Relationship between the pharmacokinetics and the analgesic and respiratory pharmacodynamics of epidural sufentanil

Pharmacokinetics of sufentanil administered with 0.2% ropivacaine as a continuous epidural infusion for postoperative pain relief in infants

BACKGROUND AND OBJECTIVES

Our objective was to assess plasma sufentanil concentrations and postinfusion pharmacokinetics in infants receiving 0.2% ropivacaine with sufentanil as a continuous epidural infusion for postoperative pain relief.

METHODS

With consent of local ethics committee and informed parental consent, 20 infants 3-36 months old (m.o.) (median 9.3 m.o., 9.0 [3.5-15] kg, ASA PS I/II) were enrolled. Epidural catheter was placed under general anesthesia in L3-L4, L4-L5, or L2-L3 interspace and threaded not farther than 4 cm into epidural space. After initial bolus of 0.2% ropivacaine, 0.5 ml·kg(-1) and sufentanil 200 ng·kg(-1) , continuous infusion of 0.2% ropivacaine, 0.3 mg·kg(-1) ·h(-1) with sufentanil 112 ng·kg(-1) ·h(-1) was started. For the postoperative period, sufentanil dose was reduced to 37 ng·kg(-1) ·h(-1) . Blood samples were drawn at the end of surgery, 24 h later, by the end of 2nd day of infusion and after 3, 6, and 18 h from the end of infusion. Sufentanil was measured using liquid-liquid extraction (LLE) procedure and HPLC-MS/MS method with LOQ = 5 pg·ml(-1) .

RESULTS AND CONCLUSIONS

Elimination of sufentanil following epidural administration was very slow, with MRT = 28.25 [18.36-44.75] h and t1/2 MRT  = 19.57 [12.72-31.01] h. In infants, during a long-term infusion of sufentanil with ropivacaine, the opioid concentration in plasma increases during the postoperative infusion itself, then increases even further after discontinuation of the infusion, in some cases reaching the values consistent with a potential risk of respiratory depression. Meticulous monitoring of the infants' vital signs is therefore mandatory not only during the infusion, but also for several hours after its discontinuation.

Highlights in opioid agonists and antagonists

This review highlights new insights in to opioid agonists and antagonists, focusing on their mechanism of action with spinal and systemic administration, chronic use and main adverse effects. Short-cuts on some opioid agonists and antagonists of clinical interest are also presented, revealing potential clinical implications and future clinical directions as part of multimodal analgesia.

The effect of prior dural puncture on cerebrospinal fluid sufentanil concentrations in sheep after the administration of epidural sufentanil

Sufentanil is a highly lipid soluble opioid that provides potent analgesia when administered in the subarachnoid space. Unfortunately, the penetration of sufentanil into the cerebrospinal fluid (CSF) after epidural administration is poor, and limits its effectiveness for epidural analgesia. Dural puncture may enhance the movement of epidural sufentanil into the subarachnoid space and increase its effectiveness. To determine whether the administration of epidural sufentanil adjacent to a dural puncture results in significantly greater CSF concentrations, 18 adult ewes were studied. Animals in the control group had an epidural catheter placed at the superior border of the pelvis without dural puncture. Animals in the study group had an epidural catheter placed, followed by a dural puncture performed using an 18-gauge Touhy needle. The dural puncture was performed one interspace cephalad to the epidural catheter. One hour after dural puncture, each animal received a loading dose of 0.35 microg/kg of sufentanil (5 microg/mL) through the epidural catheter, followed by an infusion of epidural sufentanil 0.15 microg x kg(-1) x h(-1) for a period of 4 h. After 4 h, CSF was sampled from a site one interspace caudad to the epidural catheter as well as at the cisterna magna. The mean CSF concentration of sufentanil at the level of the pelvis for animals with a dural puncture was 12.1 +/- 3.0 ng/mL compared with 1.8 ng/mL in controls with intact dura. Sufentanil concentrations at the cisterna magna were below the level of detection (0.08 ng/mL) for all animals in both groups. We conclude that an 18-gauge dural puncture significantly increases movement of sufentanil from the epidural to the intrathecal space. This increase in sufentanil concentration at the level of the pelvis was not associated with detectable levels of sufentanil at the brainstem.

IMPLICATIONS

This study addresses the effect of dural puncture on spinal fluid concentrations of sufentanil after epidural administration. A sheep model was used to measure drug concentrations in the spinal fluid at the levels of the pelvis and brainstem after epidural administration. Dural puncture significantly enhanced movement of sufentanil into the spinal fluid at the level of the pelvis, but brainstem concentrations were below the level of detection. Analgesic concentrations of spinal sufentanil in the clinical setting, as well as brainstem concentrations associated with respiratory depression, have yet to be defined.

