Clinical pharmacokinetics and pharmacodynamics of opioid analgesics in infants and children

Potential implications of DMET ontogeny on the disposition of commonly prescribed drugs in neonatal and pediatric intensive care units

Introduction: Pediatric patients, especially neonates and infants, are more susceptible to adverse drug events as compared to adults. In particular, immature small molecule drug metabolism and excretion can result in higher incidences of pediatric toxicity than adults if the pediatric dose is not adjusted.Area covered: We reviewed the top 29 small molecule drugs prescribed in neonatal and pediatric intensive care units and compiled the mechanisms of their metabolism and excretion. The ontogeny of Phase I and II drug metabolizing enzymes and transporters (DMETs), particularly relevant to these drugs, are summarized. The potential effects of DMET ontogeny on the metabolism and excretion of the top pediatric drugs were predicted. The current regulatory requirements and recommendations regarding safe and effective use of drugs in children are discussed. A few representative examples of the use of ontogeny-informed physiologically based pharmacokinetic (PBPK) models are highlighted.Expert opinion: Empirical prediction of pediatric drug dosing based on body weight or body-surface area from the adult parameters can be inaccurate because DMETs are not mature in children and the age-dependent maturation of these proteins is different. Ontogeny-informed-PBPK modeling provides a better alternative to predict the pharmacokinetics of drugs in children.

Opioid-Induced Respiratory Depression in Pediatric Palliative Care Patients with Severe Neurological Impairment-A Scoping Literature Review and Case Reports

Pediatric Palliative Care (PPC) addresses children, adolescents, and young adults with a broad spectrum of underlying diseases. A substantial proportion of these patients have irreversible conditions accompanied by Severe Neurological Impairment (SNI). For the treatment of pain and dyspnea, strong opioids are widely used in PPC. Nonetheless, there is considerable uncertainty regarding the opioid-related side effects in pediatric patients with SNI, particularly concerning Opioid-Induced Respiratory Depression (OIRD). Research on pain and OIRD in pediatric patients with SNI is limited. Using scoping review methodology, we performed a systematic literature search for OIRD in pediatric patients with SNI. Out of n = 521 identified articles, n = 6 studies were included in the review. Most studies examined the effects of short-term intravenous opioid therapy. The incidence of OIRD varied between 0.13% and 4.6%; besides SNI, comorbidities, and polypharmacy were the most relevant risk factors. Additionally, three clinical cases of OIRD in PPC patients receiving oral or transdermal opioids are presented and discussed. The case reports indicate that the risk factors identified in the scoping review also apply to adolescents and young adults with SNI receiving low-dose oral or transdermal opioid therapy. However, the risk of OIRD should never be a barrier to adequate symptom relief. We recommend careful consideration and systematic observation of opioid therapy in this population of patients.

Pharmacokinetics of Fentanyl and Its Derivatives in Children: A Comprehensive Review

Fentanyl and its derivatives sufentanil, alfentanil, and remifentanil are potent opioids. A comprehensive review of the use of fentanyl and its derivatives in the pediatric population was performed using the National Library of Medicine PubMed. Studies were included if they contained original pharmacokinetic parameters or models using established routes of administration in patients younger than 18 years of age. Of 372 retrieved articles, 44 eligible pharmacokinetic studies contained data of 821 patients younger than 18 years of age, including more than 46 preterm infants, 64 full-term neonates, 115 infants/toddlers, 188 children, and 28 adolescents. Underlying diagnoses included congenital heart and pulmonary disease and abdominal disorders. Routes of drug administration were intravenous, epidural, oral-transmucosal, intranasal, and transdermal. Despite extensive use in daily clinical practice, few studies have been performed. Preterm and term infants have lower clearance and protein binding. Pharmacokinetics was not altered by chronic renal or hepatic disease. Analyses of the pooled individual patients' data revealed that clearance maturation relating to body weight could be best described by the Hill function for sufentanil (R ² = 0.71, B _max 876 mL/min, K ₅₀ 16.3 kg) and alfentanil (R ² = 0.70, B _{max (fixed)} 420 mL/min, K ₅₀ 28 kg). The allometric exponent for estimation of clearance of sufentanil was 0.99 and 0.75 for alfentanil clearance. Maturation of remifentanil clearance was described by linear regression to bodyweight (R ² = 0.69). The allometric exponent for estimation of remifentanil clearance was 0.76. For fentanyl, linear regression showed only a weak correlation between clearance and bodyweight in preterm and term neonates (R ² = 0.22) owing to a lack of data in older age groups. A large heterogeneity regarding study design, clinical setting, drug administration, laboratory assays, and pharmacokinetic estimation was observed between studies introducing bias into the analyses performed in this review. A limitation of this review is that pharmacokinetic data, based on different modes of administration, dosing schemes, and parameter estimation methods, were combined.

Regional anesthesia for sternotomy and bypass-Beyond the epidural

Systemic opioids have been the main stay for the management of perioperative pain in children undergoing cardiac surgery with sternotomy. The location, distribution, and duration of pain in these children have not been studied as extensively as in adults. Currently, there is no consensus to the dose of opioids required to provide optimum analgesia and attenuate the stress response while minimizing their unwanted side effects. At present there is a tendency to use lower dose aiming for early extubation and minimize opioid-related side effects, but this may not obtund the stress response in all children. The development of chronic pain although rare when compared to adults is still a risk that needs further investigation. Regional anesthetic techniques, by blocking the afferent impulses, have been shown to be advantageous in reducing the stress response to surgery as well as pain and opioid requirements in children up to 24 hours after cardiac surgery. Central neuraxial blockades have not gained wide spread acceptance in these procedures due to the worry of hematoma, although rare, leading to catastrophic neurological outcomes. This review focuses on blocks outside the vertebral column, ie, peripheral nerve blocks, performed either in the front or the back of the chest wall to target the thoracic intercostal nerves. Techniques of ultrasound-guided bilateral single shot paravertebral block and erector spinae block posteriorly and transversus thoracic plane block anteriorly are discussed. In addition, parasternal block and wound infiltration by surgeon as well as continuous local anesthetic infusion via catheters placed at end of procedures are summarized. Current evidence available for use of these techniques in children undergoing cardiac surgery are reviewed. These are based on small studies and case series and further studies are required to evaluate the risks and benefits of local anesthetic blocks in children undergoing cardiac surgery.

