Pharmacokinetics and pharmacodynamics of vecuronium in children receiving phenytoin or carbamazepine for chronic anticonvulsant therapy

Donepezil-related inadequate neuromuscular blockade during laparoscopic surgery: A case report

BACKGROUND

Donepezil is an acetylcholinesterase inhibitor used to improve cognition and delay disease progression in dementia patients by increasing acetylcholine levels. This drug may potentially interact with neuromuscular blocking agents (NMBAs) that act on muscular acetylcholine receptors during general anesthesia. Herein, we present a case of inadequate neuromuscular blockade with rocuronium, a nondepolarizing NMBA, in a dementia patient who had taken donepezil.

CASE SUMMARY

A 71-year-old man was scheduled for laparoscopic gastrectomy. He had been taking donepezil 5 mg for dementia. General anesthesia was induced with propofol and remifentanil. The depth of neuromuscular blockade was monitored by train-of-four (TOF) stimulation. After the administration of rocuronium, the TOF ratio decreased at an unusually slow rate, and a TOF count of 0 was detected 7 min later. After intubation, a TOF count of 1 was detected within 1 min, and a TOF ratio of 12% was detected within 2 min. The TOF count remained at 4 even with an additional bolus and continuous infusion of rocuronium, suggesting resistance to this NMBA. Instead of propofol, an inhalation anesthetic was administered alongside another NMBA (cisatracurium). Then, the quality of neuromuscular blockade improved, and the TOF count remained at 0-1 for the next 70 min. No further problems were encountered with respect to surgery or anesthesia.

CONCLUSION

Donepezil may be responsible for inadequate neuromuscular blockade during anesthesia, especially when total intravenous anesthesia is used.

Prediction of Clearance in Children from Adults Following Drug-Drug Interaction Studies: Application of Age-Dependent Exponent Model

Background and Objective

Pharmacokinetic drug–drug interaction (DDI) studies are conducted in adult subjects during drug development but there are limited studies that have characterized pharmacokinetic DDI studies in children. The objective of this study was to evaluate if the DDI clearance values from adults can be allometrically extrapolated from adults to children.

Methods

Fifteen drugs were included in this study and the age of the children ranged from premature neonates to adolescents (30 observations across the age groups). The age-dependent exponent (ADE) model was used to predict the clearance of drugs in children from adults following DDI studies.

Results

The prediction error of drug clearances following DDIs in children ranged from 4 to 67%. Of 30 observations, 17 (57%) and 27 (90%) observations had a prediction error ≤ 30% and ≤ 50%, respectively.

Conclusion

This study indicates that it is possible to predict the clearance of drugs with reasonable accuracy in children from adults following DDI studies using an ADE model. The method is simple, robust, and reliable and can replace other complex empirical models.

Prolonged therapy with the anticonvulsant carbamazepine leads to increased plasma clearance of fentanyl

OBJECTIVES

Fentanyl is a potent analgesic that accounts for an increasing number of overdose deaths in the United States. This study tested whether altered pharmacokinetics plays a pivotal role in the increased fentanyl dose requirements in patients receiving the enzyme-inducing anticonvulsant, carbamazepine.

METHODS

Neurosurgical patients receiving carbamazepine for >6 weeks (N = 11) or no carbamazepine (N = 6, controls) received a single bolus dose of fentanyl (200 μg) intravenously. Plasma was collected before and for up to 9 h after the bolus. Fentanyl concentrations were measured using liquid chromatography-mass spectrometry. Pharmacokinetic variables were derived from plasma concentration-time curves best fitted to a two-compartment model.

KEY FINDINGS

Fentanyl clearance was significantly higher in the carbamazepine group compared to controls (mean ± SD: 20.1 ± 6.8 vs 13.2 ± 4.8 ml/min per kg, P < 0.05), and area under the plasma concentration curve (AUC) was significantly lower (150 ± 65 vs 233 ± 70 ng/ml × min, P < 0.02). Volume of distribution was larger in the carbamazepine group, but the difference was not statistically significant (5.4 ± 3.1 vs 3.6 ± 1.2 l/kg, P > 0.15). The terminal elimination half-life did not differ between the two groups.

CONCLUSIONS

Chronic carbamazepine therapy leads to increased fentanyl clearance and decreased AUC, which may result in decreased duration of therapeutic plasma concentrations of fentanyl and an increased dose requirement. Assuming that carbamazepine does not change fentanyl pharmacodynamics, patients on chronic carbamazepine therapy may require more frequent or higher fentanyl doses to maintain therapeutic plasma concentrations.

Antiepileptic drugs and anesthesia

Anesthetists commonly encounter epileptic patients when undergoing surgery. This review article discusses the drugs used to treat epilepsy and their relevant effects on anesthesia.

