Prediction of human CNS pharmacokinetics using a physiologically-based pharmacokinetic modeling approach.

Knowledge of drug concentration-time profiles at the central nervous system (CNS) target-site is critically important for rational development of CNS targeted drugs. Our aim was to translate a recently published comprehensive CNS physiologically-based pharmacokinetic (PBPK) model from rat to human, and to predict drug concentration-time profiles in multiple CNS compartments on available human data of four drugs (acetaminophen, oxycodone, morphine and phenytoin). Values of the system-specific parameters in the rat CNS PBPK model were replaced by corresponding human values. The contribution of active transporters for the four selected drugs was scaled based on differences in expression of the pertinent transporters in both species. Model predictions were evaluated with available pharmacokinetic (PK) data in human brain extracellular fluid and/or cerebrospinal fluid, obtained under physiologically healthy CNS conditions (acetaminophen, oxycodone, and morphine) and under pathophysiological CNS conditions where CNS physiology could be affected (acetaminophen, morphine and phenytoin). The human CNS PBPK model could successfully predict their concentration-time profiles in multiple human CNS compartments in physiological CNS conditions within a 1.6-fold error. Furthermore, the model allowed investigation of the potential underlying mechanisms that can explain differences in CNS PK associated with pathophysiological changes. This analysis supports the relevance of the developed model to allow more effective selection of CNS drug candidates since it enables the prediction of CNS target-site concentrations in humans, which are essential for drug development and patient treatment.

The effect of morphine on regional cerebral blood flow measured by 99mTc-ECD SPECT in dogs.

To gain insights into the working mechanism of morphine, regional cerebral blood flow (rCBF) patterns after morphine administration were assessed in dogs. In a randomized cross-over experimental study, rCBF was estimated with 99mTc-Ethylcysteinate Dimer single photon emission computed tomography in 8 dogs at baseline, at 30 minutes and at 120 minutes after a single bolus of morphine. Perfusion indices (PI) in the frontal, parietal, temporal and occipital cortex and in the subcortical and cerebellar region were calculated. PI was significantly decreased 30 min after morphine compared to baseline in the right frontal cortex. The left parietal cortex and subcortical region showed a significantly increased PI 30 min after morphine compared to baseline. No significant differences were noted for the other regions or at other time points. In conclusion, a single bolus of morphine generated a changing rCBF pattern at different time points.

Characteristics of distribution of morphine and metabolites in cerebrospinal fluid and plasma with chronic intrathecal morphine infusion in humans.

BACKGROUND: Despite widespread use of chronic intrathecal (IT) infusions of morphine, there is little systematic human work evaluating the steady state morphine concentrations or cerebrospinal (CSF) chemistry after long-term IT morphine delivery. We sought to address these issues in patients receiving chronic IT morphine infusion. METHODS: Pain patients with implanted catheters and pumps (range: 127 to 2165 days), receiving a stable dosing (>1 week) of IT morphine by infusion, were entered into the study. The following sequence was performed: (1) estimation of pain score; (2) radiograph localization of catheter tip; (3) percutaneous sampling of lumbar CSF at the L4 to 5 or L5-S1 space. CSF/plasma samples were assayed for chemistry, and morphine and its 3/6 glucuronide metabolites (M3G, M6G) by liquid chromatography mass spectrometry. RESULTS: Nineteen patients were enrolled. CSF samples were obtained from 16 subjects. Three patients were not included in the primary analysis because 1 catheter was epidural, 1 catheter was fractured, and 1 had a granuloma at the catheter tip. Of the 13 sampled patients, the range of daily doses, rates, and concentrations were 1.6 to 25 mg/d and 0.1 to 1 mL/d, 5 to 50 mg/mL, respectively. The principal observations were as follows: (i) morphine, M3G, and M6G were present in the CSF and plasma and showed a significant regression slope when plotted versus daily dose; (ii) in contrast, the regression slope of the group ratio morphine:M3G:M6G plotted versus daily dose in CSF or plasma was not different from zero; (iii) plotting "normalized" CSF analyte concentration (e.g., concentration at site/daily IT morphine dose) against the segmental distance of the sampling site from the catheter tip revealed a significant decline in concentration of morphine, but not of conjugates as a function of distance from the catheter tip; (iv) plotting CSF protein, glucose, and red and white cell counts versus daily morphine dose or morphine concentration at the sampling site revealed no significant regression; and (v) patients with a catheter failure or a granuloma showed reduced concentrations of morphine in their CSF. CONCLUSION: Chronic infusion of morphine shows high concentrations, which correlate with the infusion dose and the proximity of the sampling site to the infusion site with no effects on CSF chemistry.

