A novel form of dependency of hepatic extraction ratio of opioids in vivo upon the portal vein concentration of drug: comparison of morphine, diamorphine, fentanyl, methadone and buprenorphine in the chronically cannulated cow

Fentanyl for neuropathic pain in adults

BACKGROUND

Opioid drugs, including fentanyl, are commonly used to treat neuropathic pain, and are considered effective by some professionals. Most reviews have examined all opioids together. This review sought evidence specifically for fentanyl, at any dose, and by any route of administration. Other opioids are considered in separate reviews.

OBJECTIVES

To assess the analgesic efficacy of fentanyl for chronic neuropathic pain in adults, and the adverse events associated with its use in clinical trials.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Embase from inception to June 2016, together with the reference lists of retrieved articles, and two online study registries.

SELECTION CRITERIA

We included randomised, double-blind studies of two weeks' duration or longer, comparing fentanyl (in any dose, administered by any route, and in any formulation) with placebo or another active treatment in chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched for studies, extracted efficacy and adverse event data, and examined issues of study quality and potential bias. We did not carry out any pooled analyses. We assessed the quality of the evidence using GRADE.

MAIN RESULTS

Only one study met our inclusion criteria. Participants were men and women (mean age 67 years), with postherpetic neuralgia, complex regional pain syndrome, or chronic postoperative pain. They were experiencing inadequate relief from non-opioid analgesics, and had not previously taken opioids for their neuropathic pain. The study used an enriched enrolment randomised withdrawal design. It was adequately blinded, but we judged it at unclear risk of bias for other criteria.Transdermal fentanyl (one-day fentanyl patch) was titrated over 10 to 29 days to establish the maximum tolerated and effective dose (12.5 to 50 µg/h). Participants who achieved a prespecified good level of pain relief with a stable dose of fentanyl, without excessive use of rescue medication or intolerable adverse events ('responders'), were randomised to continue with fentanyl or switch to placebo for 12 weeks, under double-blind conditions. Our prespecified primary outcomes were not appropriate for this study design, but the measures reported do give an indication of the efficacy of fentanyl in this condition.In the titration phase, 1 in 3 participants withdrew because of adverse events or inadequate pain relief, and almost 90% experienced adverse events. Of 258 participants who underwent open-label titration, 163 were 'responders' and entered the randomised withdrawal phase. The number of participants completing the study (and therefore continuing on treatment) without an increase of pain by more than 15/100 was 47/84 (56%) with fentanyl and 28/79 (35%) with placebo. Because only 63% responded sufficiently to enter the randomised withdrawal phase, this implies that only a maximum of 35% of participants entering the study would have had useful pain relief and tolerability with transdermal fentanyl, compared with 22% with placebo. Almost 60% of participants taking fentanyl were 'satisfied' and 'very satisfied' with their treatment at the end of the study, compared with about 40% with placebo. This outcome approximates to our primary outcome of moderate benefit using the Patient Global Impression of Change scale, but the group was enriched for responders and the method of analysis was not clear. The most common adverse events were constipation, nausea, somnolence, and dizziness.There was no information about other types of neuropathic pain, other routes of administration, or comparisons with other treatments.We downgraded the quality of the evidence to very low because there was only one study, with few participants and events, and there was no information about how data from people who withdrew were analysed.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the suggestion that fentanyl works in any neuropathic pain condition.

Buprenorphine for neuropathic pain in adults

BACKGROUND

Opioid drugs, including buprenorphine, are commonly used to treat neuropathic pain, and are considered effective by some professionals. Most reviews have examined all opioids together. This review sought evidence specifically for buprenorphine, at any dose, and by any route of administration. Other opioids are considered in separate reviews.

OBJECTIVES

To assess the analgesic efficacy of buprenorphine for chronic neuropathic pain in adults, and the adverse events associated with its use in clinical trials.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE from inception to 11 June 2015, together with reference lists of retrieved papers and reviews, and two online study registries.

SELECTION CRITERIA

We included randomised, double-blind studies of two weeks' duration or longer, comparing any oral dose or formulation of buprenorphine with placebo or another active treatment in chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched for studies, extracted efficacy and adverse event data, and examined issues of study quality. We did not carry out any pooled analyses.

MAIN RESULTS

Searches identified 10 published studies, and one study with results in ClinicalTrials.gov. None of these 11 studies satisfied our inclusion criteria, and so we included no studies in the review.

AUTHORS' CONCLUSIONS

There was insufficient evidence to support or refute the suggestion that buprenorphine has any efficacy in any neuropathic pain condition.

Sedation in intensive care: morphine and renal function

Intravenous morphine infusions have been administered to 12 critically-ill patients during controlled ventilation. Acute oliguric renal failure was present in 4 patients, who were treated with a combination of haemofiltration and haemodialysis. Severity of physiological disturbance was assessed using a modified APACHE Score, level of sedation by a linear-analogue scale, and blood morphine levels by high-pressure liquid chromatography. Morphine clearance was impaired in renal failure, and was dependent on haemofiltration volumes; accumulation of morphine did not occur during this form of treatment. Conscious level was clearly more closely related to the degree of physiological disturbance than blood morphine levels; and for a given blood morphine level, depression of consciousness was more pronounced the greater the degree of physiological disturbance. Use of a physiological sickness score may help to clarify some of the factors influencing cerebral function during critical illness. Careful clinical monitoring of level of sedation is important in patients with oliguric renal failure receiving morphine, and haemofiltration appears to reduce the risk of morphine accumulation in these patients.

Systemic availability of oral slow-release morphine in man

In a within-patient crossover study on twelve patients we investigated plasma morphine concentrations for 48 hours after administration of intravenous morphine sulphate followed 24 hours later by oral MST Continus [MST]. Patients received either 10 mg i.v. morphine followed by 10 mg MST or 20 mg i.v. morphine followed by 2 X 10 mg MST tablets. Systemic clearance of morphine was low, being about 3 ml/min/kg after both intravenous and oral administration. The ratio of the areas under the concentration-time curve for MST relative to that for i.v. morphine was about 1:1 for 20 mg doses, but was significantly greater than 1:1 for 10 mg doses. The results suggest high oral systemic availability for morphine and low hepatic morphine metabolism.

Renal failure and the use of morphine in intensive care

Intravenous morphine infusions were given to 20 patients in the intensive-care unit to provide sedation and analgesia. In 10 of the patients renal impairment was already present or developed during intensive care. Plasma morphine concentrations for a given dose of morphine and morphine clearance depended on renal function; dose-related plasma morphine concentrations rose as renal function deteriorated. Reduced morphine clearance leads to increased elimination half-life of the drug, and neurological impairment caused by unrecognised high concentrations of morphine could result in an incorrect diagnosis of cerebral damage in patients in intensive care.