Carin M. A. Rademaker

Effects of Hypothermia on Pharmacokinetics and Pharmacodynamics

Examples of clinical applications of therapeutic hypothermia in modern clinical medicine include traumatic cardiac arrest, ischaemic stroke and, more recently, acute perinatal asphyxia in neonates. The exact mechanism of (neuro)protection by hypothermia is unknown. Since most enzymatic processes exhibit temperature dependency, it can be expected that therapeutic hypothermia may cause alterations in both pharmacokinetic and pharmacodynamic parameters, which could result in an increased risk of drug toxicity or therapy failure. Generalizable knowledge about the effect of therapeutic hypothermia on pharmacokinetics and pharmacodynamics could lead to more appropriate dosing and thereby prediction of clinical effects. This article reviews the evidence on the influence of therapeutic hypothermia on individual pharmacokinetic and pharmacodynamic parameters. A literature search was conducted within the PubMed, Embase and Cochrane databases from January 1965 to September 2008, comparing pharmacokinetic and/or pharmacodynamic parameters in hypothermia and normothermia regarding preclinical (animal) and clinical (human) studies. During hypothermia, pharmacokinetic parameters alter, resulting in drug and metabolite accumulation in the plasma for the majority of drugs. Impaired clearance is the most striking effect. Based on impaired clearance, dosages should be decreased considerably, especially for drugs with a low therapeutic index. Hypothetically, high-clearance compounds are affected more than low-clearance compounds because of the additional effect of impaired hepatic blood flow. The volume of distribution also changes, which may lead to therapy failure when it increases and could lead to toxicity when it decreases. The pH-partitioning hypothesis could contribute to the changes in the volumes of distribution for weak bases and acids, depending on their acid dissociation constants and acid-base status. Pharmacodynamic parameters may also alter, depending on the hypothermic regimen, drug target location, pharmacological mechanism and metabolic pathway of inactivation. The pharmacological response changes when target sensitivity alters. Rewarming patients to normothermia can also result in toxicity or therapy failure. The integrated effect of hypothermia on pharmacokinetic and pharmacodynamic properties of individual drugs is unclear. Therefore, therapeutic drug monitoring is currently considered essential for drugs with a low therapeutic index, drugs with active metabolites, high-clearance compounds and drugs that are inactivated by enzymes at the site of effect. Because most of the studies (74%) included in this review contain preclinical data, clinical pharmacokinetic/pharmacodynamic studies are essential for the development of substantiated dose regimens to avoid toxicity and therapy failure in patients treated with hypothermia.

Pediatric Drug Formulations: A Review of Challenges and Progress

Children differ from adults in many aspects of pharmacotherapy, including capabilities for drug administration, medicine-related toxicity, and taste preferences. It is essential that pediatric medicines are formulated to best suit a child’s age, size, physiologic condition, and treatment requirements. To ensure adequate treatment of all children, different routes of administration, dosage forms, and strengths may be required. Many existing formulations are not suitable for children, which often leads to off-label and unlicensed use of adult medicines. New regulations, additional funding opportunities, and innovative collaborative research initiatives have resulted in some recent progress in the development of pediatric formulations. These advances include a paradigm shift toward oral solid formulations and a focus on novel preparations, including flexible, dispersible, and multiparticulate oral solid dosage forms. Such developments have enabled greater dose flexibility, easier administration, and better acceptance of drug formulations in children. However, new pediatric formulations address only a small part of all therapeutic needs in children; moreover, they are not always available. Five key issues need to be addressed to stimulate the further development of better medicines for children: (1) the continued prioritization of unmet formulation needs, particularly drug delivery in neonates and treatment gaps in pediatric cancers and childhood diseases in developing countries; (2) a better use of existing data to facilitate pediatric formulation development; (3) innovative technologies in adults that can be used to develop new pediatric formulations; (4) clinical feedback and practice-based evidence on the impact of novel formulations; and (5) improved access to new pediatric formulations.

