Can Determining the Minimum Alveolar Anesthetic Concentration of Volatile Anesthetic Be Used as an Objective Tool to Assess Antinociception in Animals?

We intended to evaluate the reliability of the minimum anesthetic alveolar concentration (MAC)-sparing effect as an objective measure of the antinociceptive properties of a drug. For this purpose, we tested different variables and analyzed the significance of the results obtained. In a first set of experiments, we studied rats under mechanical ventilation and sevoflurane anesthesia. Outcome variables such as gross purposeful movements consecutive to tail clamping, paw withdrawal consecutive to increasing pressure, and cardio-circulatory reactivity (MACBAR) after these stimuli were recorded. In a second set of experiment, sevoflurane-anesthetized rats under spontaneous breathing conditions were used. Thermal stimuli were compared with pressure. The MAC-sparing effect of several doses of sufentanil and clonidine was evaluated in both anesthetized and awake rodents. When considering the stimulus applied, larger concentrations of sevoflurane were required to suppress reactivity after tail clamp than after paw pressure or radiant heat (1.81 +/- 0.28 versus 1.45 +/- 0.22 and 1.53 +/- 0.26; P < 0.05). For the two first stimuli, no significant differences were noted between the concentrations that suppress motor or cardio-circulatory reactions. All doses of sufentanil tested significantly reduced (P < 0.05) the different MAC values except the smallest one (0.005 micro g x kg(-1) x min(-1)) that significantly increased MACBAR in ventilated animals and both MAC and MACBAR in spontaneously breathing rodents (P < 0.05). Clonidine, at its optimal dose (10 micro g/kg), significantly reduced both MAC and MACBAR to the same degree. In awake animals submitted to radiant heat or pressure challenge, none of the clonidine doses nor sufentanil doses (0.005 and 0.07) were active. In conclusion, the MAC-sparing effect provides several reliable and quantifiable variables that allow comparison between different analgesic substances. However, the observations made are not simply the result of antinociceptive effects of the tested drugs but rather that of complex interactions between these drugs and a halogenated vapor.

IMPLICATIONS

The MAC-sparing effect provides several variables that allow comparison between different analgesic substances. However, the observations made are not simply the result of the antinociceptive effects of the tested drugs but rather the result of complex interactions between these drugs and a halogenated vapor.

Bilateral interpleural versus lumbar epidural bupivacaine-morphine analgesia for upper abdominal surgery

This randomized study was designed to compare the effectiveness of bilateral interpleural analgesia with lumbar epidural analgesia, on postoperative pain relief in upper abdominal surgery. The studied patients were randomely allocated into either interpleural group "IP" (n = 15) or epidural group "EP" (n = 15). In "IP" group, preanesthetic bilateral interpleural block was done using a mixture of bupivacaine 0.5% (0.8 mg/kg) and 2 mg morphine diluted to 50 ml saline for each side. In "EP" group, the same mixture-diluted in 20 ml saline-was injected in the epidural space (L2-3). The general anesthetic technique was the same in both groups. Hemodynamic, gasometric, verbal pain score (VPS) values and complications were compared in both techniques. Heart rate (HR) and mean arterial pressure (MAP) readings were in the accepted normal range in the perioperative period although significant lower readings were detected in "EP" group. No significant differences were displayed in blood gasometric variables between the two groups. There were considerable level of analgesia in both groups in the postoperative period although "EP" analgesia was superior to "IP". More pain free patients (9 versus 4) and significant lower consumption of nalbuphine were detected in "EP" group. The results of this study indicate that bilateral "IP" analgesia may offer a satisfactory analgesia for upper abdominal surgery when the use of other analgesic techniques may be contraindicated.

Bioavailability of a morphine suppository is increased after intracolostomal administration in colostoma-constructed rabbits

This study was performed to assess the pharmacokinetics of morphine and its major metabolites after its rectal or colostomal administration in rectal-resected (ROP) or colostoma-constructed (SOP) rabbits, respectively. The pharmacokinetics of morphine, morphine-3-glucuronide (M3G), and M6G in normal rabbits appeared to be similar to those in human, judging from their plasma concentration-time profiles and the susceptibility of morphine to first-pass metabolism. In SOP, but not ROP, rabbits, the plasma concentrations of morphine, M3G and M6G were significantly increased compared with those in normal rabbits. The AUC of morphine and its metabolites, and the F value of the former in the SOP group were greater than those in the control group, while the elimination half-life (t(1/2)) values were comparable in the two groups. In addition, the disposition of morphine and its metabolites after intravenous (i.v.) administration to SOP rabbits was almost the same as that in normal rabbits, suggesting that an increase in the rate of absorption of morphine in SOP rabbits was not due to inflammation at the absorption site caused by operation, but probably due to its increased solubility in loose stools. Therefore, great attention should be paid when morphine suppositories are intracolostomally administered to colostoma-constructed patients.

