Oral morphine in chronic cancer pain

Extensive clinical experience has been obtained in the use of opiates during the last decade in special units devoted to symptom control in advanced cancer. Important contradictions have emerged with the clinical pharmacological literature on opiates calling into question its relevance to the treatment of chronic pain. Specifically in the case of morphine it is clear that: it is a very effective analgesic given orally, dosage must be individualized, parenteral use or exotic analgesic 'cocktails' are usually unnecessary, and tolerance, dependence and respiratory depression are rarely common or serious problems which prevent effective pain control provided morphine is used appropriately in accordance with its pharmacological characteristics. Heroin is a suitable alternative to morphine (particularly for intramuscular administration) if differences in milligram potency are taken into account, but has no advantages in terms of either analgesic efficacy or side effects. This paper summarizes clinical experience in the use of oral morphine for cancer pain at St. Christopher's Hospice, any data from clinical investigations which support this approach, and comments on the areas of controversy which have emerged.     

Intraventricular morphine administration for control of chronic cancer pain

Twenty cancer patients with severe chronic pain have been treated with intraventricular morphine sulfate. Adequate pain relief until death was achieved in 10 patients; 1 patient has been treated for 9 months and is still being treated. In 2 patients, the effects of the morphine sulfate on their unilateral pelvic pain wore off after 4 and 6 months because of tumor progression. At that time, they underwent chordotomy procedures elsewhere. The treatment was discontinued in 4 patients for reasons other than inadequate pain relief, such as medical complications or resolution of pain. In 3 patients, the procedure was abandoned when emotional and psychological factors interfered with pain control. Dose requirements of intraventricular morphine sulfate varied greatly, depending on the total daily dose of systemic narcotic intake at the onset of the study. Intraventricular morphine sulfate is a feasible and reliable method to achieve pain relief in selected cancer patients with severe chronic pain when the maximum tolerated dose of systemic narcotic analgesics has become insufficient to control their pain.     

Plasma morphine concentrations during chronic oral administration in patients with cancer pain

Plasma concentrations of morphine were studied in 16 patients with chronic pain due to advanced cancer, treated with regular doses of morphine chloride by the oral route. Doses ranged from 20 to 125 mg every 4 h and a significant, positive, linear correlation was found between dose (range 0.22–3.01 mg/kg) and mean plasma concentration (range 22–364 ng/ml). The profile of the 4 h concentration curve is described and found to be subject to considerable, individual variation. The present investigation supports the experience that good pain relief can be obtained, if individual requirements as to dose and dose interval are taken into consideration.     

CSF and plasma morphine concentrations in cancer patients during chronic epidural morphine therapy and its relation to pain relief

Seventeen patients with advanced cancer pain, treated with chronic epidural morphine, were studied. Minimum plasma and CSF morphine concentrations (Css_min) were determined at pharmacokinetic steady state. A linear relationship was found between epidural morphine dose and concentrations obtained in plasma (r = 0.92) as well as CSF (r = 0.90). The line for best fit was much steeper for CSF than for plasma. The CSF/plasma concentration gradient of morphine at Css_min was 132 ± 31 (mean ± S.E.M.). Large interindividual variations of morphine concentrations in CSF were found. It is suggested that the variations are due to substantial differences in transdural morphine diffusion between individuals. No correlation was found between pain relief, evaluated with a visual analog scale, and CSF morphine concentrations at pharmacokinetic steady state, when calculated in 9 patients. Mean duration of treatment was 104 days (range 14–366) and the daily dose was increased from 18 ± 2 to 87 ± 31 mg/day (mean ± S.E.M.). A total of 39 epidural catheters were inserted in 14 patients. The catheters were patent for 2–223 days with a mean of 38 days. When re-examined later during treatment, 2 out of 8 patients demonstrated decreased CSF morphine concentrations in spite of increased doses given. One patient with extremely high dose demand is reported on separately and data supporting the concept of a combined spinal and systemic brain morphine effect in such cases are presented. Side effects were not a major problem but the possibility of infectious complications should be considered during chronic epidural morphine therapy.     

Cannabinoid-opioid interaction in chronic pain

Cannabinoids and opioids share several pharmacologic properties and may act synergistically. The potential pharmacokinetics and the safety of the combination in humans are unknown. We therefore undertook a study to answer these questions. Twenty-one individuals with chronic pain, on a regimen of twice-daily doses of sustained-release morphine or oxycodone were enrolled in the study and admitted for a 5-day inpatient stay. Participants were asked to inhale vaporized cannabis in the evening of day 1, three times a day on days 2-4, and in the morning of day 5. Blood sampling was performed at 12-h intervals on days 1 and 5. The extent of chronic pain was also assessed daily. Pharmacokinetic investigations revealed no significant change in the area under the plasma concentration-time curves for either morphine or oxycodone after exposure to cannabis. Pain was significantly decreased (average 27%, 95% confidence interval (CI) 9, 46) after the addition of vaporized cannabis. We therefore concluded that vaporized cannabis augments the analgesic effects of opioids without significantly altering plasma opioid levels. The combination may allow for opioid treatment at lower doses with fewer side effects.     