High prevalence of methotrexate intolerance in juvenile idiopathic arthritis: development and validation of a methotrexate intolerance severity score

OBJECTIVE To design and validate a new questionnaire for identifying patients with methotrexate (MTX) intolerance, and to determine the prevalence of MTX intolerance in patients with juvenile idiopathic arthritis (JIA) using this questionnaire. METHODS The MTX Intolerance Severity Score (MISS) questionnaire was constructed, consisting of 5 domains: stomach ache, nausea, vomiting, sore mouth, and behavioral symptoms. The domains each consisted of 3 questions pertaining to the presence of a symptom upon, prior to (anticipatory), and when thinking of (associative) MTX intake. The MISS questionnaire was validated in 86 patients by determining its discriminative power between patients with and those without MTX intolerance, identified as such by a gold standard (physicians opinion). Using the MISS questionnaire, the prevalence of MTX intolerance was determined in 297 JIA patients. RESULTS The MISS questionnaire discriminated well between MTX-intolerant and MTX-tolerant patients. A cutoff score of 6 yielded the best sensitivity (88%) and specificity (80%). MTX intolerance was found in 150 (50.5%) of 297 patients. Of 220 patients receiving oral MTX, 98 (44.5%) experienced MTX intolerance, whereas 67.5% of 77 patients receiving parenteral MTX experienced intolerance to the drug (P = 0.001). CONCLUSION Our findings indicate that the MISS questionnaire is a highly sensitive and specific tool for the diagnosis of MTX intolerance, and that there is a high prevalence of MTX intolerance among JIA patients. The prevalence of intolerance in patients receiving parenteral MTX exceeds that in patients receiving oral MTX. The frequent occurrence of anticipatory and associative symptoms suggests that classic conditioning plays an important role in MTX intolerance.

Treatment of symptomatic congenital cytomegalovirus infection with valganciclovir.

Abstract Cytomegalovirus (CMV) is the most common cause of congenital infection in humans. Some congenitally infected infants will develop sequelae later in life, especially sensorineural hearing loss (SNHL) and mental retardation. There is no generally accepted antiviral therapy for the treatment of symptomatic congenital CMV infections yet. We present a neonate with symptomatic congenital CMV infection, who was treated with intravenous (iv) ganciclovir (GCV) during 18 days and subsequently with oral valganciclovir (VGCV) for 5.5 months, in an attempt to prevent development of SNHL. GCV was given intravenously 10 mg/kg/day in two doses and VGCV doses ranged from 280–850 mg/m2 bidaily (bid). Our experience shows that it is not possible to give a fixed dosing regime for VGCV in neonates and that continuous adaptation of dose is necessary to achieve stable target levels of GCV and to keep the viral load in urine at undetectable level. At 18 months of age no hearing deterioration has occurred. While the current findings are encouraging, the limitations of a single case report with a relatively short follow-up emphasizes the need for further prospective randomized studies to evaluate pharmacokinetics, efficacy and safety of VGCV therapy in neonates with congenital CMV infection.

Maternal Allopurinol During Fetal Hypoxia Lowers Cord Blood Levels of the Brain Injury Marker S-100B

BACKGROUND: Fetal hypoxia is an important determinant of neonatal encephalopathy caused by birth asphyxia, in which hypoxia-induced free radical formation plays an important role. HYPOTHESIS: Maternal treatment with allopurinol, will cross the placenta during fetal hypoxia (primary outcome) and reduce S-100B and free radical formation (secondary outcome). METHODS: In a randomized, double-blind feasibility study, 53 pregnant women in labor (54 fetuses) with a gestational age of >36 weeks and fetal hypoxia, as indicated by abnormal/nonreassuring fetal heart rate tracing or fetal scalp pH of <7.20, received 500 mg of allopurinol or placebo intravenously. Severity of fetal hypoxia, brain damage and free radical formation were assessed by arterial cord blood lactate, S-100B and non-protein-bound-iron concentrations, respectively. At birth, maternal and cord blood concentrations of allopurinol and its active metabolite oxypurinol were determined. RESULTS: Allopurinol and oxypurinol concentrations were within the therapeutic range in the mother (allopurinol > 2 mg/L and/or oxypurinol > 4 mg/L) but not always in arterial cord blood. We therefore created 3 groups: a placebo (n = 27), therapeutic allopurinol (n = 15), and subtherapeutic allopurinol group (n = 12). Cord lactate concentration did not differ, but S-100B was significantly lower in the therapeutic allopurinol group compared with the placebo and subtherapeutic allopurinol groups (P < .01). Fewer therapeutic allopurinol cord samples had measurable non–protein-bound iron concentrations compared with placebo (P < .01). CONCLUSIONS: Maternal allopurinol/oxypurinol crosses the placenta during fetal hypoxia. In fetuses/newborns with therapeutic allopurinol/oxypurinol concentrations in cord blood, lower plasma levels of the brain injury marker protein S-100B were detected. A larger allopurinol trial in compromised fetuses at term seems warranted. The allopurinol dosage must be adjusted to achieve therapeutic fetal allopurinol/oxypurinol concentrations.