Plasma fentanyl concentrations in awake cats and cats undergoing anesthesia and ovariohysterectomy using transdermal administration

OBJECTIVE

To measure the plasma fentanyl concentrations achieved over time with transdermal fentanyl patches in awake cats and cats undergoing anesthesia and ovariohysterectomy.

STUDY DESIGN

Randomized prospective experimental study.

ANIMALS

Twenty-four purpose-bred cats.

METHODS

Cats were randomly assigned to three groups for Part I of a larger concurrent study. Group P received only a 25 micro g hour-1 transdermal fentanyl patch. Group P/A received the patch and anesthesia. Group A received only anesthesia. After a minimum 1-week washout period, the cats were randomly reassigned to two groups for Part II of the larger study. Group P/A/O received the patch, anesthesia and ovariohysterectomy. Group A/O received anesthesia and ovariohysterectomy. Patches were left in place for 72 hours and plasma samples were obtained for fentanyl analysis while the patches were in place, and for 8 hours after patch removal for cats in Group P, P/A, and P/A/O.

RESULTS

The 25 micro g hour-1 transdermal fentanyl patches were well tolerated by the cats in this study (mean body weight of 3.0 kg) and no overt adverse effects were noted. Mean plasma fentanyl concentrations over time, mean plasma fentanyl concentrations at specific times (8, 25, 49, and 73 hours after patch placement), time to first detectable plasma fentanyl concentration, time to reach maximum plasma fentanyl concentration, maximum plasma fentanyl concentration, mean plasma fentanyl concentration from 8 to 73 hours, elimination half-life, and total area under concentration (AUC) were not statistically different among the groups.

CONCLUSIONS

Halothane anesthesia and anesthesia/ovariohysterectomy did not significantly alter the plasma fentanyl concentrations achieved or pharmacokinetic parameters measured, when compared with awake cats. There was a high degree of individual variability observed both within and between groups of cats in parameters measured.

CLINICAL SIGNIFICANCE

The high degree of variability observed suggests that careful observation of cats with fentanyl patches in place is required to assess efficacy and any potential adverse effects. Anesthesia and anesthesia/ovariohysterectomy do not appear to alter plasma fentanyl concentrations achieved by placement of a 25 micro g hour-1 transdermal fentanyl patch when compared to cats not undergoing these procedures.

The analgesic effect of oral delta-9-tetrahydrocannabinol (THC), morphine, and a THC-morphine combination in healthy subjects under experimental pain conditions

From folk medicine and anecdotal reports it is known that Cannabis may reduce pain. In animal studies it has been shown that delta-9-tetrahydrocannabinol (THC) has antinociceptive effects or potentiates the antinociceptive effect of morphine. The aim of this study was to measure the analgesic effect of THC, morphine, and a THC-morphine combination (THC-morphine) in humans using experimental pain models. THC (20 mg), morphine (30 mg), THC-morphine (20 mg THC+30 mg morphine), or placebo were given orally and as single doses. Twelve healthy volunteers were included in the randomized, placebo-controlled, double-blinded, crossover study. The experimental pain tests (order randomized) were heat, cold, pressure, single and repeated transcutaneous electrical stimulation. Additionally, reaction time, side-effects (visual analog scales), and vital functions were monitored. For the pharmacokinetic profiling, blood samples were collected. THC did not significantly reduce pain. In the cold and heat tests it even produced hyperalgesia, which was completely neutralized by THC-morphine. A slight additive analgesic effect could be observed for THC-morphine in the electrical stimulation test. No analgesic effect resulted in the pressure and heat test, neither with THC nor THC-morphine. Psychotropic and somatic side-effects (sleepiness, euphoria, anxiety, confusion, nausea, dizziness, etc.) were common, but usually mild.

Effect site concentrations of remifentanil and pupil response to noxious stimulation

BACKGROUND

Opioid drugs block reflex pupillary dilatation in response to noxious stimulation. The relationship between the target effect site concentration (Ce(T)) of remifentanil and the pupil diameter and reactivity in response to a standard noxious stimulus were evaluated.