Morphine produces immunosuppressive effects in nonhuman primates at the proteomic and cellular levels.

Morphine has long been known to have immunosuppressive properties in vivo, but the molecular and immunologic changes induced by it are incompletely understood. To explore how these changes interact with lentiviral infections in vivo, animals from two nonhuman primate species (African green monkeys and pigtailed macaques) were provided morphine and studied using a systems biology approach. Biological specimens were obtained from multiple sources (e.g. lymph node, colon, cerebrospinal fluid, and peripheral blood) before and after the administration of morphine (titrated up to a maximum dose of 5 mg/kg over a period of 20 days). Cellular immune, plasma cytokine, and proteome changes were measured and morphine-induced changes in these parameters were assessed on an interorgan, interindividual, and interspecies basis. In both species, morphine was associated with decreased levels of Ki-67(+) T-cell activation but with only minimal changes in overall T-cell counts, neutrophil counts, and NK cell counts. Although changes in T-cell maturation were observed, these varied across the various tissue/fluid compartments studied. Proteomic analysis revealed a morphine-induced suppressive effect in lymph nodes, with decreased abundance of protein mediators involved in the functional categories of energy metabolism, signaling, and maintenance of cell structure. These findings have direct relevance for understanding the impact of heroin addiction and the opioids used to treat addiction as well as on the potential interplay between opioid abuse and the immunological response to an infective agent.

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.

Enhancement by grapefruit juice of morphine antinociception.

The aim of this study was to investigate the effect of grapefruit juice intake on the antinociception of morphine in rats. The antinociception of morphine (30 mg/kg, per os (p.o.)) was significantly enhanced by the oral administration of grapefruit juice (2 ml/rat). Further, the effect of grapefruit juice was examined in morphine-tolerant rats. The repeated administration of morphine (100 mg/kg p.o.) for 5 d caused a marked decrease in the antinociception, indicating the development of morphine-tolerance. In the morphine-tolerant rats, oral administration of grapefruit juice potentiated significantly the antinociceptive effect of morphine. To examine the pharmacokinetics of morphine after the repeated treatment with morphine for 5 d, microdialysis probes were implanted into the jugular vein and spinal intrathecal space in rats. The morphine concentrations in the blood and intrathecal cerebrospinal fluid (CSF) were gradually decreased by the repeated treatment with morphine. The grapefruit juice treatment significantly increased the blood concentration of morphine in morphine-tolerant rats. These results suggest that oral administration of grapefruit juice enhances the morphine antinociception by increasing the intestinal absorption of this agent.

Morphine reduces spinal c-fos expression dose-dependently during experimental laparotomy in pigs: a combined pharmacokinetic and surgical study.

The pharmacokinetics of intravenous morphine 2.5mg/kg (n=4) and 10mg/kg (n=4) in plasma and cerebrospinal fluid (CSF) of pigs was studied. Plasma half-life was 1.0+/-0.1h and the main metabolite was morphine-3-glucuronide, whereas morphine-6-glucuronide was negligible. CSF morphine concentration peaked after 20-30min (2.5mg/kg) and 60-120min (10mg/kg), and elimination half-life was 3.5+/-0.3h. Subsequently, the effect of morphine on surgery-induced spinal nociception in pigs subjected to unilateral laparotomy was evaluated by stereological quantification of the total number of Fos-like-immunoreactive (Fos-LI) spinal neurons of the dorsal horn. Surgery (n=4) induced 91,680+/-14,974 Fos-LI neurons ipsilaterally and morphine reduced this number to 45,771+/-8755 following the 2.5mg/kg dose (p<0.01; n=6) and 14,981+/-2327 following the 10mg/kg dose (p<0.001; n=6). These results indicate that morphine dose-dependently reduces the number of surgery-induced Fos-LI neurons in the spinal cord. As even a high dose of morphine does not reduce spinal c-fos expression to basal level, it may be appropriate to use other analgesics simultaneously with morphine during surgery.

Serum and cerebrospinal fluid morphine pharmacokinetics after single doses of intravenous and intramuscular morphine after hip replacement surgery.

