Diazepam elimination in premature and full term infants, and children

Benzodiazepines in the Management of Seizures and Status Epilepticus: A Review of Routes of Delivery, Pharmacokinetics, Efficacy, and Tolerability

Status epilepticus (SE) is an acute, life-threatening medical condition that requires immediate, effective therapy. Therefore, the acute care of prolonged seizures and SE is a constant challenge for healthcare professionals, in both the pre-hospital and the in-hospital settings. Benzodiazepines (BZDs) are the first-line treatment for SE worldwide due to their efficacy, tolerability, and rapid onset of action. Although all BZDs act as allosteric modulators at the inhibitory gamma-aminobutyric acid (GABA)_A receptor, the individual agents have different efficacy profiles and pharmacokinetic and pharmacodynamic properties, some of which differ significantly. The conventional BZDs clonazepam, diazepam, lorazepam and midazolam differ mainly in their durations of action and available routes of administration. In addition to the common intravenous, intramuscular and rectal administrations that have long been established in the acute treatment of SE, other administration routes for BZDs-such as intranasal administration-have been developed in recent years, with some preparations already commercially available. Most recently, the intrapulmonary administration of BZDs via an inhaler has been investigated. This narrative review provides an overview of the current knowledge on the efficacy and tolerability of different BZDs, with a focus on different routes of administration and therapeutic specificities for different patient groups, and offers an outlook on potential future drug developments for the treatment of prolonged seizures and SE.

Population Pharmacokinetics and Exploratory Exposure-Response Relationships of Diazepam in Children Treated for Status Epilepticus

Diazepam is labeled for status epilepticus (SE) in children, but there are limited data characterizing its disposition in pediatric patients. We developed a population pharmacokinetic (PK) model of i.v. diazepam in children with SE. We evaluated relationships between PK parameters and both safety and efficacy, and simulated exposures using dosing regimens from the product label and clinical practice. The model was developed using prospective data from a pediatric clinical trial comparing diazepam to lorazepam for treatment of SE. Altogether, 87 patients aged ≥ 3 months to < 18 years contributed 162 diazepam concentrations. Diazepam PKs were well characterized by a two‐compartment model scaled by body size. No significant or clinically important relationships were observed between diazepam PKs and safety or efficacy. Simulations demonstrated that, compared with label dosing, the study dose (0.2 mg/kg i.v., maximum 8 mg) resulted in greater frequency in rapidly achieving the target therapeutic range of 200–600 ng/mL.

Pain Management and Conscious Sedation for the Pediatric Patient

Pain management in children was previously ignored primarily because of myths and misconceptions about childhood pain. Undertreatment of pain was once a common and accepted practice. However, in recent years, with increased knowledge and understanding coupled with improved pain assessment tools, health care providers are more conscious about providing adequate and safe analgesia to children. Because of the differences in patient response to various pharmacological agents, it is important to understand the pharmacokinetic and pharmacodynamic differences of the various agents. Choices of pain management should be individualized, and adjustments should be made based on the patient's clinical condition. Conscious sedation before diagnostic and therapeutic procedures should be approached with caution. Deaths and complications related to conscious sedation therapy have prompted the development of guidelines for safer and more effective pharmacological interventions. The recently published guidelines include recommendations for skilled personnel, continuous monitoring, appropriate use of drugs, and ability to manage unforeseen complications. Selection of the most appropriate sedatives should take into consideration the type of procedure, the patient's clinical condition, and the desired level and duration of consciousness. Similar to pain management, individualization is crucial. This article will discuss the principles of pain management and conscious sedation in children. Facts and scientific findings will be presented to discredit the myths and misconceptions often associated with pediatric pain. Various pain assessment tools will be summarized. The newly published sedation guidelines set forth by the American Academy of Pediatrics Committee on Drugs will be briefly discussed. Furthermore, commonly used agents will be reviewed. Copyright © 1996 by W.B. Saunders Company

Opportunities in low-level radiocarbon microtracing: applications and new technology

¹⁴C-radiolabeled (radiocarbon) drug studies are central to defining the disposition of therapeutics in clinical development. Concerns over radiation, however, have dissuaded investigators from conducting these studies as often as their utility may merit. Accelerator mass spectrometry (AMS), originally designed for carbon dating and geochronology, has changed the outlook for in-human radiolabeled testing. The high sensitivity of AMS affords human clinical testing with vastly reduced radiative (microtracing) and chemical exposures (microdosing). Early iterations of AMS were unsuitable for routine biomedical use due to the instruments' large size and associated per sample costs. The situation is changing with advances in the core and peripheral instrumentation. We review the important milestones in applied AMS research and recent advances in the core technology platform. We also look ahead to an entirely new class of ¹⁴C detection systems that use lasers to measure carbon dioxide in small gas cells.

Clinical report—Guidelines for the determination of brain death in infants and children: an update of the 1987 task force recommendations

OBJECTIVE

To review and revise the 1987 pediatric brain death guidelines.

METHODS

Relevant literature was reviewed. Recommendations were developed using the GRADE system.