METHODS

Anaesthesia was induced with propofol TCI to obtain loss of consciousness (LOC) in 12 ASA I/II patients. Thereafter, remifentanil Ce(T) was titrated by increments of 1 up to 5 ng ml(-1). In the awake state, at LOC and at each plateau level of remifentanil Ce(T), arterial pressure, heart rate, and BIS (A2000) were recorded. Pupil size and dilatation after a 100 Hz tetanic stimulation (T100) were measured at LOC and at each plateau level of remifentanil Ce(T).

RESULTS

LOC was observed at a mean propofol Ce(T) of 3.53 (SD 0.43) microg ml(-1). Arterial pressure and heart rate decreased progressively from LOC to 5 ng ml(-1) remifentanil Ce(T) without any statistical difference between each incremental dose of remifentanil. Mean BIS values decreased from 96 (2) in the awake state, to 46 (12) at LOC (P<0.05) and then remained unchanged at all remifentanil Ce(T). Pupil dilatation in response to 100 Hz tetanic stimulation decreased progressively from 1.55 (0.72) to 0.01 (0.03) mm and was more sensitive than pupil diameter measured before and after 100 Hz tetanus. An inverse correlation between pupil dilatation in response to 100 Hz tetanus and an increase in remifentanil Ce(T) from 0 to 5 ng ml(-1) was found (R(2)=0.68).

CONCLUSIONS

During propofol TCI in healthy patients, the decrease in pupil response to a painful stimulus is a better measurement of the progressive increase of remifentanil Ce(T) up to 5 ng ml(-1) than haemodynamic or BIS measurements.

Tentative Identification of Novel Oxycodone Metabolites in Human Urine

Oxycodone is a semisynthetic codeine derivative that has been used both as an analgesic and antitussive. In the mid 1990s, OxyContin was introduced as a slow-release formulation of oxycodone for use in patients with moderate to severe chronic pain from such ailments as arthritis, vertebral disc disease, and cancer. Doctors wrote 6.9 million prescriptions for OxyContin from May 2000 through May 2001. Thus, it is no surprise that hospitals and medical examiners' offices across the country have seen an increasing number of admissions and deaths resulting from oxycodone abuse and overdose. The laboratory identifies oxycodone as part of its routine abused and therapeutic drug-testing procedures. Routine gas chromatographic analysis of bile or urine in many of these cases revealed unidentified peaks in the region of oxycodone that appeared to be oxycodone metabolites. In humans, the only documented metabolites of oxycodone are oxymorphone and N-desmethyloxycodone (noroxycodone). This study attempts to characterize these compounds as "presumptive" metabolites based on circumstantial evidence from known metabolic pathways of oxycodone in other species, as well as of other opiates and narcotic analgesics.

Extraction and quantitation of carfentanil and naltrexone in goat plasma with liquid chromatography-mass spectrometry

This method is the first analytical method for the detection and quantitation of carfentanil and naltrexone at clinically relevant concentrations using liquid chromatography-mass spectrometry. Samples were alkalinized with 100 microl of 1 M NaOH and extracted 2x with 2 ml of toluene. The extractions were combined and dried under N(2) at 40 degrees C in a H(2)O bath. Chromatography was performed using a Zirchrom PBD column and a mobile phase of 30:70 acetonitrile/10 mM ammonium acetate and 0.1 mM citrate (pH=4.4) at a flow rate of 0.3 ml/min. The lower limit of quantitation was 8.5 pg/ml for carfentanil and 0.21 ng/ml for naltrexone.

Elimination of alfentanil delivered by infusion is not altered by the chronic administration of atorvastatin

BACKGROUND AND OBJECTIVE

Statins are prescribed for patients with hypercholesterolemia. Atorvastatin is metabolized by cytochrome P4503A4 and inhibits P4503A4 activity in vitro. Alfentanil is a potent opioid used in clinical anaesthetic practice and is also metabolized by P4503A4. This study tested the hypothesis that chronic atorvastatin administration inhibits the metabolism of alfentanil.

METHODS

Sixteen patients undergoing elective surgery were studied as matched pairs. One member of each pair was maintained on standard doses of atorvastatin for at least 4 months. Each patient received an alfentanil bolus (80 microg kg(-1)) intravenously (i.v.), followed by an alfentanil infusion (0.67 microg kg(-1) min(-1)) for 90 min. Serial plasma alfentanil concentrations were measured using gas chromatography-nitrogen phosphorous detection. Pharmacokinetic parameters were calculated using two-compartment linear modelling.

