Morphine kinetics during and after renal transplantation

The Therapeutic Equivalence of Oral and Subcutaneous/Intramuscular Morphine Sulphate in Cancer Patients

Clinical use suggests that the oral-to-subcutaneous / intramuscular potency ratio for morphine sulphate when given regularly to cancer patients is of the order of 1:2 or 1:3. Published data indicate that the mean bioavailability after oral administration is 38%, ranging from 15% to 64%. Recent pharmacokinetic studies have highlighted the important contribution made by an active metabolite, morphine-6-glucuronide, to the total effect of morphine. This is several times more potent than morphine and, on chronic administration, is present in higher concentrations than morphine itself. The need for caution when prescribing morphine to patients with impaired renal function is stressed.

Transdermal buprenorphine in chronic pain: indications and clinical experience

Transdermal buprenorphine has been shown to be effective in managing moderate-to-severe cancer pain and severe pain that is unresponsive to nonopioid analgesics. In clinical trials, it provided better pain relief than placebo, despite a higher consumption of rescue analgesia by placebo patients. Analgesia was rated as satisfactory or better by 90% of patients in a long-term follow-up study and 94.6% considered the buprenorphine matrix patch to be user friendly. Transdermal buprenorphine is well tolerated; most adverse events are transient local reactions to the patch or systemic effects typical of treatment with opioids. Even in opioid-experienced volunteers, buprenorphine does not cause respiratory depression at doses up to 70-times higher than those used for analgesia. No problems have been encountered when switching from another opioid to transdermal buprenorphine, or in combining the buprenorphine patch with intravenous morphine or tramadol for breakthrough pain. There is a growing body of evidence that transdermal buprenorphine may be particularly useful for managing neuropathic pain. Most notably, it appears to be effective in treating hyperalgesic states and syndromes characterized by pronounced central sensitization.

Dose conversion in opioid rotation from continuous intravenous infusion of morphine hydrochloride injection to fentanyl patch in the management of cancer pain

Opioid rotation has been proposed for management of cancer pain. No studies directly investigating dose equivalence between morphine injection (continuous IV administration) and the transdermal fentanyl patch have been reported. Therefore, we examined dose conversion ratios in patients undergoing opioid rotation from morphine injection to fentanyl patches. The subjects consisted of 45 patients admitted to Kitasato University East Hospital. Medical records were consulted to determine the "basic dose of morphine injection immediately prior to rotation" and the "basic dose of fentanyl patch after rotation". Equivalent doses and conversion ratios obtained with the expression of (daily dose of morphine injection (mg)/daily delivered dose of fentanyl patch (mg)) were determined from the relationship between the data by regression analysis. The regression equation obtained was Y=50.882X-13.96, r²=0.8922, where X and Y are daily doses of morphine injection and fentanyl patch, respectively. Equivalent doses and conversion ratios for daily dose of morphine injection (mg): daily delivered dose of fentanyl patch (mg) (patch dose mg/3 days) were 16.6 mg: 0.6 mg (2.5 mg)=28:1, 47.1 mg: 1.2 mg (5 mg) = 39:1 and 169.2 mg: 3.6 mg (15 mg)=47:1. In other reports, the ratio of morphine vs. fentanyl at 50:1 had no relation to the dose. While the present study suggested that in opioid rotation from low dose, 50:1 is not enough for the fentanyl patch. The dose conversion ratio of morphine injection to fentanyl patch was different at the low doses and high doses of morphine.

Transdermal buprenorphine in the treatment of chronic pain

The transdermal matrix patch formulation of buprenorphine has been shown to be effective in managing moderate-to-severe cancer pain and severe pain unresponsive to nonopioid analgesics. Clinical trials have revealed that it is possible to switch from weak opioids or low doses of step III opioids to transdermal buprenorphine without any problems. With buprenorphine patches, the sublingual buprenorphine intake was dose-dependently reduced and was superior to placebo in this respect. The proportion of responders increased with the buprenorphine dose, and a higher proportion of patients receiving buprenorphine patches reported uninterrupted sleep for longer than 6 h compared with those receiving placebo. In a long-term, open, follow-up study in which the mean duration of treatment was 7.5 months, analgesia was rated as at least satisfactory by 90% of patients. Almost 60% of patients could manage their pain with one patch alone or with one additional sublingual tablet a day during the whole period of treatment, indicating a low incidence of tolerance development. The buprenorphine transdermal patch was assessed as user friendly by 94.6% of patients. In a postmarketing surveillance study, pain relief with transdermal buprenorphine was rated as good or very good by 70% of the responders. Postmarketing surveillance studies have shown that transdermal buprenorphine is also effective in the management of nociceptive and neuropathic pain, which some studies have shown to be relatively insensitive to mu-opioid analgesics, such as morphine. Transdermal buprenorphine was well tolerated. Most adverse events were either local reactions to the patch that generally subsided within 24 h or systemic events typical of treatment with opioid analgesics, such as nausea, vomiting and constipation.