CONCLUSIONS AND RECOMMENDATIONS

(1) Determination of brain death in term newborns, infants and children is a clinical diagnosis based on the absence of neurologic function with a known irreversible cause of coma. Because of insufficient data in the literature, recommendations for preterm infants less than 37 weeks gestational age are not included in this guideline. (2) Hypotension, hypothermia, and metabolic disturbances should be treated and corrected and medications that can interfere with the neurologic examination and apnea testing should be discontinued allowing for adequate clearance before proceeding with these evaluations. (3) Two examinations including apnea testing with each examination separated by an observation period are required. Examinations should be performed by different attending physicians. Apnea testing may be performed by the same physician. An observation period of 24 hours for term newborns (37 weeks gestational age) to 30 days of age, and 12 hours for infants and chi (> 30 days to 18 years) is recommended. The first examination determines the child has met the accepted neurologic examination criteria for brain death. The second examination confirms brain death based on an unchanged and irreversible condition. Assessment of neurologic function following cardiopulmonary resuscitation or other severe acute brain injuries should be deferred for 24 hours or longer if there are concerns or inconsistencies in the examination. (4) Apnea testing to support the diagnosis of brain death must be performed safely and requires documentation of an arterial Paco(2) 20 mm Hg above the baseline and ≥ 60 mm Hg with no respiratory effort during the testing period. If the apnea test cannot be safely completed, an ancillary study should be performed. (5) Ancillary studies (electroencephalogram and radionuclide cerebral blood flow) are not required to establish brain death and are not a substitute for the neurologic examination. Ancillary studies may be us d to assist the clinician in making the diagnosis of brain death (i) when components of the examination or apnea testing cannot be completed safely due to the underlying medical condition of the patient; (ii) if there is uncertainty about the results of the neurologic examination; (iii) if a medication effect may be present; or (iv) to reduce the inter-examination observation period. When ancillary studies are used, a second clinical examination and apnea test should be performed and components that can be completed must remain consistent with brain death. In this instance the observation interval may be shortened and the second neurologic examination and apnea test (or all components that are able to be completed safely) can be performed at any time thereafter. (6) Death is declared when the above criteria are fulfilled.

Influence of antiepileptic drugs on amplitude-integrated electroencephalography

Amplitude-integrated electroencephalography monitors different aspects of cerebral function in neonatal intensive care units. To examine the influence of various antiepileptic drugs on the background patterns and voltage of amplitude-integrated electroencephalography recordings, we screened 191 tracing segments originating from 77 newborns treated with antiepileptic drugs. The influences of lorazepam, diazepam, and phenobarbital given as bolus doses, and midazolam and lidocaine given in continuous infusion, were examined. Voltages and patterns before and after drug administration were assessed. Time taken to return to previous voltage was assessed in clinically significant cases. Chi-square and Wilcoxon tests were used for statistical analyses. Significant changes were evident after lorazepam, diazepam, phenobarbital, and midazolam administration. Depending on the voltage-assessment method, a clinically significant depression of the lower voltage border occurred in 25-35% of tracings, and of the upper border in 16-32%. In 12% of tracings, change to a worse pattern was noted. The average time for recovery to predrug administration voltage was 2.5 hours (range, 15 minutes to 15 hours). Changes in amplitude-integrated electroencephalography tracings occur after antiepileptic drugs are infused. These changes include deterioration of pattern and depression of voltage that may persist for a considerable period. The potential depressing effects of these drugs should be taken into consideration when assessing amplitude-integrated electroencephalogram tracings.

Benzodiazepines in epilepsy: pharmacology and pharmacokinetics

Benzodiazepines (BZDs) remain important agents in the management of epilepsy. They are drugs of first choice for status epilepticus and seizures associated with post-anoxic insult and are also frequently used in the treatment of febrile, acute repetitive and alcohol withdrawal seizures. Clinical advantages of these drugs include rapid onset of action, high efficacy rates and minimal toxicity. Benzodiazepines are used in a variety of clinical situations because they have a broad spectrum of clinical activity and can be administered via several routes. Potential shortcomings of BZDs include tolerance, withdrawal symptoms, adverse events, such as cognitive impairment and sedation, and drug interactions. Benzodiazepines differ in their pharmacologic effects and pharmacokinetic profiles, which dictate how the drugs are used. Among the approximately 35 BZDs available, a select few are used for the management of seizures and epilepsy: clobazam, clonazepam, clorazepate, diazepam, lorazepam and midazolam. Among these BZDs, clorazepate has a unique profile that includes a long half-life of its active metabolite and slow onset of tolerance. Additionally, the pharmacokinetic characteristics of clorazepate (particularly the sustained-release formulation) could theoretically help minimize adverse events. However, larger, controlled studies of clorazepate are needed to further examine its role in the treatment of patients with epilepsy.

Benzodiazepines: some aspects of their clinical pharmacology

Benzodiazepine derivatives are the most commonly prescribed anti-anxiety agents in clinical practice. Six benzodiazepine anxiolytics are now available in the United States. Additional drugs are used in other parts of the world, and many others are in various stages of clinical testing. All these benzodiazepine derivatives have similar neuropharmacological properties--they reduce anxiety, produce sedation and sleep, have anticonvulsant effects, and can produce muscle relaxation. Faced with this bewildering array of drugs from the same class which are very similar in intrinsic effects upon the brain, the clinician may well ask how best to make a rational choice among the available derivatives. Despite neuropharmacological similarities, there are differences among benzodiazepines in patterns of absorption, distribution, and elimination by the human body. These pharmacokinetic differences may in turn lead to apparent differences in clinical action. This review summarizes pertinent pharmacokinetic characteristics of benzodiazepine anti-anxiety agents.

