title: Survey of methadone-drug interactions among patients of methadone maintenance treatment program in Taiwan.
abstract: BACKGROUND
  Although methadone has been used for the maintenance treatment of opioid dependence for decades, it was not introduced in China or Taiwan until 2000s. Methadone-drug interactions (MDIs) have been shown to cause many adverse effects. However, such effects have not been scrutinized in the ethnic Chinese community.
  
  
  METHODS
  The study was performed in two major hospitals in southern Taiwan. A total of 178 non-HIV patients aged ≥ 20 years who had participated in the Methadone Maintenance Treatment Program (MMTP) ≥ 1 month were recruited. An MDI is defined as concurrent use of drug(s) with methadone that may result in an increase or decrease of effectiveness and/or adverse effect of methadone. To determine the prevalence and clinical characteristics of MDIs, credible data sources, including the National Health Insurance (NHI) database, face-to-face interviews, medical records, and methadone computer databases, were linked for analysis. Socio-demographic and clinical factors associated with MDIs and co-medications were also examined.
  
  
  RESULTS
  128 (72%) MMTP patients took at least one medication. Clinically significant MDIs included withdrawal symptoms, which were found among MMTP patients co-administered with buprenorphine or tramadol; severe QTc prolongation effect, which might be associated with use of haloperidol or droperidol; and additive CNS and respiratory depression, which could result from use of methadone in combination with chlorpromazine or thioridazine. Past amphetamine use, co-infection with hepatitis C, and a longer retention in the MMTP were associated with increased odds of co-medication. Among patients with co-medication use, significant correlates of MDIs included the male gender and length of co-medication in the MMTP.
  
  
  CONCLUSIONS
  The results demonstrate clinical evidence of significant MDIs among MMTP patients. Clinicians should check the past medical history of MMTP clients carefully before prescribing medicines. Because combinations of methadone with other psychotropic or opioid medications can affect treatment outcomes or precipitate withdrawal symptoms, clinicians should be cautious when prescribing these medications to MMTP patients and monitor the therapeutic effects and adverse drug reactions. Although it is difficult to interconnect medical data from different sources for the sake of privacy protection, the incumbent agency should develop pharmacovigilant measures to prevent the MDIs from occurring. Physicians are also advised to check more carefully on the medication history of their MMTP patients.
authors.affiliation: School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, No,100 Shih-Chuan 1st Road, Kaohsiung City 807, Taiwan.
authors.forename: Hsin-Ya
authors.initials: HY
authors.lastname: Lee
authors.forename: Jih-Heng
authors.initials: JH
authors.lastname: Li
authors.forename: Li-Tzy
authors.initials: LT
authors.lastname: Wu
authors.forename: Jin-Song
authors.initials: JS
authors.lastname: Wu
authors.forename: Cheng-Fang
authors.initials: CF
authors.lastname: Yen
authors.forename: Hsin-Pei
authors.initials: HP
authors.lastname: Tang
mesh_terms: D000328:Adult; D000928:Antidepressive Agents / Q000009:adverse effects / Q000627:therapeutic use*; D014150:Antipsychotic Agents / Q000009:adverse effects / Q000627:therapeutic use*; D001145:Arrhythmias, Cardiac / Q000209:etiology; D004347:Drug Interactions; D005260:Female; D006509:Hepatitis B / Q000150:complications; D006526:Hepatitis C / Q000150:complications; D006801:Humans; D006993:Hypnotics and Sedatives / Q000009:adverse effects / Q000627:therapeutic use*; D008297:Male; D008691:Methadone / Q000627:therapeutic use*; D008875:Middle Aged; D009294:Narcotics / Q000009:adverse effects / Q000627:therapeutic use*; D058850:Opiate Substitution Treatment; D009293:Opioid-Related Disorders / Q000150:complications / Q000188:drug therapy*; D011446:Prospective Studies; D012131:Respiratory Insufficiency / Q000209:etiology; D012307:Risk Factors; D013375:Substance Withdrawal Syndrome / Q000209:etiology; D013624:Taiwan
chemical_list: D000928:Antidepressive Agents; D014150:Antipsychotic Agents; D006993:Hypnotics and Sedatives; D009294:Narcotics; D008691:Methadone