Long-term neuroprotective effects of allopurinol after moderate perinatal asphyxia: follow-up of two randomised controlled trials

Objective Free-radical-induced reperfusion injury has been recognised as an important cause of brain tissue damage after birth asphyxia. Allopurinol reduces the formation of free radicals, thereby potentially limiting the amount of hypoxia–reperfusion damage. In this study the long-term outcome of neonatal allopurinol treatment after birth asphyxia was examined. Design Follow-up of 4 to 8 years of two earlier performed randomised controlled trials. Setting Leiden University Medical Center, University Medical Center Groningen and University Medical Center Utrecht, The Netherlands. Patients Fifty-four term infants were included when suffering from moderate-to-severe birth asphyxia in two previously performed trials. Intervention Infants either received 40 mg/kg allopurinol (with an interval of 12 h) starting within 4 h after birth or served as controls. Main outcome measures Children, who survived, were assessed with the Wechsler Preschool and Primary Scales of Intelligence test or Wechsler Intelligence Scale for Children and underwent a neurological examination. The effect of allopurinol on severe adverse outcome (defined as mortality or severe disability at the age of 4–8 years) was examined in the total group of asphyxiated infants and in a predefined subgroup of moderately asphyxiated infants (based on the amplitude integrated electroencephalogram). Results The mean age during follow-up (n=23) was 5 years and 5 months (SD 1 year and 2 months). There were no differences in long-term outcome between the allopurinol-treated infants and controls. However, subgroup analysis of the moderately asphyxiated group showed significantly less severe adverse outcome in the allopurinol-treated infants compared with controls (25% vs 65%; RR 0.40, 95%CI 0.17 to 0.94). Conclusions The reported data may suggest a (neuro)protective effect of neonatal allopurinol treatment in moderately asphyxiated infants.

The availability and age‐appropriateness of medicines authorized for children in the Netherlands

AIM To study the number of medicines and active chemical entities that are authorized and commercially available for children in the Netherlands and to evaluate the age-appropriateness of the available paediatric medicines. METHODS The availability of paediatric medicines and active chemical entities was studied with the help of a Dutch medicines database and the Summary of Product Characteristics. Medicines were categorized with respect to their route of administration, type of oral dosage form and therapeutic category. The age-appropriateness was assessed on three aspects: dose capability, suitability of the dosage form and inclusion of potentially harmful excipients. RESULTS Three thousand five hundred and forty-two paediatric medicines containing 703 different active chemical entities were identified. This equalled half of all the medicines and chemical entities available for human use. The percentage of paediatric medicines increased with age and varied for the route of administration from 22% (dermal) to 81% (inhalation) and for the therapeutic category from 11% (uro-genital, sex hormones) to 89% (anti-parasites). The appropriateness of the paediatric medicines with respect to their authorization status, dose capability and dosage form increased with age from 27-88%. Fifty-two percent of all oral paediatric liquid formulations contained a potentially harmful excipient. CONCLUSION This study confirms the limited availability of paediatric medicines for a broad range of therapeutic areas and shows that paediatric medicines may not be age-appropriate, even if authorized. While confirming the need for a legislative incentive, the results also provide baseline information for an estimation of the effect of the European Paediatric Regulation in the near future.

Pharmacokinetics and pharmacodynamics of medication in asphyxiated newborns during controlled hypothermia. The PharmaCool multicenter study

BackgroundIn the Netherlands, perinatal asphyxia (severe perinatal oxygen shortage) necessitating newborn resuscitation occurs in at least 200 of the 180–185.000 newly born infants per year. International randomized controlled trials have demonstrated an improved neurological outcome with therapeutic hypothermia. During hypothermia neonates receive sedative, analgesic, anti-epileptic and antibiotic drugs. So far little information is available how the pharmacokinetics (PK) and pharmacodynamics (PD) of these drugs are influenced by post resuscitation multi organ failure and the metabolic effects of the cooling treatment itself. As a result, evidence based dosing guidelines are lacking. This multicenter observational cohort study was designed to answer the question how hypothermia influences the distribution, metabolism and elimination of commonly used drugs in neonatal intensive care.Methods/DesignMulticenter cohort study. All term neonates treated with hypothermia for Hypoxic Ischemic Encephalopathy (HIE) resulting from perinatal asphyxia in all ten Dutch Neonatal Intensive Care Units (NICUs) will be eligible for this study. During hypothermia and rewarming blood samples will be taken from indwelling catheters to investigate blood concentrations of several antibiotics, analgesics, sedatives and anti-epileptic drugs. For each individual drug the population PK will be characterized using Nonlinear Mixed Effects Modelling (NONMEM). It will be investigated how clearance and volume of distribution are influenced by hypothermia also taking maturation of neonate into account. Similarly, integrated PK-PD models will be developed relating the time course of drug concentration to pharmacodynamic parameters such as successful seizure treatment; pain assessment and infection clearance.DiscussionOn basis of the derived population PK-PD models dosing guidelines will be developed for the application of drugs during neonatal hypothermia treatment. The results of this study will lead to an evidence based drug treatment of hypothermic neonatal patients. Results will be published in a national web based evidence based paediatric formulary, peer reviewed journals and international paediatric drug references.Trial registrationNTR2529.

