic, lab-confirmed (or clinically diagnosed) COVID-19.

— Mild–moderate severity (SpO₂ ≥94% room air, no LRT compromise needing O₂).

— ≥1 risk factor for progression.

— Within drug-specific symptom-onset window.

1. Nirmatrelvir/ritonavir (Paxlovid) — preferred first-line for most outpatients; oral, highly effective (~86–89% relative risk reduction in hospitalization in unvaccinated high-risk).

2. Remdesivir IV × 3 days — preferred when nirmatrelvir/ritonavir contraindicated (severe DDIs, eGFR <30, severe hepatic impairment) or when infusion access exists.

3. Molnupiravir — alternative only when neither above is feasible; lower efficacy; contraindicated in pregnancy and not for <18 yrs.

— Use Liverpool COVID-19 Drug Interactions database or institutional pharmacist.

— Strategies: temporarily hold, dose-reduce, or switch agents.

— Hard contraindications with Paxlovid: alfuzosin, ranolazine, eplerenone, lurasidone, pimozide, lovastatin/simvastatin, sildenafil for PAH, rivaroxaban (often), salmeterol, St. John's wort, rifampin, carbamazepine, phenytoin, apalutamide, certain ergots.

Step 3 management: The branch-point logic on a vignette is: risk factor + within window? → yes → DDI check → if clean and eGFR ≥30 → Paxlovid; if DDI or renal/hepatic issue → remdesivir IV × 3 d; if neither feasible → molnupiravir (not pregnant, ≥18 y).

Step 1 — Confirm eligibility:

Step 2 — Choose the antiviral (NIH/IDSA preference order):

Step 3 — Drug interaction check:

Step 4 — Renal/hepatic dose adjustment.

Step 5 — Counsel and dispense same-day — efficacy depends on early initiation.

Monoclonal antibodies: most have been deauthorized due to variant resistance. Do not select bamlanivimab, casirivimab/imdevimab, sotrovimab, or bebtelovimab as current outpatient therapy on the exam unless a stem explicitly reactivates them. Pemivibart is reserved for pre-exposure prophylaxis in severely immunocompromised patients, not treatment.

Pharmacotherapy — First-Line Drug Regimens

— Dose: 300 mg nirmatrelvir + 100 mg ritonavir PO BID × 5 days (eGFR ≥60).

— eGFR 30–<60: 150 mg/100 mg PO BID × 5 days.

— eGFR <30 or severe hepatic impairment: not recommended.

— Start within 5 days of symptom onset.

— Common AEs: dysgeusia ("Paxlovid mouth" — metallic taste), diarrhea, nausea, hypertension, myalgia.

— Rebound: symptom/test recurrence 2–8 days after completion in ~10–20%; typically mild and self-limited; no retreatment indicated in most cases; isolate again 5 days from rebound symptoms.

— Dose: 200 mg IV Day 1, then 100 mg IV Days 2 and 3 (3-day outpatient course).

— Start within 7 days of symptom onset.

— eGFR cutoffs: previously avoided <30, but newer data support use; institutional protocols vary — for Step 3, avoid in eGFR <30 unless benefit clearly outweighs risk.

— AEs: nausea, transaminitis (check baseline and during therapy), infusion reactions, bradycardia.

— Logistic barrier: requires infusion center access × 3 consecutive days.

— Dose: 800 mg PO BID × 5 days; start within 5 days.

— Contraindicated in pregnancy and <18 years (theoretical risk to bone/cartilage and mutagenesis).

— Lower efficacy (~30% RRR); reserve for last-line.

Board pearl: Paxlovid + tacrolimus in a transplant patient — coordinate with transplant team; either hold tacrolimus during therapy and resume after a washout, or use remdesivir instead. Do not co-prescribe blindly.

Nirmatrelvir/ritonavir (Paxlovid) — protease inhibitor + CYP3A4 inhibitor booster.

Remdesivir — RNA polymerase inhibitor, IV.

Molnupiravir — nucleoside analog, mutagenic mechanism.

Symptomatic care for all: acetaminophen, hydration, antitussives; do not prescribe azithromycin, ivermectin, hydroxychloroquine, or systemic steroids in outpatients without hypoxia — steroids in non-hypoxic COVID increase harm.

Expanded Pharmacology — Drug Interactions and Practical Prescribing

— Statins:

▸ Hold simvastatin and lovastatin entirely (during + 5 days after).

