Which of the following drug is used for long term maintenance in opioid addiction?

Methadone has a long half life of 15-40 hours. Because of the extended duration of action it suppresses the withdrawal symptoms in dependent patients and is therefore used for long term maintenance in opioid addiction. Methadone is a slow-acting agonist of -opioid receptor. It is absorbed well from the GI tract and can be detected in plasma within 30 minutes of oral ingestion. Peak concentrations occur in brain within 1-2 hours of subcutaneous or intramuscular administration. It is primarily used for the relief of chronic pain, in the treatment of opioid abstinence syndromes, and for treating heroin users. Methadone causes prolongation of QT interval. It causes serious cardiac arrhythmias including torsade de pointes. Ref: Yaksh T.L., Wallace M.S. (2011). Chapter 18. Opioids, Analgesia, and Pain Management.