Absorption characteristics of epidural levobupivacaine with adrenaline and clonidine in children

Levobupivacaine plasma concentrations following repeat caudal anesthetics

AIM

A single caudal anesthetic at the start of lower abdominal surgery is unlikely to provide prolonged analgesia. A second caudal at the end of the procedure extends the analgesia duration but total plasma concentrations may be associated with toxicity. Our aim was to measure total plasma levobupivacaine concentrations after repeat caudal anesthesia in infants and to generate a pharmacokinetic model for prediction of plasma concentrations after repeat caudal anesthesia in neonates, infants and children.

METHODS

Infants undergoing definitive repair of anorectal malformations or Hirschsprung's disease received a second caudal anesthesia at the end of the procedure. Total levobupivacaine concentrations were assayed 3-4 times in the first 6 h after the initial caudal. These data were pooled with data from four studies describing plasma concentrations after levobupivacaine caudal or spinal anesthesia. Population pharmacokinetic parameters were estimated using nonlinear mixed-effects models. Covariates included postmenstrual age and body weight. Parameter estimates were used to simulate concentrations after a repeat levobupivacaine 2.5 mg kg^-1 caudal at 3 or 4 h following an initial levobupivacaine 2.5 mg kg^-1 caudal.

RESULTS

Twenty-one infants (postnatal age 11-32 weeks, gestation 37-39 weeks, weight 5.2-8.6 kg) were included. The measured peak plasma concentration after repeat caudal levobupivacaine 2.5 mg kg^-1 4 h after initial caudal was 1.38 mg L^-1 (95% prediction interval 0.60-2.6 mg L^-1 ) and 3 h after initial caudal was 1.46 mg L^-1 (0.60-2.80) mg L^-1 . Simulation of total plasma concentrations in neonates (7 kg, 57 weeks postmenstrual age) given caudal levobupivacaine 4 h after the initial caudal were 1.76 mg L^-1 (0.68-3.50) mg L^-1 if 2.5 mg kg^-1 levobupivacaine was used and 0.88 mg L^-1 (0.34-1.73) mg L^-1 if 1.25 mg kg^-1 of 0.125% levobupivacaine was used. In simulated older children (20 kg, 6 years), the mean maximum concentration was 1.43 mg L^-1 (0.60-2.70) mg L^-1 if 2.5 mg kg^-1 levobupivacaine was repeated at 3 h.

CONCLUSION

Repeat caudal levobupivacaine 2.5 mg kg^-1 at 3 h after an initial 2.5 mg kg^-1 dose does not exceed the concentration associated with systemic local anesthetic toxicity. In 2.5% of simulated neonates (weight 3.8 kg, PMA 40 weeks), repeat caudal anesthesia demonstrates broaching of the lower concentration limit associated with toxicity at both 3 and 4 h after initial caudal.

Prediction of levobupivacaine concentrations in neonates and infants following neuraxial rescue blocks

AIM

Pharmacokinetic simulation was used to characterize levobupivacaine disposition after regional anesthetic rescue for failed spinal anesthesia in neonates and infants.

METHODS

Population pharmacokinetics of levobupivacaine were estimated after spinal blockade in a cohort of neonates and infants (n = 25, postnatal age 5-18 weeks, gestation 21-41 weeks, weight 2.4-6 kg). Total levobupivacaine concentrations were assayed 3-4 times in the first hour after spinal levobupivacaine 1 mg kg^-1 administration. Parameters were estimated using nonlinear mixed-effects models and supported by priors. Covariates included postnatal age and total body weight. Parameter estimates were used to simulate total levobupivacaine concentrations after a primary spinal levobupivacaine 1 mg kg^-1 with rescue caudal levobupivacaine 1.5-2.5 mg kg^-1 .

RESULTS

A one-compartment model with a mature clearance 21.5 L h^-1  70 kg^-1 (CV 47.3%) and central volume 189 L 70 kg^-1 (CV 37%) adequately described time-concentration profiles. Clearance maturation was described using a maturation half-time of 11.5 weeks postnatal age. The absorption half-time for spinal levobupivacaine was 2.6 min (CV 56.8%). The upper (97.5% prediction) for peak concentrations after rescue caudal levobupivacaine were 1.5 mg kg^-1 , 2 mg kg^-1 , and 2.5 mg kg^-1 was 2.05 mg L^-1 , 2.5 mg L^-1 , and 2.9 mg L^-1 respectively.

CONCLUSION

Total bupivacaine concentrations greater than 2.5 mg L^-1 are associated with neurotoxicity in adults. Predicted concentrations after either a repeat spinal or a caudal rescue dose of levobupivacaine 1.5 mg kg^-1 1 h after spinal levobupivacaine administration are below the neurotoxic concentration threshold.