AIM: To compare the time course of morphine and metabolite concentrations in serum and cerebrospinal fluid (CSF) after intravenous and intramuscular administration after surgery. METHODS: This was a randomized double-blind, double-dummy study in patients who had undergone hip replacement surgery. Morphine (M, 10 mg) was administered intravenously (IV) or intramuscularly (IM). Arterial blood and CSF samples (from a spinal catheter) were drawn simultaneously at 10, 30, 60, and 120 min after administration. Morphine and metabolites [morphine-3-glucuronide (M-3-G), morphine-6-glucuronide (M-6-G), and normorphine (NM)] were determined by a validated liquid chromatography-tandem mass spectrometry method. RESULTS: Thirty-eight patients were included: 13 men and 25 women, 20 in the IV, 18 in the IM group. Serum concentrations of M after 10 min were consistently higher after IM than IV, concentrations of M-3-G and M-6-G after IM surpassed those of IV after 45 min. NM was not found. None of the metabolites was found in CSF. CSF morphine concentrations and CSF/serum concentration ratios were consistently higher after IV compared to IM. The mean AUC(CSF)/AUC(serum) (0-120 min) concentration ratios were 0.18 and 0.09 after IV and IM, respectively. CONCLUSIONS: The uptake of morphine to the CSF was consistently higher after IV administration than after IM already after 10 min. The higher CSF concentration may be caused by an initially higher morphine blood/CSF gradient following IV morphine injection. The pharmacokinetic findings are compatible with a more rapid and extensive initial effect of IV morphine compared with IM.

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.

Time course and role of morphine dose and concentration in intrathecal granuloma formation in dogs: a combined magnetic resonance imaging and histopathology investigation.

BACKGROUND: Intrathecal morphine infusion leads to intrathecal granulomas. In dogs, the authors examined time course of granuloma formation and the role of concentration in granuloma development. METHODS: Dogs were prepared with lumbar intrathecal catheters and vest-mounted pumps. To define the time course of granuloma formation, serial magnetic resonance imaging was performed in animals receiving 10 or 31 days of morphine infusion (12.5 mg/ml at 40 microl/h). At these times, morphine was removed from the infusate, and further magnetic resonance images were acquired over 14-35 additional days. To assess dose versus concentration, dogs received 28-day infusions of vehicle, 12 mg morphine/day as 12.5 mg/ml at 40 microl/h, or 1.5 mg/ml at 334 microl/h (12 mg/day) for 28 days. Additional dogs received 3 mg/day as 12.5 mg/ml at 10 mul/h. RESULTS: Serial magnetic resonance images in dogs receiving morphine (12.5 mg/ml at 40 microl/h) revealed pericatheter-enhancing tissues as early as 3 days with a prominent signal by 10 days. Removal of morphine reduced the mass volume within 7 days. At a fixed infusion rate, the incidence of granuloma formation with the continuous intrathecal infusion of morphine ranged from 0 in vehicle-treated dogs to 100% in dogs treated with 12.5 mg/ml at 40 microl/h (12 mg/day). Infusion of 12 mg/day at 1.5 mg/ml (334 microl/h) resulted in granuloma in one of four animals. The authors found that infusion of morphine in different concentrations at a fixed rate resulted in a dose-dependent increase in concentration, with the granuloma-producing, dose-yielding lumbar cerebrospinal fluid morphine concentrations around 40 microg/ml. CONCLUSIONS: Serial magnetic resonance imaging showed a rapid formation and regression of the masses initiated by intrathecal morphine infusion. These masses are dependent on local concentration.

Disposition of morphine in plasma and cerebrospinal fluid varies during neonatal development in pigs.

The pharmacological effects of morphine are mediated via the central nervous system (CNS) but its clearance from the CNS in neonates has not been investigated. We have proposed that neonatal development of the blood-brain barrier affected CNS clearance mechanisms and CNS exposure to morphine. Male piglets (n = 5) aged one, three and six weeks were given morphine sulfate (0.5 mg kg(-1), i.v.). Serial blood and cerebrospinal fluid (CSF) samples were withdrawn over 360 min after morphine administration. Morphine concentration was measured by radioimmunoassay. A three-compartment model was fitted to individual data. Estimated parameters were reported as median and range. The peak morphine concentrations in plasma were not significantly different in the one-, three- or six-week-old piglets. Plasma clearance at one week (4.5, 3.8-8.6 mL min(-1) kg(-1)) was significantly lower than at three weeks (30.0, 19.1- 39.0 mL min(-1) kg(-1)) and six weeks (37.0, 29.7-82.8 mL min(-1) kg(-1)). The peak morphine concentration in CSF at one week (59.84, 31-67 ng mL(-1)) was higher than at three weeks (18.8, 17.7-25 ng mL(-1)) and six weeks (24.51, 16.5-84 ng mL(-1)), while CSF clearance was lower at one week (1.0, 0.18-9 mL min(-1) kg(-1)) compared with three weeks (6.2, 2.3-9.3 mL min(-1) kg(-1)) and six weeks (3.95, 1.3-85.7 mL min(-1) kg(-1)). Apparent plasma:CSF transfer ratio at one week was greater than at three and six weeks. The reduced plasma and CSF morphine clearance in early infancy resulted in elevated systemic and central morphine exposure in neonatal pigs.

