What is the best course of action for a patient with a suspected rib fracture, potential penicillin allergy, and impaired renal function?

Management of Suspected Rib Fracture with Penicillin Allergy and Renal Impairment

For a patient with suspected rib fracture, potential penicillin allergy, and impaired renal function, administer a first-generation cephalosporin (cefazolin) without delay after managing life threats, as the cross-reactivity risk is negligible (<2%) and renal dosing adjustments can be safely implemented. 1, 2

Immediate Antibiotic Management

Primary Recommendation: Cefazolin Administration

• Administer cefazolin 1-2g IV immediately after life threats are managed, even with reported penicillin allergy. 3, 4
• Cefazolin is specifically safe because it does not share side chains with penicillins, making cross-reactivity risk approximately 1-2%. 2
• The Dutch Working Party and American Academy of Allergy, Asthma, and Immunology support administering cephalosporins with dissimilar side chains regardless of severity or timing of the penicillin reaction. 1, 2

Renal Dosing Adjustments for Cefazolin

• Adjust cefazolin dosing based on creatinine clearance: standard 1-2g loading dose, then maintenance doses reduced by 50% if CrCl 10-50 mL/min, or by 75% if CrCl <10 mL/min. 5
• Extend dosing intervals rather than reducing individual doses to maintain therapeutic peaks while avoiding accumulation. 5
• Monitor renal function closely, as impaired clearance increases risk of drug accumulation even with hepatically-metabolized antibiotics. 5

Alternative if Cefazolin Unavailable

• Carbapenems (meropenem, ertapenem) can be administered directly without testing, with cross-reactivity rate of only 0.87%. 1
• The American Academy of Allergy, Asthma, and Immunology recommends carbapenems without additional precautions in penicillin-allergic patients. 1
• Dose adjustment required: reduce carbapenem doses by 50% if CrCl <50 mL/min. 5

Imaging Strategy for Rib Fracture

When to Obtain CT vs. Radiography

• Order chest CT if any of the following are present: high-energy mechanism, multiple suspected fractures, age ≥65 years, respiratory compromise, or concern for intra-thoracic/abdominal injury. 5
• The number and displacement of rib fractures on CT carries prognostic significance for pulmonary morbidity and mortality, particularly in elderly patients. 5
• Standard chest radiographs detect only 46% of rib fractures compared to CT, but radiographic detection correlates better with pulmonary morbidity (odds ratio 3.8). 5

High-Risk Features Requiring CT

• Six or more rib fractures, bilateral fractures, flail chest, three severely displaced fractures, first rib fracture, or fractures in all three anatomic areas (anterior, lateral, posterior) predict adverse pulmonary outcomes. 5
• Lower rib fractures (ribs 7-12) with multiple injuries warrant contrast-enhanced CT even with normal examination, as 67% have associated abdominal organ injury. 5
• Multiple rib fractures occur in 46% of patients with blunt aortic injury, though positive predictive value is low. 5

Low-Risk Scenarios

• For isolated, low-energy mechanism with normal vital signs and examination, chest radiographs are sufficient. 5
• Negative physical examination after low-energy impact has 100% negative predictive value for abdominal injury with lower rib fractures. 5

Critical Pitfalls to Avoid

Antibiotic Selection Errors

• Never avoid cephalosporins or carbapenems based solely on penicillin allergy history—this leads to suboptimal outcomes. 1
• Do not confuse carbapenem cross-reactivity (0.87%) with cephalosporin cross-reactivity (~2%), as both are substantially lower than historically cited 10%. 1, 2
• Avoid only three specific cephalosporins with similar side chains: cephalexin (12.9% cross-reactivity), cefaclor (14.5%), and cefamandole (5.3%). 2

Nephrotoxic Agents to Avoid

• Absolutely avoid aminoglycosides (gentamicin, tobramycin) and tetracyclines in renal impairment due to nephrotoxicity. 5
• Nitrofurantoin produces toxic metabolites causing peripheral neuritis in renal failure. 5
• Even hepatically-metabolized drugs require dose adjustment in renal failure due to altered distribution and elimination. 5

Monitoring Requirements

• Monitor blood pressure throughout evaluation, as hypertension is common in renal impairment and stress may exacerbate it. 5
• Observe for hypersensitivity reactions during first antibiotic dose, particularly with severe prior reactions. 1
• No penicillin skin testing is required before cephalosporin or carbapenem administration. 1

Consultation and Referral Considerations

• Consult nephrology for antibiotic dosing guidance if creatinine clearance <30 mL/min or patient on dialysis. 5
• Consider allergy/immunology referral only if prior reaction was severe (anaphylaxis, Stevens-Johnson syndrome) or if multiple drug allergies complicate management. 1
• Trauma surgery consultation indicated if CT reveals ≥6 fractures, flail chest, severe displacement, or associated injuries requiring operative management. 5