Pharmacokinetics of opioids in renal dysfunction

Patients with renal insufficiency commonly require the administration of an opioid analgesic to provide adequate pain relief. The handling of morphine, pethidine (meperidine) and dextropropoxyphene in patients with renal insufficiency is complicated by the potential accumulation of metabolites. While morphine itself remains largely unaffected by renal failure, accumulation, as denoted by an increase in both mean peak concentrations and the area under the concentration-time curve, of both the active metabolite (morphine-6-glucuronide) and the principal metabolite (morphine-3-glucuronide, thought to possess opiate antagonist properties) have been reported. The increased elimination half-lives of the toxic metabolites norpethidine and norpropoxyphene in patients with poor renal function administered pethidine and dextropropoxyphene, respectively, makes their routine use ill advised. Case reports of prolonged narcosis associated with the use of both codeine and dihydrocodeine in patients with renal insufficiency call for care to be used when prescribing these agents under such conditions. Although the pharmacokinetics of buprenorphine, alfentanil, sufentanil and remifentanil change little in patients with renal failure, the continuous administration of fentanyl can lead to prolonged sedation.

Clinical pharmacokinetic considerations in the elderly. An update

There are numerous studies of drug handling in the elderly, but it is difficult to assess the significance of changes seen in vitro, or after single-dose administration, because they are often compensated by other mechanisms at steady-state. However, a knowledge of these studies is important as the results alert the investigator to possible treatment problems. The high incidence of adverse drug reaction in the elderly population leaves no doubt that improvements in therapy are needed. Research has been directed at seeking patterns of abnormality in the elderly on which to base recommendations for alterations in dosage regimens. The major shortcoming of this approach has been the failure to distinguish between the effect of chronological age on drug pharmacokinetics, and drug kinetics in elderly people with multiple pathology. The latter concern appreciates the variety of factors involved and the importance of treating each patient as an individual: presentation of mean data is confusing and misleading. The objective of drug treatment in any age group, but particularly in the elderly, is to administer the smallest possible dose which gives adequate therapeutic benefit throughout the entire dosage interval with the minimum of side effects. For most drugs the safe starting dose in the elderly is one-third to half that recommended in the young. Vigilance for potential side effects with plasma concentration monitoring, if available, should help keep toxicity to a minimum. When other medications are added or changed, the possibility of interaction should be anticipated. Methods for individualisation of dosage regimens and the use of sustained-release formulations in the elderly are discussed. Dosage alteration in the elderly in terms of reduced dose frequency, rather than dose size, may help improve compliance. A knowledge of the pharmacokinetics of a drug helps determine which approach will be most beneficial.

The United States experience with oral controlled-release morphine (MS Contin tablets). Parts I and II. Review of nine dose titration studies and clinical pharmacology of 15-mg, 30-mg, 60-mg, and 100-mg tablet strengths in normal subjects

The results of nine US multicenter, sequential crossover, dose titration studies of controlled-release oral morphine (MS Contin 30 mg tablets [MSC], Purdue Frederick, Norwalk, CT) are reviewed in Part I. The studies demonstrated the prolonged analgesic efficacy of the preparation in the treatment of patients with moderate to severe cancer-related pain. Approximately 93% of the patients achieved satisfactory to excellent analgesia on a 12-hour regimen when appropriate dose titration was allowed. The remaining patients were successfully maintained on an 8-hour regimen. The preparation was well-tolerated and comparable in safety to immediate-release oral morphine. In global evaluations, MSC was judged to be significantly (P less than 0.05) more effective, and with significantly (P less than 0.05) fewer side effects than both the prestudy opioid analgesics and 4-hour immediate-release oral morphine. Patients had a broad range of morphine requirements (mean daily MSC dose, 240 mg; range, 60 mg/day to 1800 mg/day); therefore various MSC tablet strengths were developed. Part II presents three studies in which the MSC formulations (15-mg, 60-mg, and 100-mg tablets) were compared to the 30-mg tablet within three randomized, single-dose, two-way crossover, analytically blinded bioavailability protocols, to determine bioequivalence and dose proportionality. The maximum morphine concentration, time of maximum morphine concentration, and area under the plasma morphine versus 12-hour and 24-hour time curve (AUC 0.12; AUC 0.24) were determined in each study. There were no significant differences between the values associated with MSC 1 X 30 mg tablet and 2 X 15 mg tablets (study 1), MSC 2 X 30 mg tablets and 1 X 60 mg tablet (study 2), and MSC 3 X 30 mg tablets and 1 X 100 mg tablet (study 3, values adjusted to dose of 90 mg), except for one marginally significant difference in study 3 (AUC 0.24; P = 0.04) which was not clinically or biopharmaceutically significant. The results showed that MSC 15-mg, 30-mg, 60-mg, and 100-mg dosage strengths are bioequivalent and dose proportional, and, therefore, therapeutically interchangeable. It was concluded that with routine assessment of the patient and adherence to the principles of analgesic dosing, MSC can be successfully used to control cancer-related pain. Furthermore, the availability of various MSC tablet strengths can be expected to facilitate the analgesic management of a patient population with widely differing opioid requirements.