Continuing war on pain: a personalized approach to the therapy with nonsteroidal anti-inflammatory drugs and opioids

Successful pain management requires the delivery of analgesia with minimal risk of adverse drug reactions. Nonsteroidal anti-inflammatory drugs and opioids remain the mainstay of treatment for the majority of patients. Unfortunately, almost 50% of all patients experience inadequate pain relief and serious side effects. Allelic variants in genes coding for target proteins, transporters and enzymes, which govern analgesic drugs action and their fate in the organism, might explain inter-individual variability in pain severity and in drug-induced pain relief and toxicities. Additionally, it seems that epigenetic changes contribute to the highly variable response to pain treatment. Therefore, pharmacogenomic testing might be a valuable tool for personalization of pain treatment, with a multidisciplinary team approach involved.

Shortened Taper Duration after Implementation of a Standardized Protocol for Iatrogenic Benzodiazepine and Opioid Withdrawal in Pediatric Patients: Results of a Cohort Study

Supplemental Digital Content is available in the text.

Introduction:

Methadone and lorazepam prescribing discrepancies for the use of iatrogenic withdrawal were observed among providers. A standardized pharmacist-managed methadone and lorazepam taper protocol was implemented at a pediatric tertiary care facility with the aim to reduce the length of taper for patients with iatrogenic withdrawal.

Methods:

A multidisciplinary team of nurses, pharmacists, and physicians reviewed the current literature, then developed and implemented a standardized withdrawal taper protocol. Outcomes were compared with a retrospective control group using past prescribing practices. The primary endpoint was the length of methadone and/or lorazepam taper. Secondary endpoints included evaluation for significant differences between the control and standardized protocol groups regarding additional breakthrough withdrawal medications, pediatric intensive care unit (PICU) and hospital length of stay. We also evaluated provider satisfaction with the protocol.

Results:

The standardized protocol group included 25 patients who received methadone and/or lorazepam taper. A retrospective control group contained 24 patients. Median methadone taper length before protocol implementation was 9.5 days with an interquartile range (IQR) of 5.5–14.5 days; after protocol implementation, it was 6.0 (IQR, 3.0–9.0) days (P = 0.0145). Median lorazepam taper length before protocol implementation was 13.0 (IQR, 8.0–18.0) days; after protocol implementation, it was 6.0 (4.0–7.0) days (P = 0.0006). A statistical difference between PICU length of stay, hospital length of stay, or the number of additional medications for breakthrough withdrawal was not found.

Conclusions:

The use of a standardized withdrawal protocol resulted in shorter taper duration for both the methadone and lorazepam groups. There was no difference in PICU or hospital length of stay.

Correction to: Pharmacokinetics of Fentanyl and Its Derivatives in Children: A Comprehensive Review

Fentanyl and its derivatives sufentanil, alfentanil, and remifentanil are potent opioids. A comprehensive review of the use of fentanyl and its derivatives in the pediatric population was performed using the National Library of Medicine PubMed. Studies were included if they contained original pharmacokinetic parameters or models using established routes of administration in patients younger than 18 years of age. Of 372 retrieved articles, 44 eligible pharmacokinetic studies contained data of 821 patients younger than 18 years of age, including more than 46 preterm infants, 64 full-term neonates, 115 infants/toddlers, 188 children, and 28 adolescents. Underlying diagnoses included congenital heart and pulmonary disease and abdominal disorders. Routes of drug administration were intravenous, epidural, oral-transmucosal, intranasal, and transdermal. Despite extensive use in daily clinical practice, few studies have been performed. Preterm and term infants have lower clearance and protein binding. Pharmacokinetics was not altered by chronic renal or hepatic disease. Analyses of the pooled individual patients' data revealed that clearance maturation relating to body weight could be best described by the Hill function for sufentanil (R ² = 0.71, B _max 876 mL/min, K ₅₀ 16.3 kg) and alfentanil (R ² = 0.70, B _{max (fixed)} 420 mL/min, K ₅₀ 28 kg). The allometric exponent for estimation of clearance of sufentanil was 0.99 and 0.75 for alfentanil clearance. Maturation of remifentanil clearance was described by linear regression to bodyweight (R ² = 0.69). The allometric exponent for estimation of remifentanil clearance was 0.76. For fentanyl, linear regression showed only a weak correlation between clearance and bodyweight in preterm and term neonates (R ² = 0.22) owing to a lack of data in older age groups. A large heterogeneity regarding study design, clinical setting, drug administration, laboratory assays, and pharmacokinetic estimation was observed between studies introducing bias into the analyses performed in this review. A limitation of this review is that pharmacokinetic data, based on different modes of administration, dosing schemes, and parameter estimation methods, were combined.

Clinical pharmacology of analgosedatives in neonates: ways to improve their safe and effective use

OBJECTIVES

To propose approaches tailored to the specific needs of neonates, such as structured product development programmes, with the ultimate goal to improve the safe and effective use of analgosedatives in these fragile patients.

KEY FINDINGS

The feasibility and relevance of a structured product development programme in neonates (optimal study design based on preliminary data; model development; internal, external and prospective evaluation; an individualized dosing regimen; long-term safety; pharmacogenetics) are illustrated for the use of morphine. Based on changes in clinical practices, similar development plans are in progress for short-acting analgosedatives such as propofol, but are in need of tailored pharmacodynamic tools to assess and quantify effects. Furthermore, for drugs like paracetamol where there is already sufficient clinical pharmacology knowledge, attention needs to be given to long-term safety aspects. Finally, new covariates such as pharmacogenetics might further improve neonatal pain management, but clearly need to be integrated with other well-established covariates like age or weight.