▸ Atorvastatin: max 20 mg/day or hold.

▸ Rosuvastatin: max 10 mg/day.

▸ Pravastatin, fluvastatin, pitavastatin: generally safe.

— Anticoagulants:

▸ Apixaban: reduce dose (if on 5 mg BID → 2.5 mg BID); if already on 2.5 mg BID, consider alternative or remdesivir.

▸ Rivaroxaban: avoid.

▸ Warfarin: monitor INR closely.

▸ Dabigatran: caution, P-gp effect.

— Antiarrhythmics: amiodarone, flecainide, propafenone — avoid or use remdesivir.

— Immunosuppressants: tacrolimus, cyclosporine, sirolimus, everolimus — co-manage with specialist; usually switch to remdesivir.

— Antiseizure: carbamazepine, phenytoin, phenobarbital — contraindicated (induce CYP3A4 → loss of nirmatrelvir efficacy).

— Hormonal contraception: ritonavir reduces ethinyl estradiol efficacy → use backup barrier method during therapy and through next menstrual cycle.

— Inhaled steroids: salmeterol contraindicated; fluticasone increases systemic exposure.

— Opioids: fentanyl, oxycodone, methadone — monitor for toxicity; methadone may need adjustment.

— PDE5 inhibitors: sildenafil for PAH contraindicated; for ED, reduce dose and lengthen interval.

Step 3 management: When a stem lists a complex med list, the highest-yield answer is often "consult pharmacy and initiate 3-day IV remdesivir course" rather than forcing Paxlovid through a minefield of DDIs. Recognize when remdesivir is the right answer despite the inconvenience.

Mechanism of DDIs with nirmatrelvir/ritonavir: ritonavir is a potent CYP3A4 inhibitor (intentionally boosts nirmatrelvir levels) — also boosts levels of many cosubstrates, and is a CYP2D6 inhibitor and P-gp inhibitor.

High-yield DDI management:

Workflow: pharmacist co-sign or formal interaction screen documented in the chart.

Special Populations — Elderly and Renal/Hepatic Impairment

— Highest absolute benefit from antivirals; NNT to prevent hospitalization is lowest.

— Age ≥65 alone qualifies for antivirals even without other comorbidities.

— Polypharmacy is the rule — DDI screen is mandatory; expect to encounter statins, anticoagulants, antihypertensives, AChE inhibitors.

— Monitor for orthostasis (ritonavir can interact with antihypertensives).

— Frailty and dysphagia: tablets are not crushable for Paxlovid — confirm ability to swallow whole.

— Calculate eGFR using current creatinine (acute illness may transiently worsen renal function).

— eGFR ≥60: full-dose Paxlovid.

— eGFR 30–<60: reduced-dose Paxlovid (150/100 BID).

— eGFR <30 or dialysis: Paxlovid not recommended; remdesivir is acceptable per updated data despite the historical eGFR <30 cutoff (cyclodextrin vehicle concern outweighed by efficacy); institutional protocol varies — on the exam, choose remdesivir in ESRD/dialysis if Paxlovid is contraindicated and the patient is high-risk.

— Molnupiravir: no renal dose adjustment but lower efficacy.

— Child-Pugh A–B: Paxlovid can be used with caution.

— Child-Pugh C: avoid Paxlovid; use remdesivir (monitor LFTs) or molnupiravir.

— Remdesivir: hold if ALT >10× ULN or ALT elevation with signs of liver injury.

— Nirmatrelvir is renally cleared; ritonavir is hepatically cleared.

— Remdesivir metabolites accumulate in renal impairment but clinically tolerated.

Board pearl: A 78-year-old with eGFR 25 and recent COVID symptom Day 2 → 3-day IV remdesivir, not dose-adjusted Paxlovid. Don't be lured by oral convenience.

Elderly (≥65):

Renal impairment:

Hepatic impairment:

Drug clearance pearls:

Special Populations — Pregnancy, Lactation, and Pediatrics

— COVID in pregnancy increases risk of severe disease, preterm birth, stillbirth, and maternal mortality — treat aggressively.

— Nirmatrelvir/ritonavir: preferred; ritonavir has extensive safety data in pregnancy from HIV use; observational data with Paxlovid in pregnancy reassuring. SMFM and ACOG support use in symptomatic pregnant patients with risk factors.