Pharmacotherapy of opioids: present and future developments

The clinically available opioids have different physicochemical properties, resulting in differences in clinical profile with regard to potency, onset, and duration of activity. However, they all have comparable side-effects after acute systemic application. Several approaches can be used to overcome these side-effects. The following approaches, with special emphasis on the perioperative use of the opioids, are discussed: (1) the use of alternative routes of administration, such as via the spine (epidurally and intrathecally); (2) optimization of opioid delivery by means of slow-release preparations, chronic infusions with indwelling catheters, and transdermal delivery systems; (3) use of additional agents to potentiate the analgesic properties of the opioids so that the dose of opioid can be reduced; and (4) searching for new analgesics on the basis of knowledge of the pain-transmission system and the different opioid receptors with their functional interactions.

Side effects of intrathecal and epidural opioids

The purpose of this article is to review the literature on the side effects of intrathecal and epidural opioids. English-language articles were identified through a MEDLINE search and through review of the bibliographies of identified articles. With the increasing utilization of intrathecal and epidural opioids in humans during the 1980s, a wide variety of clinically relevant side effects have been reported. The four classic side effects are pruritus, nausea and vomiting, urinary retention, and respiratory depression. Numerous other side effects have also been described. Most side effects are dose-dependent and may be more common if the opioid is administered intrathecally. Side effects are less common in patients chronically exposed to either intrathecal, epidural, or systemic opioids. Some side effects are mediated via interaction with specific opioid receptors while others are not. It is concluded that the introduction of intrathecal and epidural opioids marks one of the most important breakthroughs in pain management in the last two decades. However, a wide variety of clinically relevant non-nociceptive side effects may occur. All physicians utilizing intrathecal and epidural opioids must be aware of these side effects, for while most are minor, others are potentially lethal.

The effect of epidural administration of alfentanil on intra-operative intravenous alfentanil requirements during nitrous oxide-oxygen-alfentanil anaesthesia for lower abdominal surgery

The effects of epidural administration of alfentanil on the intravenous alfentanil dose requirements and the plasma concentrations required to suppress responses to surgical stimulation during nitrous oxide-oxygen-alfentanil anaesthesia in 20 patients undergoing lower abdominal surgery were studied. Before induction of anaesthesia, patients in one group (E) received an epidural injection of 1 mg alfentanil, followed by an epidural infusion of alfentanil 0.2 mg.h-1 until skin closure, whilst patients in the other group (C, control) received a continuous infusion of sodium chloride via a sham catheter in order to blind the main investigator to the treatment. Anaesthesia was induced and maintained with nitrous oxide (66%) in oxygen and a 'target'-controlled intravenous infusion of alfentanil. During surgery, the 'target' alfentanil concentration was increased or decreased according to patients' responses. The number of responses to surgical stimulation was smaller in patients from group E (median 1, range 0-3) than in patients from group C (median 4, range 1-15; p < 0.005), even though the alfentanil intravenous infusion rates were smaller in group E [mean (SD): 1.6(0.5) micrograms.kg-1 min-1] than in group C [2.9(1.2) micrograms.kg-1 min-1, p < 0.02]. Both the lowest concentrations associated with no response [133(40) ng.ml-1] and the highest concentrations associated with a response [155(65) ng.ml-1] in group E were lower than those in group C [238(100) ng.ml-1, p < 0.01 and 334(163) ng.ml-1, p < 0.05, respectively]. We concluded that epidural administration of alfentanil reduces intravenous alfentanil requirements during nitrous oxide-oxygen-alfentanil anaesthesia for lower abdominal surgery. The results indicate a spinal mechanism of action of epidural alfentanil.