RESULTS

One patient and the corresponding match were excluded from the analysis. The elimination half-life of alfentanil was similar in the control and atorvastatin groups (98.8 +/- 12.4 versus 98.3 +/- 11.3 min, respectively). The clearance (Cl), volume of distribution at steady-state (Vdss) and area under the curve (AUC) were similar in the two groups (Cl = 0.20 (+/- 0.06) and 0.22 (+/- 0.04) L min(-1), Vdss = 0.38 (+/- 0.07) and 0.39 (+/- 0.07) L kg(-1), AUC = 0.05 (+/- 0.02) and 0.04 (+/- 0.01) mg min mL(-1)).

CONCLUSIONS

Concurrent atorvastatin administration does not alter the pharmacokinetics of alfentanil in patients undergoing elective surgery.

A new formulation of nasal fentanyl spray for postoperative analgesia: a pilot study

Twenty-four gynaecological patients receiving postoperative patient-controlled analgesia were enrolled in an open cross-over pilot study evaluating two new formulations of nasal fentanyl spray. The primary outcome was the bioavailability of nasal fentanyl in comparison with intravenous fentanyl. This manuscript describes the clinical outcomes of quality of postoperative analgesia and patient acceptability. There were 21 complete data sets for both sequences of the cross-over design. In randomised order, patients received approximately 50 microg of fentanyl in a single dose by intranasal and intravenous administration, but separated by at least 2 h. Analgesia was of rapid onset (within 5 min) and similar quality. There was no significant difference in side-effects. Four patients experienced mild nasal stinging and although 10 (42%) preferred intravenous administration, seven (29%) preferred intranasal and six (25%) had no preference. We conclude that these formulations of fentanyl, delivered as nasal spray, have potential clinical utility.

Epidural, cerebrospinal fluid, and plasma pharmacokinetics of epidural opioids (part 2): effect of epinephrine

BACKGROUND

The ability of epinephrine to improve the efficacy of epidurally administered drugs is assumed to result from local vasoconstriction and a consequent decrease in drug clearance. However, because drug concentration in the epidural space has never been measured, our understanding of the effect of epinephrine on epidural pharmacokinetics is incomplete. This study was designed to characterize the effect of epinephrine on the epidural, cerebrospinal fluid, and plasma pharmacokinetics of epidurally administered opioids.

METHODS

Morphine plus alfentanil, fentanyl, or sufentanil was administered epidurally with and without epinephrine (1:200,000) to pigs. Opioid concentration was subsequently measured in the epidural space, central venous plasma, and epidural venous plasma, and these data were used to calculate relevant pharmacokinetic parameters.

RESULTS

The pharmacokinetic effects of epinephrine varied by opioid and by sampling site. For example, in the lumbar epidural space, epinephrine increased the mean residence time of morphine but decreased that of fentanyl and sufentanil. Epinephrine had no effect on the terminal elimination half-life of morphine in the epidural space, but it decreased that of fentanyl and sufentanil. In contrast, in the lumbar intrathecal space, epinephrine had no effect on the pharmacokinetics of alfentanil, fentanyl, or sufentanil, but it increased the area under the concentration-time curve of morphine and decreased its elimination half-life.

CONCLUSIONS

The findings indicate that the effects of epinephrine on the spinal pharmacokinetics of these opioids are complex and often antithetical across compartments and opioids. In addition, the data clearly indicate that the pharmacokinetic effects of epinephrine in spinal "compartments" cannot be predicted from measurements of drug concentration in plasma, as has been assumed for decades.

Epidural, cerebrospinal fluid, and plasma pharmacokinetics of epidural opioids (part 1): differences among opioids

BACKGROUND

The pharmacokinetics of epidurally administered drugs has been the subject of many studies, yet drug concentration in the epidural space has never been measured. This study was undertaken to characterize the epidural, cerebrospinal fluid, and plasma pharmacokinetics of epidurally administered opioids on the basis of measurement of drug concentration in each of these compartments after epidural administration.

METHODS

Morphine plus alfentanil, fentanyl, or sufentanil were administered epidurally in anesthetized pigs. Microdialysis was used to sample the epidural space and the cerebrospinal fluid for measurement of opioid concentration over time. Plasma samples were obtained from the central venous plasma and the epidural venous plasma. These data were used to calculate relevant pharmacokinetic parameters, including mean residence time, elimination half-lives, areas under the concentration versus time curves, clearance, and volume of distribution for each opioid in each compartment.

RESULTS

Some of the more important findings were that the cerebrospinal fluid and plasma pharmacokinetics of the opioids did not parallel their epidural pharmacokinetics and that their hydrophobic character governed multiple aspects of their lumbar epidural pharmacokinetics.

