Dose ratio between morphine and methadone in patients with cancer pain

Abstract

The results highlight the general underestimation of methadone potency and the consequent risk of potential life-threatening toxicity. The strongly positive correlation between dose ratio and previous morphine dose suggests the need for a highly individualized and cautious approach when rotating from morphine to methadone in patients with cancer pain.

The use of intermittent subcutaneous injections of oxycodone for opioid rotation in patients with cancer pain

“…An alternative explanation for this observation of different ratios is related to the aforementioned opioid neurotoxicity in our patient population, which was not present in other populations reported previously. This study also supports the view that opioid rotation is often necessary and can be performed safely in this very ill patient population [19,32,33]. The pain intensity level, as shown in Table 4, may be higher than reported from survey studies conducted in palliative care units and hospices.…”

Effectiveness and safety of oral extended-release oxymorphone for the treatment of cancer pain: a pilot study

“…For some patients, effective analgesia may have been obtainable with smaller doses of oxymorphone, thereby leading to overestimates of the amounts of oxymorphone needed for equivalent analgesia. It is also possible that the observed ratio may vary when patients rotate from oxymorphone to either morphine or oxycodone, because ratios are not always the same in both directions [29]. Future double-blind studies with the availability of multiple dose strengths of oxymorphone will be needed to more accurately assess these ratios and to determine whether these ratios apply bidirectionally.…”

Serum concentrations of opioids when comparing two switching strategies to methadone for cancer pain

“…1). The equianalgesic methadone dose was calculated dose-dependently [12,21,22] from the total dose of orally administered morphine or oxycodone administered the last 24 h before the switch (mean opioid rescue dose taken the previous 48 h was included), as follows: 30-90 mg morphine 4:1, 91-300 mg morphine 6:1, 301-600 mg morphine 8:1, 601-1000 mg morphine 10:1, and >1000 mg morphine 12:1. Parenterally administered morphine and oxycodone were converted to oral equivalents by factors of three and two, respectively.…”

“…Two commonly used switching strategies to methadone are the stop and go (SAG) strategy, in which the initial opioid is substituted with methadone the same day [8][9][10], and the 3-days switch (3DS), in which the initial opioid is substituted stepwise with methadone over 3 days [11][12][13][14]. Proponents of the 3DS strategy claim that it prevents methadone accumulation [12,15], whereas SAG proponents favor the faster removal of morphine/metabolites and a faster achievement of steady state for methadone [9].…”

“…Proponents of the 3DS strategy claim that it prevents methadone accumulation [12,15], whereas SAG proponents favor the faster removal of morphine/metabolites and a faster achievement of steady state for methadone [9]. However, conclusive evidence for these claims is lacking [16].…”