Drugs and chemicals in human milk

There is continuing emphasis by many professionals and organizations on the importance of breastfeeding as optimal infant nutrition. Pediatricians are frequently asked about the safety of medications taken by the nursing mother and the risk to the infant. Most drugs and many chemicals will be transferred into milk. For a vast majority of these compounds, there is no risk to the infant. It is almost always possible for the mother to continue nursing while taking the necessary medication. This article presents an introduction to the pharmacology of the transfer of drugs into milk, discusses the importance of the infant's age in assessing safety and presents a number of maternal conditions for which drugs need to be used.

Nerve agent attacks on children: diagnosis and management

Nerve agents (NAs) are the most lethal chemical weapons. We review the pathophysiology and management of NA poisoning of children. NAs cause cholinergic crisis. Children may manifest signs of cholinergic poisoning differently than adults. Children may be less likely to manifest miosis and glandular secretions. They may present with neurologic derangements alone. The goals of treatment should be to limit additional exposure, to provide respiratory support, and to prevent neurologic morbidity. Autoinjectors are optimal delivery vehicles for intramuscular antidotes and are likely to be used in civilian prehospital care. Antidotes include anticholinergics, oximes, and benzodiazepines. Several medications may be available within each class of antidotes. Clinicians will select an antidote based on the status of the individual victim, the accessibility of supportive care, and the availability of the drug. Atropine is well-tolerated and high doses may be required. The oxime pralidoxime chloride has a longer half-life in children. Currently, diazepam is the standard NA anticonvulsant. Midazolam may be the most effective intramuscular anticonvulsant after NA exposure, but, despite its efficacy, it is not an approved agent for seizures. Supportive care and long-term complications are summarized.

Treatment of neonatal abstinence syndrome

Neonatal abstinence syndrome (NAS) is suffered by infants withdrawing from substances on which they have become physically dependent after in utero exposure. They may require prolonged treatment and spend weeks or even months in hospital. A wide range of drugs have been used to treat NAS. The efficacy of few, however, have been adequately investigated. Evidence suggests that opioids are the most appropriate, at least in infants exposed to diamorphine or methadone. In all "head to head" trials, diazepam has been shown to be ineffective. Morphine and methadone are currently the most commonly prescribed opioids to treat NAS, but randomised trials have not been undertaken to determine which is the more beneficial. Many infants with NAS have been exposed to multiple substances in utero. Further research is required into whether a single opiate or a multiple drug regimen is the best option for such patients.

Pharmacokinetics and anticonvulsant effects of diazepam in children with severe falciparum malaria and convulsions

AIMS

Convulsions are a common complication of severe malaria in children and are associated with poor outcome. Diazepam is used to terminate convulsions but its pharmacokinetics and pharmacodynamics have not been studied in this group. Accordingly, we carried out a comparative study of the pharmacokinetics of intravenous (i.v.) and rectal (p.r.) diazepam.

METHODS

Twenty-five children with severe malaria and a convulsion lasting >5 min were studied. Sixteen children received diazepam intravenously (i.v.; 0.3 mg kg(-1)) and nine rectally (p.r.; 0.5 mg kg(-1)). Plasma diazepam concentrations were measured by reversed phase high-performance liquid chromatography. The duration of convulsions, depth of coma, respiratory and cardiovascular parameters were monitored.

RESULTS

Median maximum plasma diazepam concentrations of 634 (range 402-1507) ng ml(-1) and 423 (range 112-1953) ng ml(-1) were achieved at 5 and 25 min following i.v. and p.r. administration, respectively. All patients except three (one i.v. and two p.r.) achieved plasma diazepam concentration >200 ng ml(-1) within 5 min. Following p.r. administration, plasma diazepam concentrations were more variable than i.v. administration. A single dose of i.v. diazepam terminated convulsions in all children but in only 6/9 after p.r. administration. However, nine children treated with i.v. and all those treated with p.r. diazepam had a recurrence of convulsions occurring at median plasma diazepam concentrations of 157 (range: 67-169) and 172 (range: 74-393) ng ml(-1) , respectively. All the children in the i.v. and four in the PR diazepam group who had recurrence of convulsions required treatment. None of the children developed respiratory depression or hypotension.

CONCLUSIONS

Administration of diazepam i.v. or p.r. resulted in achievement of therapeutic concentrations of diazepam rapidly, without significant cardio-respiratory adverse effects. However, following p.r. administration, diazepam did not terminate all convulsions and plasma drug concentrations were more variable.

Pharmacokinetics of orally administered omeprazole in children. International Pediatric Omeprazole Pharmacokinetic Group

OBJECTIVES

The aim of this study was to examine the pharmacokinetics of orally administered omeprazole in children.