Oral morphine in cancer pain: influences on morphine and metabolite concentration

One hundred fifty-one patients with chronic cancer pain were studied during chronic treatment with oral morphine. Plasma concentrations of morphine and metabolites (M3G and M6G) were measured. The ratio of plasma morphine to metabolites was not affected by dose. Generalized linear interactive modeling analysis using morphine dose, age, sex, renal and hepatic dysfunction, and concomitant medication as explanatory variables accounted for 70% of the variance in plasma concentrations of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Increasing morphine dose was a significant factor for increased plasma concentrations of morphine, M3G, and M6G. Other significant factors were: age greater than 70 years (increased M3G and M6G plasma concentrations), plasma creatinine greater than 150 mumol/L (increased M3G and M6G plasma concentrations), male sex (decreased morphine and M6G plasma concentrations), raised creatinine plus coadministration of tricyclic antidepressants (increased M3G plasma concentrations), ranitidine (increased morphine plasma concentrations), and raised creatinine plus coadministration of ranitidine (increased M6G plasma concentrations).     

Pharmacological consequences of long-term morphine treatment in patients with cancer and chronic non-malignant pain.

BACKGROUND: In patients with pain of malignant origin morphine may be administered in high and often increasing doses during extended periods of time. In patients with chronic pain of non-malignant origin morphine may be an important remedy, and in these cases the goal is to keep the morphine dose stable. The pharmacokinetic as well as the pharmacodynamic consequences of long-term morphine treatment with special reference to the two most important metabolites of morphine morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G) remain to be settled. METHODS: Assessments for pain, sedation and other morphine induced side effects were made several times for 19 cancer patients treated with changing doses of oral sustained release (SR) morphine and twice for 17 non-cancer patients treated with stable doses of SR morphine. Blood samples were obtained simultaneously and analysed for contents of morphine, M-3-G and M-6-G by high-performance liquid chromatography (HPLC). RESULTS: Significant correlations were found between the daily dose of SR morphine and plasma morphine (r = 0.469, p < 0.01), plasma M-6-G (r = 0.677, p < 0.01), and plasma M-3-G ((r = 0.827, p < 0.01), in the cancer patient group, but only between the daily dose of SR morphine and plasma M-3-G (0.662, p < 0.01) and plasma M-6-G (0.571, p < 0.01) in the non-cancer patient group. Normalised M-3-G/M and M-6-G/M ratios for the cancer patient group were independent of duration of treatment and daily dose of SR morphine. Likewise in the non-cancer patient group duration of treatment did not influence the metabolite ratios. Correlations between pain score and plasma morphine, M-6-G and M-6-G/M were weak in the cancer patient as well as in the non-cancer patient group making it impossible to draw any conclusion regarding the potential contributory analgesic effect of M-6-G. Dryness of the mouth was the most frequent adverse effect reported in the non-cancer as well as the cancer patient group. In the latter group patients complaining of dryness of the mouth had significantly higher plasma morphine and M-6-G concentrations than patients who did not suffer from this side effect. This difference persisted (or was close to significance) when excluding patients receiving antidepressants. CONCLUSION: In the cancer patient group neither dose nor treatment period seems to influence morphine glucuronidation. Likewise in the non-cancer patient group receiving stable doses of morphine duration of treatment does not seem to influence morphine glucuronidation. Dryness of the mouth was positively correlated to high plasma concentrations of morphine and M-6-G.     

Clinical observations on controlled-release morphine in cancer pain

The authors report the data from two studies on the use of controlled-release morphine sulphate tablets for cancer pain relief. This preparation allows just two administrations per day, in comparison with immediate release oral aqueous morphine solution. The first study, a randomized trial carried out on 70 patients suffering from advanced cancer pain, evaluated the analgesic efficacy and side effects of this drug. The second, an open study of 113 patients, assessed analgesic efficacy, incidence of side effects, and the effects of age on dose. The analgesia provided by controlled-release morphine administration proved to be superimposable to those of the oral aqueous morphine solution. Moreover, the use of controlled-release morphine was associated with a statistically significant reduction of some side effects. Ninety-one percent of patients needed controlled-release morphine every 12 hr, while 9% required it every 8 hr.     

Tramal in the treatment of acute and chronic pain syndromes in cancer patients

The study of 65 cancer patients has demonstrated the advantages and disadvantages of tramal as an agent used for the relief of acute and chronic pain syndrome. In 18 patients tramal was used in postoperative analgesia, in 17 patients it was used for the treatment of chronic pain syndrome. It has been shown that in the postoperative period tramal has no noticeable advantages over promedol. However, tramal had definite advantages over other opiate agonists when used for the treatment of chronic pain syndrome in incurable cancer patients. Thus, the data obtained show that tramal, a synthetic analgesic of a new generation, has no dangerous side effects, is effective in a convenient, non-invasive drug form, interacts well with non-narcotic and supplementary agents and causes no clinical signs of drug tolerance or addiction in prolonged application.     