SUMMARY

Product development programmes for analgosedatives in neonates are needed. These programmes should be tailored to their specific needs (short-acting sedation, pain relief), should include long-term safety and should incorporate the exploration of newer covariates like pharmacogenetics.

Effectiveness of a clinical pathway with methadone treatment protocol for treatment of neonatal abstinence syndrome following in utero drug exposure to substances of abuse*

OBJECTIVE

To evaluate the effectiveness of methadone for the treatment of neonatal abstinence syndrome when used according to a preexisting clinical pathway.

DESIGN

This is a 3-year retrospective study conducted at a single institution. In this study, neonates who received methadone for the treatment of neonatal abstinence syndrome according to a predefined clinical treatment pathway were evaluated for treatment success: defined as adherence to the methadone regimen with no residual signs of withdrawal. Data were collected for methadone dosages, Lipsitz scores, length of methadone treatment, total length of hospital stay, and relevant clinical data.

SETTING

Level III neonatal ICU.

PATIENTS

Newborn infants with in utero exposure to substances of abuse.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Sixty patients were included. The mean gestational age and birth weight were 37.07 ± 3.05 weeks and 2.77 ± 0.6 kg. All 60 patients exhibited neonatal abstinence syndrome within first 72 hours of life. Fifty-seven of 60 patients (95%) initiated methadone treatment according to protocol. There was deviation from the protocol at 48 and 72 hours of treatment with approximately 59% and 13% of the patients still on methadone at more than the prescribed amount to control neonatal abstinence syndrome. The mean ± SD total methadone exposure was 1.99 ± 1.63 mg/kg, length of treatment 11.66 ± 9.02 days, and total hospital length of stay 22.43 ± 29.3 days, suggesting significant variability in response. No significant correlation was found between birth weight or gestational age and length of treatment.

CONCLUSION

Clinical pathway for treating neonatal abstinence syndrome was closely followed at the initial diagnosis. The doses of methadone used in the first 24-48 hours of this study were insufficient for adequate symptom control. Despite a formal treatment protocol, there was substantial variability in total methadone exposure, length of treatment, and length of stay, suggesting other contributory factors for the observed variability.

Chemotherapy in newborns and preterm babies

The determination of appropriate dosing regimens for the treatment of infants and very young children with cancer represents a major challenge in paediatric oncology. Whereas dose reductions are commonplace for many chemotherapeutics in this patient group, the appropriateness of dose reductions for drugs is unclear when the limited number of published studies reporting on pharmacokinetics in infant patient populations are considered. Developmental physiological changes, potentially impacting significantly on drug disposition, occur throughout childhood, with a number of important changes observed within the first few weeks from birth. The current review focuses on the developmental physiology of preterm babies and infants and the potential impact of physiological changes on drug disposition, clinical response and toxicity. Dose reductions for a number of important anticancer drugs are compared between tumour types and clinical protocols. Where data exist, differences in pharmacokinetics between infants and older children are highlighted. In addition, the impact of confounding factors relating to the availability of appropriate drug formulations and ethical challenges concerning the conduct of clinical pharmacology studies in infant patient populations are addressed. As many currently used drugs are highly likely to be important in the treatment of cancer in infants and young children for the foreseeable future, it would seem advantageous for appropriately planned population pharmacokinetic studies to be carried out in this patient population.

Opioid analgesia in the newborn

Pain in neonates is now well established. Studies of the developmental neurobiology of pain have revealed that pain processing in the immature is very different from that in the mature nervous system. Neonates undergo considerable maturation of peripheral, spinal and supraspinal afferent pain transmission over the early postnatal period but are able to respond to tissue injury with specific behaviour and with autonomic, hormonal and metabolic signs of stress and distress. Opioid analgesia is now widely used in neonates. There is evidence that morphine requirements may be low in the youngest patients. Sensory threshold testing in rat pups has shown that the analgesic potency of systemic morphine mechanical stimulation is significantly greater in the neonate and declines with postnatal age. The changing morphine sensitivity in the postnatal period may be part of a general reorganisation in the structure and function of primary afferent synapses, neurotransmitter/receptor expression and function and excitatory and inhibitory modulation from higher brain centres. Importantly opioid receptor expression undergoes significant developmental regulation - mu opioid receptors, observed to be exuberantly expressed in the neonatal rat, have been found to be functional. These findings have important implications for the human neonate as they provide a possible explanation for the differences in morphine requirements observed in the youngest patients. The study of the underlying mechanisms of pain and analgesia in development has enabled important changes in clinical practice. However, pain in the newborn remains poorly understood and continued research and intensive study in this area is essential for further effective analgesic intervention and the discovery of new targets for therapy.

Parenteral opioids in emergency medicine - A systematic review of efficacy and safety

