Pharmacological Treatment of Cancer Pain: Alternative Routes of Opioid Administration

Developing an animal model to detect drug-drug interactions impacting drug-induced respiratory depression

Opioids and benzodiazepines were frequently co-prescribed to patients with pain and psychiatric or neurological disorders; however, co-prescription of these drugs increased the risk for severe respiratory depression and death. Consequently, the U.S. Food and Drug Administration added boxed label warnings describing this risk for all opioids and benzodiazepines. Sedating psychotropic drugs with differing mechanisms of action (e.g., antipsychotics, antidepressants, non-benzodiazepine sedative-hypnotics, etc.) may be increasingly prescribed in place of benzodiazepines. Despite being marketed for years, many sedating psychotropic drugs have neither human nor animal data that quantify or qualify the potential for causing respiratory depression, either alone or in combination with an opioid. In this study, diazepam was selected as the benzodiazepine to detect any additive or synergistic effects on respiratory depression caused by the opioid, oxycodone. Pharmacokinetic studies were conducted at three doses with oxycodone (6.75, 60, 150 mg/kg) and with diazepam (2, 20, 200 mg/kg). Dose dependent decrease in arterial partial pressure of oxygen and increase in arterial partial pressure of carbon dioxide were observed with oxycodone. Diazepam caused similar partial pressure changes only at the highest dose. Further decreases in arterial partial pressure of oxygen and increases in arterial partial pressure of carbon dioxide consistent with exacerbated respiratory depression were observed in rats co-administered oxycodone 150 mg/kg and diazepam 20 mg/kg. These findings confirm previous literature reports of exacerbated opioid-induced respiratory depression with benzodiazepine and opioid co-administration and support the utility of this animal model for assessing opioid-induced respiratory depression and its potential exacerbation by co-administered drugs.

Opioid and adjuvant analgesics: compared and contrasted

An adjuvant (or co-analgesic) is a drug that in its pharmacological characteristic is not necessarily primarily identified as an analgesic in nature but that has been found in clinical practice to have either an independent analgesic effect or additive analgesic properties when used with opioids. The therapeutic role of adjuvant analgesics (AAs) is to increase the therapeutic index of opioids by a dose-sparing effect, add a unique analgesic action in opioid-resistant pain, or reduce opioid side effects. A notable difference between opioids and AAs is that unlike opioids some AAs are associated with permanent organ toxicity, for example, nonsteroidal anti-inflammatory drugs (NSAIDs) and renal failure. It is impossible to predict in advance in a given individual what opioid dose they may require to control cancer pain. Most AAs have a ceiling effect for their analgesic actions, but often with continued dose-related toxicities and side effects (with the exception of glucocorticoids). The blood levels of opioids (and their metabolites) can be measured with great precision and accuracy. There is sometimes a role for drug blood levels of certain AAs, like tricyclic antidepressants or anticonvulsants when used for neuropathic pain. Age affects metabolism of most opioids. The therapeutic window of opioids is wide, with no ceiling effect. Most AAs (except corticosteroids) have a narrow therapeutic window. Naloxone is a pure opioid antagonist that competes and displaces opioids from their receptor sites. All clinically useful opioids are mu opioid receptor agonists. Not all routes of administration are available to all opioids. Adjuvant analgesics lack the versatility in routes of administration that opioids possess. Dosing flexibility is a major advantage when treating cancer-related pain with opioids. Dose flexibility is much less with AAs than opioids. Unlike opioids, the analgesic response is usually observed within hours to days of attaining an adequate dose with most AAs (1-2 days). Rotation among opioids is a useful therapeutic strategy to improve analgesic response or minimize toxicity. Most AAs are unsuitable for rescue dosing because of their pharmacological characteristics. The mu agonist side effect profile is similar among the different opioid agents, regardless of the route of administration. The appropriate use of AAs will reduce opioid-related side effects. No apparent tolerance to analgesia develops with AAs. Abrupt discontinuation of an opioid after chronic repeated use for more than a few days will cause a withdrawal syndrome of variable severity. Adjuvant analgesics are an essential tool in cancer pain.