METHODS

Plasma concentrations of omeprazole were measured at steady state over a 6-h period after administration of the drug. Patients were a subset of those in a multicenter study to determine the dose, safety, efficacy, and tolerability of omeprazole in the treatment of erosive reflux esophagitis in children. Children were 1-16 yr of age, with erosive esophagitis and pathological acid reflux on 24 h-intraesophageal pH study. The "healing dose" of omeprazole was that at which subsequent intraesophageal pH study normalized. Children remained on this dose for 3 months, and during this period the pharmacokinetics were measured.

RESULTS

A total of 57 children were enrolled in the overall healing phase of the study. Pharmacokinetic study was optional for subjects and was performed in 25 of the 57 enrolled. The doses of omeprazole required were substantially higher doses per kilogram of body weight than in adults. Values of the pharmacokinetic parameters of omeprazole were generally within the ranges previously reported in adults. However, the plasma levels, area under the plasma concentration versus time curve (AUC), plasma half-life (t(1/2)), and maximal plasma concentration (Cmax), were lower in the younger age group, when the AUC and Cmax were normalized to a dose of 1 mg/kg. Furthermore, within the group as a whole, these values showed a gradation from lowest in the children 1-6 yr of age to higher in the older age groups.

CONCLUSIONS

The pharmacokinetics of omeprazole in children showed a trend toward higher metabolic capacity with decreasing age, being highest at 1-6 yr of age. This may explain the need for higher doses of omeprazole on a per kilogram basis, not only in children overall compared with adults but, in many cases, particularly in younger children.

Use of midazolam for refractory status epilepticus in pediatric patients

Status epilepticus is more common among children than young adults. Children might be less likely to die and might be resistant to permanent neurologic damage due to status epilepticus, but significant sequelae also have been demonstrated. Aggressive intervention and rapid termination of seizures contribute significantly to better prognosis and reduced mortality from status epilepticus. Initial treatment of status epilepticus typically consists of either diazepam or lorazepam, immediately followed by phenytoin or phenobarbital. However, approximately 100% to 15% of status epilepticus episodes are refractory to these conventional therapies. Traditionally, refractory status epilepticus is treated with barbiturate coma or general anesthetics, both of which require invasive cardiorespiratory and hemodynamic monitoring and are associated with significant complications. Midazolam is a water-soluble benzodiazepine with a fast onset of action, a short half-life, and inactive metabolites that has been very effective in terminating seizures refractory to diazepam, lorazepam, phenytoin, and phenobarbital in pediatric patients. Midazolam is a valuable treatment option for refractory status epilepticus, especially in pediatric patients.

Anesthesia for neonatal surgical emergencies

In this review of the anesthetic considerations for the neonate who requires anesthesia for emergency surgery, the authors discuss preoperative, intraoperative, and postoperative management from an anesthetic perspective. Monitoring the cardiorespiratory and metabolic status of neonates during anesthesia is usually difficult because the neonate is not physically accessible. Specific monitoring techniques that provide accurate measurements are discussed. General anesthesia is usually required for the surgery, the airway must be secured and anesthesia managed with a combination of inhalational and intravenous agents. Regional anesthesia and opioids may be included to decrease the intraoperative anesthetic requirements and prevent pain in the postoperative period. The pharmacology of specific anesthetic and adjuvant agents are discussed.

Clinical pharmacology of midazolam in infants and children

Midazolam is a parenteral benzodiazepine with sedative, amnesic, anxiolytic, muscle relaxant and anticonvulsant properties. The drug exerts its clinical effect by binding to a receptor complex which facilitates the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Midazolam has a faster onset and shorter duration of action than other benzodiazepines such as diazepam and lorazepam. The most serious adverse events associated with midazolam in children include hypoventilation, decreased oxygen saturation, apnoea and hypotension. It is water soluble in the commercially prepared formulation but becomes lipid soluble at physiological pH and can then cross the blood brain barrier. It is metabolised in the liver by the cytochrome P450 system, and its chief metabolite is 1-hydroxymethyl midazolam. The latter is conjugated to the glucuronide form, and it has only minimal biological activity. Midazolam is excreted primarily by the kidney. Its half-life in children over 12 months is reported to be 0.8 to 1.8 hours, with a clearance of 4.7 to 19.7 ml/min/kg. Doses given to children must be calculated on a mg/kg basis. For children 6 months to 5 years of age the initial dose is 0.05 to 0.1 mg/kg. A total dose up to 0.6 mg/kg titrated slowly may be necessary to achieve the desired endpoint. For children 6 to 12 years of age the initial dose is 0.025 to 0.05 mg/kg with a total dose up to 0.4 mg/kg to achieve the desired end-point.

