[61] Like a lot of other cardiotoxic drugs, methadone blocks the hERG K+ channel. The 2 enantiomers of methadone inhibit hERG channels with unique potency. Dextromethadone, which happens to be significantly less potent as an opioid, is much more potent at blocking the hERG channel with an IC50 of ~12 ?M. Levomethadone incorporates a lower affinity,