Cerebrospinal fluid pharmacokinetics of paracetamol after intravenous propacetamol in a former preterm infant

The paracetamol concentration-effect relation in neonates

OBJECTIVES

We suggested a loading dose (20 mg · kg(-1) ) followed by 10 mg · kg(-1) q6h of intravenous (IV) paracetamol to achieve an effect compartment concentration of 11 mg · l(-1) in neonates. Since there are no pharmacodynamic data to support such an effect compartment concentration, pain scores collected in neonates treated with an IV paracetamol loading dose (20 mg · kg(-1) ) were used to validate this effect compartment concentration.

METHODS

Pain scores (Leuven Neonatal Pain Score, LNPS, 0-14) before and 0.5, 1, 2, 3, 4, 5, and 6 h after IV paracetamol loading dose administration in neonates to whom IV paracetamol was administered as single analgesic (PARANEO, www.clinicaltrials.gov, NCT00969176) were collected. Trends were analyzed using repeated measures anova. An E(max) model with a delayed response compartment was fitted to data using population modeling.

RESULTS

Nineteen of 60 neonates included in the PARANEO study received monotherapy with IV paracetamol to treat mild to moderate pain (e.g., alprostadil administration, delivery related trauma). Using repeated measures anova, there was a trend (P = 0.02) for lower pain scores within 30 min after administration, with a slight increase in pain scores from 5 to 6 h. An E(max) model had a maximum effect of 4.15 pain units, an EC(50) of 2.07 mg · l(-1). Equilibration halftime (T(1/2) keo) was 1.58 h.

CONCLUSION

Intravenous paracetamol is effective for moderate pain. An effect compartment concentration of 10 mg · l(-1) (loading dose of 20 mg · kg(-1) ) is associated with a pain score reduction of 3.4 LNPS units. This analysis suggests a similar paracetamol effect compartment concentration in neonates compared to children.

Survey of i.v. paracetamol (acetaminophen) use in neonates and infants under 1 year of age by UK anesthetists

BACKGROUND

The license for i.v. paracetamol has recently been extended to include term neonates and infants aged 1 year, at a uniform dose across this age range of 7.5 mg.kg(-1), total daily dose 30 mg.kg(-1).day(-1). We were interested to survey current i.v. paracetamol prescribing practices of anesthetists in the UK, in neonates and infants under 1 year of age.

METHODS

We conducted an online survey of 94 linkmen of the Association of Pediatric Anesthetists of Great Britain and Ireland Linkmen representing both general and specialist hospitals and 90 members of the British Pediatric Pain Travelling Club representing the pediatric acute pain teams throughout the UK and Ireland.

RESULTS

A total of 105/184 (57%) responded to the survey on behalf of 78 regions and 27 pediatric acute pain teams. Over half (54%) of the respondents indicated i.v. paracetamol use in infants under 1 year of age. A wide range of loading and maintenance doses were used. Total daily doses exceeded the license for age 1-12 months in 70% of cases; for the 36 week postconceptional age (PCA)-1 month age range the proportion was 50%. Over 80% of total daily dosing from age 36 weeks PCA to 1 year fell within dosing suggested by pharmacokinetic studies. Close to 40% of respondents who used i.v. paracetamol in infants, also indicated use in preterm age groups. The total daily dose used in preterm neonates was within the range suggested by pharmacokinetic studies, in over 90% of cases in the age range 32-36 weeks PCA, and for 60% in the under 32 weeks PCA age group.

CONCLUSIONS

This survey demonstrates i.v. paracetamol dosing in infants in the UK and Ireland is frequently above the licensed dose and outside the licensed age range but is in keeping with doses suggested by pharmacokinetic studies.