Effects of morphine and endomorphins on the polysynaptic reflex in the isolated rat spinal cord.

At the spinal level, mu-opioids exert their actions on nociceptive primary afferent neurons both pre- and postsynaptically. In the present study, we used an in vitro isolated neonatal rat (11-15 days old) spinal cord preparation to examine the effects of morphine and the endogenous mu-opioid ligands endomorphin-1 (EM-1) and endomorphin-2 (EM-2) on the polysynaptic reflex (PSR) of dorsal root-ventral root (DR-VR) reflex. The actions of mu-opioids on spinal nociception were investigated by quantification of the firing frequency and the mean amplitude of the PSR evoked by stimuli with 20 x threshold intensity. EM-1 decreased the mean amplitude of PSR, whereas EM-2 and morphine decreased the firing frequency. The pattern of the effects elicited by morphine was the same as that for EM-2, except at high concentration. Naloxonazine, a selective mu(1) opioid receptor antagonist, had no significant effect on PSR by itself, but blocked the inhibition of PSR firing frequency or amplitude induced by EM-1, -2 and morphine. This may suggest that EM-1, EM-2 and morphine modulate spinal nociception differently and act mainly at the mu(1)-opioid receptors. Although they all act via mu(1)-opioid receptors, their different effects on the PSR may suggest the existence of different subtypes of the mu(1)-opioid receptor. The present data is also consistent with a further hypothesis, namely, that morphine and EM-2 activate a subtype of mu(1)-opioid receptor presynaptically, while EM-1 acts mainly through another subtype postsynaptically. However, since other reports indicate that EM-2, but not EM-1, could stimulate the release of enkephalins or dynorphin, presynaptic delta and kappa receptors may be also involved indirectly in the different regulation by mu-opioids at the spinal level.

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.

Cephalad movement of morphine and fentanyl in humans after intrathecal injection.

BACKGROUND: Despite decades of use, controversy remains regarding the extent and time course of cephalad spread of opioids in cerebrospinal fluid (CSF) after intrathecal injection. The purpose of this study was to examine differences between two often used opioids, morphine and fentanyl, in distribution in the CSF after intrathecal injection. METHODS: Eight healthy volunteers received intrathecal injection of morphine (50 microg) plus fentanyl (50 microg) at a lower lumbar interspace. CSF was sampled through a needle in an upper lumbar interspace for 60-120 min. At the end of this time, a sample was taken from the lower lumbar needle, and both needles were withdrawn. CSF volume was determined by magnetic resonance imaging. Pharmacokinetic modeling was performed with NONMEM. RESULTS: Morphine and fentanyl peaked in CSF at the cephalad needle at similar times (41 +/- 13 min for fentanyl, 57 +/- 12 min for morphine). The ratio of morphine to fentanyl in CSF at the cephalad needle increased with time, surpassing 2:1 by 36 min and 4:1 by 103 min. CSF concentrations did not correlate with weight, height, or lumbosacral CSF volume. The concentrations of morphine and fentanyl at both sampling sites were well described by a simple pharmacokinetic model. The individual model parameters did not correlate with the distance between the needles, CSF volume, patient height, or patient weight. CONCLUSIONS: Fentanyl is cleared more rapidly from CSF than morphine, although their initial distribution in the first hour after injection does not differ greatly. The pharmacokinetic model demonstrates that mixing is the primary determinant of early concentrations and is highly variable among individuals.

Safety of chronic intrathecal morphine infusion in a sheep model.

