An observational study examining the effects of a surgically induced inflammatory response on the distribution of morphine and its metabolites into cerebrospinal fluid.

PURPOSE: Morphine is administered intravenously for pain management in the perioperative period. The effect of the inflammatory response to surgery on morphine distribution across the blood-brain barrier (BBB) in humans was investigated. We hypothesized that a graded surgically induced, systemic inflammatory response alters cerebrospinal fluid (CSF) levels of morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) through a temporary reduction in BBB drug efflux transporter function. METHODS: We conducted a prospective pharmacokinetic study of the plasma and CSF distribution of the P-glycoprotein (PGP) substrate morphine in 33 patients undergoing open thoracic (n = 18) or endovascular (n = 15) aortic aneurysm repair. Morphine was administered with induction of anesthesia and in the intensive care unit. Plasma and CSF concentrations of interleukin (IL)-6, morphine, M3G, M6G, and albumin were measured prior to surgery (baseline), during surgery, and postoperatively every six hours until removal of the CSF drain. The area under the curve (AUC) was determined for plasma and CSF IL-6, morphine, M3G, and M6G concentrations vs time. The primary endpoint measures were the correlations between the morphine, M6G, and M3G AUC CSF/plasma ratios and systemic inflammation as quantified by the time-normalized IL-6 exposure, which was calculated for each individual by dividing the total exposure (AUC) by time (t). A Bonferroni corrected P < 0.017 indicated a significant correlation. RESULTS: Plasma and CSF IL-6 concentrations increased postoperatively. The median [interquartile range] IL-6 exposures were significantly higher in the open vs endovascular surgical group for plasma (105 [40-256] pg·mL-1 vs 29 [16-70] pg·mL-1, respectively; P = 0.013) and CSF (79 [26-133] pg·mL-1 vs 16 [9-80] pg·mL-1, respectively; P = 0.013). For the primary endpoint, the plasma IL-6 AUC/t did not correlate with the CSF accumulation of morphine (r = -0.009; P = 0.96) or M3G (r = 0.37; P = 0.04) when corrected for surgical procedure, age, and sex. There were insufficient data on CSF concentration to complete the primary analysis for M6G. CONCLUSION: Morphine distribution into the CSF was not significantly altered in patients undergoing thoracic aortic aneurysm repair. This suggests that BBB PGP function may not be affected by the perioperative inflammatory response. TRIAL REGISTRATION: www.clinicaltrials.gov , NCT 00878371. Registered 7 April 2009.

Lethal morphine intoxication in a patient with a sickle cell crisis and renal impairment: case report and a review of the literature.

Morphine-6-glucuronide, the active metabolite of morphine, and to a lesser extent morphine itself are known to accumulate in patients with renal failure. A number of cases on non-lethal morphine toxicity in patients with renal impairment report high plasma concentrations of morphine-6-glucuronide, suggesting that this metabolite achieves sufficiently high brain concentrations to cause long-lasting respiratory depression, despite its poor central nervous system penetration. We report a lethal morphine intoxication in a 61-year-old man with sickle cell disease and renal impairment, and we measured concentrations of morphine and morphine-6-glucuronide in blood, brain and cerebrospinal fluid. There were no measurable concentrations of morphine-6-glucuronide in cerebrospinal fluid or brain tissue, despite high blood concentrations. In contrast, the relatively high morphine concentration in the brain suggests that morphine itself was responsible for the cardiorespiratory arrest in this patient. Given the fatal outcome, we recommend to avoid repeated or continuous morphine administration in renal failure.

Effect of acute inflammatory brain injury on accumulation of morphine and morphine 3- and 6-glucuronide in the human brain.