Dexmedetomidine versus clonidine adjuvants to levobupivacaine for ultrasound-guided transversus abdominis plane block in paediatric laparoscopic orchiopexy: Randomized, double-blind study

BACKGROUND

Laparoscopic surgeries are associated with less postoperative pain and adverse events compared to open procedures. But, it still reduces the quality of life in children. Transversus abdominis plane (TAP) block is used to reduce pain. We hypothesized that dexmedetomidine or clonidine could improve the analgesic profile of levobupivacaine to the same extent during TAP block in children.

METHODS

Ninety children were randomly allocated in a randomized double-blind trial to receive bilateral TAP block with levobupivacaine plus normal saline (group B, n = 30), or dexmedetomidine (group D, n = 30) or clonidine (group C, n = 30). Primary outcome was the modified Children's Hospital of Eastern Ontario Pain Scale score. Secondary outcomes included time to initial analgesic request, number of analgesic claims, total analgesic consumption, parents' satisfaction, sedation score and complications.

RESULTS

Children of group D showed reduced pain scores compared to other groups. They represented the longest period of analgesia (565.00 ± 71.5 min) with p < 0.001, and fewer patients required two doses of analgesia during the first postoperative day. The cumulative amount of backup analgesia was significantly different between these groups (p = 0.026). Higher parents' satisfaction scores were recorded in groups D and C compared to group B. Sedation among the study groups revealed significant differences (p = 0.035), but no severe complications were recorded.

CONCLUSIONS

Adding dexmedetomidine to levobupivacaine can extend the time of analgesia and reduce the use of postoperative backup analgesics with minimal sedation effects when used in TAP block in paediatrics undergoing laparoscopic orchiopexy. Clonidine can be used as an alternative adjuvant to local anaesthetics with good postoperative analgesic profiles.

SIGNIFICANCE

Clonidine can alternate dexmedetomidine during TAP block with local anesthetics for pediatrics laparoscopies. Both can lead to better postoperative analgesic profiles. Clonidine may be preferred, especially in our developing regions, because of its easy availability and lower cost than that of dexmedetomidine.

Pharmacokinetics of an intravenous bolus dose of clonidine in children undergoing surgery

BACKGROUND

Clonidine is used off-label in children but only limited pediatric pharmacokinetic data are available for intravenously administered clonidine.

OBJECTIVES

To determine pharmacokinetic parameter estimates of clonidine in healthy children undergoing surgery and to investigate age-related differences. Furthermore, to investigate possible pharmacokinetic differences of clonidine between this group of children and a cohort with cardiac diseases.

METHODS

In a randomized placebo-controlled trial (The PREVENT AGITATION trial), blood samples for clonidine pharmacokinetic analysis were collected in a proportion of the enrolled patients. Healthy children with ASA score 1-2 in the age-groups 1 to <2 years and 2-5 years were randomized for blood sampling. Clonidine was administered as a single intravenous bolus of 3 µg/kg intraoperatively. Blood samples were drawn at baseline, 5, 10, 15, 30, 60 minutes after dosing and additionally every hour until discharge from the PACU. Clonidine analysis was performed on liquid chromatography-mass spectrometry.

RESULTS

Data form eighteen children were available for pharmacokinetic analysis (ASA I; male/female: 17/1; age: 1-5 years; weight 8.7-24 kg). Population parameter estimates for the 2-compartment model were similar to previous published data for children who underwent cardiac surgery. A pooled analysis including data from 59 children indicated clearance of 14.4 L h^-1  70 kg^-1 and volume of distribution of 192.6 L 70 kg^-1 . No age-related pharmacokinetic differences and no difference in time from administration of study medication to awakening were found. Children 1 to <2 years had a shorter PACU stay than children 2-5 years (mean difference 17% 95% CI:3%-34%, P = .02).

CONCLUSION

Pharmacokinetic parameter estimates were similar for children undergoing general surgery and cardiac surgery given a single dose of intravenous clonidine. These results indicated that no dose reduction is needed in children aged 1 to <2 years compared with those 2-5 years, which was supported by pharmacodynamic observations.

A study of the dosage and duration for levobupivacaine infusion by the caudal-epidural route in infants aged 3-6 months

BACKGROUND

The local anesthetic, levobupivacaine, is the safer enantiomer of racemic bupivacaine. Present protocols for levobupivacaine are based on studies and pharmacokinetic modeling with racemic bupivacaine.