Neonatal withdrawal syndrome and behavioral effects produced by maternal drug use

Over the last two decades, drug and alcohol abuse by pregnant women has spread to epidemic proportions. Maternal drug abuse has neurobehavioral and somatic effects which may be long-lasting and devastating to the offspring. Opiates, such as heroin and pain killers that contain a narcotic component, are widely abused today. A prominent manifestation of fetal exposure to these drugs is the neonatal withdrawal syndrome, which typically includes wakefulness, jitteriness and other symptoms of cerebral irritability. These, in turn, may interrupt early mother-infant interaction, affecting the infant's long-term emotional and cognitive development. Fetal cocaine exposure may cause neonatal cerebral irritability, changes in habituation responses, reduced head circumference, poor mental development and long-lasting impairment of the brain. Benzodiazepines can cause fetal dysmorphism (including microcephaly), neurological and behavioral impairments and neonatal withdrawal symptoms. Maternal use of amphetamines may cause neonatal dysphoria and agitation, as well as long-term lassitude and drowsiness that may result in poor feeding. Fetal exposure to alcohol may cause neonatal withdrawal symptoms, maladaptive behavior in childhood and the fetal alcohol syndrome (including microcephaly). Maternal alcohol consumption is also a common cause of mental retardation. Fetal exposure to marijuana may delay maturation of the visual system and impair memory and verbal performance at 2 years of age. The inevitable conclusion is that society must seek ways not only to treat, but also to prevent this epidemic. To this end, a key factor would be to identify potential drug abusing mothers before they reach the stage of prenatal care and educate them regarding the fatal consequences of drug abuse.

[Severe head injuries in neonates and infants: physiopathological and therapeutic aspects]

Severe head injuries in infants have specific circumstances such as obstetrical injury, battered infant, shaken infant. Pediatric scales must be used for neurological evaluation, the Bicêtre scale being a sensitive index of clinical course. Transfontanellar ultrasound can be useful as first line tool of evaluation of brain injury, but computerized tomography scan is necessary to correctly assess the brain lesions and the presence of hematoma. Hemorragic lesions can rapidly lead to hypovolemic state which must be prevented, or treated without delay. Treatment requires hemodynamics and hydroelectrolytic support, measures to control intracranial hypertension, sedation, and neurosurgical intervention according to the hemorragic lesions.

Sedation in pediatric patients

Sedation is being used increasingly in children to allay anxiety and discomfort. Sedation can also increase the efficiency of performing both diagnostic and therapeutic procedures in children. There are a wide array of available sedation methods that are used by radiologists, gastroenterologists, hematologists/oncologists and emergency room physicians everyday. Indiscriminate use of sedatives has led to seizures, respiratory arrests and death in a variety of practice settings. With improved monitoring capability, more potent drugs and better understanding of the pharmacokinetics in children, it is possible to provide batter care.

Sedation for the pediatric patient. A review

Safe sedation of a pediatric patient requires a thorough knowledge of the pharmacokinetics and pharmacodynamics of the drugs used to sedate the patient and the skills necessary to deal effectively with potential adverse events as a result of the sedation. The Sedation Guidelines of the American Academy of Pediatrics are reviewed. Emphasis is placed on monitoring and appropriate selection of drugs.

Pharmacokinetics of midazolam during continuous infusion in critically ill neonates

Midazolam is a water soluble benzodiazepine, with a short elimination half-life in adults and children. An IV bolus (0.2 mg.kg-1) immediately followed by continuous infusion of 0.06 mg.kg-1.h-1 was administered to 15 critically ill neonates at a gestational age of 32.8 weeks, who required sedation for mechanical ventilation. Heart rate and blood pressure were closely monitored. Hypotension occurred in 4 patients after the bolus dose or during the continuous infusion. Three of them had also been given fentanyl. Individual pharmacokinetic parameters were calculated: plasma clearance was 3.9 ml.min-1, elimination half-life was 12.0 h. Because of its short half-life compared to diazepam, midazolam may be used during the neonatal period to achieve rapid, brief sedation. However, it should be administered cautiously to neonates, particularly in premature infants, or if fentanyl is also given.

Pharmacokinetics of midazolam in critically ill neonates

Midazolam is a water soluble benzodiazepine, with a short elimination half-life in adults and children. An IV bolus of midazolam 0.2 mg.kg-1 was administered to 10 critically ill neonates receiving intensive care who required sedation. The plasma clearance was 6.85 ml.min-1 and the elimination half-life was 6.52 h. Midazolam was well tolerated during and after administration. Because of its short half-life compared to diazepam, midazolam could be used during the neonatal period to produce brief rapid sedation.

Teratogenic effects of benzodiazepine use during pregnancy

Eight children exposed in utero to benzodiazepines had characteristic dysmorphic features, growth aberrations, and central nervous system abnormalities from birth. Their dysmorphic characteristics resembled those of the fetal alcohol syndrome, although they had greater focal involvement of cranial nerves, with a sullen and expressionless face, and they more often had impairment of vitality at birth. One infant died and at autopsy had varying degrees of distortion of neuronal migration, with concomitant heterotopias. Five of the eight mothers had regularly consumed benzodiazepines, and the three remaining mothers had blood samples during pregnancy revealing benzodiazepine concentrations indicative of regular use. Our findings indicate that maternal consumption of benzodiazepines may be teratogenic in humans.

Aspects of antiepileptic treatment in children

About 75% of patients with epilepsy have seizures during childhood, often requiring antiepileptic therapy. Children possess all the drug-specific pharmacokinetic features of adults (e.g., nonlinearity of phenytoin elimination and autoinduction of carbamazepine metabolism), plus other factors (e.g., age, intercurrent illness, comedication) that influence dosage. Kinetic differences are maximal in newborns and infants, with limited drug elimination in premature and full-term babies, soon followed by accelerated elimination during infancy and childhood, before lower adult elimination rates develop during late childhood or early adolescence. Most children with epilepsy require two- to fourfold larger doses relative to bodyweight than adults, to achieve comparable drug levels and therapeutic effects. Although rapid growth may require increased dosage, the need is limited as relative clearance declines with age. Children of any age, but particularly premature and newborn babies, show greater individual variability in drug handling and therefore in dose requirements than adults. Clinical response and antiepileptic drug concentrations should both be monitored carefully in children.