OBJECTIVE: In animals, central nervous system inflammation increases drug accumulation in the brain partly due to a loss of central nervous system drug efflux transporter function at the blood-brain barrier. To determine whether a similar loss of active drug efflux occurs in humans after acute inflammatory brain injury. DESIGN: Observational human pharmacokinetic study. SETTING: Medical-surgical-neurosurgical intensive care unit at a university-affiliated, Canadian tertiary care center. PATIENTS: Patients with acute inflammatory brain injury, including subarachnoid hemorrhage (n = 10), intracerebral and/or intraventricular hemorrhage (n = 4), or closed head trauma (n = 2) who received morphine intravenously after being fitted with cerebrospinal fluid ventriculostomy and peripheral arterial catheters. INTERVENTIONS: We correlated the cerebrospinal fluid distribution of morphine, morphine-3-glucuronide, and morphine-6-glucuronide with the cerebrospinal fluid and plasma concentration of the proinflammatory cytokine interleukin-6 and the passive marker of blood-brain barrier permeability, albumin. MEASUREMENTS AND MAIN RESULTS: Acute brain injury produced a robust inflammatory response in the central nervous system as reflected by the elevated concentration of interleukin-6 in cerebrospinal fluid. Penetration of morphine metabolites into the central nervous system increased in proportion to the neuroinflammatory response as demonstrated by the positive correlation between cerebrospinal fluid interleukin-6 exposure and the area under the curve cerebrospinal fluid/plasma ratio for morphine-3-glucuronide (r = .49, p < .001) and morphine-6-glucuronide (r = .51, p < .001). In contrast, distribution of morphine into the brain was not linked with cerebrospinal fluid interleukin-6 exposure (r = .073, p = .54). Albumin concentrations in plasma and cerebrospinal fluid were consistently in the normal range, indicating that the physical integrity of the blood-brain barrier was likely undisturbed. CONCLUSIONS: Our results suggest that central nervous system inflammation following acute brain injury may selectively inhibit the activity of specific drug efflux transporters within the blood-brain barrier. This finding may have significant implications for patients with neuroinflammatory conditions when administered centrally acting drugs normally excluded from the brain by such transporters.

Comparative measurement of spinal CSF microdialysate concentrations and concomitant antinociception of morphine and morphine-6beta-glucuronide in rats.

Morphine-6beta-glucuronide (M6G) is well known as a potent active metabolite in humans. To clarify concentration-antinociceptive effect relationships for morphine and M6G, we evaluated comparatively the pharmacokinetics and antinociceptive effects of morphine and M6G. The spinal CSF concentration and antinociception were simultaneously measured by using the combination of a microdialysis method and the formalin test in conscious rats after the s.c. administration of morphine (0.3-3 mg/kg) and M6G (0.1-3 mg/kg). The plasma concentration of M6G after s.c. administration was higher than that of morphine, as shown by the 2.1 times greater value of area under the concentration-time curve (AUC(plasma)). The spinal CSF concentrations of morphine and M6G increased dose-dependently. The AUC(CSF) of M6G was 1.6-1.8 times higher than that of morphine at each dose. Administration of morphine and M6G dose-dependently suppressed the flinching behavior induced by formalin injection. The ED(50) values for M6G were 3 times lower than those of morphine, although the spinal CSF concentration versus antinociceptive effect curves of morphine and M6G were very similar, with similar EC(50) values. These results suggest that the antinociceptive potencies of morphine and M6G, evaluated by simultaneous measurements of spinal CSF drug concentration and antinociception, are equivalent. Simultaneous measurement of spinal CSF concentration and antinociception by using microdialysis should be useful for elucidating the relationship between pharmacokinetics and pharmacodynamics of various opioids.

Postmortem distribution of heroin metabolites in femoral blood, liver, cerebrospinal fluid, and vitreous humor.