CONCLUSIONS

The findings indicate that the spinal pharmacokinetics of these drugs are complex and, in some ways, counterintuitive. Also, the bioavailability of opioids in the cerebrospinal fluid and epidural space is determined primarily by their hydrophobicity, with less hydrophobic drugs having greater bioavailability.

Post-mortem SNP analysis of CYP2D6 gene reveals correlation between genotype and opioid drug (tramadol) metabolite ratios in blood

Tramadol is an opioid drug metabolised in phase I by cytochrome P450 (CYP) enzymes, of which CYP2D6 is mainly responsible for the O-demethylation of tramadol, but is not involved in N-demethylation. Defects in the genes encoding drug metabolising enzymes (DMEs) may lead to adverse drug effects, even to death. To aid interpretation of the forensic toxicology results, we studied how the genetic variation of the CYP2D6 gene is reflected in tramadol metabolite ratios found in post-mortem samples. In 33 Finnish autopsy cases where tramadol was found, we analysed both the CYP2D6 genotype and the concentrations of tramadol and its metabolites O- and N-demethyltramadol. As expected, we found a correlation between the number of functional CYP2D6 alleles and the ratio of tramadol to O-demethyltramadol. We also found a correlation between the number of functional alleles and the ratio of tramadol to N-demethyltramadol. This can be explained by the complementary nature of the two main tramadol demethylation pathways. No known CYP2D6 inhibitors were associated with exceptional metabolic ratios. Furthermore, no accidental tramadol poisonings were associated with a defective CYP2D6 gene. Our results on the tramadol are among the first to demonstrate that genetic variation in drug metabolising enzymes can be analysed in post-mortem blood, and that it correlates well with the parent drug to metabolite ratios. The results also suggest that genetic factors play, in general, a dominant role over other factors in the metabolism of individual drugs.

Sensitive determination of pethidine in body fluids by gas chromatography-tandem mass spectrometry

We have presented a simple and sensitive method for determining pethidine, a narcotic analgesic drug in body fluids by gas chromatography-tandem mass spectrometry (GC-MS/MS). Pethidine and 4'-piperidinoacetophenone (internal standard) were extracted from body fluids with Bond Elut C(18) columns; the recoveries were above 85% for both compounds. The calibration curves for blood and urine showed good linearities in the range of 1.25-40 ng/ml. Its detection limits (signal-to-noise ratio=3) were estimated to be approximately 0.5 ng/ml of whole blood and urine.

Influences on serum concentrations of morphine, M6G and M3G during routine clinical drug monitoring: a prospective survey in 300 adult cancer patients

BACKGROUND

In order to make treatment decisions physicians should have knowledge about the relations between patient characteristics and drug disposition. Dose, route of administration, gender, age and renal function are reported to influence the serum concentrations of morphine, morphine-6-glucurnide (M6G) and morphine-3-glucuronide (M3G) during chronic treatment of cancer pain. These factors, however, are not evaluated in studies with a sample size sufficient to explore predictive factors.

METHODS

Three hundred consecutive morphine users admitted because of a malignant disease were recruited. The relations of serum concentrations of morphine, M6G and M3G to patient characteristics (gender, age, weight, renal function, liver function, dose, route of administration) were explored, and regression analysis performed to investigate whether these characteristics predicted serum concentrations obtained during routine clinical drug monitoring.

RESULTS

Morphine dose was associated with serum concentrations of morphine (r = 0.69), M6G (r = 0.76) and M3G (r = 0.76). Oral morphine resulted in higher dose-adjusted M6G and M3G serum concentrations compared with s.c. morphine. Creatinine serum concentrations correlated with serum concentrations of M6G and M3G. Dose and route of administration predicted morphine serum concentrations, while dose and renal function predicted M6G and M3G serum concentrations. Age was an additional factor predicting M3G concentrations. Dose was the only factor that explained a clinically significant part of the observed variability.

CONCLUSION

Patient characteristics predict only minor parts of the variability of morphine, M3G and M6G serum concentrations observed during routine clinical drug-monitoring in cancer patients.

Pharmacokinetics of fentanyl following intravenous and transdermal administration in horses

REASONS FOR PERFORMING STUDY

Although fentanyl has been reported to cause CNS excitation in horses, a transdermal therapeutic system (TTS) containing this mu agonist has recently been used empirically in equine medicine to treat moderate to severe pain. A better understanding of the disposition of fentanyl following transdermal administration would facilitate the clinical use of TTS fentanyl to obtain analgesia in horses.

