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Heroin Addiction and Related Clinical Problems: 2008, 10, 1 (pages: 25 - 38)

Evidence of Reliability and Validity of the Opiate Dosage Adequacy Scale (ODAS) in a Sample of Methadone Maintenance Patients

González-Saiz F., Rojas O. L., Gómez R. B., Acedos I. B., Martínez J. G., Collantes M. A. G., Fernández A. L., Serum Methadone Levels Study Group

Summary: Introduction: The testing and adjusting of methadone dosing is a clinical procedure that must be individualized to meet the needs of each patient. So far no evidence has been published of a tool capable of providing a global measurement of dose adequacy. For this reason, we have devised the Opiate Dosage Adequacy Scale (ODAS), which is intended as a means of implementing a theoretical construct called ‘dose adequacy'. Aim: To provide evidence of the reliability and validity of the ODAS. Methods: The study was carried out on a total of 300 patients on MMT, randomly selected from 10 public out-patient drug abuse treatment centres. We used ODAS, Addiction Severity Index (ASI), Outcomes Clinical Impression Form (OCIF) and laboratory tests (serum methadone levels, serum EDDP levels, serum a-1 acid glycoproteins levels [AAG] and urinanalysis). Results: Internal consistency for the ODAS was acceptable (a Cronbach = 0.70). Very high inter-rater reliability was found across items (kappa values between 0.95 and 1). The factor analysis yielded a four factor structure exactly coinciding with the dimensions of the ‘dose adequacy' construct proposed a priori (‘opiate withdrawal syndrome' ‘craving' ‘overmedication' and ‘drug use'. As far as construct validity is concerned, methadone dose adequacy as measured by the ODAS was correlated with clinical stabilization variables (heroin use, OCIF, ASI), while neither the methadone dose nor SML values correlated significantly with these variables. Conclusions: This study provides sufficient evidence for the reliability and validity of the ODAS as a tool for measuring methadone dose adequacy. The results of the construct validity test support the hypothesis put forward by several authors that an individualized clinical assessment of methadone dose adequacy is better able to account for a patient's condition than either the methadone dose or the patient's serum level.