— Remdesivir: acceptable alternative; used in pregnancy throughout the pandemic.

— Molnupiravir: contraindicated in pregnancy (mutagenicity concern).

▸ Counsel reproductive-age patients on contraception during therapy and for 4 days after in females, 3 months after in males.

— Continue or initiate vaccination as appropriate; antivirals are independent of vaccination status.

— Paxlovid: limited data; generally considered compatible — temporary interruption not routinely recommended.

— Remdesivir: compatible.

— Molnupiravir: avoid or pump-and-discard during therapy + 4 days after.

— Paxlovid: authorized for ≥12 years and ≥40 kg.

— Remdesivir: authorized for ≥28 days old and ≥3 kg (broader pediatric range).

— Molnupiravir: not authorized <18 years (effects on bone/cartilage growth).

— Most healthy pediatric patients do not require antivirals; reserve for high-risk children (immunocompromised, complex chronic conditions, severe obesity, sickle cell, neurodevelopmental disorders requiring respiratory support).

— MIS-C is a separate, post-infectious entity not treated by these antivirals.

— Higher risk of prolonged shedding and severe disease.

— Some experts use extended antiviral courses or combination therapy in protocols — refer to ID.

— Consider pemivibart prophylaxis for severely immunocompromised who cannot mount vaccine response.

Key distinction: Pregnancy → Paxlovid or remdesivir, never molnupiravir. This is among the most reliable Step 3 stems on COVID antivirals.

Pregnancy:

Lactation:

Pediatrics:

Immunocompromised:

Complications and Adverse Outcomes

— Hospitalization, hypoxemic respiratory failure, ARDS.

— Thromboembolism (DVT, PE) — COVID is prothrombotic; consider in any post-COVID patient with new dyspnea.

— Myocarditis/pericarditis, arrhythmias.

— Acute kidney injury, secondary bacterial pneumonia.

— Post-acute sequelae (Long COVID): fatigue, dyspnea, dysautonomia, cognitive symptoms; some observational data suggest Paxlovid may reduce Long COVID risk, though not an approved indication.

— Death.

— Paxlovid:

▸ Dysgeusia (metallic taste) — very common, self-limited.

▸ GI upset, diarrhea.

▸ Hypertension elevations.

▸ Hepatotoxicity (rare).

▸ DDI-mediated toxicity: rhabdomyolysis with statins, bleeding with DOACs, serotonin syndrome with SSRIs + opioids, immunosuppressant toxicity (tacrolimus nephrotoxicity), prolonged sedation with benzodiazepines.

▸ Hypersensitivity: anaphylaxis, SJS, TEN — rare but reported.

— Remdesivir:

▸ Transaminitis (check LFTs before, hold if ALT >10× ULN).

▸ Infusion reactions.

▸ Bradycardia (often asymptomatic).

▸ Nausea.

— Molnupiravir:

▸ Diarrhea, nausea, dizziness.

▸ Theoretical mutagenicity — basis for pregnancy contraindication.

— 10–20% with Paxlovid (also occurs without treatment ~5%); symptoms typically mild.

— Re-isolate for 5 days from rebound symptom onset and mask through Day 10.

— Retreatment generally not recommended; ID consult if rebound is severe or in immunocompromised.

Board pearl: A patient on tacrolimus who received Paxlovid without dose hold presents 5 days later with tremor, AKI, and tacrolimus level 35 ng/mL — this is drug-interaction toxicity, not COVID complication. Manage with immediate tacrolimus hold and nephrology/transplant input.

Disease-related complications (what antivirals aim to prevent):

Drug-related adverse events:

Viral rebound:

Secondary infection: bacterial pneumonia, candidiasis (especially with concurrent steroid use in misclassified outpatients).

When to Escalate Care — ED, Inpatient, and Consult Triggers

— SpO₂ <94% on room air at rest, or significant ambulatory desaturation.

— Respiratory rate >24–30.

— Chest pain, syncope, altered mental status.

— Hemodynamic instability (SBP <90, HR >120 sustained).

— Inability to tolerate POs, severe dehydration.

— Signs of bacterial sepsis or alternative emergency (PE, MI, stroke).

— Hypoxemia requiring supplemental O₂.

— Severe comorbidity decompensation.

— Social/safety inability to monitor at home in high-risk patient.