The presence of 6-monoacetylmorphine (6-MAM) is often used to distinguish between heroin (diacetylmorphine) and morphine exposures. 6-MAM, however, is rapidly metabolized to morphine and may not be present in detectable quantities in blood following heroin exposure. Recent studies have shown that 6-MAM may persist in cerebrospinal fluid (CSF) and this specimen may be preferable for establishing heroin exposure. This study reports postmortem distribution of 6-MAM, unconjugated morphine, and codeine in different tissues from 25 deceased individuals. In all cases, 6-MAM was detected in vitreous humor, and in CSF in 16 of the 25 cases (64%). When 6-MAM was detected in blood (13 of 25 cases), the level of 6-MAM in vitreous humor and CSF was higher than in blood, with a mean concentration ratio of 11.3 (range: 1.7-27) for vitreous humor and 6.6 (range: 2.6-17.3) for CSF. 6-MAM was not detected in liver in any of the cases examined. Free morphine levels were highest in liver, followed by blood, CSF, and vitreous humor. The concentration ratios (mean +/- standard deviation) for free morphine in vitreous humor, CSF, and liver to that in blood were 0.36 +/- 0.18, 0.64 +/- 0.27, and 2.99 +/- 2.12, respectively. The liver/blood ratio was consistent with previously reported values for morphine in heart and femoral blood. Codeine levels following heroin overdose were consistently low relative to the morphine concentration. For blood, liver, and CSF, the ratio of codeine to morphine was essentially the same (0.06), whereas the vitreous codeine/morphine concentration ratio was slightly higher (0.19). These results characterize the distribution of heroin metabolites in postmortem tissues. Vitreous humor appears to be a useful specimen for determining 6-MAM and establishing the morphine was derived from heroin.

Different distribution of morphine and morphine-6 beta-glucuronide after intracerebroventricular injection in rats.

(1) We investigated the distribution of morphine and morphine-6beta-glucuronide (M6G) in the brain and spinal cord after intracerebroventricular (i.c.v.) injection of each drug in rats. (2) The cerebrospinal fluid (CSF) concentration of M6G was 5-37 times greater than that of morphine 10, 60 and 120 min after the i.c.v. injection. The apparent elimination clearance of M6G from the CSF was 10 times lower than that of morphine. (3) The intrathecal CSF concentration of M6G measured by the microdialysis method was 29-79 times greater than that of morphine, and M6G was rapidly distributed into the intrathecal space after the i.c.v. injection. (4) M6G was detected in the cerebrum, brainstem, cerebellum and spinal cord at concentrations 2-21 times higher than morphine after the i.c.v. injection of each drug. The distribution volume of M6G in rat brain slices was three times lower than that of morphine, and close to the extracellular fluid space in the brain regions corresponding to the vicinity of the opioid receptors. (5) These brain distribution characteristics of M6G, namely, low clearance from the central nervous system, localization in the extracellular fluid and rapid distribution into the intrathecal space, may contribute to the potent analgesic effect of M6G after i.c.v. injection.

Pharmacokinetic modelling of morphine, morphine-3-glucuronide and morphine-6-glucuronide in plasma and cerebrospinal fluid of neurosurgical patients after short-term infusion of morphine.

AIMS: Concentrations in the cerebrospinal fluid (CSF) are a useful approximation to the effect site for drugs like morphine. However, CSF samples, are available only in rare circumstances. If they can be obtained they may provide important insights into the pharmacokinetics/pharmacodynamics of opioids. METHODS: Nine neurological and neurosurgical patients (age 19-69 years) received 0.5 mg kg-1 morphine sulphate pentahydrate as an intravenous infusion over 30 min. Plasma and CSF were collected for up to 48 h. Concentration time-course and interindividual variability of morphine (M), morphine-3-glucuronide (M3G) and morphine-6 glucuronide (M6G) were analysed using population pharmacokinetic modelling. RESULTS: While morphine was rapidly cleared from plasma (total clearance = 1838 ml min-1 (95% CI 1668, 2001 ml min-1)) the glucuronide metabolites were eliminated more slowly (clearance M3G = 44.5 ml min-1 (35.1, 53.9 ml min-1), clearance M6G = 42.1 ml min-1 (36.4, 47.7 ml min-1)) and their clearance could be described as a function of creatinine clearance. The central volumes of distribution were estimated to be 12.7 l (11.1, 14.3 l) for morphine. Transfer from the central compartment into the CSF was also rapid for M and considerably slower for both glucuronide metabolites. Maximum concentrations were achieved after 102 min (M), 417 min (M3G) and 443 min (M6G). A P-glycoprotein exon 26 polymorphism previously found to be linked with transport activity could be involved in CSF accessibility, since the homozygous mutant genotype was associated (P < 0.001) with high maximum CSF concentrations of M but not M3G or M6G. CONCLUSIONS: From the population pharmacokinetic model presented, CSF concentration profiles can be derived for M, M3G and M6G on the basis of dosing information and creatinine clearance without collecting CSF samples. Such profiles may then serve as the link between dose regimen and effect measurements in future clinical effect studies.

