A Horse Wormer: Immunostimulant?

Levamisole, best known as an anthelmintic, stimulates the immune system in immunologically incompetent animals.

Levamisole affects all phases of the immune system, possibly by affecting cyclic nucleotide metabolism. It increases the breakdown of c-AMP and decreases the rate of inactivation of c-GMP. Levamisole affects the proliferative responses of lymphocytes, lymphokine synthesis, antibody production, chemotaxis, phagocytosis, and intracellular killing by macrophages and granulocytes. Precursor T lymphocytes are facilitated in their differentiation into mature T-cells with an increase in the ratio of helper to suppressor cells. Cell-mediated immunity is thus restored.

The drug may be administered orally or parentally. It is rapidly absorbed from the gastrointestinal tract, with peak plasma levels being obtained in 1-2 hours. The plasma half-life is about 4h in man. Levamisole is metabolized in the liver and the parent drug and metabolites are eliminated in the urine. The urinary excretion of levamisole is slow and is influenced by pH( low pH enhances the elimination rate).

Levamisole may produce toxic manifestations at high doses, with signs of excessive cholinergic stimulation becoming apparent. In humans, there is a low incidence of severe hematological toxicity, including leukopenia and agranulocytosis. In addition, levamisole may exacerbate those diseases caused by excessive T cell function.

Administered either orally or parenterally, at doses of 2-15mg/kg/day, levamisole can restore normal immune function in animals with impaired cell-mediated responses. However, in animals with intact defense mechanisms, the effect is only marginal. This agent may be used for the treatment of chronic infections and neoplastic diseases. Levamisole has been found to be beneficial in the management of acute infectious diseases associated with depression of the immune system.