— Remdesivir ± dexamethasone 6 mg/day × up to 10 days for those needing O₂.

— Baricitinib or tocilizumab for rapidly progressing inflammatory phenotypes per protocol.

— Anticoagulation: prophylactic dose for hospitalized non-ICU patients (therapeutic in select non-ICU per protocols); prophylactic in ICU.

— Paxlovid is not standard inpatient therapy.

— ID: immunocompromised, prolonged or relapsing COVID, antiviral resistance concerns.

— Pharmacy: complex DDIs.

— Transplant team: solid organ or stem cell transplant recipients.

— OB: pregnant patients with severe disease or complex comorbidities.

— Cardiology: suspected myocarditis (elevated troponin, new chest pain, arrhythmia).

CCS pearl: On a CCS-style case where the patient deteriorates on Paxlovid (new hypoxia at Day 3): order pulse ox, CXR, ECG, troponin, D-dimer; arrange transfer to ED; do not simply continue oral therapy. Escalation supersedes completing the antiviral course.

Immediate ED referral (do not start oral antivirals; arrange transfer):

Inpatient admission criteria (once at ED):

Inpatient therapy differs:

Specialist consults (outpatient):

Telehealth utility: appropriate for symptom triage, prescribing, follow-up — but require in-person evaluation or ED referral if SpO₂ unobtainable in a high-risk patient.

Key Differentials — Other Respiratory Viral Causes

— Overlapping presentation: fever, myalgia, cough, fatigue.

— Higher fever and abrupt onset more typical than COVID.

— Treat with oseltamivir 75 mg PO BID × 5 days within 48 hours of symptom onset for high-risk patients (or any hospitalized).

— Multiplex PCR distinguishes; treat both if coinfected.

— Oseltamivir has minimal DDIs — easier than Paxlovid in polypharmacy elderly.

— Increasing recognition in older adults and those with cardiopulmonary disease.

— Often presents with wheezing and bronchitis-like illness.

— No effective outpatient antiviral; supportive care.

— Prevention: RSV vaccine for adults ≥60 (shared decision-making) and ≥75 (universal recommendation), maternal vaccine, nirsevimab in infants.

— Cause common-cold syndromes; no specific therapy; not detected by SARS-CoV-2 testing.

— Nasal congestion, sore throat predominate; lower fever.

— Supportive care.

— Conjunctivitis, pharyngitis, GI symptoms; supportive.

— Croup/laryngitis in kids, bronchitis in adults; supportive.

— Consider in prolonged cough >2 weeks with paroxysms, post-tussive emesis, or whoop; treat with macrolide.

Key distinction: Influenza vs COVID is the single most important diagnostic fork during respiratory virus season because both have specific antivirals with narrow time windows. Test for both with a multiplex PCR when available; don't anchor on the first positive result — coinfection is possible.

Board pearl: An elderly patient with classic flu-like illness, abrupt onset, Day 2 of symptoms, negative COVID antigen but flu testing not yet done → send multiplex PCR and start empiric oseltamivir if high risk; switch or add Paxlovid if SARS-CoV-2 returns positive.

Influenza A/B:

RSV:

Other coronaviruses (HCoV-229E, OC43, NL63, HKU1):

Rhinovirus / enterovirus:

Adenovirus:

Parainfluenza, hMPV:

Pertussis:

Key Differentials — Non-Viral and Mimics

— Productive cough with purulent sputum, lobar consolidation on CXR, leukocytosis with left shift, higher fever.

— Treat with amoxicillin or doxycycline (outpatient, no comorbidities) or amoxicillin-clavulanate + macrolide / respiratory fluoroquinolone (with comorbidities).

— Strep pneumo, Mycoplasma, H. flu, Legionella considerations.

— Coinfection with COVID is possible — treat both.

— Centor criteria; rapid strep / throat culture.

— Treat with penicillin/amoxicillin.

— Cough up to 3 weeks, low-grade or no fever; no antibiotics, supportive care.

— Sudden dyspnea, pleuritic chest pain, tachycardia, hypoxia disproportionate to lung exam.

— Wells score, D-dimer, CTPA; anticoagulate.

— Post-COVID PE is a recognized entity — keep on differential in worsening patients.

— Dyspnea, orthopnea, PND, JVD, peripheral edema, BNP elevation.

— Diurese, optimize GDMT.