Acute decreases in cerebrospinal fluid glutathione levels after intracerebroventricular morphine for cancer pain.

UNLABELLED: Intracerebroventricular (ICV) morphine administration is effective for the management of refractory cancer pain. Recent preclinical observations of acute depletion of the major endogenous intracellular antioxidant glutathione (GSH) in brain and peripheral organs after ICV morphine in rodents led us to apply microchemical methods to profile the neurochemical effects of ICV morphine in three patients treated for intractable cancer pain. Assessment of morphine, morphine-6-glucuronide, and a panel of endogenous compounds and metabolites in ventricular and cisternal cerebrospinal fluid (CSF) demonstrated transient, postdose increases in morphine and morphine-6-glucuronide in ventricular and cistemal CSF, accompanied by acute decreases in CSF GSH levels. Significant changes were also observed in the CSF levels of 4-hydroxybenzoic acid, homovanillic acid, 5-hydroxyphenyllactic acid, and uric acid. These pilot clinical observations of acute central GSH depletion after ICV morphine suggest a novel mechanism for neuropsychiatric toxicity or preclinical findings, such as hyperalgesia or increased motoric activity observed in nonhuman species after central morphine administration. Because ICV morphine is a mainstay of treatment for refractory cancer pain, elucidation of a mechanism's (or mechanisms') mediating a potential pro-oxidant state in the central nervous system induced by ICV morphine is important. IMPLICATIONS: We observed acute decreases in glutathione levels in cerebrospinal fluid sampled from patients after intracerebroventricular doses of morphine for intractable cancer pain. Such doses may, by depleting the antioxidant glutathione, render the central nervous system vulnerable to damage from oxidative stress.

Elevated concentrations of morphine 6-beta-D-glucuronide in brain extracellular fluid despite low blood-brain barrier permeability.

1 This study was done to find out how morphine 6-beta-D-glucuronide (M6G) induces more potent central analgesia than morphine, despite its poor blood-brain barrier (BBB) permeability. The brain uptake and disposition of these compounds were investigated in plasma and in various brain compartments: extracellular fluid (ECF), intracellular space (ICS) and cerebrospinal fluid (CSF). 2 Morphine or M6G was given to rats at 10 mg kg(-1) s.c. Transcortical microdialysis was used to assess their distributions in the brain ECF. Conventional tissue homogenization was used to determine the distribution in the cortex and whole brain. These two procedures were combined to estimate drug distribution in the brain ICS. The blood and CSF pharmacokinetics were also determined. 3 Plasma concentration data for M6G were much higher than those of morphine, with Cmax and AUC 4-5 times more higher, Tmax shorter, and VZf-1 (volume of distribution) and CL f(-1) (clearance) 4-6 times lower. The concentrations of the compounds in various brain compartments also differed: AUC values for M6G were lower than those of morphine in tissue and CSF and higher in brain ECF. AUC values in brain show that morphine levels were four times higher in ICS than in ECF, whereas M6G levels were 125 higher in ECF than in ICS. 4 Morphine entered brain cells, whereas M6G was almost exclusively extracellular. This high extracellular concentration, coupled with extremely slow diffusion into the CSF, indicates that M6G was predominantly trapped in the extracellular fluid and therefore durably available to bind at opioid receptors.