Introduction and aim Pain is a frequent symptom in emergency patients and opioids are commonly used to treat it at emergency departments and at pre-hospital settings. The aim of this systematic review is to examine the efficacy and safety of parenteral opioids used for acute pain in emergency medicine. Method Qualitative review of randomized controlled trials (RCTs) on parenteral opioids for acute pain in adult emergency patients. Main outcome measures were: type and dose of the opioid, analgesic efficacy as compared to either placebo or another opioid and adverse effects. Results Twenty double-blind RCTs with results on 2322 patients were included. Seven studies were placebo controlled. Majority of studies were performed in the emergency department. Only five studies were in prehospital setting. Prehospital studies Four studies were on mainly trauma-related pain, one ischemic chest pain. One study compared two different doses of morphine in mainly trauma pain showing faster analgesia with the larger dose but no difference at 30 min postdrug. Three other studies on the same pain model showed equal analgesic effects with morphine and other opioids. Alfentanil was more effective than morphine in ischemic chest pain. Emergency department studies Pain models used were acute abdominal pain seven, renal colic four, mixed (mainly abdominal pain) three and trauma pain one study. Five studies compared morphine to placebo in acute abdominal pain and in all studies morphine was more effective than placebo. In four out of five studies on acute abdominal pain morphine did not change diagnostic accuracy, clinical or radiological findings. Most commonly used morphine dose in the emergency department was 0.1 mg/kg (five studies). Other opioids showed analgesic effect comparable to morphine. Adverse effects Recording and reporting of adverse effects was very variable. Vital signs were recorded in 15 of the 20 studies (including all prehospital studies). Incidence of adverse effects in the opioid groups was 5-38% of the patients in the prehospital setting and 4-46% of the patients in the emergency department. Nausea or vomiting was reported in 11-25% of the patients given opioids. Study drug was discontinued because of adverse effects five patients (one placebo, two sufentanil, two morphine). Eight studies commented on administration of naloxone for reversal of opioid effects. One patient out of 1266 was given naloxone for drowsiness. Ventilatory depression defined by variable criteria occurred in occurred in 7 out of 756 emergency department patients. Conclusion Evidence for selection of optimal opioid and dose is scarce. Opioids, especially morphine, are effective in relieving acute pain also in emergency medicine patients. Studies so far are small and reporting of adverse effects is very variable. Therefore the safety of different opioids and doses remains to be studied. Also the optimal titration regimens need to be evaluated in future studies. The prevention and treatment of opioid-induced nausea and vomiting is an important clinical consideration that requires further clinical and scientific attention in this patient group.

Buprenorphine TTS for children--a review of the drug's clinical pharmacology

OBJECTIVE

The transdermal therapeutic system (TTS) with buprenorphine is currently being used 'off-label' to treat chronic pediatric pain. We compiled available pharmacokinetic (PK), pharmacodynamic (PD), and clinical pediatric data on buprenorphine to rationalize treatment regimens.

METHODS

We conducted a systematic biomedical literature review focusing on pediatric buprenorphine data.

RESULTS

There are few relevant pediatric buprenorphine data, particularly in children suffering chronic pain. There are no pediatric PK and PD data for children with chronic pain given sublingual or TTS formulations. Children given single dose buprenorphine have increased drug clearance referenced to bodyweight with a possible paradoxical longer duration of action. Buprenorphine metabolism is independent of renal function, which is advantageous in renal insufficiency. The risk of respiratory depression after buprenorphine is difficult to quantify. A concentration-response relationship for respiratory effects has not been described and it is unknown whether children have a ceiling effect similar to that described in healthy adult volunteers.

CONCLUSIONS

Buprenorphine is of interest in pediatric postoperative pain and cancer pain control because of its multiple administration routes, long duration of action, and metabolism largely independent of renal function. There is little reason to expect buprenorphine effects in children out of infancy are fundamentally different to those in adults. From the limited pediatric data available, it appears that buprenorphine has no higher adverse potential than the more commonly used opioids. There is an urgent need for focused PK, PD, and safety studies in children before use in children becomes more widespread.

Tolerance and withdrawal from prolonged opioid use in critically ill children

OBJECTIVE

After prolonged opioid exposure, children develop opioid-induced hyperalgesia, tolerance, and withdrawal. Strategies for prevention and management should be based on the mechanisms of opioid tolerance and withdrawal.

PATIENTS AND METHODS

Relevant manuscripts published in the English language were searched in Medline by using search terms "opioid," "opiate," "sedation," "analgesia," "child," "infant-newborn," "tolerance," "dependency," "withdrawal," "analgesic," "receptor," and "individual opioid drugs." Clinical and preclinical studies were reviewed for data synthesis.

RESULTS

Mechanisms of opioid-induced hyperalgesia and tolerance suggest important drug- and patient-related risk factors that lead to tolerance and withdrawal. Opioid tolerance occurs earlier in the younger age groups, develops commonly during critical illness, and results more frequently from prolonged intravenous infusions of short-acting opioids. Treatment options include slowly tapering opioid doses, switching to longer-acting opioids, or specifically treating the symptoms of opioid withdrawal. Novel therapies may also include blocking the mechanisms of opioid tolerance, which would enhance the safety and effectiveness of opioid analgesia.

CONCLUSIONS

Opioid tolerance and withdrawal occur frequently in critically ill children. Novel insights into opioid receptor physiology and cellular biochemical changes will inform scientific approaches for the use of opioid analgesia and the prevention of opioid tolerance and withdrawal.

Disposition of morphine in plasma and cerebrospinal fluid varies during neonatal development in pigs

The pharmacological effects of morphine are mediated via the central nervous system (CNS) but its clearance from the CNS in neonates has not been investigated. We have proposed that neonatal development of the blood-brain barrier affected CNS clearance mechanisms and CNS exposure to morphine. Male piglets (n=5) aged one, three and six weeks were given morphine sulfate (0.5 mg kg−1, i.v.). Serial blood and cerebrospinal fluid (CSF) samples were withdrawn over 360 min after morphine administration. Morphine concentration was measured by radioimmunoassay. A three-compartment model was fitted to individual data. Estimated parameters were reported as median and range. The peak morphine concentrations in plasma were not significantly different in the one-, three- or six-week-old piglets. Plasma clearance at one week (4.5, 3.8-8.6 mL min−1 kg−1) was significantly lower than at three weeks (30.0, 19.1- 39.0 mL min−1 kg−1) and six weeks (37.0, 29.7–82.8 mL min−1 kg−1). The peak morphine concentration in CSF at one week (59.84, 31–67 ng mL−1) was higher than at three weeks (18.8, 17.7–25 ng mL−1) and six weeks (24.51, 16.5–84 ng mL−1), while CSF clearance was lower at one week (1.0, 0.18-9 mL min−1 kg−1) compared with three weeks (6.2, 2.3–9.3 mL min−1 kg−1) and six weeks (3.95, 1.3–85.7 mL min−1 kg−1). Apparent plasma: CSF transfer ratio at one week was greater than at three and six weeks. The reduced plasma and CSF morphine clearance in early infancy resulted in elevated systemic and central morphine exposure in neonatal pigs.