— Wheezing, expiratory prolongation, prior history.

— Bronchodilators, steroids if indicated, antibiotics if purulent sputum.

— Lack of systemic features; nasal exam findings.

— Atypical presentations in elderly/diabetic — ECG and troponin if any chest pain or dyspnea concern.

Step 3 management: A high-risk patient with confirmed COVID and focal lobar consolidation + elevated WBC = co-treat with antivirals + outpatient antibiotics; don't force a single diagnosis. Address bacterial superinfection or community-acquired bacterial coinfection.

Bacterial community-acquired pneumonia:

Streptococcal pharyngitis:

Acute bronchitis:

Pulmonary embolism:

Heart failure exacerbation:

COPD/asthma exacerbation:

Allergic rhinitis / acute sinusitis:

Acute coronary syndrome:

Anxiety/hyperventilation, post-viral cough, GERD-related cough in non-acute settings.

Discharge Plan, Secondary Prevention, and Long-Term Care

— Confirm symptom resolution trajectory; counsel on possible rebound (Days 2–8 post-therapy) and that retesting/retreatment is generally not needed unless symptoms severe.

— Isolation: 5 days from symptom onset, then mask through Day 10; isolate again 5 days if rebound symptoms occur.

— Return-to-work guidance per CDC and employer policy.

— Update COVID-19 vaccination with current season's formulation; recommended for everyone ≥6 months, with additional doses for ≥65 and immunocompromised.

— Wait ~3 months after acute infection for next dose per CDC guidance (optional, based on individual risk).

— Co-administer influenza and RSV vaccines when appropriate (RSV ≥75 universal; 60–74 shared decision-making for high-risk).

— Pneumococcal vaccination (PCV15/PCV20 or PCV21 per latest ACIP) if age- or comorbidity-indicated.

— DM: A1c control; SGLT2/GLP-1 as indicated.

— HTN: confirm BP at home; restart held antihypertensives.

— CKD: re-evaluate eGFR 1–2 weeks post-illness.

— COPD/asthma: confirm controller adherence; review inhaler technique.

— Tobacco cessation counseling and pharmacotherapy.

— Obesity: lifestyle and pharmacotherapy as indicated.

Board pearl: Every COVID encounter is a preventive medicine opportunity — update vaccines, reassess chronic disease control, and counsel on lifestyle. Step 3 rewards the longitudinal lens.

At completion of antiviral therapy:

Vaccination:

Chronic disease optimization (the Step 3 outpatient ethos):

Anticoagulation reassessment: if DOAC was dose-adjusted, return to standard dose after Paxlovid completion (no washout typically needed; check institutional guidance).

Statin and other held medications: restart after the 5-day course + appropriate washout for CYP3A4 (generally 2–3 days).

Long COVID screening at follow-up visits; refer to multidisciplinary clinics if persistent symptoms >4–12 weeks.

Follow-Up, Monitoring, and Counseling

— Telehealth or phone check at Day 3–5 of therapy: confirm symptom trajectory, adherence, side effects, no new red flags.

— In-person or telehealth at Day 7–14: confirm resolution, assess for rebound, address held medications.

— 4-week follow-up for high-risk patients or those with persistent symptoms: screen for Long COVID, cardiopulmonary sequelae.

— Subjective: symptoms, ability to tolerate POs, side effects.

— Objective if obtainable: home pulse ox, BP (especially if antihypertensives interact with ritonavir).

— Labs: not routinely; recheck renal function at 1–2 weeks if eGFR was borderline or AKI suspected during illness; LFTs at 1 week if on remdesivir.

— INR within 3–5 days of Paxlovid initiation in warfarin patients.

— Tacrolimus/sirolimus levels post-therapy if exposure occurred.

— Take Paxlovid with or without food; swallow whole; do not split.

— Metallic taste is expected, not allergic — encourage completion.

— Hydrate; avoid grapefruit juice (CYP3A4 inhibitor compounding).

— Use backup contraception during ritonavir therapy and through next menstrual cycle.

— Continue isolation precautions even on therapy — antivirals reduce progression, not immediate transmissibility.

— Report any chest pain, severe dyspnea, syncope, severe rash, or jaundice immediately.

Step 3 management: Build a 24-hour safety net at every outpatient COVID encounter: home pulse ox, written warning signs, clear callback number, and a scheduled Day 3 telehealth touchpoint. Demonstrates the longitudinal, ambulatory thinking the Step 3 exam rewards.

