Velosef (Cephradine) is acid stable. It is rapidly absorbed after oral administration in the fasting state. Following single doses of 250 mg, 500 mg, and 1 g in normal adult volunteers, average peak serum concentrations within one hour were approximately 9 µg/mL, 16.5 µg/mL, and 24.2 µg/mL, respectively. In vitro studies by an ultracentrifugation technique show that at therapeutic serum antibiotic concentrations, cephradine is minimally bound (8 to 17 percent) to normal serum protein. Cephradine does not pass across the blood-brain barrier to any appreciable extent. The presence of food in the gastrointestinal tract delays absorption but does not affect the total amount of cephradine absorbed. Over 90 percent of the drug is excreted unchanged in the urine within six hours. Peak urine concentrations are approximately 1600 µg/mL, 3200 µg/mL, and 4000 µg/mL following single doses of 250 mg, 500 mg, and 1 g, respectively.

Microbiology

In vitro tests demonstrate that the cephalosporins are bactericidal because of their inhibition of cell-wall synthesis. Cephradine is active against the following organisms in vitro:

• Group A beta-hemolytic streptococci
• Staphylococci, including coagulase-positive, coagulase-negative, and penicillinase-producing strains
• Streptococcus pneumoniae (formerly Diplococcus pneumoniae)
• Escherichia coli
• Proteus mirabilis
• Klebsiella species
• Hemophilus influenzae

Cephradine is not active against most strains of Enterobacter species, P morganii, and P vulgaris. It has no activity against Pseudomonas or Herellea species. When tested by in vitro methods, staphylococci exhibit cross-resistance between cephradine and methicillin-type antibiotics.

Note - Most strains of enterococci (Streptococcus faecalis) are resistant to cephradine.

Disc Susceptibility Tests

Quantitative methods that require measurement of zone diameters give the most precise estimates of antibiotic susceptibility. One recommended procedure (21 CFR § 460.1) uses cephalosporin class discs for testing susceptibility; interpretations correlate zone diameters of this disc test with MIC values for cephradine. With this procedure, a report from the laboratory of "resistant" indicates that the infecting organism is not likely to respond to therapy. A report of "intermediate susceptibility" suggests that the organism would be susceptible if the infection is confined to the urinary tract, as high antibiotic levels can be obtained in the urine, or if high dosage is used in other types of infection.

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