Analgesic responses to intrathecal morphine in relation to CSF concentrations of morphine-3,beta-glucuronide and morphine-6,beta-glucuronide.

This study was performed to determine whether variations in analgesic responses to intrathecal morphine could be explained by cerebrospinal fluid (CSF) concentrations of morphine metabolites. Twenty-four CSF samples were collected at the beginning, middle and end of treatment periods in seven cancer patients with pain of malignant origin. CSF concentrations of morphine-3,beta-glucuronide (M3G) and morphine-6,beta-glucuronide (M6G) metabolites were measured by gas chromatography/mass spectrometry. Analgesic responses to morphine were estimated concurrent with CSF collection using a visual analog scale representing percentages of pain relief. Effective analgesia was defined as > or = 75% pain relief. CSF concentration of M3G and M6G in the 24 samples were 722 +/- 116 ng/ml and 699 +/- 158 ng/ml, respectively. CSF samples were categorized into two groups: (1) those collected during effective analgesia (N=14), and (2) those collected during ineffective analgesia (N=10). M6G levels detected in group 1 samples (effective analgesia) were significantly greater than those found in group 2 samples (ineffective analgesia) (978 +/- 243 ng/ml vs 309 +/- 68 ng/ml, P<0.05). Intergroup differences in CSF M3G concentrations and M3G/M6G ratios were not significant. It is concluded that CSF M6G may be indicative of effectiveness of analgesia in cancer patients subjected to intrathecal morphine.

Morphine and morphine-6-glucuronide in the plasma and cerebrospinal fluid of children.

AIMS: To measure morphine and morphine-6-glucuronide in the plasma and cerebrospinal fluid of children following a single intravenous dose of morphine. METHODS: Twenty-nine paired samples of cerebrospinal fluid and plasma were collected from children with leukaemia undergoing therapeutic lumbar puncture. An intravenous dose of morphine was administered at selected intervals before the procedure. Concentrations of morphine and morphine-6-glucuronide (M6G) were measured in each sample. Morphine was measured using a specific radioimmunoassay (r.i.a.) and M6G was measured using a novel enzyme-linked immunosorbent assay (ELISA). RESULTS: The ELISA for measuring M6G was highly sensitive. The intra-and interassay variations were less than 15%. Using a two-compartment model for plasma morphine, the area under the curve to infinity (AUC, 7143 ng ml-1 min), volume of distribution (3.6 l kg-1 ) and elimination half-life (88 min) were comparable with those reported in adults. Clearance (35 ml min-1 ) was higher than that in adults. Morphine-6-glucuronide was readily synthesized by the children in this study. The elimination half-life (321 min) and AUC (35507 ng ml-1 min) of plasma M6G were much greater than those of morphine. CONCLUSIONS: Extensive metabolism of morphine to M6G in children with cancer has been demonstrated. These data provide further evidence to support the importance of M6G accumulation after multiple doses. There was no evidence that morphine passed more easily into the CSF of children than adults.

Detection of 6-acetylmorphine in vitreous humor and cerebrospinal fluid--comparison with urinary analysis for proving heroin administration in opiate fatalities.

The concentrations of morphine and 6-acetylmorphine (6-AM) in urine, cerebrospinal fluid (CSF), and vitreous humor (VH) and the morphine concentrations in blood were determined by gas chromatography-mass spectrometry for 29 fatalities after abuse of heroin either alone or in combination with alcohol and other drugs. 6-AM was found above a quantitation limit of 1 ng/mL in urine in 89% of the cases, in CSF in 68% of the cases, and in VH in 75% of the cases. The 6-AM concentrations in CSF (mean, 10 ng/mL) and VH (mean, 17 ng/mL) were in general much smaller than in urine (mean, 170 ng/mL); therefore, the different pharmacokinetic behavior of the fluids is discussed. There is no uniformity between the three fluids with respect to the presence or absence of 6-AM. Therefore, CSF or VH may be used as complementary or alternative materials to urine in order to prove heroin uptake in opiate fatalities.