Pediatric palliative care: use of opioids for the management of pain

Pediatric palliative care (PPC) is provided to children experiencing life-limiting diseases (LLD) or life-threatening diseases (LTD). Sixty to 90% of children with LLD/LTD undergoing PPC receive opioids at the end of life. Analgesia is often insufficient. Reasons include a lack of knowledge concerning opioid prescribing and adjustment of opioid dose to changing requirements. The choice of first-line opioid is based on scientific evidence, pain pathophysiology, and available administration modes. Doses are calculated on a bodyweight basis up to a maximum absolute starting dose. Morphine remains the gold standard starting opioid in PPC. Long-term opioid choice and dose administration is determined by the pathology, analgesic effectiveness, and adverse effect profile. Slow-release oral morphine remains the dominant formulation for long-term use in PPC with hydromorphone slow-release preparations being the first rotation opioid when morphine shows severe adverse effects. The recently introduced fentanyl transdermal therapeutic system with a drug-release rate of 12.5 microg/hour matches the lower dose requirements of pediatric cancer pain control. Its use may be associated with less constipation compared with morphine use. Though oral transmucosal fentanyl citrate has reduced bioavailability (25%), it inherits potential for breakthrough pain management. However, the gold standard breakthrough opioid remains immediate-release morphine. Buprenorphine is of special clinical interest as a result of its different administration routes, long duration of action, and metabolism largely independent of renal function. Antihyperalgesic effects, induced through antagonism at the kappa-receptor, may contribute to its effectiveness in neuropathic pain. Methadone also has a long elimination half-life (19 [SD 14] hours) and NMDA receptor activity although dose administration is complicated by highly variable morphine equianalgesic equivalence (1 : 2.5-20). Opioid rotation to methadone requires special protocols that take this into account. Strategies to minimize adverse effects of long-term opioid treatment include dose reduction, symptomatic therapy, opioid rotation, and administration route change. Patient- or nurse-controlled analgesia devices are useful when pain is rapidly changing, or in terminal care where analgesic requirements may escalate. In this article, we present detailed pediatric pharmacokinetic and pharmacodynamic data for opioids, their indications and contraindications, as well as dose-administration regimens that include practical strategies for opioid switching and dose reduction. Additionally, we discuss the problem of hyperalgesia and the use of adjuvant drugs to support opioid therapy.

Oxycodone as a component of multimodal analgesia for lactating mothers after Caesarean section: relationships between maternal plasma, breast milk and neonatal plasma levels

BACKGROUND

Oxycodone has become popular for post-Caesarean section (CS) analgesia yet it is not currently recommended for use in breast-feeding mothers because of limited information on its excretion into breast milk.

AIM

To investigate the relationship between maternal ingestion of oxycodone after CS and the resultant maternal plasma, breast milk and neonatal plasma drug levels up to 72-h post-partum.

METHODS

Fifty breast-feeding mothers taking oxycodone had blood and breast milk samples analysed for oxycodone levels at 24 h intervals after CS. Forty-one neonates had blood samples taken at 48 h.

RESULTS

Oxycodone was detected in the milk of mothers who had taken any dose in a 24-h period, with significant correlation between maternal plasma and milk levels (R(2) = 0.81). The median milk:plasma (M:P) ratio for the same period was 3.2:1. Over the subsequent 48 h, the relationship between plasma and milk levels was less strong (R(2) = 0.59) and there was a larger range of M:P levels with evidence of persistence of oxycodone in the breast milk of some mothers. Oxycodone levels up to 168 ng/mL were detected in breast milk (20% > 100 ng/mL). Oxycodone was detected in the plasma of one infant.

CONCLUSIONS

Oxycodone is concentrated in human breast milk up to 72-h post-partum. Breastfed infants may receive > 10% of a therapeutic infant dose. However, maternal oxycodone intake up to 72-h post-CS poses only minimal risk to the breast-feeding infant as low volumes of breast milk are ingested during this period.

Fentanyl concentrations in 23 postmortem cases from the hennepin county medical examiner's office

The purpose of this study was to compare blood fentanyl concentrations in fentanyl-related deaths with fentanyl concentrations found incidentally at autopsy, as well as with fentanyl concentrations found in hospitalized patients receiving fentanyl. Between the years 1997 to 2005, 23 fentanyl-positive postmortem cases were identified. Nineteen of 23 (82.6%) cases were deemed to be drug overdoses. Fentanyl alone was responsible for 8 of the 19 (42.1%) overdose deaths. Mean and median fentanyl concentrations were 36 (SD 38) microg/L and 22 microg/L, respectively, range 5-120 microg/L. Seven of the cases were accidental, one undetermined. The remaining 11 of the 19 (57.9%) cases were mixed drug overdoses. Fentanyl concentrations in these cases were 31 (SD 46) microg/L, range 5-152 microg/L. All of the mixed drug overdoses were determined to be accidental. Four cases where fentanyl was considered an incidental postmortem finding were determined to be natural deaths. In hospitalized inpatients (n = 11) receiving fentanyl 2 of the patients receiving fentanyl for chronic pain for more than 3 months had concentrations of 8.5 microg/L and 9.9 microg/L. The other nine inpatient concentrations were less than 4 microg/L. In conclusion, blood fentanyl concentrations found in cases where fentanyl alone was determined to be the cause of death were similar to cases where fentanyl was part of a mixed drug overdose. There was also considerable overlap between fentanyl concentrations in fentanyl-related overdose deaths compared to hospitalized patients being treated for chronic pain. Fentanyl concentrations in postmortem cases must be interpreted in the context of the deceased's past medical history and autopsy findings.

Analgesia and sedation during mechanical ventilation in neonates

BACKGROUND

Endotracheal intubation and mechanical ventilation are major components of routine intensive care for very low birth weight newborns and sick full-term newborns. These procedures are associated with physiologic, biochemical, and clinical responses indicating pain and stress in the newborn. Most neonates receive some form of analgesia and sedation during mechanical ventilation, although there are marked variations in clinical practice. Clinical guidelines for pharmacologic analgesia and sedation in newborns based on robust scientific data are lacking, as are measures of clinical efficacy.

