[Labelling of ceftizoxime with 99mTc].
OBJECTIVE
A new method to label antibiotics with 99mTc, using a third generation, wide spectrum cephalosporine (ceftizoxime), is presented.


METHODS
2.5 mg of ceftizoxime, 6.25 mg sodium dithionite in sodium bicarbonate buffer (pH=11.4) as a reductor agent, and 300 MBq of 99mTc were used. The final pH was adjusted to 8.4 with NaOH 0.1N. Radiochemical purity was assessed using ITLC-SG/MEK, ITLC-SG/0.9% NaCl and reverse phase HPLC. Biologic activity was assessed with the agar diffusion technique soaked with E. Coli in disks containing 10.5 microg labelled and non-labelled antibiotic. The maintenance of antibiotic activity was assessed by the diameter of the inhibition halos measured after 24 hours of incubation at 37 degrees C.


RESULTS
The labelling efficiency was 94.9 +/- 2.4% (n = 20) and the complex was stable up to 6 h post-labelling. The HPLC chromatography showed five peaks: two of them at 1.7-2.0 min, which corresponds to the ceftizoxime derived product (82%-83% of the absorbance and about 90% of the radioactivity) and a third one at 4.7 min which corresponds to the intact ceftizoxime (6% of absorbance). The remaining two peaks appeared at 3.8 and 6.7 min and represented about 7%-8% of the absorbance. The antibiotic activity of the ceftizoxime-derived compound (CDC) was 83% of the unlabelled one.


CONCLUSIONS
1) The labelling method of ceftizoxime described causes a modification in its structure. 2) The 99mTc binds to the newly formed compound with high labelling efficiency and an acceptable shelf life stability. 3) The 99mTc-CDC maintains 83% of the original antibiotic activity and could be used for the detection of in vivo infection.
Gomes Barreto
V
V
Becaria del CAPES, Brasil.
Iglesias
F
F
Roca
M
M
Tubau
F
F
Martín-Comín
J
J
D015296:Ceftizoxime; D002511:Cephalosporins; D007553:Isotope Labeling / Q000379:methods*; D013667:Technetium
D002511:Cephalosporins; D013667:Technetium; D015296:Ceftizoxime