Efficacy of epidurally administered sufentanil versus bupivacaine during thoracic surgery. A randomised placebo-controlled double-blind study

The efficacy of thoracic epidural sufentanil 50 micrograms was compared with bupivacaine 0.5% with adrenaline 5 micrograms.ml-1 (dose 40 mg) or saline, in 30 patients (n = 10 in each group) undergoing lateral thoracotomy. Sufentanil, bupivacaine or saline was administered epidurally after induction of anaesthesia with sufentanil 1 microgram.kg-1 and thiopentone 2-5 mg.kg-1. Anaesthesia was maintained with nitrous oxide 66% and halothane 0.3%. Supplementary sufentanil 25 micrograms was given whenever the systolic arterial blood pressure increased more than 15 mmHg above the pre-operative value, whenever heart rate exceeded 90 beat.min-1 in the absence of hypovolaemia, or when other autonomic or somatic signs occurred. Fewer patients in the epidural sufentanil (n = 4, p < 0.005) and bupivacaine (n = 1, p < 0.001) groups required supplementary sufentanil compared to the placebo group, in which all patients needed supplementary sufentanil, but there was no statistical difference between the sufentanil and bupivacaine groups. One or more hypotensive episodes occurred in five patients in the sufentanil group, in all patients in the bupivacaine group and in no patient in the placebo group, and the differences were significant (p < 0.02).

An intra-operative comparison of lumbar with thoracic epidural sufentanil for thoracotomy

The efficacy of thoracic epidural sufentanil 50 micrograms was compared with lumbar epidural sufentanil 50 micrograms in 30 patients (n = 15 in each group) undergoing lateral thoracotomy. Sufentanil was administered epidurally after induction of anaesthesia with sufentanil 1 microgram.kg-1 and thiopentone 2-5 mg.kg-1 intravenously. Anaesthesia, nitrous oxide 66%, halothane 0.3% and sufentanil 25 micrograms intravenously were given whenever the systolic arterial blood pressure increased more than 15 mmHg above the preoperative value and heart rate exceeded 90 beat.min-1 in the absence of hypovolaemia, or when other autonomic or somatic signs were seen. Four patients in the thoracic epidural group and five in the lumbar epidural group needed supplementary sufentanil. Six patients in the thoracic epidural group and three in the lumbar epidural group each had a single hypotensive episode. Lumbar and thoracic epidural sufentanil are equally effective in contributing to intra-operative analgesia for lateral thoracotomy.

Comparative absorption and distribution pharmacokinetics of intravenous and epidural sufentanil for major abdominal surgery

The pharmacokinetics of absorption and distribution of a single bolus dose of sufentanil 150 micrograms for major abdominal surgery were compared in 20 patients after random intravenous or epidural administration. Samples of plasma and cerebrospinal fluid were taken at regular intervals from time zero to 180 min after injection and at the time of tracheal extubation (3.43 to 12.66h). Sufentanil was analysed by radioimmunoassay. The area under the concentration-time curve (AUC) from zero to 1h, 2h, 3h, tracheal extubation and infinity, the absorption and distribution half-lives, maximum plasma and CSF concentrations, time to the peak concentration of sufentanil, and the fraction of sufentanil that reached the central circulation after epidural administration were assessed. Except in the first sample, plasma concentrations of sufentanil were comparable between the 2 groups. The initial transfer of sufentanil from the epidural space to the systemic circulation appeared to be very rapid. Explanations for this phenomenon are given. In only 3 patients could an uptake of sufentanil from the systemic circulation into the CSF be demonstrated. The transfer of sufentanil from the epidural space into the CSF is slower than the transfer into the plasma and it varied interindividually.

Pharmacokinetics of clonidine after epidural administration in surgical patients. Lack of correlation between plasma concentration and analgesia and blood pressure changes

The pharmacokinetics of epidural clonidine 150 micrograms was studied in 13 patients who had undergone abdominal hysterectomy. Plasma clonidine concentrations were measured up to 19 h in eight patients. In another five patients frequent blood sampling was performed only during the first 20 min to define early vascular uptake better. Peak plasma clonidine concentrations of 1.08 +/- 0.35 ng ml-1 (mean +/- s.d.) were reached between 5 and 10 min after injection. Plasma elimination half-life was 829 +/- 157 min and plasma clearance was 177 +/- 28 ml min-1. There was a significant decrease in arterial blood pressure within 10 min of the injection of clonidine. The maximum decrease in systolic blood pressure, from a pre-injection value of 135 +/- 24.7 to 99 +/- 14.4 mmHg (18.0 +/- 3.3 to 13.2 +/- 1.9 kPa), occurred at 60 min. Blood pressure remained significantly lower than the pre-injection value for 4 h. There was no change in heart rate. Verbal analogue pain scores, on a scale 0-10, decreased from a median of 7.6 before clonidine to 5.0 after 30 min (P less than 0.05). The median score at 60 min was 4.3. Thereafter, pain scores were not significantly different from the control score. We conclude that epidural clonidine 150 micrograms produces only moderate and short-lived postoperative analgesia. Absorption of clonidine from the epidural space into the blood is very rapid and may contribute to the hypotension that occurs.