Special pharmacokinetic considerations in children

Pediatric patients have greater degrees of pharmacokinetic variability and unpredictability than adults. This variability results from the effects of pharmacogenetics, age and growth, prior and current comedication, and disease. Newborns with seizures have the least predictable dosage requirements, and their needs change as drug-eliminating mechanisms mature in the neonatal period. Infants have the highest relative capacities to eliminate antiepileptics of any age group and require the largest relative doses. In addition to age-related trends, children demonstrate the same drug-specific, pharmacokinetic phenomena that adults do, including nonlinear phenytoin elimination, nonlinear valproate binding, and autoinduction of carbamazepine. Intercurrent illness and drug interactions further modify the age-related pharmacokinetic patterns in children and make dosage requirements even more unpredictable. Recent studies have shown that febrile illness can affect drug elimination, sometimes decreasing drug levels by 50% or more. Intermittent treatment with benzodiazepines administered either orally or rectally can be an important adjunct and help minimize this type of problem for children with marginally controlled epilepsy. Intermittent benzodiazepines are also helpful for children who have febrile seizures and who need only occasional antiepileptic protection.

Mechanisms of anticonvulsant drug action. II. Drugs primarily used for absence epilepsy

The usefulness of the anticonvulsant drugs is determined by the mechanisms by which the agent acts and its pharmacokinetics. The general mechanisms of action of these agents include (1) effects on neurotransmitter action, (2) effects on repetitive neuronal firing mechanisms, (3) effects on neuronal networks, and (4) effects on neuronal ionic transport. Ethosuximide, valproic acid and clonazepam are used primarily in absence epilepsy. Valproic acid is also effective against generalized tonic-clonic epilepsy. Diazepam is used primarily in status epilepticus. Valproic acid enhances gamma aminobutyric acid (GABA)-mediated inhibition, reduces repetitive firing, and reduces both inhibition and excitation in neuronal networks. Clonazepam and diazepam enhance the inhibitory action of GABA, decrease inhibition in neuronal networks and affect calcium ion transport with lesser effects on repetitive firing. Ethosuximide reduces inhibition in neuronal networks, may interact with dopamine, and possibly affects sodium and potassium ion transport. Further work is needed to assess the degree of involvement of these effects in the anticonvulsant action versus the adverse effects of these agents.

Post-marketing studies of drug efficacy: why?

In order to quantify the need for post-marketing studies of drug efficacy, the 100 drug uses (i.e., drug-indication pairs) that were most common in 1978 were reviewed. Of the 100 most common drug uses, 31 were not Food and Drug Administration (FDA)-approved at the time of initial marketing and 18 had not become FDA-approved, even subsequently. In 13, the use was based on the drug's secondary effect rather than on the primary effects investigated before marketing. The efficacy of all was subject to modification by incompletely explored factors, including other drugs, patient age, other illnesses, pregnancy, etc. Specific examples are provided of important modifiers of the efficacy of these drugs that were not investigated prior to marketing. Thus, despite the existence of sufficient data for the regulatory process to permit the marketing of these commonly used drugs, considerable gaps remain in the information needed for their optimal clinical use. Post-marketing studies of drug efficacy will be needed to fill these gaps.

The effect of exposure to diazepam through the placenta or through the mother's milk. Histological findings in slices of rat brain

Exposure to diazepam during the prenatal or early postnatal developmental period has been reported to result in later behavioural deficits. In the present study morphological changes in the brains of rats that were exposed to diazepam (DZP) prenatally or through the mother's milk postnatally were investigated. The results showed that prolonged prenatal exposure (16 days) to diazepam (10 mg/kg) resulted in characteristic and extensive pathological changes, i.e. gliosis and perivascular cuffing in the brains of the rats. These changes could be observed under the light microscope a long time after exposure to the drug had been terminated. Limiting the prenatal exposure to a single trimester of 7 days reduced somewhat the number of lesions but did not prevent their occurrence. Rats exposed to diazepam postnatally through the mothers' milk showed very few lesions.

The effects of exposure to diazepam during various stages of gestation or during lactation on the development and behavior of rat pups

In the present study we have investigated the effects of diazepam (DZP) (10 mg/kg) treatment of rat dams during different periods of gestation or during lactation on the development and behavior of their offspring. The results show that DZP exposure during different phases of early development has differing effects on later behavior. Exposure during mid-gestation resulted in early and transient hyperactivity, but no learning or memory deficits at 2 months of age were observed. However, both late prenatal and early postnatal exposure to DZP resulted in significant behavioral changes. Late prenatal treatment caused no hyperactivity but resulted in poor performance on the learning and retention of a choice discrimination task, while early postnatal exposure resulted in consistent and lasting hyperactivity and in substantial discrimination learning and retention deficits at 2 months of age.