Proglumide potentiates morphine analgesia for acute postsurgical pain

Proglumide, an antagonist of cholecystokinin, has been shown to potentiate morphine analgesia in animal and human experimental pain models. This study was undertaken to determine whether proglumide enhances morphine analgesia for patients experiencing postoperative pain. At onset of pain after the removal of impacted third molars, patients (n = 60) received intravenously either 4 mg morphine, 8 mg morphine, or 4 mg morphine plus proglumide (0.05, 0.5, or 5 mg). The administration of 8 mg morphine significantly reduced pain, in comparison with baseline and 4 mg morphine, for the first 30 minutes. The addition of 0.05 mg proglumide resulted in a significant increase in the magnitude and duration of the analgesic activity of 4 mg morphine; 0.5 and 5.0 mg proglumide did not produce this effect. No difference was seen in respiratory rate or in the frequency of side effects among the various forms of treatment. These data indicate that a low dose of proglumide potentiates both the magnitude and the duration of morphine analgesia in a clinical model of acute pain, without any detectable increase in side effects.     

Analgesic effects of dextromethorphan and morphine in patients with chronic pain

N-methyl-aspartate (NMDA) receptor antagonists have been shown to improve opioid analgesia in the animal model. The cough suppressant dextromethorphan is a clinically available NMDA-receptor antagonist. In this randomised, double-blind, placebo-controlled study 20 patients with chronic pain of several years duration were given 100 mg of oral dextromethorphan or matching placebo 4 h prior to an intravenous infusion of morphine 15 mg. Pain intensity and adverse effects were assessed at 0, 4, 5 and 7 h. Dextromethorphan had no effect on morphine analgesia: the mean (+/-SEM) visual analogue scores for pain relief (VAS, 0-100 mm) at the end of the morphine infusion were 38 (+/-6) for dextromethorphan+morphine and 38 (+/-7) for placebo+morphine. VAS scores for pain intensity were comparable both at rest and at movement at all time points. The most common adverse effects reported were dizziness, nausea and sedation. There were no significant differences in either the incidence or severity of adverse effects. In conclusion, oral dextromethorphan 100 mg had no effect on pain relief by intravenous morphine 15 mg in patients with chronic pain.     

Low morphine doses in opioid-naive cancer patients with pain

Cancer pain can be managed in most patients through the use of the analgesic ladder proposed by the World Health Organization. Recent studies have proposed to skip the second "rung" of the ladder by using a so-called "strong" opioid for moderate pain. However, usual doses of strong opioids commonly prescribed for the third rung of the analgesic ladder may pose several problems in terms of tolerability in opioid-naive patients. The aim of this multicenter study was to evaluate the efficacy and tolerability of very low doses of morphine in advanced cancer patients no longer responsive to nonopioid analgesics. A sample of 110 consecutive opioid-naive patients with moderate-to-severe pain were given oral morphine at a starting dose of 15 mg/day (10 mg in those older than 70 years). Doses were then titrated according to the clinical situation. Pain intensity, morphine doses, symptom intensity, quality of life, and the requirement for dose escalation were monitored for a period of 4 weeks. The treatment was effective and well tolerated by most patients, who were able to maintain relatively low doses for the subsequent weeks (mean dose 45 mg at Week 4). Only 12 patients dropped out due to poor response or other reasons. The use of very low doses of morphine proved to be a reliable method in titrating opioid-naive advanced cancer patients who were also able to maintain their dose, in a 4-week period, below the dose level commonly used when prescribing strong opioids.     

A comparative study of controlled-release morphine (CRM) suspension and CRM tablets in chronic cancer pain.

This study compared the efficacy and the adverse effects of controlled-release morphine (CRM) suspension (SAR 213) and CRM tablets (Moscontin) in the treatment of cancer pain. This multicenter, randomized, double-blind, double-dummy, crossover study was carried out on 52 patients. Each patient received both study treatments given at an equivalent dosage of morphine during each of two 7-day periods. The primary outcome variable was the severity of pain assessed three times daily by means of a visual analogue scale. Secondary criteria of efficacy were the severity of pain assessed by verbal rating scale, the need for "rescue" doses of immediate-release morphine, treatment preference, and indices of quality of life (activity, mood, sleep). There were no statistically significant differences in the parameters assessed when comparing the two groups. This study shows that, when prescribed at the same doses, CRM suspension and CRM tablets have similar efficacy and adverse effects, as well as the same duration of action. The results of this first clinical study carried out on CRM suspension are especially relevant for patients with cancer pain who have difficulty swallowing.