Originally developed as an anthelmintic, levamisole exhibits broad-spectrum activity against nematodes by causing paralysis through nicotinic acetylcholine receptor agonism. It is particularly effective against Ascaris, Haemonchus, and Oesophagostomum species in veterinary medicine, administered orally or subcutaneously at 7.5 mg/kg doses. In human medicine, it gained FDA approval as an immunomodulator for adjuvant treatment of colorectal cancer, though this use has declined due to safety concerns. The drug stimulates T-cell function and macrophage activity, explaining its historical use in rheumatoid arthritis and recurrent aphthous ulcers. Veterinarians commonly employ levamisole in livestock, poultry, and aquaculture for parasite control, with withdrawal periods of 7-14 days depending on species. Its unique ability to enhance immune responses led to off-label uses in chronic infections and as an adulterant in illicit drugs (notably ), though such practices carry severe neurological risks. Regulatory agencies including FDA, EMA, and WHO provide strict guidelines for its medical use due to potential agranulocytosis and vasculitis side effects. Current research explores its potential in combination therapies against resistant parasites and as an immune checkpoint modulator in oncology, though clinical applications remain limited by its narrow therapeutic index. Proper handling requires PPE due to its moderate toxicity (LD50 oral rat = 480 mg/kg).
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