The stability of cefprozil in oral suspension CEFZIL.

The stability of cefprozil in oral suspension CEFZIL was studied by means of the stress stability test. Degradation was evaluated by using an HPLC method with UV detection (280 nm), as described in the monograph of Cefprozil for Oral Suspension, in USP 25. At increased temperature and relative air humidity the degradation of cefprozil in CEFZIL occurs as reversible-consecutive and parallel reactions. The reversible reaction of isomerization is approx. 10 times faster than the parallel degradation reaction of individual isomers. The first-order rate constants of the parallel reactions Z-cefprozil --> product 1 and E-cefprozil --> product 2 were determined at RH = 76.4% at T = 333, 338, 343, 348 and 353 K, and at T = 333 K and RH = 50.9, 66.5, 76.4 and 90.0%. The thermodynamic parameters E(a), deltaH(double dagger) and deltaS(double dagger) of these reactions were calculated.