Errors in opioid prescribing: a prospective survey in cancer pain

CONTEXT

Cancer pain is debilitating and has multidimensional consequences. It can be treated adequately in up to 90% of patients by following pain management guidelines. Nevertheless, inadequate pain control remains a global problem.

OBJECTIVES

We surveyed prescribing patterns in patients referred to our Palliative Medicine Program (PMP) to identify common errors in opioid use.

METHODS

Consecutive cancer patients seen by our PMP were prospectively surveyed for the presence of pain and errors in opioid prescribing at the time of initial consultation. Our recommendations to correct and optimize pain management also were recorded.

RESULTS

One hundred eighty-six consecutive cancer patients were screened. One hundred seventeen (63%) had cancer pain, 151 opioid prescribing errors were detected, and 147 different recommendations were made. Most common were failure to order around-the-clock opioids for constant pain, and the failure to treat or prevent opioid side effects. Multiple errors were more common in females, but the sex difference did not reach statistical significance. There was no difference in the errors by pain severity or reason for consultation.

CONCLUSION

Opioid prescribing errors were common. Females may be at greater risk of multiple errors. A PM consultation program is effective in identifying and correcting a wide variety of opioid prescribing errors.

Opioid equianalgesic tables: are they all equally dangerous?

Pain is one of the most common symptoms in cancer patients. Opioids are widely prescribed for this and other purposes. Properly used, they are safe, but they have serious and potentially lethal side effects. Successful use of opioids to manage cancer pain requires adequate knowledge about opioid pharmacology and equianalgesia for the purpose of both drug rotation and route conversion. The aim of this study was to demonstrate variations in equianalgesic ratios, as quoted in equianalgesic tables and various educational materials widely available to practicing physicians. We surveyed commercially available educational materials in package inserts, teaching materials provided by pharmaceutical companies, and the Physicians' Desk Reference for equianalgesic tables of commonly used opioids. We found inconsistent and variable equianalgesic ratios recommended for both opioid rotation and conversion. Multiple factors like inter- and intraindividual differences in opioid pharmacology may influence the accuracy of dose calculations, as does the heterogeneity of study design used to derive equianalgesic ratios. Equianalgesic tables should only serve as a general guideline to estimate equivalent opioid doses. Clinical judgment should be used and individual patient characteristics considered when applying any table. Professional organizations and regulators should establish a rotation and conversion consensus concerning opioid equianalgesic ratios. Systematic research on equianalgesic opioid dose calculation is recommended to avoid adverse public health consequences of incorrect or inappropriate dosing. Current information in equianalgesic tables is confusing for physicians, and dangerous to the public.

Levorphanol: the forgotten opioid

BACKGROUND

Levorphanol (levo-3-hydroxy-N-methylmorphinan) is a strong opioid that is the only available opioid agonist of the morphinan series. Levorphanol was originally synthesized as a pharmacological alternative to morphine more than 40 years ago. It is considered a step-3 opioid by the World Health Organization (WHO) and has a greater potency than morphine. Analgesia produced by levorphanol is mediated via its interactions with mu, delta, and kappa opioid receptors. Levorphanol is also an N-methyl-D-aspartate (NMDA) receptor antagonist. There is evidence that levorphanol may inhibit uptake of norepinephrine and serotonin. Similar to morphine, levorphanol undergoes glucuronidation in the liver, and the glucuronidated products are excreted in the kidney. Levorphanol can be given orally, intravenously, and subcutaneously.

OBJECTIVE

This article reviews the pharmacodynamics, pharmacology, and clinical efficacy for this often overlooked step-3 opioid.

CONCLUSION

The long half-life of the drug increases the potential for drug accumulation. Levorphanol has clinical efficacy in neuropathic pain.