Alfentanil infusions on the intensive therapy unit

We have investigated the use of alfentanil by infusion to sedate 14 patients during controlled ventilation on the intensive therapy unit (ITU). An initial rate of 24 micrograms.kg-1.h-1 was chosen and altered thereafter according to patient response. Incremental doses of midazolam (2.5-5.0 mg) were given intravenously (i.v.) if indicated. In 4 patients, the use of a muscle relaxant was necessary to allow adequate controlled ventilation of the patient. The mean duration of infusion was 27.9 h (range 10-141 h), and the mean total dose of alfentanil was 69.3 mg (12.5-240 mg). Spontaneous ventilation was rapidly achieved in 11 patients after stopping the infusion. The mean arterial carbon dioxide tension (PaCO2) was 5.38 kPa, 15-30 min after stopping the infusion. The clinical condition of 2 patients necessitated a change in sedation technique and one patient died during the alfentanil infusion. Alfentanil by infusion caused no major cardiovascular effects and did not influence the plasma cortisol response to trauma. There was no major alteration in blood biochemistry or haematology during the infusions of alfentanil. The plasma concentrations of alfentanil during infusion showed a wide variability. These probably relate to both changes in the volume of distribution of the drug and in hepatic clearance.

Influence of renal function on the elimination of morphine and morphine glucuronides

The influence of renal function, measured by 51Cr-EDTA clearance, on morphine and morphine glucuronide kinetics has been studied in 13 patients after a single i.v. injection of morphine. Unconjugated morphine and morphine glucuronides were measured by a sensitive, specific RIA after extraction from plasma. No significant correlation was found between total body clearance of unconjugated morphine and 51Cr-EDTA clearance. However, patients with renal insufficiency had impaired elimination of morphine glucuronides, and the apparent clearance was significantly correlated with the 51Cr-EDTA clearance (r = 0.94, p less than 0.001). A relatively long terminal elimination of half-life of morphine was found in all patients (mean +/- SD: 9.2 +/- 2.5 h), irrespective of glomerular function.

Effects of renal insufficiency on the pharmacokinetics and pharmacodynamics of opioid analgesics

The disposition and pharmacologic activities of morphine, meperidine, methadone, propoxyphene, dihydrocodeine, and codeine are reviewed. Dose-related toxicities of these opioid analgesics include mental obtundation, respiratory depression, and hypotension. Furthermore, convulsions have been associated with normeperidine and cardiac toxicities with norpropoxyphene. Hepatic metabolism is the primary route of elimination, except for methadone, for which there is also significant renal excretion. Although the pharmacokinetics of morphine are unchanged in renal insufficiency, accumulation of active metabolites may lead to narcosis. Similar accumulation of normeperidine and norpropoxyphene, metabolites of meperidine and propoxyphene, respectively, as well as propoxyphene itself, and dihydrocodeine and codeine may explain reports of adverse reactions in patients with impaired renal function. A high index of suspicion of opioid-induced toxicities should be maintained in patients who have renal dysfunction and receive opioids.

Profound reduction in morphine clearance and liver blood flow in shock

In six patients with septic shock apparent liver blood flow was significantly reduced compared with two patients restudied on recovery from shock and a group of four matched unshocked patients undergoing intensive care (287 +/- 23 ml/min vs 870 +/- 164 ml/min; mean +/- SEM). In the shocked patients the elimination half-life of morphine was significantly prolonged (13.2 +/- 3.5 h vs 5.9 +/- 1.4 h; mean +/- SEM) and the systemic clearance of morphine reduced by 53%, in comparison with the non-shocked patients. In both groups, morphine elimination was markedly delayed compared with previously reported observations in normal subjects and surgical patients. Care should be exercised with the use of drugs with a high hepatic extraction ratio in shocked patients.