OBJECTIVES

To determine the pharmacokinetics of fentanyl following i.v. and TTS patch administration in healthy, mature horses and to evaluate the tolerance of horses to TTS fentanyl administration.

METHODS

The pharmacokinetics of fentanyl in serum were assessed following a single i.v. dose, a single TTS dose, and multiple TTS doses in 6 healthy horses. Physical examinations, haematology and serum biochemistry analyses during transdermal fentanyl application were then performed to determine tolerance of continuous fentanyl administration.

RESULTS

Fentanyl was very rapidly and completely absorbed following a single TTS dose. Mean serum fentanyl concentrations consistent with analgesia in other species were reached by 1 h and maintained until 32 h after patch application. Similar steady state serum concentrations were obtained when multiple doses of TTS fentanyl were administered every 48 or 72 h over 8 or 9 days, with less fluctuation in serum concentrations during the 48 h dosing interval. Three horses exhibited brief (< 12 h) episodes of increased body temperature; however, transdermal fentanyl administrations were not associated with other significant changes in haematology and biochemistry panels or physical examination findings.

CONCLUSIONS AND POTENTIAL RELEVANCE

Although the pharmacodynamics of fentanyl have not been investigated fully in horses, transdermally-administered fentanyl exhibited a favourable pharmacokinetic profile without clinically relevant side effects and may be a useful analgesic in equine patients.

Validation of a method for quantification of ketobemidone in human plasma with liquid chromatography-tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC-MS-MS) method for determination of the analgesic aminophenol ketobemidone in human plasma is presented. Two preparation methods for plasma samples containing ketobemidone were compared, liquid-liquid extraction (LLE) and solid-phase extraction (SPE). Both methods showed good precision (n=10), 1.7% and 2.9%, respectively (0.04 micro M) and 1.1% and 2.5%, respectively (0.14 micro M). The accuracy was 98% and 103%, respectively (0.04 micro M) and 105% and 99%, respectively (0.14 micro M). Ketobemidone could be quantified at 0.43 nM, with a relative standard deviation of 17.5% (n=19) using LLE and 18.6% (n=10) using SPE. This level was an order of magnitude lower than earlier reported quantification limits. Quantitative data from plasma samples analyzed with LC-MS-MS were in good agreement with those obtained by gas chromatography with chemical ionization mass spectrometry (GC-CI/MS). This indicates that LC-MS-MS is a good alternative method to GC-MS as it is more sensitive and time-consuming derivatization can be avoided.

[Stereoselectivity in biliary excretion of trans tramadol and trans O-demethyltramadol in rats]

AIM

To investigate the stereoselectivity in biliary excretion of trans tramadol (trans T) and trans O-demethyltramadol (M1) in rats.

METHODS

After a single intravenous dose of trans T hydrochloride (10 mg.kg-1) or M1 (2.5 mg.kg-1) to rats, the bile was collected for 30 min, then, blood was obtained from the heart. The enantiomers of trans T, M1 and M1 conjugated with glucuronic acid (M1c) in the bile and plasma were analyzed by high performance capillary electrophoresis (HPCE).

RESULTS

After the rats were given trans T, the bile concentrations of (+)-trans T were higher than those of (-)-trans T, and the (+)/(-)-trans T ratios were lower compared with those in the plasma. After the rats were given M1, the bile concentrations of (+)-M1 were higher than those of (-)-M1, and the bile concentrations of (+)-M1c were lower than those of (-)-M1c. The glucuronidation rate of (+)-M1 was lower than that of (-)-M1 in the bile.

CONCLUSION

The biliary excretion of trans T and M1 was stereoselective, (+)-trans T and (-)-M1 being preferentially excreted.

Systemic uptake of buprenorphine by cats after oral mucosal administration

The plasma concentration of buprenorphine was measured by radioimmunoassay in six female cats after the administration of 0.01 mg/kg (0.033 ml/kg) buprenorphine hydrochloride solution into the side of the cat's mouth. Blood samples were taken through a preplaced jugular catheter before and one, two, four, six, 10, 15, 30, 45 and 60 minutes, and two, four, six, 12 and 24 hours after the dose was administered. The buprenorphine was accepted well by all the cats and did not cause salivation or vomiting. Its median peak plasma concentration was 7.5 ng/ml and was reached after 15 minutes. The pharmacokinetic data were similar to the pharmacokinetic data obtained after the intramuscular and intravenous administration of buprenorphine to cats from the same colony, suggesting that the mucosal route of administration should be as effective as intravenous and intramuscular injections. In addition, the pH of the oral cavity of 26 cats was measured with pH paper, and 100 cat owners were asked their preferred method of administering drugs to cats. The pH of the cats' mouths was between 8 and 9, and the technique preferred by the cat owners was the use of drops placed in the mouth.

