No experience using levamisole, but being it’s a dewormer and nitrofurazone is an antibiotic they are probably fine to mix. You can safely combine nitrofurazone with prazi (another dewormer). In all cases it’s best to mix these as powdered medications. When you try mixing a liquid medication (such as Prazipro) with other meds that’s when problems can arise due to the solubilizing agent contained therein.