[61] Like several other cardiotoxic drugs, methadone blocks the hERG K+ channel. The two enantiomers of methadone inhibit hERG channels with various potency. Dextromethadone, which can be a lot less potent being an opioid, is more potent at blocking the hERG channel with an IC50 of ~12 ?M. Levomethadone contains a lower affinity, with an IC50 of ~2