Switching from morphine to methadone to improve analgesia and tolerability in cancer patients: a prospective study

Opioid plasma concentration during switching from morphine to methadone: preliminary data

Opioid switching is often used to improve the opioid response in cancer patients experiencing poor analgesia or adverse effects. However, no data are available on plasmatic changes of opioids and their metabolites during these phases, and whether there exists a relationship with the clinical events. In a prospective study of 10 consecutive cancer patients on oral morphine but with uncontrolled pain (greater >4 on a numerical scale of 0 to 10) and/or moderate to severe opioid adverse effects (on a level of 2 and 3 of a verbal scale) and not responsive to adjuvant medications, switching to oral methadone was performed using a fixed ratio of 5:1, leaving extra-doses of 1/5 of the daily dose of methadone calculated as needed. Blood samples were obtained at the same hour for four days, before the switching, and then on day 1, 2, and 3. The intensity of pain and the adverse effects were assessed daily to calculate the switching score before and after switching. Completed blood samples were obtained in 9 patients. One patient was separately considered, because of his renal impairment. Significant improvements in pain intensity as well as adverse effects within an average period of 1-2 days were observed. Morphine, morphine-6-glucuronide, and morphine-3-glucuronide were progressively cleared from plasma to almost disappear within three days. Methadone rapidly achieved a stable concentration in 1-2 days. The doses of methadone were changed, but not significantly, and tended to decrease in the following days, according to the clinical situation. The results of this study confirm the need to stop rapidly morphine, and to use a priming dose of methadone, rather than using progressive decrements and increments of morphine and methadone, respectively, during opioid switching. This method allows for a rapid clearance of morphine and its metabolites are rapidly cleared, except in patients with renal failure. Opioid plasma changes substantially overlap the clinical changes observed in these patients, in terms of benefit between analgesia and adverse effects.

An ad libitum schedule for conversion of morphine to methadone in advanced cancer patients: an open uncontrolled prospective study in a Chinese population

Methadone has been used as an alternative strong opioid to morphine in the management of cancer pain. The conversion of morphine to methadone is not straightforward because of the high individual variability and unpredictability in the pharmacokinetics of methadone. An ad libitum schedule for conversion of morphine to methadone was used in 37 cancer patients who had intolerable morphine-related side effects or had pain not satisfactorily controlled by morphine. Oral morphine was discontinued on the day of conversion. Methadone was given at a dose calculated as one-twelfth of the total daily dose of morphine, up to a maximum of 30 mg/dose. Methadone was administered at patient-controlled intervals not more frequent than three hours, the need of which was indicated by the presence of pain of moderate intensity or above as rated by a verbal rating scale. When the demand for methadone was stabilized, the total daily dose was given regularly in divided doses. Pain control on day 7 was taken as the primary endpoint. Twenty-seven patients completed the study. Twenty-four patients (88.9%) were in good pain control on day 7, and all reached good pain control by day 11. The median time required to achieve good pain control was three days (range 1-11 days). A majority (88.6%) of morphine-related adverse effects improved or resolved after conversion to methadone. This ad libitum schedule is effective in conversion of morphine to methadone in these patients.

Advances in cancer pain management

Although most patients with cancer pain can attain a favorable balance between analgesia and side effects with a conventional approach to opioid therapy, a substantial minority cannot. For these patients, an important subgroup of whom have neuropathic pain, alternative therapeutic strategies are needed. With a detailed assessment, clinicians should be able to choose among the large and diverse group of options available and implement an approach, or combination of approaches, that have a high probability of improving analgesic outcomes.

The use of methadone for cancer pain

Methadone is not a new analgesic drug [69]. Several studies have demonstrated that methadone is a valid alternative to morphine, hydromorphone, and fentanyl for the treatment of cancer-related pain, and extensive reviews on the subject have been published in recent years [10,23,25,64,70,71]. Most people involved in pain therapy, however, are not well informed about the properties of methadone. The authors believe that the low cost of methadone paradoxically contributes to the limited knowledge of its characteristics and to the restricted therapeutic use of this drug. The low cost of methadone means there is little financial incentive for pharmaceutical companies to invest in research or to disseminate scientific information. Unfortunately, the lack of scientific information from pharmaceutical companies frequently results in a lack of knowledge on the part of physicians. Unless the existing approach changes, both culturally and politically, ignorance about methadone will persist among medical experts. The low cost of methadone, rather than being an advantage, will result in the limited exploitation of an effective drug.

The panorama of opioid-related cognitive dysfunction in patients with cancer: a critical literature appraisal

BACKGROUND

Opioids have an essential role in the management of pain in cancer patients, particularly those with advanced disease. Cognitive dysfunction is a recognized complication of opioid use. However, misconceptions and controversy surround the nature and prevalence of its occurrence. A projected increase in the aging cancer population highlights the need for a better understanding of this phenomenon.

METHODS

A critical appraisal of the literature evidence in relation to the pattern, pathophysiology, assessment, impact, and management of cognitive dysfunction due to opioid use in cancer pain management is given.

RESULTS

Studies in cancer patients with less advanced disease reveal subtle evidence of cognitive impairment, largely related to initial dosing or dose increases. In advanced cancer, opioid-induced cognitive dysfunction usually occurs in the form of delirium, a multifactorial syndrome. The presence of both cognitive impairment and delirium frequently is misdiagnosed or missed. Potential risk factors include neuropathic and incidental pain, opioid tolerance, somatization of psychologic distress, and a history of drug or alcohol abuse. Elevation of opioid metabolites with renal impairment may contribute to cognitive dysfunction. Recognition of opioid-related cognitive dysfunction is improved by objective screening. Successful management requires either dose reduction or a change of opioid, in addition to addressing other reversible precipitants such as dehydration or volume depletion.

CONCLUSIONS

Opioid-related cognitive dysfunction tends to be subtle in the earlier stages of cancer, whereas delirium, a more florid form with behavioral disturbance is likely to be present in the advanced cancer population. In patients with advanced disease, an optimal management approach requires careful clinical assessment, identification of risk factors, objective monitoring of cognition, maintenance of adequate hydration, and either dose reduction or switching to a different opioid.

Methadone use in cancer patients with pain: a review

In recent years a better understanding of the pharmacologic and pharmacokinetic properties of methadone, including equianalgesic ratios has led to its increased use as a second line opioid for the treatment of pain in patients with cancer. Methadone may be an important alternative for those who have side effects related to the use of other opioids because it has no known active metabolites, is well absorbed by oral and rectal routes, and also has the advantage of very low cost. However, it has a long, unpredictable half-life, which can result in accumulation and toxicity in some patients. In addition, rotation to methadone as a second line agent is more complex than with other opioids because of its increased potency in those patients who are opioid tolerant, particularly those who have been on higher doses of other opioids. Future research should address the use of methadone as a first-line agent in the management of cancer pain, its use in patients with neuropathic pain, and in those who develop rapid tolerance to other opioids. In some patients with cancer the long half-life of methadone offers the advantage of extended dosing intervals to 12 and even 24 hours, further research is also needed in this area.