OBJECTIVE

This article represents a preliminary attempt to develop a scientific rationale for analgesia sedation in mechanically ventilated newborns based on a systematic analysis of published clinical trials.

METHODS

The current literature was reviewed with regard to the use of opioids (fentanyl, morphine, diamorphine), sedative-hypnotics (midazolam), nonsteroidal anti-inflammatory drugs (ibuprofen, indomethacin), and acetaminophen in ventilated neonates. Original meta-analyses were conducted that collated the data from randomized clinical comparisons of morphine or fentanyl with placebo, or morphine with fentanyl.

RESULTS

The results of randomized trials comparing fentanyl, morphine, or midazolam with placebo, and fentanyl with morphine were inconclusive because of small sample sizes. Meta-analyses of the randomized controlled trials indicated that morphine and fentanyl can reduce behavioral and physiologic measures of pain and stress in mechanically ventilated preterm neonates but may prolong the duration of ventilation or produce other adverse effects. Randomized trials of midazolam compared with placebo reported significant adverse effects (P < 0.05) and no apparent clinical benefit; the findings of a meta-analysis suggest that there are insufficient data to justify use of IV midazolam for sedation in ventilated neonates.

CONCLUSIONS

Despite ongoing research in this area, huge gaps in our knowledge remain. Well-designed and adequately powered clinical trials are needed to establish the safety, efficacy, and short- and long-term outcomes of analgesia and sedation in the mechanically ventilated newborn.

Buprenorphineinsatz bei Kindern

There is a paucity of relevant pediatric data on buprenorphine, especially with respect to the long-term application in children suffering chronic pain or to pediatric pharmacokinetic as well as pharmacodynamic data after repeated sublingual or long-term transdermal administration. Compared to adults, after single-dose buprenorphine, children seem to exhibit a larger clearance related to body weight and a longer duration of action. If combined with other opioids or sedatives or if the metabolite norbuprenorphine cumulates, it is difficult to estimate the risk of respiratory depression. Clear-cut evidence is missing that in children there is a ceiling of buprenorphine-induced respiratory depression. Due to its various application routes, long duration of action, and metabolism largely independent of renal function buprenorphine is of special clinical interest in pediatrics, especially for postoperative pain and cancer pain control. There is no reason to expect effects fundamentally different from those in adults.

Drug interactions between psychoactive substances and antiretroviral therapy in individuals infected with human immunodeficiency and hepatitis viruses

The liver disease characteristic of alcohol dependence encompasses three main related entities: steatosis, alcoholic hepatitis, and cirrhosis. Alcoholic cirrhosis is a leading cause of global morbidity and mortality. Alcohol intake among injecting drug users is a major contributor to transmission of viral infections, such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C viruses (HCV). HIV and HCV coinfected patients develop liver diseases earlier and more severely than the monoinfected individuals, including hepatocellular carcinoma. Interactions exist between the therapeutic drugs used to minimize and control the drug and alcohol dependence. Furthermore, drug-drug interactions occur between the highly active antiretroviral therapy (HAART) and alcohol, different HAART components and methadone, or each one of the therapies with the other, thus contributing to a higher toxicity level. With the evolution of effective antiretroviral therapy, survival of persons with HIV, and the syndrome it causes, acquired immunodeficiency syndrome (AIDS) has increased dramatically. Drug-drug interactions may appear between alcohol and anti-HBV or anti-HCV, therapy in the presence or absence of anti-HIV therapy. Several other medical-, social-, and drug-related factors of this population have to be considered when providing HAART. Because many coinfected patients also have problems with substance use, dealing with their drug dependence is an important first step in an attempt to improve adherence to and tolerance of antiviral therapy. It is necessary to minimize the risk of liver disease acceleration and/or reinfection with hepatitis viruses. Knowledge of potential drug interactions between methadone, antiretroviral therapy, psychoactive drugs, and antipsychotics and the role of coinfection with HBV or HCV and the drugs used in eradicating viral hepatitis permits suitable antiretroviral combinations.

Use of opioids in asphyxiated term neonates: effects on neuroimaging and clinical outcome

Perinatal asphyxia is a common cause of neurologic morbidity in neonates who are born at term. Asphyxiated neonates are frequently treated with analgesic medications, including opioids, for pain and discomfort associated with their care. On the basis of previous laboratory studies suggesting that opioids may have neuroprotective effects, we conducted a retrospective review of medical records of 52 neonates who were admitted to our neonatal intensive care unit between 1995 and 2002 and had undergone magnetic resonance imaging (MRI) of the brain. Our review revealed that 33% of neonates received morphine or fentanyl. The neonates who received opioids also had experienced hypoxic/ischemic insults of greater magnitude as suggested by higher plasma lactate levels and lower 5-min Apgar scores. It is interesting that the MRI studies of neonates who were treated with opioids during the first week of life demonstrated significantly less brain injury in all regions studied. More important, follow-up studies of a subgroup of opioid-treated neonates whose MRI scans were obtained in the second postnatal week had better long-term neurologic outcomes. Our results suggest that the use of opioids in the first week of life after perinatal asphyxia have no significant long-term detrimental effects and may increase the brain's resistance to hypoxic-ischemic insults.