Cerebrospinal fluid and plasma concentrations of morphine, morphine-3-glucuronide, and morphine-6-glucuronide in patients before and after initiation of intracerebroventricular morphine for cancer pain management.

UNLABELLED: Twenty-three patients treated with intracerebroventricular (ICV) morphine in this study not only obtained excellent pain relief without rapid increases in dose, but also experienced a reduction in morphine-related side effects. By 24 h after initiation of ICV morphine, the mean trough cerebrospinal fluid (CSF) morphine concentration (approximately 20 microM) was 50-fold higher than the baseline concentration (approximately 0.4 microM), and the CSF concentration of morphine-6-glucuronide (M6G) was undetectable (<0.01 microM). The mean CSF concentration of morphine-3-glucuronide (M3G) decreased 90%, from a baseline concentration of 1 microM to 0.1 microM by Day 7 postventriculostomy. Thereafter, the mean trough CSF M3G concentration remained relatively constant while ICV morphine was continued, although the concomitant M3G plasma concentrations were undetectable (<0.01 microM). The large increase in the CSF morphine concentration in patients receiving ICV morphine strongly suggests that increased CSF morphine levels are unlikely to be the primary cause of analgesic tolerance or undesirable excitatory side effects (hyperalgesia, myoclonus, seizures) experienced by some patients receiving chronic large-dose systemic morphine. IMPLICATIONS: After initiation of intracerebroventricular morphine, cancer patients experienced excellent pain relief. Although the mean morphine concentration in cerebrospinal fluid increased 50-fold relative to preventriculostomy levels, rapid dose increases did not occur, which suggests that increased cerebrospinal fluid morphine levels are unlikely to be the main cause of analgesic tolerance.

Systematic review of factors affecting the ratios of morphine and its major metabolites.

In a systematic review of 57 studies with information on 1232 patients we examined the effect of age, renal impairment, route of administration, and method of analysis on the ratios of morphine-3-glucuronide:morphine (M3G:M) and morphine-6-glucuronide:morphine (M6G:M) and the relative concentrations of M3G and M6G. Across all studies the range of the ratios of metabolites to morphine was wide (0.001-504 for M3G:M, and 0-97 for M6G:M). Neonates produced morphine glucuronides at a lower rate than older children or adults. Metabolite ratios were higher in renal impairment. Routes of administration which avoided first pass metabolism (intravenous, transdermal, rectal, intramuscular, epidural and intrathecal) resulted in lower metabolite production than oral, buccal or sublingual. Metabolite production was similar for single and multiple dosing. There was no evidence of differences between methods of assay. There was a high correlation between the two glucuronide metabolites in spite of the different situations studied, supporting a single glucuronidating enzyme. Morphine was present in CSF at a fourfold higher concentration than the glucuronide metabolites.

Morphine, morphine-3-glucuronide, morphine-6-glucuronide, and 6-monoacetylmorphine determined by means of atmospheric pressure chemical ionization-mass spectrometry-liquid chromatography in body fluids of heroin victims.

Morphine, morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G), and 6-monoacetylmorphine (6-MAM) were isolated from body fluids using solid-phase extraction and determined by means of atmospheric pressure chemical ionization-mass spectrometry-liquid chromatography (APCI-LC-MS) in selected ion monitoring mode. The following ions were monitored: m/z 286 for morphine; m/z 286 and 462 for M3G and M6G; m/z 211, 268, and 328 for 6-MAM; and m/z 289 for morphine-d3 (internal standard). The recoveries ranged from 82 to 89% The limits of detection were as follows: 0.1 ng/mL (morphine), 0.5 ng/mL (6-MAM), and 1 ng/mL (M3G and M6G). The analytes were determined in samples taken from 21 heroin-overdose victims. Twenty-one blood samples, 11 cerebrospinal fluid (CSF) samples, 12 vitreous humor (VH) samples, and 6 urine samples were investigated. Blood concentrations (ng/mL) of morphine ranged from 8 to 1539, of M3G from 111 to 941, of M6G from 32 to 332, and of 6-MAM from 0 to 73. The levels of morphine were correlated with glucuronide values and with 6-MAM. The concentrations of morphine, M3G, and M6G in CSF were, as a rule, lower than in blood and lower in VH than in CSF. The concentrations of morphine and molar ratios of M6G-morphine in blood and CSF were correlated. Low ratios of M3G-morphine and M6G-morphine in blood of heroin-overdose victims indicated short survival time after drug intake.