Oxymorphone: a review

Oxymorphone (oxymorphone hydrochloride) (14-hydroxy-dihydromorphinone), a semisynthetic mu-opioid agonist, was first approved by the US Food and Drug Administration in 1959. Oxymorphone is considered a more potent opioid than its parent compound, morphine. Recently, an immediate-release and long-acting oral formulation of this drug was developed that makes oxymorphone a new option in treating moderate to severe pain. This article reviews the pharmacodynamics, pharmacology, and clinical efficacy for this new option in treating moderate to severe pain.

Palliative care in a national cancer center: results in 1987 vs. 1993 vs. 2000

In the last few years, palliative care for advanced and terminal cancer patients has undergone considerable evolution. We determined the characteristics of patients admitted to the 4-bed Palliative Care Unit (PCU) of the National Cancer Institute (NCI) of Milan in 1987, 1993 and 2000 to evaluate how our diagnostic and therapeutic approaches have changed over the years. We reviewed the charts of every patient admitted to the PCU in 1987, 1993, and the first ten months of 2000. We recorded demographic data; the primary tumor sites; the main reason for admission; the types of therapies administered (oncologic, analgesic, surgical, neurosurgical analgesic procedures, and supportive therapy); the type and number of cardiological, radiological and endoscopic examinations, as well as specialist consultations; the duration of stay and eventual death on the Unit. There were no significant differences regarding gender, age, primary tumor site and death in hospital of the patients admitted during these years. The time spent in hospital increased over time (P = 0.006). A significant increase was observed in the percentage of patients admitted for supportive therapy (P < 0.001) and investigation concerning the stage of the disease (P < 0.001). There was a significant decrease in admission for invasive analgesic procedures (P < 0.001), as well as for pain diagnosis and/or uncontrolled pain. Uncontrolled pain remained the most frequent reason for admission. Over the years, during hospitalization, 7% to 12% of the patients underwent radiotherapy,1% to 9% had computerized tomography, and 4% to 8% had palliative surgery. More than 50% of the patients received intravenous hydration; a few patients received hypodermoclysis in 1987. Over time, there was a significant increase in "as needed" administration of nonsteroidal anti-inflammatory drugs and a significant reduction in their regular administration (from 24% in 1987 and 1993 to 3% in 2000) (P < 0.001). The use of codeine, tramadol and methadone increased (P < 0.001), whereas the use of oral morphine, buprenorphine and oxycodone decreased in 2000 (P < 0.001). There was a reduction in the use of antidepressants (no significant constant trend) and a significant increase in the use of anticonvulsants, laxatives and pamidronate (P < 0.001). Regularly administered hypnotics decreased in 1993 and increased in 2000 (P < 0.001). Over these years, no significant differences were found in the routes of opioid administration, in route switching and in the mean maximum oral opioid dose (ranging from 108 to 126 mg/day). The percentage of patients undergoing percutaneous cordotomy significantly decreased in 1993 and 2000 (P < 0.001). Over time, there was an increase in requests for specialist consultations, which was significant for neurological, cardiological and oncological consults (P < 0.001). Although the characteristics of the patients admitted to the PCU did not change over these years, there have been significant modifications in our therapeutic approaches, above all in the use of supportive therapy, adjuvant drugs, opioids and neurosurgical invasive procedures. Moreover, a major collaborative interaction with other specialists of the NCI took place with the aim to tailor treatment for each single patient.

