We've been copied on correspondence involving a long-time methadone patient who has not been doing well on doses that very slowly and grudgingly were raised to about 80-mg per day. The "clinic" insisted she have peak-trough blood concentration testing done - and pay for it! Based on the results they claim there's no rationale for increasing the dosage and instead are threatening to decrease it. Some comments on peak-trough testing follow:
Tom Payte is the expert on this... My understanding: peak-trough relationship merely indicates that one might have a "fast metabolizer". It's indicated not to determine adequacy of dosage, but to help formulate response to patient discomfort and less than optimal therapeutic results.
If one has a patient not doing well, and there's a big big gap between the peak concentration and the lowest in the course of a day, then it might make much more sense to split the dose rather than "just" increase it. In fact, increasing it in such cases might lead to more discomfort/problems, because there'll be a higher peak, still a very rapid metabolism and thus in the course of the day an even greater gap between the high and low concentrations. Thus: rationale for splitting doses - I've heard Tom Payte talk about some (very few) patients whom he had to give doses six times a day before they responded well.
I see zero rationale ever for decreasing a dose based on P-T levels. Ultimately, I'm a believer in clinical observation rather than fancy and expensive lab tests. Patient's dojng well on a dose, great. If not, and most definitely if patient has been getting dosage that for most is sub-optimal (e.g., less than 80) then of course increase the dose! It's when the dose gets up[ to 150-200 and the patient still reports doing poorly, especially toward end of day, then logic dictates trial of splitting the dose - say half AM and half PM. What counts is how the patient is doing - NOT what a lab test shows (identical reasoning for my disdain for urine tests!).