Recent pharmacological advances in paediatric analgesics

Growth and development are two linked processes that distinguish children from adults. The use of size as the primary covariate during pharmacokinetic (PK) analyses allows exploration of the effects of age. Allometric scaling models have assisted understanding of the developmental clearance changes in common analgesic drugs such as paracetamol, morphine, tramadol and local anaesthetics agents. Single nucleotide polymorphisms (pharmacogenomics [PG]) and their impact on hepatic drug metabolism for opioids, tramadol, non-steroidal anti-inflammatory drugs (NSAIDs) and drug receptor responses are increasingly reported. Altered chemical structure or formulations of common analgesics alter pharmacodynamic (PD) effects enhancing safety and efficacy for NSAIDs by stereoselectivity and the addition of nitric oxide, for intravenous paracetamol by formulation and structural difference from propacetamol and for local anaesthetics through stereoselectivity. This article focuses upon recent data for analgesics used in paediatric pain management including paracetamol, NSAIDs, morphine, tramadol, amide local anaesthetics and ketamine. It centres on PK and clinical studies in neonates, infants and children. PG studies are acknowledged as potentially allowing individual drug therapy tailoring through a decrease in between-patient population variability, although the impact of PG in the very young is less certain. There are few data describing age-related PD changes in children despite recognition that the number, affinity and type of receptors or the availability of natural ligands changes with age.

Recent developments in the pharmacological management of pain in children

PURPOSE OF REVIEW

This review explores progress in developmental pharmacokinetics, pharmacogenomics and formulations of analgesic agents, and discusses potential implications for pain therapy.

RECENT FINDINGS

Characterization of the developmental pharmacokinetics of morphine, tramadol, paracetamol and nonsteroidal anti-inflammatory drugs has improved dosing in children. Oral sugar solutions have replaced the brandy/sugar pacifier and are effective for single painful events in neonates. Intravenous paracetamol offers increased dosing accuracy, and avoids absorption and bioavailability variability. New nitric-oxide-releasing versions of paracetamol and nonsteroidal anti-inflammatory drugs offer safer alternatives to their parent drugs with enhanced potency. Ketamine has come under a cloud for its possible effects on the neonatal developing brain, but it is being used increasingly in children to supplement opioids for pain after major surgery. Hopes that morphine analgesia may improve neurological outcome in premature babies have not materialized. Reports concerning chronic pain are generally case series and controlled trials are rare and nearly nonexistent in children.

SUMMARY

Unlicensed drug use in the very young will increase as familiarity increases. Pharmacogenomic studies have the potential to tailor drug therapy to the individual and decrease between-patient variability. Unfortunately, the pharmacodynamic knowledge in children of analgesic agents remains neglected and is usually extrapolated from adult data.

Anesthesia and analgesia during and after surgery in neonates

BACKGROUND

Historically, the use of anesthetics and analgesics in neonates and infants has been based on extrapolations from studies performed in adults and older children. Over the past 20 years, there has been a growing body of research on the clinical pharmacology and clinical outcomes of these agents in neonates and infants.

OBJECTIVE

This article summarizes clinical pharmacology and clinical outcomes studies of opioids, opioid antagonists, sedative-hypnotics, nonsteroidal anti-inflammatory drugs and acetaminophen, and local anesthetics in neonates and infants to highlight gaps in the available knowledge, review some concerns about study design, and identify drugs that should receive high priority for future study.

METHODS

Relevant studies were identified through a search of MEDLINE and a review of textbooks, conference proceedings, and abstracts. The available literature was subjected to expert committee-based review.

CONCLUSIONS

There is a growing body of information on analgesic and anesthetic pharmacokinetics, pharmacodynamics, and clinical outcomes in neonates and infants, permitting safe and effective use in some clinical settings. Major gaps in knowledge persist, however. Future research may involve a combination of clinical trials and preclinical studies in suitable infant animal surrogate models.

Tramadol concentrations in blood and in cerebrospinal fluid in a neonate

Based on blood and cerebrospinal fluid samples collected in a full-term neonate, the penetration of tramadol in the central nervous system is described. Following intravenous administration of tramadol, a lag time of about 4 h was observed until full blood-brain equilibration was achieved. This pharmacokinetic observation is in line with a recent pharmacodynamic evaluation of the central opioid effects of tramadol in adults.