AIMS

The aim is to investigate total serum levobupivacaine concentrations after a caudalepidural loading dose followed by a maintenance infusion over 48 hours in infants aged 3-6 months.

METHODS

The clinical trial was conducted in eight infants aged 3-6 months, undergoing bladder exstrophy repair. Pharmacokinetic modeling allowed optimization of clinical sampling to measure total levobupivacaine and α₁ -acid glycoprotein and prediction of the effect of α₁ -acid glycoprotein on levobupivacaine plasma protein binding.

RESULTS

The observed median total levobupivacaine serum concentration was 0.30 mg/L (range: 0.20-0.70 mg/L) at 1 hour after the loading dose of 2 mg/kg. The median total levobupivacaine concentration after 47 hours of infusion, at 0.2 mg/kg/h, was 1.21 mg/L (0.07-1.85 mg/L). Concentrations of α₁ -acid glycoprotein were found to rise throughout the study period. Pharmacokinetic modeling suggested that unbound levobupivacaine quickly reached steady state at a concentration of approximately 0.03 mg/L.

CONCLUSION

The study allows the development of a pharmacokinetic model, combining levobupivacaine and α₁ -acid glycoprotein data. Modeling indicates that unbound levobupivacaine quickly reaches steady state once the infusion is started. Simulations suggest that it may be possible to continue the infusion beyond 48 hours.

Pharmacokinetics of Lidocaine Hydrochloride Administered with or without Adrenaline for the Paravertebral Brachial Plexus Block in Dogs

Adrenaline is known to prolong the duration of local anesthesia but its effects on the pharmacokinetic processes of local anesthetic drugs are not fully understood. Our objective was to develop a compartmental model for quantification of adrenaline’s impact on the pharmacokinetics of perineurally-injected lidocaine in the dog. Dogs were subjected to paravertebral brachial plexus block using lidocaine alone or adrenalinated lidocaine. Data was collected through a prospective, randomised, blinded crossover protocol performed over three periods. Blood samples were collected during 180 minutes following block execution. Compartmental pharmacokinetic models were developed and their goodness-of-fit were compared. The lowering effects of adrenaline on the absorption of lidocaine were statistically determined with one-sided tests. A one-compartment disposition model with two successive zero-order absorption processes best fitted our experimental data. Adrenaline decreased the peak plasma lidocaine concentration by approximately 60% (P < 0.001), decreased this local anesthetic’s fast and slow zero-order absorption rates respectively by 50% and 90% (P = 0.046, and P < 0.001), which respective durations were prolonged by 90% and 1300% (P < 0.020 and P < 0.001). Lidocaine demonstrated a previously unreported atypical absorption profile following its paravertebral injection in dogs. Adrenaline decreased the absorption rate of lidocaine and prolonged the duration of its absorption.

Levobupivacaine absorption pharmacokinetics with and without epinephrine during TAP block: analysis of doses based on the associated risk of local anaesthetic toxicity

PURPOSE

Cases of local anaesthetic systemic toxicity (LAST) periodically occur following transversus abdominal plane (TAP) blocks. The aim of this study was to characterize levobupivacaine absorption pharmacokinetics, with and without epinephrine, and estimate the risk of LAST, based on a previously reported toxic threshold.

METHODS

Previously reported data from 11 volunteers receiving ultrasound-guided TAP blocks with and without epinephrine on two independent occasions were analysed. Serial venous concentrations were measured for 90 min. A pharmacokinetic analysis was performed using the NONMEM statistical programme. The use of epinephrine in the solution was included in the analysis of covariates. The associated risk of LAST symptoms associated with different levobupivacaine dose schemes with and without epinephrine was estimated in 1000 simulated subjects.

RESULTS

A one-compartment first-order input and elimination model adequately fit the levobupivacaine data. Epinephrine prolonged the levobupivacaine absorption half-life {4.22 [95 % confidence interval (CI) 2.53-6.50] vs. 7.02 [95 % CI 3.74-14.1]; p < 0.05} and reduced its relative bioavailability (0.84; 95 % CI 0.72-0.97; p < 0.05) The derived model predicts that levobupivacaine dose schemes should be halved from 3 mg kg(-1) body weight with epinephrine to 1.5 mg kg(-1) without epinephrine to obtain a comparable risk of anaesthetic toxicity symptoms of approximately 0.1 %.

CONCLUSIONS

Our results strongly support the addition of epinephrine to the local anaesthetic solution, especially when doses of levobupivacaine of >1.5 mg kg(-1) are required. Recommendations regarding the maximum allowable doses of local anaesthetics should consider population analysis to determine safer dosage ranges.