Epidural bupivacaine-pethidine mixture clinical experience using a low-dose combination in labour

In an attempt to overcome some of the undesirable side-effects and sequelae traditionally associated with epidural analgesia, various mixtures containing bupivacaine and pethidine have been examined during labour. Preliminary investigations suggested that a mixture containing bupivacaine 0.125% was the most promising combination, and accordingly a prospective survey was conducted in order to assess this mixture further; 100 mothers were included in the survey and clinical assessment included analgesic efficacy, side-effects, degree of mobility, obstetric outcome and patient satisfaction. Ninety per cent of mothers described their pain relief as satisfactory following the initial dose and 67% chose to receive this mixture alone throughout labour. Among those who delivered vaginally, delivery occurred spontaneously in 63% of primiparas and 90% of multiparas. Urinary catheterization was required in only 10% of spontaneous deliveries. Mean umbilical vein blood concentrations at birth among 48 neonates were 0.12 mg/L and 0.05 mg/L respectively for pethidine and bupivacaine. Despite, in some cases, recall of severe pain at delivery patient satisfaction was extremely high. Reasons given for this high approval rating included the quality of analgesia, mood elevation, mobility, and feeling aware or in control during labour.

Analgesic effect and bioavailability of oral ketogan given as tablets or mixture to patients with chronic pain of malignant origin

Thirteen cancer patients with moderate to severe chronic pain of malignant origin on treatment with Ketogan tablets were included in an open non-randomized cross-over study comparing the analgesic effect, side effects and serum concentrations of Ketogan tablets and mixture. The patients were six days in hospital and were dosed two days with tablets, two days with mixture and finally another two days with tablets. Recordings of pain and side effects and collection of blood samples prior to dosing and hourly thereafter until remedication were performed on the second day of each dosing period in a morning dose interval. The analgesic effect judged by visual analog score (VAS) and pain intensity differences (PID), the areas under the serum concentration time curves, and the average serum concentrations for the three groups were compared. It was not possible do detect any differences among the three groups concerning the analgesic effect, duration of analgesic effect, the serum concentrations and the side effects. The mean plasma half-life of ketobemidone was 2.74 h +/- 0.90 (SD) and the mean relative bioavailability of the mixture was slightly above 100%. Linear regression analysis revealed a significant correlation between ketobemidone serum concentrations and analgesic effect, VAS, for tablet one and for the mixture but not for tablet two, possibly due to the fixed dosing schedule and to the positive effect of hospitalization on the pain.

Meperidine and normeperidine distribution in the rhesus monkey

Previous work has shown that both meperidine and normeperidine are transferred across the placenta to the fetus. Little is known in primates, however, about the tissue deposition of these compounds. Four pregnant, dated rhesus monkeys within one week of term were anesthetized for cesarean delivery. An equal mixture of meperidine and normeperidine was administered as an intravenous bolus 10 minutes before delivery (1.25 mg/kg). The infants were then sacrificed at 20 minutes after birth and the concentration of the compounds in various organ systems were analyzed by gas-liquid chromatography and mass spectroscopy (GLC-MS). The infant serum 20 minutes after delivery revealed a meperidine concentration of 2.23 micrograms/ml and a normeperidine level of 0.67 micrograms/ml (3:1). In contrast, the tissues analyzed showed a much higher concentration of the metabolite in the liver (1:7), gallbladder (1:3), and brain (1:2). Other tissues, such as muscle and kidney, demonstrated equal levels of the two compounds. The authors conclude that normeperidine is quickly transferred to fetal tissues and to a greater degree than the parent compound in certain organs. The increased distribution, particularly in the brain, could account for the toxic actions in the cerebrum of the derivatives of meperidine.

CSF and plasma pharmacokinetics of pethidine and norpethidine in man after epidural and intrathecal administration of pethidine

The disposition of pethidine and its main metabolite, norpethidine, in cerebrospinal fluid (CSF) and plasma was studied in 11 thoracic surgery patients after lumbar epidural (100 mg; n = 6) or lumbar intrathecal (25 mg; n = 5) administration of pethidine. Pethidine appeared more slowly in plasma after intrathecal than after epidural administration (tmax 2.3 h and 14 min, respectively), but systemic bioavailability was similar. The CSF concentrations of pethidine were higher than those in plasma after both routes of administration. The maximal CSF/plasma concentration ratio was 6000 to 45,000 after intrathecal administration but was only 26 to 97 after the epidural route. Pethidine was rapidly distributed in CSF; nine to ten h after the intrathecal and epidural injections the CSF/plasma concentration ratios were 12 to 89 and 2 to 33, respectively. The calculated bioavailability in CSF of epidural pethidine was 10.3%. The terminal elimination half-life of pethidine was 6.0 h (CSF) and 5.4 h (plasma) after intrathecal administration and 8.6 h (CSF) and 8.8 h (plasma) after epidural injection. The volume of distribution of unchanged pethidine in the subarachnoid space was 13 ml.kg-1 and clearance from the CSF was 15 microliters.kg-1.min-1. In all patients receiving intrathecal pethidine and in some patients after epidural pethidine, CSF norpethidine concentrations were higher than those in plasma; the maximum CSF norpethidine was 102 to 1211 ng.ml-1 and 14 to 210 ng.ml-1 and the maximum CSF/plasma norpethidine concentration ratios were 21 to 652 and 0.6 to 14 times after intrathecal and epidural administration, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Meperidine pharmacokinetics following intravenous, peroral and buccal administration in beagle dogs