Complete resistance after maximal dose of rocuronium

Rocuronium is a non-depolarizing neuromuscular blocking agent (NDNMBA), employed in the clinic as an adjunct to general anesthesia to facilitate tracheal intubation rapid sequence, and to provide skeletal muscle relaxation during surgery. Many cases of resistance to neuromuscular blocking agents (NMBAs) have been anecdotally reported. There are specific pathologic states, such as upper motor neuron lesions, severe thermal injuries, liver disease, renal failure, disuse atrophy, all of which show an increased resistance to the effects of nondepolarizing muscle relaxants. Also concurrent drug therapy can alter the efficacy of NMBAs such as some classes of antibiotics, furosemide, β receptor agonists, phosphodiesterase inhibitors, calcium antagonists, respiratory stimulants but also ketamine, propofol and barbiturates at high concentrations. In this scenario we describe an unusual case of 20-years-old man who showed a complete resistance to rocuronium maybe due to a glucocorticoids concomitant therapy.

Studies of metabolite-protein interactions: a review

The study of metabolomics can provide valuable information about biochemical pathways and processes at the molecular level. There have been many reports that have examined the structure, identity and concentrations of metabolites in biological systems. However, the binding of metabolites with proteins is also of growing interest. This review examines past reports that have looked at the binding of various types of metabolites with proteins. An overview of the techniques that have been used to characterize and study metabolite-protein binding is first provided. This is followed by examples of studies that have investigated the binding of hormones, fatty acids, drugs or other xenobiotics, and their metabolites with transport proteins and receptors. These examples include reports that have considered the structure of the resulting solute-protein complexes, the nature of the binding sites, the strength of these interactions, the variations in these interactions with solute structure, and the kinetics of these reactions. The possible effects of metabolic diseases on these processes, including the impact of alterations in the structure and function of proteins, are also considered.

Effects of valproic acid and magnesium sulphate on rocuronium requirement in patients undergoing craniotomy for cerebrovascular surgery

BACKGROUND

Many anti-epileptics cause resistance to non-depolarizing neuromuscular blocking agents, but this has not been reported for valproic acid (VPA). We hypothesized that VPA would increase the rocuronium requirement and that magnesium sulphate (MgSO(4)) may reduce this increase.

METHODS

Fifty-five patients undergoing cerebrovascular surgeries were studied. Subjects were allocated into three groups at a 1:1:1 ratio: Groups VM, VC, and C. Groups VM and VC were given VPA premedication; Group C was not. A rocuronium injection (0.6 mg kg(-1) i.v.) was administered to Group VM, followed by MgSO(4) as a 50 mg kg(-1) i.v. bolus and 15 mg kg(-1) h(-1) infusion. The same volume of 0.9% saline was administered to the other groups. Supplementary rocuronium (0.15 mg kg(-1)) was given whenever the train-of-four count reached 2. Rocuronium requirements (primary outcome), mean arterial pressure (MAP), heart rate (HR), nausea, vomiting, shivering, and use of anti-emetics and nicardipine were compared.

RESULTS

Group VC showed the highest rocuronium requirement [mg kg(-1) h(-1): 0.47 (0.08) vs 0.33 (0.12) (Group C), 0.31 (0.07) (Group VM); P<0.001]. MAP, intraoperative HR, nausea, vomiting, shivering, and use of anti-emetics and nicardipine were not significantly different among the groups. Postoperative HR was lower in Group VM than in Group VC.

CONCLUSIONS

VPA increased the rocuronium requirement, and MgSO(4) infusion attenuated this increase.

Chronic phenytoin therapy-induced vecuronium resistance

This case report highlights a clinically significant pharmacokinetic drug interaction between phenytoin, a widely used anticonvulsant and vecuronium, a non-depolarizing neuromuscular blocker which led to vecuronium resistance.

Azole antimycotics and drug interactions in the perioperative period

PURPOSE OF REVIEW

A beneficial effect of antifungal prophylaxis on the prevention of invasive fungal infections has increased the use of azole antimycotics in intensive care and during the perioperative period. At the same time more severe illnesses are treated and multiple drug therapies are employed. Thus, the potential for severe drug-drug interactions has increased. Previous studies have shown that azole antimycotics increase the risk of many clinically significant drug interactions with potentially hazardous consequences.

RECENT FINDINGS

A recent pharmacoepidemiological study has found a more than five-fold incidence ratio in the adjusted rate of sudden death from cardiac diseases among those patients who were given simultaneously inhibitors of cytochrome P450 (CYP) enzymes and their substrates. Although new triazole antifungals are well tolerated, they still cause significant inhibition of CYP enzymes.