Follow-up cadence:

Monitoring parameters during therapy:

Counseling pearls:

Pulmonary rehabilitation: consider referral for patients with persistent exertional dyspnea beyond 4–6 weeks; structured programs improve functional capacity in post-COVID lung disease.

Mental health screening: PHQ-9 / GAD-7 at follow-up — post-acute psychiatric symptoms are common, especially in elderly and those with prior mood disorders.

Ethical, Legal, and Patient Safety Considerations

— Nirmatrelvir/ritonavir is now FDA-approved for adults; the pediatric (12–17) use remains under EUA, requiring a Fact Sheet for Patients/Caregivers to be provided.

— Molnupiravir remains under EUA — fact sheet required; document discussion of risks/benefits, mutagenicity uncertainty, and contraception requirements.

— Counsel that Paxlovid is not a substitute for vaccination.

— Antivirals must be initiated within 5–7 days — delays in testing or pharmacy access disproportionately affect underserved populations.

— Test-to-Treat sites, telehealth prescribing, and home delivery programs help bridge gaps; advocate for these for patients with transportation/financial barriers.

— Document medical necessity clearly to support coverage; most insurers and Medicare cover antivirals, but pharmacy access varies.

— Hospital → outpatient: confirm if patient is still within the symptom window for outpatient antiviral; usually not relevant if discharged on dexamethasone (severity excludes outpatient antivirals).

— Outpatient → inpatient: communicate completion (or interruption) of Paxlovid to admitting team to avoid duplicate or contraindicated regimens.

— Medication reconciliation at every transition, particularly for statins, anticoagulants, immunosuppressants held during Paxlovid.

— COVID-19 is a nationally notifiable disease; positive results are reported by labs.

— Significant adverse drug events should be reported to FDA MedWatch.

— VAERS for vaccine-related events (separate but related preventive practice).

Board pearl: A patient refuses Paxlovid because of online "rebound" fears — provide balanced counseling, document shared decision-making, and offer remdesivir or molnupiravir as alternatives. Respect autonomy while ensuring informed choice.

Informed consent for EUA medications:

Equity and access:

Transitions of care:

Mandatory reporting:

Confidentiality: workplace return-to-work notes — disclose only diagnosis date and clearance, not detailed clinical history, without patient consent.

Conscientious practice: avoid prescribing ivermectin, hydroxychloroquine, or unproven supplements for COVID — these are not standard of care and may harm; document the discussion.

High-Yield Associations and Rapid-Fire Facts

Key distinction: Paxlovid is the default; remdesivir is the DDI/renal escape hatch; molnupiravir is the last resort.

Paxlovid window: 5 days from symptom onset.

Remdesivir window: 7 days from symptom onset.

Molnupiravir window: 5 days, age ≥18, never in pregnancy.

Paxlovid renal dosing: eGFR ≥60 standard; 30–<60 reduced; <30 not recommended.

Statin rule: hold simvastatin/lovastatin; reduce atorvastatin (≤20 mg) / rosuvastatin (≤10 mg).

Apixaban with Paxlovid: halve the dose (if on 5 BID → 2.5 BID); already on 2.5 BID → consider remdesivir.

Rivaroxaban + Paxlovid: avoid.

Tacrolimus + Paxlovid: hold tacrolimus or use remdesivir; coordinate with transplant team.

Antiseizure inducers (carbamazepine, phenytoin, phenobarbital): contraindicated.

St. John's wort, rifampin: contraindicated.

Pregnancy: Paxlovid preferred; remdesivir acceptable; molnupiravir never.

Pediatric Paxlovid: ≥12 yrs and ≥40 kg.

Remdesivir outpatient course: 200 mg Day 1, 100 mg Days 2–3 IV.

Vaccinated status does not exclude treatment in high-risk patients.

Age ≥65 = sufficient risk factor.

Dexamethasone not for outpatients without hypoxia.

Rebound rate ~10–20%; usually mild; no retreatment routinely.

Isolation: 5 days + mask through Day 10; restart 5-day clock if rebound symptoms.

Test-to-Treat: positive test → same-day prescription pathway.

Monoclonal antibodies for treatment: largely deauthorized; pemivibart for pre-exposure prophylaxis in severely immunocompromised.