The functional expression of mu opioid receptors on sensory neurons is developmentally regulated; morphine analgesia is less selective in the neonate

Opioid requirements in neonatal patients are reported to be lower than older infants and this may be a reflection of the developmental regulation of opioid receptors. In this study we have investigated the postnatal regulation of Mu opioid receptor (MOR) function in both rat lumbar dorsal root ganglion (DRG) cultures and behavioural mechanical and thermal reflex tests in rat pups. Immunostaining with MOR and selective neurofilament (NF200) antibodies was combined with calcium imaging of MOR function in cultured neonatal and adult rat dorsal root ganglion cells. Calcium imaging showed that a significantly greater number of neonatal DRG neurons expressed functional MOR compared to adult (56.5+/-3.4 versus 39.9+/-1.5%, n=8, mean+/-SEM, P<0.001). This expression is confined to the large, neurofilament positive sensory neurons, while expression in small, nociceptive, neurofilament negative neurons remains unchanged. Sensory threshold testing in rat pups showed that the analgesic potency of systemic morphine to mechanical stimulation is significantly greater in the neonate and declines with postnatal age. Morphine analgesic potency in thermal nociceptive tests did not change with postnatal age. These experiments show that the MOR expressed on large DRG neurons in neonates are functional and are subject to postnatal developmental regulation. This changing functional receptor profile is consistent with greater morphine potency in mechanical, but not thermal, sensory tests in young animals. These results have important clinical implications for the use of morphine in neonates and provide a possible explanation for the differences in morphine requirements observed in the youngest patients.

Pharmacokinetic parameter prediction from drug structure using artificial neural networks

Simple methods for determining the human pharmacokinetics of known and unknown drug-like compounds is a much sought-after goal in the pharmaceutical industry. The current study made use of artificial neural networks (ANNs) for the prediction of clearances, fraction bound to plasma proteins, and volume of distribution of a series of structurally diverse compounds. A number of theoretical descriptors were generated from the drug structures and both automated and manual pruning were used to derive optimal subsets of descriptors for quantitative structure-pharmacokinetic relationship models. Models were trained on one set of compounds and validated with another. Absolute predicted ability was evaluated using a further independent test set of compounds. Correlations for test compounds ranged from 0.855 to 0.992. Predicted values agreed closely with experimental values for total clearance, renal clearance, and volume of distribution, while predictions for protein binding were encouraging. The combination of descriptor generation, ANNs, and the speed and success of this technique compared with conventional methods shows strong potential for use in pharmaceutical product development.

Prediction of volume of distribution values in humans for neutral and basic drugs using physicochemical measurements and plasma protein binding data

We present a method for the prediction of volume of distribution in humans, for neutral and basic compounds. It is based on two experimentally determined physicochemical parameters, ElogD(7.4) and f(i(7.4)), the latter being the fraction of compound ionized at pH 7.4 and on the fraction of free drug in plasma (f(u)). The fraction unbound in tissues (f(ut)), determined via a regression analysis from 64 compounds using the parameters described, is then used to predict VD(ss) via the Oie-Tozer equation. Accuracy of this method was determined using a test set of 14 compounds, and it was demonstrated that human VD(ss) values could be predicted, on average, within or very close to 2-fold of the actual value. The present method is as accurate as reported methods based on animal pharmacokinetic data, using a similar set of compounds, and ranges between 1.62 and 2.20 as mean-fold error. This method has the advantage of being amenable to automation, and therefore fast throughput, it is compound and resources sparing, and it offers a rationale for the reduction of the use of animals in pharmacokinetic studies. A discussion of the potential errors that may be encountered, including errors in the determination of f(u), is offered, and the caveats about the use of computed vs experimentally determined logD and pK(a) values are addressed.

Protein binding predictions in infants

Plasma binding protein levels are lower in the newborn than in the adult and gradually increase with age. At birth, human serum albumin (HSA) concentrations are close to adult levels (75%-80%), while alpha 1-acid glycoprotein (AAG) is initially half the adult concentration. As a result, the extent of drug binding to HSA is closer to that of the adult than are those drugs bound largely to AAG. A model that incorporates the fraction unbound in adults and the ratio of the binding protein concentration between infants and adults successfully predicted the fraction unbound in infants and children.

Quantitative analysis of fentanyl in rat plasma by gas chromatography with nitrogen-phosphorus detection

A sensitive assay method was developed to determine fentanyl, an opiate agonist, in rat plasma by gas chromatography with nitrogen-phosphorus detection. For the pretreatment of plasma samples, sodium hydroxide was added to denature protein and n-butyl chloride was used to extract fentanyl. The calibration curve was linear within the concentration range 0.5 to 50 ng/ml (r=0.9997). The limit of detection was 0.1 ng/ml, and 0.5 ng/ml could be quantified with acceptable precision. Furthermore, fentanyl could be determined in only 200 microl of rat plasma. The method has been successfully applied to an intramuscular pharmacokinetic study at a dose of 10 microg/kg. Therefore, the current method is a valuable analytical tool for investigating the pharmacokinetics of fentanyl at low clinical doses.

Pharmacologic considerations for opiate analgesic and nonsteroidal anti-inflammatory drugs

When administering opioid analgesic drugs or nonsteroidal anti-inflammatory drugs, veterinarians are often not familiar enough with the underlying pharmacology of the drugs, particularly with the potential for drug interactions and adverse effects. This article considers some of the pharmacologic features of these drugs and provides a basis for important interactions, contraindications, and adverse effects.

Prevention and management of pain and stress in the neonate

This statement is intended for health care professionals caring for neonates (preterm to one month of age). The objectives of this statement are to: increase awareness that neonates experience pain; provide a physiological basis for neonatal pain and stress assessment and management by health care professionals; make recommendations for reduced exposure of the neonate to noxious stimuli and to minimize associated adverse outcomes; and recommend effective and safe interventions that relieve pain and stress.

Toxicokinetics in infants and children in relation to the ADI and TDI

Age-dependent developmental changes in toxicokinetics occur in both rats and humans, particularly in relation to renal function and hepatic xenobiotic metabolism. These processes are immature in humans at birth, especially in the pre-term neonate, but mature rapidly over the first months of life. In consequence the duration of immaturity primarily corresponds to the period of suckling. Similar developmental changes occur in the neonatal rat over the first weeks of life. Rat pups start to consume some of the adult diet in the third week of life, prior to weaning, so that there is a potential for consumption of the adult diet during the period of immaturity. There is an extensive database on the pharmacokinetics of therapeutic drugs in infants and children. The elimination/clearance of many drugs is higher in children than in adults and this difference would apply to other xenobiotics. In consequence, children frequently will have lower body burdens than adults for the same daily intake of a chemical when this is expressed on a body weight basis, as used to describe the ADI (Acceptable Daily Intake) or TDI (Tolerable Daily Intake) (e.g. mg/kg body weight/day). Therefore, an increased safety or uncertainty factor for post-suckling infants and children is not required in relation to age-related differences in toxicokinetics. Indeed, the higher clearance of many xenobiotics (toxicokinetics) by children compared with adults may compensate, at least in part, for increased organ sensitivity (toxicodynamics) during development.

