Classification Basis
Second-generation cephalosporins are characterized by enhanced activity against β-lactamase–producing organisms compared to first-generation agents, particularly against H. influenzae, M. catarrhalis, and S. aureus. 1
The American Academy of Otolaryngology-Head and Neck Surgery explicitly categorizes cefaclor alongside other second-generation agents when discussing its spectrum of activity against respiratory pathogens. 3
Cefaclor's antimicrobial spectrum aligns with second-generation characteristics: it demonstrates activity against β-lactamase-producing H. influenzae resistant to ampicillin, though its overall efficacy against bacterial respiratory tract pathogens is considered poor compared to newer agents. 3, 4
Clinical Activity Profile
Cefaclor has poor activity against H. influenzae, fair activity against penicillin-susceptible pneumococci, and no activity against drug-resistant S. pneumoniae (DRSP). 3
The standard adult dosing is 500 mg orally three times daily, as recommended by the Infectious Diseases Society of America. 1
Cefaclor carries a higher risk of serum sickness-like reactions compared to other second-generation cephalosporins, which is an important safety consideration. 1
Important Clinical Caveat
Despite being classified as second-generation, cefaclor's clinical utility is limited by its relatively poor activity profile against common respiratory pathogens compared to other agents in the same generation (such as cefuroxime or cefprozil) and certainly compared to third-generation agents. 3
In vitro studies confirm susceptibility of >95% of S. pneumoniae, M. catarrhalis, and H. influenzae isolates to cefaclor with MIC₉₀ <2 μg/mL, though clinical superiority over less expensive antibiotics has not been demonstrated. 4, 5