Decreased serum protein binding of diazepam and its major metabolite in the neonate during the first postnatal week relate to increased free fatty acid levels

The protein binding of diazepam (D) and its major active metabolite N-desmethyl diazepam (DD) was investigated in vitro in the serum of 14 mothers at birth, 21 foetuses at birth, in 100 neonates between 1 and 11 days of age and in 16 control subjects. The free (unbound) fractions of D and DD in the foetus were similar to those in the controls, but lower than those in the mothers. During the first day of life the free fractions of D and DD doubled in the neonates and subsequently declined slowly to reach near control levels at 1 week of age. The sharp increase and slow decrease of the free fractions of D and DD during the first postnatal week was closely paralleled by sharply increasing and decreasing free fatty acid (FFA) concentrations. Bilirubin and albumin levels were of lower importance in regard to the protein binding of D and DD. These results indicate that the greatly increased FFA levels shortly after birth result in increased free fractions of D and DD. Because of the known immaturity of the neonatal hepatic elimination capacity, these elevated free fractions may result in elevated free concentrations of the two compounds, which may help to explain the adverse effects observed clinically in some D-exposed neonates.

Pharmacokinetics and tissue distribution of metronidazole in the new born infant

Metronidazole pharmacokinetics and tissue distribution were studied in 11 infants varying in gestational age from 28 to 40 weeks. Elimination half-life was inversely related to gestational age, and ranged from 22.5 to 109 hours. Hepatic hydroxylation of metronidazole was not evident in infants less than 35 weeks' gestation, unless they had been exposed prenatally to betamethasone. A dosage schedule of 15 mg/kg intravenously as an initial single dose is proposed, and will provide adequate therapeutic levels for 48 hours in the preterm infant and for 24 hours in the term infant. Subsequently a dose of 7.5 mg/kg/12 hours is suggested for the first week of life.

Prenatal and neonatal drug metabolism in man

Drug oxidations are catalyzed by the liver microsomal fraction of human fetuses but not by fetal livers from most experimental animals. In contrast, glucuronidation of some substrates is catalyzed by the rat fetal liver in late gestation but not in the human fetal liver. The deficient human fetal glucuronidation seems to be compensated for by early development of sulfation activity. The inconsistency of the results from animal fetuses and human fetuses shows that animal data have little relevance for the human fetus. No generalized statements can be made about drug disposition in the newborn infant as compared to adults. Although most drugs that are oxidized have prolonged plasma half-lives in the neonatal period there are examples of drugs with half-lives similar to, or even shorter than, the average half-lives in adults. Oxazepam is conjugated with glucuronic acid in adults. The neonatal plasma half-life of this drug is considerably prolonged. This is true also for its conjugate as would be expected from the immature renal function in newborns. Adequate pharmacokinetic information is a prerequisite for rational and safe drug treatment in the neonatal period.

Psychological performance in anxious patients treated with diazepam

1. After each week of a flexible dosage treatment with either diazepam, amylobarbitone or placebo anxious patients were assessed by a comprehensive battery of psychiatrist's ratings, subjective tests and psychological performance tasks to detect the clinical and psychological effects of the drugs. 2. Self rated anxiety and insomnia were improved significantly by diazepam, while amylobarbitone improved only the self rated insomnia. 3. An impairment of performance relative to placebo was detected on two performance tasks after the barbiturate and on six performance tasks after the benzodiazepine. 4. The patient's reported level of anxiety under each treatment condition was related to the performance on the five tasks showing drug effects, thus confirming the postulated inverted U-shape relationship between drive and performance.

Plasma concentrations of diazepam and N-desmethyldiazepam in newborn infants after intravenous, intramuscular, rectal and oral administration

Five newborn infants (birth weight 2900--3600 g) were given diazepam (Valium, LaRoche) for convulsive disorders in 4 equal doses intravenously, intramuscularly, rectally and orally with at least 24 hours intervals. Three infants were given doses of 1 mg diazepam/kg body weight, and 2 0.5 mg/kg. The parenteral solution of the drug was given intravenously, intramuscularly and rectally. Powder of tablets was given orally. After intravenous administration very high peak values of plasma-diazepam concentration were obtained (5775--10800 ng/ml after 1 mg/kg, 2750 and 6450 ng/ml after 0.5 mg/kg). Next to intravenous administration rectal administration caused the most rapid increase in plasma-diazepam concentration. Presumed anticonsulsive concentrations (150--300 ng/ml) were obtained within 5 min with 1 mg/kg as well as 0.5 mg/kg rectally. Rectal administration therefore could be a suitable treatment for seizures in the newborn infant. Accumulation of the main depressive metabolite N-desmethyldiazepam occurred in all infants. This phenomenon must be taken into account when repeated doses of diazepam are administered.