Morphine, morphine-6-glucuronide, and morphine-3-glucuronide in cerebrospinal fluid and plasma after epidural administration of morphine.

BACKGROUND AND OBJECTIVES: It has been suggested that the potency of epidural morphine might be explained by spinal metabolism to the active and potent metabolite morphine-6-glucuronide (M6G). The main objective of this study was to describe the early pharmacokinetics of epidurally administered, morphine with special attention to the appearance of the glucuronated metabolites in cerebrospinal fluid (CSF). METHODS: Morphine was administered epidurally to eight patients scheduled for major abdominal surgery. The concentrations of morphine and its 6-glucuronide and 3-glucuronide metabolites were monitored in blood and CSF at 10, 30, 60, and 120 minutes and 10 and 24 hours. Postoperative pain was estimated on a visual analog scale, and analgesia requirements (administered by a patient-controlled technique) were recorded. RESULTS: Only traces of the metabolites were found in CSF and in only two patients throughout the 24 hours. Both metabolites appeared rapidly (within 30 minutes) in plasma in all patients and were found in plasma throughout the study period. Morphine concentration peaked in CSF within 30 minutes at a very high level; in plasma, it peaked at 10 minutes. No correlation was seen between initial or later concentrations of morphine in CSF and postoperative pain or morphine requirements. CONCLUSIONS: No evidence of spinal metabolism of morphine could be found. Rapid distribution of morphine to CSF and plasma occurred after epidural administration. No value of initial CSF morphine concentrations for prediction of analgesic requirements could be demonstrated.

Rapid and highly automated determination of morphine and morphine glucuronides in plasma by on-line solid-phase extraction and column liquid chromatography.

A high-performance liquid chromatography (HPLC) method has been developed for the determination of morphine and its main metabolites, morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G), in plasma or cerebrospinal fluid. Samples were extracted using on-line solid-phase extraction followed by reversed-phase HPLC with fluorescence detection. Recoveries of 20 ng morphine and morphine glucuronides in plasma were over 95%. The limit of detection using 400 microliters of a biological matrix was 0.85, 3.4 and 1.0 ng/ml of M-3-G, M-6-G and morphine, respectively. Inter- and intra-day assay precision was better than 10%. The main advantages of the present described method are increased recoveries (> 95%) and a high degree of automation allowing a high speed in routine analysis. The time required for the fully automated analysis of one sample was less than 26 min.

Plasma and cerebrospinal fluid concentrations of morphine and morphine glucuronides in rabbits receiving single and repeated doses of morphine.

The pharmacokinetics of morphine in plasma and the distribution of morphine and its glucuronidated metabolites within the cerebrospinal fluid were investigated in rabbits. After single morphine dosage, the plasma AUC ratio of morphine-3- glucuronide/morphine was 11.1 compared with 0.14 for morphine-6-glucuronide/morphine. The similar elimination half-lives of morphine (107 min), morphine-3-glucuronide (122 min), and morphine-6-glucuronide (105 min) suggested the glucuronidation to be the rate-limiting step, which was substantiated by the observation that morphine-3-glucuronide becomes eliminated four times faster when applied intravenously. Both after single and repeated morphine administration, the ratios of CSF and plasma levels of the parent drug were higher than those of morphine-3-glucuronide or morphine-6-glucuronide. These data demonstrate a poor penetration of the glucuronides across the blood-brain barrier and do not support the previously postulated accumulation of morphine-6-glucuronide in the central nervous system during chronic morphine treatment.