Strategies for the treatment of cancer pain in the new millennium

As was the case in the era before us, in the new millennium we will continue to see an abundance of patients experiencing cancer-related pain for different reasons. Although much needless pain and suffering still affects many of those with cancer, we are presented with a medical dichotomy. With the analgesic drugs available today, and the relatively simple and effective guidelines to treat cancer pain published and disseminated by the World Health Organization, why do people with cancer continue to experience pain? As we search for the answer, the horizon may hold promising new drugs, 'old drugs' with new interest and applications, and new strategies for the field of pain therapy. Possibilities include the isolation and development of analgesics or analgesic combinations that may minimise the adverse effects which are often associated with the current therapeutic class of opioid analgesics. In addition, current research points to promising results identifying the N-methyl D-aspartate non-opioid receptor as a likely component of neuropathic pain. Drugs such as gabapentin, the mechanism of action of which is not well known, have found favour within the clinical community for their analgesic properties and good tolerability. Methadone, in a phase of resurgence, has garnered the attention of the clinical community because of its unique receptor activity and pharmacoeconomic benefits. A number of clinical studies have demonstrated that methadone has a valuable role in treating cancer pain. Perhaps, an unbalanced focus on the risks of inappropriate use, rather than the benefits, should not compromise or distract from the use of methadone as an alternative to morphine. Studies are on going to assess the potential role of methadone in treating neuropathic pain. Drugs such as cannabinoids, although currently applicable for patients with anorexia, nausea and/or vomiting, may offer benefits to patients experiencing pain. Other opportunities exist with such compounds as alpha2-adrenergic agonists, nicotine, lidocaine and ketamine. New strategies such as the switching opioids and/or their route of administration may offer improved analgesia with fewer adverse effects, thus providing therapeutic alternatives for the clinical community. In addition, there is interest in the co-administration of opioids that act on different receptors. For instance, oxycodone appears to be a kappa opioid receptor agonist and may offer enhanced analgesia when combined with morphine.

Malignant bone pain: pathophysiology and treatments

Metastatic involvement of the bone is one of the most frequent causes of pain in cancer patients and represents one of the first signs of widespread neoplastic disease. The pain may originate directly from the bone, from nerve root compression, or from muscle spasms in the area of the lesions. The mechanism of metastatic bone pain is mainly somatic (nociceptive), even though, in some cases, neuropathic and visceral stimulations may overlap. The conventional symptomatic treatment of metastatic bone pain requires the use of multidisciplinary therapies, such as radiotherapy, in association with systemic treatment (hormonotherapy, chemotherapy, radioisotopes) with the support of analgesic therapy. Recently, studies have indicated the use of bisphosphonates in the treatment of pain and in the prevention of skeletal complications in patients with metastatic bone disease. In some patients, pharmacologic treatment, radiotherapy, and radioisotopes administered alone or in association are not able to manage pain adequately. The role of neuroinvasive techniques in treating metastatic bone pain is debated. The clinical conditions of the patient, his life expectancy, and quality of life must guide the physician in the choice of the best possible therapy.

Opioid and Nonopioid Therapy in Cancer Pain: The Traditional and the New

Management of cancer pain has made sidnificant progress in recent years, partly due to the Agency for Health Care Policy and Research (AHCPR) guidelines, but mostly it seems to be due to the death and dying movement in the world. However, cancer pain on occasion poses significant problems and needs accurate diganosis and appropriate intervention. Pharmacotherapy remains the mainstay of treating cancer pain. Most cancer pain syndromes present with moderate to severe pain, associated with several comorbid problems necessitating the multidisciplinary approach to optimally treat it. The psychologic factors associated wth serious illness, terminal prognoses, and dying complicate the scenario even more as compared with that of nonmalignant pain. Although such patients are entitled to more aggressive analgesic therapy, it is unfortunate that this is not achieved in a significant percentage of cases. In this review, we address some of the above issues and attempt to summarize the traditional pharmacologic therapies highlighting their modern modes of implementation in cancer pain management. Special emphasis on the state-of-the art innovations in this field wil be noted.

Novel Drug Delivery Systems

Interest in pain management is growing, with the emerging demand by our patients and colleagues, for pain relief. To meet that need, pharmaceutical and medical technology companies have provided the medical field with a variety of choices and options to deliver medication for pain control. Examination and review of the present systemic options are introduced. A more detailed look at the intrathecal route is necessary because of the tremendous potential for receptor-targeted drug delivery. The ability to treat nociceptive and neuropathic pain with drug-specific therapy makes this system all the more exciting. Because of this future, a wealth of new and old drugs are being found or reexamined for their use.