SUMMARY

This review focuses on azole antimycotics and anesthetic drugs being used during the perioperative period and discusses the possible clinically significant drug-drug interactions. Azole antimycotics are amongst the strongest inhibitors of CYP-mediated drug metabolism. Anesthesiologists must be aware of the interaction potential of azole antimycotics to be able to adjust their perioperative strategies according to the patient's condition and concomitant medication.

Cerebral hemispherectomy in infants and young children

BACKGROUND

Children with seizure disorders unresponsive to medical management may undergo surgical disconnection of a cerebral hemisphere, or hemispherectomy, in order to reduce or eliminate seizures. Because early cessation of seizures is thought to improve developmental outcomes, infants and young children with intractable seizures are undergoing hemispherectomies with increasing frequency. Previously, these procedures have been noted to be accompanied by severe cardiovascular, pulmonary, neurologic and coagulopathic complications. Newer surgical techniques (i.e. 'functional' rather than 'anatomic' hemispherectomy) and improved anesthetic management may reduce the perioperative complication rate of this procedure. The aim of this case series was to determine the incidence of major complication of functional hemispherectomy in our institution.

METHODS

A retrospective chart review was conducted of all children <3 years of age undergoing functional hemispherectomies for intractable seizures over a 4-year period at our institution.

RESULTS

Seven children were identified. No serious cardiovascular, pulmonary, neurologic or coagulopathic adverse events occurred. Perioperative blood loss and its sequelae were the most common complication. Postoperative management was generally uncomplicated, although one patient required readmission to the ICU for treatment of diabetes insipidus. All children survived and, at latest follow-up, all but one remained seizure-free.

CONCLUSION

This small case series suggests that improvements in anesthetic and surgical techniques may be associated with a decreased complication rate for infants and small children undergoing seizure surgery than previously reported.

Pharmacokinetic-pharmacodynamic modeling of the influence of chronic phenytoin therapy on the rocuronium bromide response in patients undergoing brain surgery

BACKGROUND

Antiepileptic drugs decrease the intensity of the effect of neuromuscular blocking agents. The objective of this study was to evaluate the influence of chronic phenytoin therapy (CPT) on the pharmacokinetics (PK) and pharmacodynamics (PD) of rocuronium.

METHODS

A total of 21 patients undergoing intracranial surgery were enrolled in the study. Ten of these were under CPT. Rocuronium was administered intravenously. Arterial blood samples were drawn, and the T1% (percentage change from the response to the supramaximal stimulus) derived from electromyogram was continuously recorded. NONMEM: software was used to construct, evaluate and validate the PKPD models.

RESULTS

The PKPD of rocuronium was described using a three-compartment PK model and effect compartment model. The CPT therapy was found to increase the total plasma clearance from 0.26 to 0.75 L min(-1). The PD model parameter estimates were k(e0)= 0.073 min(-1), IC(50) (the steady-state plasma concentration eliciting half of the maximum response) = 836 ng mL(-1) and gamma = 3.13.

CONCLUSIONS

Chronic phenytoin therapy increases the clearance of rocuronium from 0.26 to 0.75 L min(-1) but has no effect on the k(e0), IC(50) or gamma parameters.

Pediatric Neuroanesthesia

Recent advances in pediatric neurosurgery have drastically improved the outcome in infants and children afflicted with surgical lesions of the central nervous system (CNS). Because most of these techniques were first applied to adults, the physiologic and developmental differences that are inherent in pediatric patients present challenges to neurosurgeons and anesthesiologists alike. The aim of this paper is to highlight these age-dependent approaches to the pediatric neurosurgical patient.

Anesthesia for epilepsy surgery in children

BACKGROUND

The perioperative management of infants and children for epilepsy surgery should focus on the specific problems unique to the state of the disease, age of the child, and operative conditions. A basic understanding of age-dependent variables and the interaction of anesthetic and surgical procedures are essential in minimizing perioperative morbidity and mortality. Specific medical conditions that impact the conduct of anesthesia include congenital anomalies, chronic anticonvulsant therapies, and evolving coagulopathies. The neurosurgical procedure and neurophysiological monitoring will determine the type of anesthetic technique to be utilized during surgery.

OBJECTIVE

This review will provide a systematic approach to pediatric patients undergoing epilepsy surgery.