Ontogeny of mu opioid agonist anti-nociception in postnatal rats

Mu opiate agonists morphine, fentanyl and meperidine are administered short-term to pediatric patients, from the neonatal period through adolescence. However, there has been no assessment of the effect of age on the analgesic efficacy or the concentration-response relationship for these opioids in human pediatric patients. Few studies in animals have correlated opioid anti-nociception and tissue levels of these opioids commonly administered to pediatric patients. The present study was conducted to examined the role of age on opioid anti-nociceptive potency and efficacy and brain and plasma opioid levels to provide predictive information on the effect of opioids in developing humans. Administration of trace amounts of tritiated drug with anti-nociceptive doses of unlabeled drug was used for the assessment of anti-nociception in the tail-flick test and for the measurement of brain and plasma drug equivalent levels in postnatal rats (PND 3-21). Morphine and fentanyl were completely efficacious in all postnatal ages examined, although age-related differences in drug potency, as well as, differences in brain and plasma levels were observed. There was a good correlation between morphine (r = 0.96) and fentanyl (r = 0.89) ED(50) values and their respective brain and plasma EC(50) equivalent levels. Meperidine had limited efficacy in young rats (PND 3-9) but was completely efficacious in older rats (PND 14-17). However, PND 21 rats experienced tonic-clonic seizures which limited its efficacy to 70% anti-nociception. Our data suggest that pharmacokinetics, the development of the blood-brain barrier and ontogeny of opioid receptor function may play important roles in the sensitivity of postnatal rats to mu receptor agonists.

Systematic review of factors affecting the ratios of morphine and its major metabolites

In a systematic review of 57 studies with information on 1232 patients we examined the effect of age, renal impairment, route of administration, and method of analysis on the ratios of morphine-3-glucuronide:morphine (M3G:M) and morphine-6-glucuronide:morphine (M6G:M) and the relative concentrations of M3G and M6G. Across all studies the range of the ratios of metabolites to morphine was wide (0.001-504 for M3G:M, and 0-97 for M6G:M). Neonates produced morphine glucuronides at a lower rate than older children or adults. Metabolite ratios were higher in renal impairment. Routes of administration which avoided first pass metabolism (intravenous, transdermal, rectal, intramuscular, epidural and intrathecal) resulted in lower metabolite production than oral, buccal or sublingual. Metabolite production was similar for single and multiple dosing. There was no evidence of differences between methods of assay. There was a high correlation between the two glucuronide metabolites in spite of the different situations studied, supporting a single glucuronidating enzyme. Morphine was present in CSF at a fourfold higher concentration than the glucuronide metabolites.

Principles of analgesic drug therapy

The drugs most often used for pain relief in animals are the nonsteroidal antiinflammatory drugs (NSAIDS) and the opioid analgesics. The NSAIDS are effective, inexpensive, and long-acting drugs, but their degree of analgesia is limited by the adverse effects at high doses. The most common adverse effect from NSAIDS is gastritis and gastrointestinal hemorrhage and ulceration. This is most common from high doses, or from using NSAIDS not appropriate for dogs such as ibuprofen or indomethacin. The NSAIDS used in dogs include aspirin, phenylbutazone, naproxen, piroxicam, ketoprofen, and carprofen. Carprofen is a new drug with a low incidence of side effects and its popularity is increasing at a fast rate. For more acute pain, especially acute pain from surgery or trauma, opioids are frequently administered. Opioids have the advantage of higher efficacy when the dose is increased. The incidence of adverse effects is low, but side effects of sedation are common. An important disadvantage of opioids is their short duration and low oral absorption, which necessitates a frequent injection or i.v. infusion for most patients. Recent studies have established other applications for administration of opioids such as a transdermal fentanyl patch. These applications offer new possibilities for convenient administration.

Clinical pharmacokinetics of alfentanil, fentanyl and sufentanil. An update

Alfentanil, fentanyl and sufentanil are synthetic opioid analgesics acting at specific opioid receptors. These opioids are widely used as analgesics to supplement general anaesthesia for various surgical procedures or as primary anaesthetic agents in very high doses during cardiac surgery. Fentanyl and sufentanil especially are administered via infusion for long term analgesia and sedation in intensive care patients. Opioid analgesics are mainly administered using the intravenous route. However, other techniques of administration, including epidural, intrathecal, transdermal and intranasal applications, have been demonstrated. Important pharmacokinetic differences between alfentanil, fentanyl and sufentanil have been shown in many reports. Alfentanil has the most rapid analgesic onset and time to peak effect as well as the shortest distribution and elimination half-lives. The volume of distribution and total body clearance of this agent are smaller when compared with those of fentanyl and sufentanil. The pharmacokinetics of the opioid analgesics can be affected by several factors including patient age, plasma protein content, acid-base status and cardiopulmonary bypass, but not significantly by renal insufficiency or compensated hepatic dysfunction. In addition, pharmacokinetic properties can be influenced by changes in hepatic blood flow and administration of drug combinations which compete for the same plasma protein carrier or metabolising pathway. Although comparing specific pharmacokinetic parameters such as half-lives is deeply entrenched in the literature and clinical practice, simply comparing half-lives is not a rational way to select an opioid for specific requirements. Using pharmacokinetic-pharmacodynamic models, computer simulations based on changes in the effect site opioid concentration or context-sensitive half-times seem to be extremely useful for selecting an opioid on a more rational basis.