Age- and therapy-related effects on morphine requirements and plasma concentrations of morphine and its metabolites in postoperative infants

BACKGROUND

To investigate clinical variables such as gestational age, sex, weight, the therapeutic regimens used and mechanical ventilation that might affect morphine requirements and plasma concentrations of morphine and its metabolites.

METHODS

In a double-blind study, neonates and infants stratified for age [group I 0-4 weeks (neonates), group II > or =4-26 weeks, group III > or =26-52 weeks, group IV > or =1-3 yr] admitted to the paediatric intensive care unit after abdominal or thoracic surgery received morphine 100 micro g kg(-1) after surgery, and were randomly assigned to either continuous morphine 10 micro g kg(-1) h(-1) or intermittent morphine boluses 30 micro g kg(-1) every 3 h. Pain was measured using the COMFORT behavioural scale and a visual analogue scale. Additional morphine was administered on guidance of the pain scores. Morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) plasma concentrations were measured before, directly after, and at 6, 12 and 24 h after surgery.

RESULTS

Multiple regression analysis of different variables revealed that age was the most important factor affecting morphine requirements and plasma morphine concentrations. Significantly fewer neonates required additional morphine doses compared with all other age groups (P<0.001). Method of morphine administration (intermittent vs continuous) had no significant influence on morphine requirements. Neonates had significantly higher plasma concentrations of morphine, M3G and M6G (all P<0.001), and significantly lower M6G/morphine ratio (P<0.03) than the older children. The M6G/M3G ratio was similar in all age groups.

CONCLUSIONS

Neonates have a narrower therapeutic window for postoperative morphine analgesia than older age groups, with no difference in the safety or effectiveness of intermittent doses compared with continuous infusions in any of these age groups. In infants >1 month of age, analgesia is achieved after morphine infusions ranging from 10.9 to 12.3 micro g kg(-1) h(-1) at plasma concentrations of <15 ng ml(-1).

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.

Opioid plasma concentration during switching from morphine to methadone: preliminary data

Opioid switching is often used to improve the opioid response in cancer patients experiencing poor analgesia or adverse effects. However, no data are available on plasmatic changes of opioids and their metabolites during these phases, and whether there exists a relationship with the clinical events. In a prospective study of 10 consecutive cancer patients on oral morphine but with uncontrolled pain (greater >4 on a numerical scale of 0 to 10) and/or moderate to severe opioid adverse effects (on a level of 2 and 3 of a verbal scale) and not responsive to adjuvant medications, switching to oral methadone was performed using a fixed ratio of 5:1, leaving extra-doses of 1/5 of the daily dose of methadone calculated as needed. Blood samples were obtained at the same hour for four days, before the switching, and then on day 1, 2, and 3. The intensity of pain and the adverse effects were assessed daily to calculate the switching score before and after switching. Completed blood samples were obtained in 9 patients. One patient was separately considered, because of his renal impairment. Significant improvements in pain intensity as well as adverse effects within an average period of 1-2 days were observed. Morphine, morphine-6-glucuronide, and morphine-3-glucuronide were progressively cleared from plasma to almost disappear within three days. Methadone rapidly achieved a stable concentration in 1-2 days. The doses of methadone were changed, but not significantly, and tended to decrease in the following days, according to the clinical situation. The results of this study confirm the need to stop rapidly morphine, and to use a priming dose of methadone, rather than using progressive decrements and increments of morphine and methadone, respectively, during opioid switching. This method allows for a rapid clearance of morphine and its metabolites are rapidly cleared, except in patients with renal failure. Opioid plasma changes substantially overlap the clinical changes observed in these patients, in terms of benefit between analgesia and adverse effects.

Codeine and clinical impairment in samples in which morphine is not detected

OBJECTIVE

Codeine metabolises partly to morphine by the liver enzyme CYP2D6, which is subject to genetic polymorphism. It has been suggested that analgesic effects of codeine are due to the morphine metabolite. Codeine effects other than analgesia have been less investigated in this regard, but it has been suggested that sedation, for example, might be independent of morphine formation. The aim of our study was to investigate the influence of codeine alone, without concomitant presence of morphine, on a clinical test for drunkenness (CTD) performed in relation to suspected drugged driving.