The effect of phenytoin on rocuronium-induced neuromuscular block in the rat phrenic nerve-hemidiaphragm preparation

Anticonvulsant therapy alters the action of nondepolarizing muscle relaxants. We determined the effects of acute and chronic administration of phenytoin on rocuronium-induced neuromuscular block using the rat phrenic nerve-hemidiaphragm preparation. Rats were divided into 3 groups: a saline control group (n = 10), an acute phenytoin-treated group (n = 30), and a chronic phenytoin-pretreated group (n = 30). Phrenic nerve-hemidiaphragm was dissected, mounted in a bath containing oxygenated Krebs solution, and the nerve was stimulated at supramaximal intensity. Single twitch responses were recorded by physiogram. In the acute phenytoin-treated group, acute effects of phenytoin were determined based on the phenytoin concentration of 1, 10, or 100 microg/mL in the bath. The chronic effects of phenytoin were determined using phrenic nerve-diaphragms from rats pretreated with phenytoin (50 mg/kg/d) for 1, 7, or 28 days. In rats with phenytoin 100 microg/mL in the bath, all concentrations of rocuronium produced twitch depression significantly different from those of other groups (P < 0.05), and the concentration-response curve shifted to the left. In rats with phenytoin 10 microg/mL in the bath, the effective concentrations for 50%, 90%, and 95% twitch depression values were significantly different from those of the control group (P < 0.05). In chronically (28 days) phenytoin-pretreated rats, the concentration-response curve significantly shifted to the right (P < 0.05). These findings show that acute administration of phenytoin augmented the neuromuscular blocking effects of rocuronium, whereas chronic phenytoin treatment causes resistance to the neuromuscular blocking effects of rocuronium in target organs.

Neuromuscular pharmacodynamics of rocuronium in patients with major burns

Rocuronium, which has a short onset time and is free of hyperkalemic effects, could be considered for rapid-sequence induction of anesthesia in patients with burns. In this study, we assessed the neuromuscular pharmacodynamics of rocuronium in patients with major burns. Adults aged 18-59 yr who had a major burn injury (n = 56) and a control group of 44 nonburned patients were included. Rocuronium was used at 3 times (0.9 mg/kg) or 4 times (1.2 mg/kg) the 95% effective dose. Anesthesia consisted of propofol and fentanyl with nitrous oxide and oxygen. Neuromuscular block was monitored with an acceleromyograph by using train-of-four stimulation. The onset time to 95% neuromuscular block was prolonged in burned compared with nonburned patients (115 +/- 58 s versus 68 +/- 16 s for 0.9 mg/kg; 86 +/- 20 s versus 57 +/- 11 s for 1.2 mg/kg). Dose escalation shortened the onset time, prolonged the duration of action, and improved intubating conditions in burned patients. All recovery profiles were significantly shorter in burned versus nonburned groups with both doses. Resistance to the neuromuscular effects of rocuronium was partially overcome by increasing the dose. A dose up to 1.2 mg/kg provides good tracheal intubating conditions after major burns.

Antiepileptic-Induced Resistance to Neuromuscular Blockers

Prolonged administration of antiepileptic drugs is associated with several drug interactions. In the field of anaesthesia and critical care, patients exhibit both sensitivity and resistance to non-depolarising neuromuscular blockers (NDNMBs) after acute and long-term administration of antiepileptic drugs, respectively. Although antiepileptic therapy alone has only mild neuromuscular effects, acutely administered antiepileptic drugs can potentiate the neuromuscular effects of NDNMBs as a result of direct pre- and post-junctional effects. Resistance to NDNMBs during long-term antiepileptic therapy is due to multiple factors operating alone or in combination, including induction of hepatic drug metabolism, increased protein binding of the NDNMBs and/or upregulation of acetylcholine receptors.

Anaesthetic management of children with tuberous sclerosis

BACKGROUND

Tuberous sclerosis (TS) is a hamartomatous disease that usually presents with cutaneous and intracranial lesions, but can also affect other organ systems.

METHODS

In this report, we retrospectively reviewed the perioperative course of 24 children with TS who had medically intractable seizures as the primary disease process.

RESULTS

Cardiac rhabdomyoma was detected in 11 of 18 patients who had a cardiac evaluation, and coexisting congenital heart defects were diagnosed in six. Ten of 17 patients who had a renal evaluation were diagnosed with renal TS, presenting with azotaemia in one and hypertension in four. The major perioperative complications in the 52 anaesthetics, included death (a neonate after cardiac rhabdomyoma resection), seizures (five patients) and bradyarrhythmias (two patients).

CONCLUSIONS

Patients with TS and neurological disorders frequently have coexisting cardiac and renal disease as well. Patients with TS should be evaluated for these organ specific disorders prior to surgery.

Pediatric neuroanesthesia

The perioperative management of pediatric neurosurgical patients presents many challenges to neurosurgeons and anesthesiologists. Many conditions are unique to pediatrics. Thorough preoperative evaluation and open communication between members of the health care team are important. A basic understanding of age-dependent variables and the interaction of anesthetic and surgical procedures are essential in minimizing perioperative morbidity and mortality.