Multiplex PCR during respiratory season: always consider influenza coinfection → add oseltamivir.

Acetaminophen and hydration are the only universally appropriate adjuncts.

Document eGFR, full med list, symptom onset date, pregnancy status, vaccination history at every prescription.

Don't prescribe ivermectin or hydroxychloroquine.

Board Question Stem Patterns

— 70-year-old on simvastatin 40 mg, apixaban 5 mg BID, amiodarone, presents Day 2 of COVID symptoms, SpO₂ 96%.

— Trap answer: "Start Paxlovid."

— Correct: Start 3-day IV remdesivir (amiodarone is a hard interaction; simvastatin + apixaban manageable but stacking with amiodarone tips the balance).

— 82-year-old, eGFR 22, symptom Day 3, SpO₂ 95%.

— Correct: Remdesivir IV × 3 d (Paxlovid not recommended <30; molnupiravir lower efficacy).

— G2P1 at 28 weeks, symptom Day 2, asthma, SpO₂ 97%.

— Correct: Paxlovid (preferred in pregnancy with risk factors); never molnupiravir.

— Patient completed Paxlovid 4 days ago, now with mild recurrence of symptoms and positive antigen.

— Correct: Reassure, re-isolate 5 days, no retreatment; rule out alternative cause.

— Day 7 of symptoms, mild illness, high risk.

— Correct: Supportive care, monitor; antivirals offer no benefit outside window; arrange close follow-up.

— Kidney transplant on tacrolimus, eGFR 55, symptom Day 1.

— Correct: Remdesivir IV × 3 d (or Paxlovid with transplant team co-management and tacrolimus hold).

— Patient with SpO₂ 90%, RR 26.

— Correct: ED transfer / admission, IV remdesivir + dexamethasone; Paxlovid is NOT the answer.

— Multiplex PCR positive for both SARS-CoV-2 and influenza A.

— Correct: Paxlovid + oseltamivir within respective windows.

— 14-year-old, 50 kg, obese, symptom Day 2.

— Correct: Paxlovid (meets ≥12 yrs and ≥40 kg).

Board pearl: When a stem gives a med list, the right answer often hides in the DDIs, not the vaccine history. Read the medication list before choosing the antiviral.

Stem 1 — DDI trap:

Stem 2 — Renal cutoff:

Stem 3 — Pregnancy:

Stem 4 — Rebound:

Stem 5 — Symptom window expired:

Stem 6 — Transplant:

Stem 7 — Hospitalization criterion:

Stem 8 — Influenza coinfection:

Stem 9 — Pediatric:

One-Line Recap

In symptomatic, high-risk, non-hospitalized COVID-19 patients with SpO₂ ≥94%, initiate nirmatrelvir/ritonavir within 5 days of symptom onset as first-line therapy, switching to a 3-day IV remdesivir course when significant drug interactions, eGFR <30, severe hepatic impairment, or pregnancy-related contraindications make Paxlovid unsafe, and reserving molnupiravir as a last-line alternative — all while updating vaccines, optimizing chronic disease, and building a 24-hour safety net.

Step 3 management: Treat early, treat smart, treat the whole patient — and document the DDI screen.

Eligibility checklist: confirmed/likely SARS-CoV-2 + symptomatic + ≥1 risk factor (age ≥65 alone counts) + within symptom-onset window + SpO₂ ≥94% room air.

Drug-selection algorithm: Paxlovid first → if DDI/renal/hepatic/pregnancy-with-mutagenic-concern barriers → remdesivir IV × 3 d → if neither feasible → molnupiravir (adults only, never pregnant).

Always check: symptom onset date, eGFR, full medication list (statins, anticoagulants, immunosuppressants, antiseizure, contraception), pregnancy status, hepatic function.

Counseling pillars: rebound is usually mild and self-limited; isolation 5 days + mask to Day 10; backup contraception during/after ritonavir; resume held meds after washout; vaccinate at follow-up.

Escalation rule: SpO₂ <94%, dyspnea at rest, hemodynamic instability, or inability to tolerate POs → ED, not oral antiviral.

Preventive lens: every COVID visit doubles as a vaccine update (COVID, flu, RSV, pneumococcal), chronic disease tune-up, and Long COVID screening opportunity — the Step 3 hallmark of longitudinal, ambulatory care.