METHODS

Cases with detected codeine but not morphine, nor any other drug above the limit of detection, were selected from the database of suspected drugged drivers at National Institute for Forensic Toxicology, Oslo, Norway. Codeine blood concentration in these samples was compared with the conclusions from the corresponding individual CTD.

RESULTS

Of the 43 cases fulfilling the selection criteria, 23 were judged as "not impaired", and 20 as "impaired". Mean blood codeine concentration in the "not impaired" group was 143 ng/ml (95% CI 48-238, median 63 ng/ml). Mean concentration in the "impaired" group was 213 ng/ml (95% CI 146-279, median 159 ng/ml). There was a statistically significant concentration difference between the two groups. Codeine blood concentrations were further grouped as "moderate", "medium high" and "high". When adjusted for age, gender and chronic use, the odds ratios for being judged as impaired were 6 (95% CI 1-32, P=0.04) and 19 (95% CI 2-182, P=0.01) for the "medium high" group and the "high" group, respectively, relative to the "moderate" group.

CONCLUSION

Codeine appeared to have some dose-dependent effect on the central nervous system that may lead to impairment as judged from a CTD, independent of measurable blood morphine concentrations. This supports the view that some codeine effects do not seem to be mediated by morphine.

Intrathecal + PCA morphine improves analgesia during the first 24 hr after major abdominal surgery compared to PCA alone

PURPOSE

To compare, over a 48-hr follow-up period, the analgesia and side-effects of patient controlled iv analgesia (PCA) with morphine alone vs combined intrathecal and PCA morphine (IT+PCA) in patients undergoing major abdominal surgery.

METHODS

Sixty adult patients undergoing abdominal surgery for cancer were randomly allocated to receive preoperative IT (0.3 or 0.4 mg) plus postoperative PCA morphine or postoperative PCA morphine alone. Postoperative analgesia was tested at rest and while coughing on a visual analogue pain scale and morphine consumption was recorded. Patients' satisfaction, arterial oxygen saturation, respiratory rate, episodes of nausea, vomiting and pruritus were also noted.

RESULTS

Analgesia at rest and while coughing was significantly better in the IT+PCA morphine group (rest: P = 0.01; coughing: P = 0.005) on the first postoperative day only. IT+PCA morphine constantly provided adequate analgesia during this period. Morphine consumption was lower in the IT+PCA morphine group during this period also (IT+PCA: 9 (17) vs PCA: 40 (26); mg of morphine, mean (SD), P = 0.0001). No difference was found in pain relief and morphine consumption between the groups on the second postoperative day. Nausea and vomiting were more frequent with IT+PCA morphine on the first postoperative day. No respiratory depression occurred in either group. Satisfaction was high in both groups.

CONCLUSIONS

IT+PCA morphine improves patient comfort constantly during the first postoperative day after major abdominal surgery. However, after the first postoperative day, IT+PCA morphine provides no additional benefit.

Programming errors contribute to death from patient-controlled analgesia: case report and estimate of probability

PURPOSE

To identify the factors that threaten patient safety when using patient-controlled analgesia (PCA) and to obtain an evidence-based estimate of the probability of death from user programming errors associated with PCA.

CLINICAL FEATURES

A 19-yr-old woman underwent Cesarean section and delivered a healthy infant. Postoperatively, morphine sulfate (2 mg bolus, lockout interval of six minutes, four-hour limit of 30 mg) was ordered, to be delivered by an Abbott Lifecare 4100 Plus II Infusion Pump. A drug cassette containing 1 mg.mL(-1) solution of morphine was unavailable, so the nurse used a cassette that contained a more concentrated solution (5 mg.mL(-1)). 7.5 hr after the PCA was started, the patient was pronounced dead. Blood samples were obtained and autopsy showed a toxic concentration of morphine. The available evidence is consistent with a concentration programming error where morphine 1 mg.mL(-1) was entered instead of 5 mg.mL(-1). Based on a search of such incidents in the Food and Drug Administration MDR database and other sources and on a denominator of 22,000,000 provided by the device manufacturer, mortality from user programming errors with this device was estimated to be a low likelihood event (ranging from 1 in 33,000 to 1 in 338,800), but relatively numerous in absolute terms (ranging from 65-667 deaths).

CONCLUSION

Anesthesiologists, nurses, human factors engineers, and device manufacturers can work together to enhance the safety of PCA pumps by redesigning user interfaces, drug cassettes, and hospital operating procedures to minimize programming errors and to enhance their detection before patients are harmed.