The pharmacokinetics of meperidine was studied in Beagle dogs following intravenous, peroral and buccal administration of a meperidine hydrochloride solution. The elimination half-life after I.V., P.O. and buccal routes was 0.75 +/- 0.14 hours, 0.93 +/- 0.18 hours and 0.36 +/- 0.10 hours, respectively. The volume of distribution and total clearance following I.V., P.O. and buccal administration were 2.41 +/- 0.34 L/kg and 42.5 +/- 8.9 ml/min/kg, 2.84 +/- 1.24 L/kg and 34.6 +/- 7.8 ml/min/kg, 1.01 +/- 0.52 L/kg and 34.7 +/- 8.0 ml/min/kg, respectively. The absolute bioavailability after P.O. and buccal administration was 11.0 +/- 6.8% and 11.9 +/- 6.6%, respectively. This paper discusses the observed low bioavailabilities on hypothesis of hepatic and lung first-pass effect. A hypothesis is presented to explain the delayed onset of absorption following buccal administration.

Pharmacokinetics of intrathecal morphine and meperidine in humans

Two groups of surgical patients each comprising six individuals received an intrathecal injection of morphine 0.3 mg or meperidine 10 mg. Cerebrospinal fluid (CSF) and plasma were sampled frequently during a 6-h period and analyzed for morphine or meperidine. Maximum plasma morphine concentrations were found 5-10 min after injection, and averaged 4.5 +/- 1.1 ng.ml-1 (mean +/- SEM). Maximum CSF morphine concentrations were considerably higher than maximum plasma concentrations, 6410 +/- 1290 ng.ml-1. Maximum plasma concentrations of meperidine were also measured 5 or 10 min after injection and were low (36 +/- 9 ng.ml-1) compared with the maximum CSF concentrations (364 +/- 105 micrograms.ml-1). After a rapid initial decline for about 15 min after injection, the CSF concentrations decreased with a half-life of 89.8 +/- 16.1 min for morphine and 68.0 +/- 5.1 min for meperidine during the rest of the study period. The initial volume of distribution in CSF was similar for both drugs, or 22 +/- 8 ml for morphine and 18 +/- 5 ml for meperidine. After 6 h, 1.6 +/- 0.9% of the injected morphine dose and 0.41 +/- 0.09% of the meperidine dose remained in the initial volume of distribution. Large inter-individual differences in morphine and meperidine CSF kinetics existed, which may explain some of the reported individual differences in duration of effects. The disappearance of meperidine from CSF tended to be faster than that of morphine, which may be explained, in part, by the differences in lipid solubilities of the drugs.

Pharmacokinetics of epidural morphine and meperidine in humans

Five groups of surgical patients, each comprising six individuals, received epidural doses of morphine or meperidine, and the plasma and CSF kinetics were studied. Three groups received epidural doses of morphine 3 mg in 1 or 10 ml or meperidine 30 mg in 1 ml. Cerebrospinal fluid (CSF) and central venous blood opioid concentrations were measured intermittently for 6 h after injection. Two groups received epidural doses of morphine 3 mg in 1 ml or meperidine 30 mg in 1 ml, and opioid CSF concentrations were determined over a 24-h period. Morphine appeared rapidly in plasma, and maximum plasma concentrations were usually detected 5 min after injection and averaged 33 ng.ml-1 in the 1-ml volume group and 40 ng.ml-1 in the 10-ml volume group. The terminal plasma half-life averaged 91 +/- 34 min and 87 +/- 27 min, respectively (mean +/- SEM). Maximal plasma concentrations of meperidine were usually detected 10 or 15 min post-injection and averaged 196 +/- 29 ng.ml-1. The terminal plasma half-life averaged 124 +/- 26 min. Morphine crossed the dura relatively slowly, and the absorption half-life across the dura averaged 22 min. Maximal CSF concentrations were usually seen 60-90 min post-injection. In contrast, meperidine crossed the dura quickly, with an absorption half-life averaging 7.6 +/- 2.0 min. Maximal CSF concentrations were seen 15 or 30 min post-injection. Morphine and meperidine concentrations remained several times higher in the CSF than in the plasma. The fraction of the opioid dose crossing the dura was calculated to be 3.6% for morphine and 3.7% for meperidine. There were no significant differences in the kinetics of morphine administered in 1 or in 10 ml when CSF was sampled close to the site of lumbar epidural injection. The CSF concentration-time curves of both drugs decreased biexponentially after the initial rise due to diffusion across the dura. The early half-life in CSF averaged 73.3 +/- 11.5 min for morphine and 71.3 +/- 3.1 min for meperidine, and the late half-life averaged 369 +/- 113 min for morphine and 982 +/- 449 min for meperidine. Dose-normalized morphine and meperidine CSF concentrations after epidural administration showed that meperidine concentrations were down to one-fourth the corresponding morphine concentrations from the 2nd to the 15th h after administration, which may partly explain the longer duration of analgesia from morphine.(ABSTRACT TRUNCATED AT 400 WORDS)

