BROAD RANGES |
According to Mitchell Bradbury, PhD, opiate toxicology and patient self-reports are the most commonly used indicators of appropriate methadone dose, but they can be misleading without also assessing plasma levels.[6] Bradbury and Philip Paris, MD have reported on 55 patients evaluated for methadone dose / opiate withdrawal-related problems, with trough methadone plasma levels obtained on all patients upon entry into the study.[3] Of interest, there was a wide range of plasma levels at each daily methadone dose. For example, among 4 patients receiving 60 mg/d (milligrams per day), trough levels ranged 10-170 ng/mL; 20 patients receiving 100 mg/d ranged 90-520 ng/mL; and for 10 patients at 120 mg/d the range was 10-440 ng/mL. At each daily methadone dose there were patients well below optimum trough levels. [3] Curiously, in the Bradbury/Paris research, there also was a strong positive correlation between patient weight and methadone plasma level. Heavier patients had higher trough levels. [3] Bradbury notes the reasons for this aren't clear and further research is needed. [6] However, one patient in this study had a trough level of 700 ng/mL and exhibited excessive sedation with small pupils, so dose was accordingly adjusted downward. Byrne recommends examining all high-dose patients three hours after witnessed dosing to exclude clinical toxicity.[6] |