[Clinical pharmacokinetics of diazepam and its biologically active metabolites (author's transl)]

The pharmacokinetics of diazepam and its biologically active metabolites desmethyldiazepam and oxazepam is critically evaluated from a clinically relevant point of view. The slow elimination of diazepam is dependent on the degree of plasma protein binding, the duration of the medication, the age and the liver function of the patient. While the normal half-life (T1/2(beta)) varies between 1 and 2 days, it can be increased to up to 80--100 h in subjects over 60 years of age. In patients with liver disease T1/2(beta) is about doubled, which is caused by a reduction (factor 2) of the normal hepatic clearance of 26 ml/min. After subchronic treatment with diazepam the elimination rate is reduced about 20--70% in healthy subjects, but liver patients exhibit only a slightly further prolongation in T1/2(beta). The major metabolite desmethyldiazepam has a T1/2(beta) of 51 h and a Cl of 11 ml/min and accumulates after multiple doses of diazepam since its elimination is much slower than that of its parent compound. The elimination of this drug is also impaired (factor 2) in patients with liver disease. In contrast to these findings oxazepam is excreted as glucuronide in the urine relatively fast and independently of the liver function with a T1/2(beta) of 5.5 h and a Cl of 130 ml/min.

The pharmacokinetics and metabolism of the anilide local anaesthetics in neonates. I. Lignocaine

The pharmacokinetics and metabolism of lignocaine in premature neonates was studied after subcutaneous administration. The collection of serial urine together with a limited number of blood samples from neonates enabled simultaneous computer fitting of data to a pharmacokinetic model. The disposition kinetics of lignocaine in four neonates were compared with similar data reported for adults. Neonates had prolonged t1/2 (neonate mean: 3.16 h; adult mean: 1.80 h), and an increased total volume of distribution (neonate mean: 2.75 l/kg; adult mean: 1.11 l/kg) compared with adults. Total plasma clearance (Cltp) normalised on body weight showed no significant difference between neonates (mean: 0.610 l/h/kg) and adults (mean: 0.550 l/h/kg). The urinary excretion of lignocaine and several of its metabolites was studied in 8 neonates and 11 adults. Neonates were shown to excrete much more unchanged lignocaine (mean: 19.67%) compared with adults (mean: 4.27%) and the proportion of the dose excreted as 4-hydroxyxylidine is considerably reduced in neonates (neonate mean: 8.89%; adult mean: 63.78%). The use of the two pharmacokinetic parameters, t1/2 and Cltp, as indices of drug elimination ability are discussed.

Determination of desmethyldiazepam in plasma by electron-capture GLC: application to pharmacokinetic studies of clorazepate

Plasma desmethyldiazepam concentrations were quantitated by a rapid and sensitive technique using electron-capture GLC. Following addition of diazepam as the internal standard, plasma is extracted at physiological pH into benzene-isoamyl alcohol. The extract is evaporated to dryness and reconstituted with toluene-isoamyl alcohol prior to chromatography. Both diazepam and desmethyldiazepam are quantitatively extracted. The variation of identical samples is 5%, and the sensitivity is 5 ng of desmethyldiazepam/ml of original sample. The method is applicable to pharmacokinetic studies of clorazepate, a benzodiazepine derivative transformed to desmethyldiazepam prior to absorption.

Plasma-diazepam in infants after rectal administration in solution and by suppository

Twenty infants aged 1-2 years who had previously had one attack of febrile convulsions were randomly given a single dose of diazepam rectally, either as a solution (0.7 mg/kg) or by suppository (5 mg). Plasma-diazepam levels were determined repeatedly during the first hour using gas chromatography. Rectal administration of diazepam in solution resulted in anticonvulsant plasma values within 4 +/- 1 min. Similar plasma levels were obtained only after 20-30 min in the group treated with suppositories. Diazepam in solution given rectally may therefore be useful in the acute treatment of febrile convulsions, while treatment by suppository would seem to be of little value in this respect. Moreover, diazepam in solution given rectally seems suitable for use at home in case of recurrent febrile convulsions. This treatment, however, cannot be recommended until the anticonvulsant effect and side-effects have been elucidated further.

Pharmacokinetic observations of phenytoin disposition in the newborn and young infant

The pharmacokinetic profile of phenytoin (DPH) was studied in 30 infants aged 2 days to 96 weeks. The plasma DPH half-life during the first week of life in term infants was prolonged and very variable (20-7 +/- 11-6 h, mean +/-SD). Thereafter the plasma half-life was much shorter (7-6 +/- 3-5 h). In preterm infants the half-life was much longer (75-4 +/- 64-5 h) and more variable. The mean apparent volume of distribution was similar in these groups of infants: preterm newborn 0-80 +/- 0-22 l/kg, term infants during the first week of life 0-80 +/- 0-26 l/kg, and term infants greater than 2 weeks of age 0-73 +/- 0-18 l/kg. Predictions of steady-state plasma DPH concentrations, based on these kinetic parameters, were confirmed. Very low "trough" plasma DPH concentrations were observed after the 14th postnatal day in 19 infants receiving 8 mg/kg per 24 h orally. On the other hand, infants of less than one week of age receiving the same dose, especially if preterm, frequently showed drug accumulation to toxic plasma DPH concentrations. The impaired binding of DPH to newborn plasma protein was confirmed but "normal adult values" were approached by the age of 3 months. An intravenous loading dose of 8 mg/kg (sodium phenytoin) can be expected to generate a mean plasma DPH concentration of 10 mg/l (40 micronmol/l) in the newborn. Loading doses of up to 12 mg/kg were given without untoward effects. During the first week or so of life plasma Dph half-life is so variable that no fixed dosage regimen can be derived from the available data. Beyond the second week of life, however, a dose of 8 mg/kg per 24 h is probably inadequate for most infants.