ABSENCE OF SIGNIFICANT EFFECTS BY LEVAMISOLE ON CIRCULATING NEUTROPHIL LEVELS IN NORMAL MICE TREATED WITH 5-FU

When B6C3F1 mice were given a single intravenous (iv) injection of 150 mg/kg 5-fluorouracil (5-FU) their levels of circulating neutrophils p lummeted, reaching a nadir at 6 to 7 days postdosing and then graduall y increasing to normal and above-normal levels. Neutropenia (actual ne utrophil count (ANC) below 100 ANC/mu l) extended until 8.7 +/- 0.2 da ys after 5-FU injection. When these mice were also given levamisole (2 .5 mg/kg, po) on days 0-2 the mean time to ANC recovery greater than 1 00/mu l was 7.7 +/-:0.3 days, (p<0.05 vs. controls), while IL-1 (2 mu g/day, ip) positive controls yielded a mean time to > 100 ANG of 6.5 /- 0.2 days. Although levamisole-treated mice attained normal neutroph il levels one day faster than controls did and this more rapid recover y led, to their neutrophil levels being between 2- and 3-fold greater, these differences were not statistically significant. Effects were on ly manifested on neutrophil recoveries. There were no differences betw een levamisole-treated mice and controls when recovery rates for plate lets, monocytes or lymphocytes were examined. These results demonstrat e that levamisole has, at best, only weak myelopoietic properties agai nst 5-FU-induced myelotoxicity in mice.