Antibiotic Selection for Multiple Drug Allergies
For a woman with allergies to cephalexin (Keflex), sulfonamides, and penicillin requiring treatment for both ear infection and UTI, a fluoroquinolone—specifically levofloxacin 500 mg orally once daily or ciprofloxacin 500 mg orally twice daily—is the most appropriate choice, as these agents provide excellent coverage for both otitis media and urinary tract pathogens while avoiding all beta-lactam and sulfa drug classes. 1, 2, 3
Rationale for Fluoroquinolone Selection
Fluoroquinolones are the preferred alternative when patients have documented allergies to both penicillins and cephalosporins, as they belong to a completely different antibiotic class with no cross-reactivity risk 1, 4
Levofloxacin and ciprofloxacin both achieve excellent urinary concentrations and provide robust coverage against common UTI pathogens including E. coli, Klebsiella pneumoniae, Proteus mirabilis, and Enterobacter species 2, 3
These fluoroquinolones also cover respiratory pathogens responsible for otitis media, including Streptococcus pneumoniae (including multi-drug resistant strains), Haemophilus influenzae, and Moraxella catarrhalis 2
Specific Dosing Recommendations
Levofloxacin 500 mg orally once daily is the most convenient option, with FDA-approved dosing for both UTI and respiratory infections 2
Ciprofloxacin 500 mg orally every 12 hours is an alternative with equivalent efficacy, though requires twice-daily dosing 3
Treatment duration should be 7 days for uncomplicated UTI and typically 5-10 days for otitis media, depending on clinical response 5, 6
Important Clinical Considerations
Verify the allergy history before completely excluding beta-lactams, as less than 10% of patients reporting penicillin allergy are truly allergic, and cross-reactivity between penicillins and cephalosporins is only 1-3% 1, 4
However, since this patient has documented allergies to BOTH penicillin AND cephalexin (a first-generation cephalosporin), avoiding all beta-lactams is prudent 7, 4
The sulfa allergy eliminates trimethoprim-sulfamethoxazole, which would otherwise be a first-line option for uncomplicated UTI 5
Geographic Resistance Patterns
Consider local fluoroquinolone resistance patterns before prescribing, as resistance has become problematic in many regions 1
If fluoroquinolone resistance is high in your area (>10-20% for E. coli), obtain urine culture before initiating therapy and adjust based on susceptibility results 1
Alternative Options if Fluoroquinolones Cannot Be Used
Doxycycline 100 mg orally twice daily is an alternative that covers both UTI and respiratory pathogens, though it is less effective than fluoroquinolones for UTI 6
Azithromycin has been shown safe in penicillin and cephalosporin-allergic patients and provides coverage for respiratory pathogens, but has limited UTI coverage 8
Aminoglycosides (gentamicin) could be considered for severe infections, but require parenteral administration and are impractical for outpatient dual-site infection treatment 7
Critical Pitfalls to Avoid
Do not use any cephalosporin, even though some newer cephalosporins have minimal cross-reactivity with penicillin, because this patient has a documented cephalexin allergy 4, 9
Do not use trimethoprim-sulfamethoxazole or any sulfonamide-containing antibiotic due to the documented sulfa allergy 5
Avoid macrolides (erythromycin, azithromycin) as monotherapy for UTI, as they have poor urinary tract penetration and limited activity against common uropathogens 10