The influence of drug polarity on the absorption of opioid drugs into CSF and subsequent cephalad migration following lumbar epidural administration: application to morphine and pethidine

This study examines the influence of drug polarity on the rate and extent of drug absorption into cerebrospinal fluid (CSF) following lumbar epidural administration. Twelve patients with pain secondary to cancer were simultaneously administered both morphine (10 mg) and pethidine (50 mg) in 10 ml of normal saline via an epidural catheter inserted in the lumbar region (usually L2,3) and attached to a subcutaneously implanted portal reservoir. Frequent blood samples were collected to characterise the vascular uptake of both opioids. In addition, a single CSF sample was collected in each patient from the C7-T1 interspace at one of the following times: 10, 30, 60, 120, 180 and 240 min. There was a rapid vascular uptake of morphine from the epidural space with a mean (+/- S.D.) peak concentration of 173 +/- 80 ng/ml (range 52-345 ng/ml) and a time-to-peak concentration of 8 +/- 6 min (range 2-17 min). In contrast, the vascular uptake of pethidine was more variable with a mean (+/- S.D.) concentration of 274 +/- 294 ng/ml (range 80-1113 ng/ml) and the time-to-peak concentration was 21 +/- 26 min (range 2-75 min). There was a rapid absorption of pethidine across the dura mater into the CSF with peak CSF concentrations between 1400 and 1650 ng/ml occurring between 10 and 60 min in samples collected cephalad (C7-T1 interspace) from the administration point in the lumbar region. However, the peak morphine concentration in CSF was delayed relative to the pethidine peak and occurred at 120 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of low-dose intravenous pethidine in patients with renal dysfunction

The kinetics and elimination of pethidine (meperidine) after intravenous administration (150 micrograms/kg) to ten healthy volunteer subjects were compared with those obtained from 18 patients who suffered from varying degrees of renal dysfunction. In both groups of subjects, pethidine was eliminated triexponentially from plasma. However, plasma concentrations in the patients (who were subdivided into patients with severe dysfunction, moderate dysfunction, and mild dysfunction) were consistently higher. The mean +/- SEM elimination half-life (t1/2) of pethidine was significantly longer in the three groups of renal patients: 7.9 +/- 1.1, 20.2 +/- 13.6, 16.6 +/- 5.4, and 14.3 +/- 3.1 hr, respectively, for healthy volunteers, patients with severe, moderate, and mild dysfunction; their mean +/- SEM creatinine clearances were 97.3 +/- 7.5, less than 9.5, 30.0 (3.7), and 63.3 +/- 8.5 mL/min respectively. The mean plasma clearance of the drug was higher in healthy subjects (342.7 +/- 62.5 mL/min) than various groups of renal patients (99.9 +/- 11.6, 120.9 +/- 45.8, and 123.8 +/- 34.1, respectively, for patients with severe, moderate, and mild dysfunction). Impairment of renal function also reduced total plasma protein binding: 58.2 +/- 5.0% in healthy subjects and 31.8 +/- 3.9%, 44.5 +/- 5.0%, and 42.5 +/- 5.6%, respectively, for the three renal patient groups. The percentage of pethidine recovered in the urine was significantly lower in the severe dysfunction group while norpethidine recovery was significantly lower in all three groups of renal patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic extraction of long- and short-acting narcotics in the isolated perfused rabbit liver

Hepatic extraction of the long-acting narcotic, methadone, was compared to that of the short-acting narcotics, morphine, diacetylmorphine, and meperidine, using an isolated perfused rabbit liver preparation. Methadone was avidly extracted from portal venous blood (86.1 +/- 0.81%) in a single pass through the liver after a bolus injection (1.5 mg) into a nonrecirculating perfusion system. Hepatic extraction of methadone was independent of rate of hepatic blood flow (0.59 to 1.53 ml per g of liver per min) but was altered by increasing the total amount of methadone injected. After a bolus injection of 15.0 and 75.0 mg, the proportions of methadone extracted were reduced to 75 and 56%, respectively. The hepatic extraction of morphine (1.5 mg) was 25%, of diacetylmorphine (1.5 mg) 59%, and of meperidine (1.5 mg) 66% in a single pass, all significantly lower (P less than 0.01) than that of methadone. Subcellular fractionation of whole liver homogenates after a single pass of drug showed that methadone and its metabolites were localized primarily in the fractions containing nuclei, mitochondria, microsomes, and other membranes, whereas morphine was primarily localized in the supernatant cytosol. Unchanged methadone was shown to be slowly released from the liver into hepatic effluent blood along with small amounts of the inactive pyrrolidine and pyrroline metabolites (identified by gas chromatography and mass spectrometry). These findings suggest that the liver may serve not only as a site of biotransformation of methadone, but also as a major reservoir for storage and subsequent release of unchanged compound.