Renal failure does not impair the metabolism of morphine

The pharmacokinetics of morphine were measured using gas chromatography-mass spectrometry (GCMS) with specific ion monitoring after the intramuscular administration of papaveretum to four patients with renal failure (one anephric) and three normals. The apparent t1/2 of absorption and t1/2 of elimination were significantly shorter in the patients with renal failure (P less than 0.05). Morphine glucuronides are eliminated slowly in these patients as expected. Renal failure does not impair the elimination of morphine.

Renal disease and drug metabolism: an overview

Renal disease will perturb the disposition of drugs that primarily depend upon renal excretory function for elimination. While changes in drug half-life (T1/2) are often cited as evidence of altered drug disposition, it must be remembered that T1/2 is a dependent variable whose magnitude varies directly with volume of distribution (Vd) and indirectly with total body clearance (ClT). ClT is the one term that succinctly describes drug elimination. ClT is defined as the sum of the renal (ClR) and nonrenal (ClNR), or metabolic, clearances of a drug. Renal failure has been shown to alter the hepatic microsomal mixed-function oxidase system of drug metabolizing enzymes. Therefore, in end-stage renal failure, the potential exists for the modification of the disposition of drugs whose elimination is primarily hepatic. The kidneys themselves contain many of the enzymes important in hepatic drug metabolism. Drugs such as morphine, paracetamol, and p-aminobenzoic acid are metabolized in the kidney and experimental renal disease has been shown to reduce drug metabolism in the diseased kidney compared with the contralateral normal kidney. Renal disease, then, has the potential to alter not only the renal clearance of unchanged drug but also may substantially modify the metabolic transformation of drugs in both the liver and the kidneys. It can no longer be assumed that the pharmacokinetics of drugs that are disposed mainly by metabolism will be unaltered in renal failure.

Kinetic disposition of morphine in young males after intravenous loading and maintenance infusions

Loading and maintenance infusions of morphine sulfate were administered to 5 young male patients 23-34-yr-old prior to elective surgery. Apparent steady-state plasma concentrations were achieved 30 minutes after the start of the drug infusion. The volume of distribution at steady-state (2.43 +/- 0.48 L X kg-1), beta elimination rate constant (0.700 +/- 0.162/h) and plasma clearance (1.66 +/- 0.33 L X kg-1 X h-1) were similar to values previously determined in young healthy subjects receiving a single bolus infusion. These data confirm our findings concerning morphine disposition in healthy young subjects and demonstrate the feasibility of achieving predictable plasma concentrations of morphine for future assessment of pharmacodynamic/pharmacokinetic relationships for this drug.

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.

Dihydrocodeine in renal failure: further evidence for an important role of the kidney in the handling of opioid drugs

The pharmacokinetics of a single oral dose of dihydrocodeine were studied in nine patients with chronic renal failure treated by haemodialysis and nine subjects with normal renal function. In the patients the mean peak plasma dihydrocodeine concentration occurred later and the area under the curve was greater than in the normal subjects. Furthermore, the drug was still detectable after 24 hours in all the patients but only three of the normal subjects. These data, together with those obtained from previously published clinical case reports, contradict the traditional view that the body's ability to cope with opioid drugs is not altered in renal failure.

Cimetidine alters pethidine disposition in man

The effect of concurrent cimetidine administration on the disposition of pethidine was investigated in eight healthy male volunteers (18-31 years). The subjects received 70 mg i.v. pethidine HCl doses before and during cimetidine treatment (1200 mg/day p.o.). During cimetidine treatment, pethidine total body clearance (CL) decreased by 22% (0.611 +/- 0.101 [mean +/- s.d.] to 0.474 +/- 0.098 1 kg-1 h, P less than 0.05) and pethidine volume of distribution at steady state (Vss) decreased by 13% (4.79 +/- 0.82 to 4.16 +/- 0.75 l/kg, P less than 0.05). A cimetidine-induced reduction in pethidine oxidation to norpethidine was suggested by a 23% reduction in norpethidine area under the curve from 0 to 24 h (472 +/- 93 to 362 +/- 38 ng ml-1 h, P less than 0.05) and a 29% reduction in peak norpethidine concentration (26.7 +/- 5.3 to 18.9 +/- 1.9 ng/ml, P less than 0.05). There were no significant linear correlations of serum trough cimetidine concentration with percentage reductions in pethidine CL, pethidine Vss, norpethidine AUC (24), or norpethidine peak concentrations. It would appear that the cimetidine-pethidine kinetic interaction may be of sufficient magnitude to be clinically significant. Caution is advised when patients are treated concurrently with these two agents.