Clinical Management of Seizures in Newborns

Neonatal seizures can be classified as tonic, clonic, myoclonic, and subtle. A clinical diagnosis is not easy as seizures are usually subtle in neonates. In the majority of newborn infants seizures are subclinical. On the other hand, not all abnormal movements identified by clinicians as clinical seizures are accompanied by electroencephalographic seizure discharges in the EEG. Precise incidence is difficult to delineate and depends on study population and criteria used for diagnosis of seizures. Controversy exists as to whether neonatal seizures themselves cause damage to the developing brain, or if the damage is primarily due to the underlying cause of the seizures. As a result of this controversy there is ongoing discussion whether all seizures (both clinical and subclinical) should be treated. In addition, when (sub)clinical seizures are treated, there is no consensus about the most appropriate treatment for neonatal seizures and how to assess the efficacy of treatment.Current therapeutic options to treat neonatal seizures (i.e. primarily first-generation antiepileptic drugs [AEDs]) are relatively ineffective. In practice, phenobarbital still remains the drug of first choice for EEG confirmed or suspected seizures. Benzodiazepines are also used in (phenobarbital) refractory cases. Several (small) studies indicate that lidocaine is an effective drug for refractory seizures as second- or third-line treatment. Although data are scarce, some AEDs with a wide acceptance in adult and pediatric neurology practice are being used to treat neonatal seizures (i.e. second-generation AEDs). These drugs are chemically different from all first-generation AEDs and they have an effect on other pathways so they provide new pharmacological targets for controlling seizures in newborns. Levetiracetam, topiramate, felbamate, bumetanide, lamotrigine and vigabatrin are examples of these second-generation AEDs.There is an urgent need for prospective, randomized, controlled trials to assess the efficacy and safety of these second-generation AEDs in neonates.The aim of this review is to provide an overview of the current knowledge of diagnosis, the effect on brain injury, and the treatment of neonatal seizures.

Anticonvulsant treatment of asphyxiated newborns under hypothermia with lidocaine: efficacy, safety and dosing

Background Lidocaine is an antiarrythmicum used as an anticonvulsant for neonatal seizures, also during therpeutic hypothermia following (perinatal) asphyxia. Hypothermia may affect the efficacy, safety and dosing of lidocaine in these patients. Objective To study the efficacy and safety of lidocaine in newborns with perinatal asphyxia during moderate hypothermia, and to develop an effective and safe dosing regimen. Methods Hypothermic newborns with perinatal asphyxia and lidocaine for seizure control were included. Efficacy was studied using continuous amplitude-integrated electroencephalography. Safety was assessed using continuous cardiac monitoring. An optimal dosing regimen was developed with simulations using data from a pharmacokinetic model. Plasma samples were collected during hypothermia on consecutive mornings. Results A total of 22 hypothermic and 26 historical normothermic asphyxiated newborns with lidocaine were included. A response of 91% on epileptiform activity on the amplitude-integrated EEG was observed for lidocaine add-on therapy. No relationship between lidocaine or MEGX plasma concentrations and heart frequency could be identified. None of the newborns experienced cardiac arrythmias. Hypothermia reduced lidocaine clearance by 24% compared with normothermia. A novel dosing regimen was developed an initial bolus loading dose of 2 mg/kg, for patients with body weight 2.0–2.5 kg followed by consecutive continuous infusions of 6 mg/kg/h (for 3.5 h), 3 mg/kg/h (for 12 h), 1.5 mg/kg/h (for 12 h), or for patients with bodyweights 2.5–4.5 kg 7 mg/kg/h (for 3.5 h), 3.5 mg/kg/h (for 12 h), 1.75 mg/kg/h (for 12 h), before stopping. Conclusions Lidocaine can be assumed to be an effective antiepileptic drug during hypothermia in asphyxiated neonates.