BACKGROUND: The safety of chronically administered intrathecal morphine has been questioned. Therefore, the authors examined the behavioral and neurologic effects and neurotoxicity of continuous intrathecal morphine administration in sheep. METHODS: Groups of three sheep were implanted with intrathecal infusion systems for the continuous administration of morphine (3, 6, 9, 12, or 18 mg/day) or saline at a fixed infusion rate of 1.92 ml/day beginning approximately 7 days after implantation. Sheep were examined daily for any changes in behavior or neurologic function. After 28-30 days, the animals were humanely killed. Cerebrospinal fluid samples were collected and analyzed for protein, erythrocytes and leukocytes, and morphine content. The spinal cord and meninges with the catheter in situ was removed en bloc and fixed in formalin for histologic analysis. RESULTS: Unilateral hind-leg gait deficits were observed in two of three animals in each of the 12- and 18-mg/day dose groups. Gross and microscopic evaluation of spinal cord tissue from these animals revealed intradural-extramedullary inflammatory masses that compressed the spinal cord at the catheter-tip and mid-catheter areas. This inflammation was ipsilateral to extremities that exhibited gait deficits and had acute and chronic cellular components. CONCLUSIONS: The toxicity of intrathecal morphine seems to be dependent on the amount of morphine infused, although the effects of dose versus concentration cannot be clearly distinguished in this study. Intrathecal morphine doses of 12- 18 mg/day produced inflammatory masses extending from the catheter tip down the length of the catheter within the subarachnoid space. Doses of 6-9 mg/day produced mild-to-moderate inflammation 5 cm cranial to the catheter tip. A dose of 3 mg/day produced no neurotoxicity and spinal histopathologic changes that were equivalent to those observed in the saline-treated animals.

Encapsulation of an intrathecal catheter.

A 47-year-old patient with cancer pain underwent implantation of an intrathecal drug delivery device. When the patient suffered from an infection with fever, pain on injection into the catheter and an elevated number of granulocytes in the cerebrospinal fluid 7 weeks later, radiologic examination showed an encapsulation of the catheter tip. Concentrations of morphine and morphine-6-glucuronide in the cerebrospinal fluid suggested transport of morphine into the systemic circulation via the vascularisation of the encapsulating membrane. After antibiotic therapy and removal of the catheter, morphine was administered intravenously with a one to one conversion ratio.

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.

The efficacy of intrathecal morphine and clonidine in the treatment of pain after spinal cord injury.

We performed a double-blinded, randomized, controlled trial in 15 patients to determine the efficacy of intrathecal morphine or clonidine, alone or combined, in the treatment of neuropathic pain after spinal cord injury. The combination of morphine and clonidine produced significantly more pain relief than placebo 4 h after administration; either morphine or clonidine alone did not produce as much pain relief. In addition, lumbar and cervical cerebrospinal fluid (CSF) concentrations, sampled at these levels at different times after administration were examined for a relationship between pain relief and CSF drug concentration. Lumbar CSF drug concentrations were initially several orders of magnitude larger than those in cervical CSF. After 1-2 h, the concentrations of morphine in cervical CSF markedly exceeded those of clonidine. The concentration of morphine in the cervical CSF and the degree of pain relief correlated significantly. We conclude that intrathecal administration of a mixture of clonidine and morphine is more effective than either drug administered alone and is related to the CSF-borne drug concentration above the level of spinal cord injury. If there is pathology that may restrict CSF flow, consideration should be given to intrathecal administration above the level of spinal cord damage to provide an adequate drug concentration in this region.

Intrathecal grafting of unencapsulated adrenal medullary tissue can bring CD4 T lymphocytes into CSF: a potentially deleterious event for the graft.

Adrenal medullary tissue including chromaffin cells was grafted intrathecally in cancer patients to relieve intractable pain. The central nervous system (CNS) is considered an immune privileged site. Therefore, non-HLA-matched and unencapsulated tissue was grafted in 15 patients and 1 sham control in a series of at least 20 grafts. We observed an increase in CSF lymphocyte counts in 15/20 allografts (75%). In contrast to peripheral blood, CD4 T cells predominated in the CSF, but failed to exhibit an activated phenotype (CD25+ CD45RO+ HLA-DR+). The positive effect of graft on pain, the high met-enkephalin levels, the absence of any increase in CSF cytokine levels particularly for IFN-gamma or IL-2 (but not IL-10 and IL-6), indirectly indicated that the graft was tolerated despite the presence of CSF lymphocytes. The single treatment failure and three of four cases of partial efficacy occurred in grafts where CSF lymphocytes were present. Moreover, when assayed (n = 7), the CD4+ CSF lymphocytes still retained the capacity to exhibit ex vivo a normal or enhanced frequency of T CD4 cells producing IFN-gamma and IL-2. Taken together, our observations indicate that impairment of the local immunosuppressive balance can lead to activation of those CSF CD4 T cells and drive a rejection process. This study suggests further work on the purification and/or the immunoisolation of tissues grafted in the CNS will be necessary, particularly when the possibility of long-term and repeated grafting is considered.