Alteration of carbamazepine pharmacokinetics in patients with traumatic brain injury

Management of Elevated Intracranial Pressure

Elevated intracranial pressure (ICP) is a primary cause of morbidity and mortality for many neurologic disorders. The relationship between ICP and brain volume is influenced by autoregulatory processes that can become dysfunctional. As a result, neurologic damage can occur by systemic and intracranial insults such as ischemia and excitatory amino acids. Therefore, survival is dependent on optimizing ICP and cerebral perfusion pressure. Treatment of intracranial hypertension requires intensive monitoring and aggressive therapy. Intracranial pressure monitoring techniques such as intraventricular catheters are useful for determining ICP elevations before changes in vital signs and neurologic status. Therapeutic modalities, generally aimed at reducing cerebral blood volume, brain tissue, and cerebrospinal fluid (CSF) volume, include nonpharmacologic (CSF removal, controlled hyperventilation, and elevating the patient’s head) and pharmacologic management. Mannitol and sedation are first-line agents used to lower ICP. Barbiturate coma may be beneficial in patients with elevated ICP refractory to conventional treatment. The use of prophylactic antiseizure therapy and optimal nutrition prevents significant complication. Currently, investigations are directed at discovering useful neuroprotective agents that prevent secondary neurologic injury.

Dosing and therapeutic monitoring of phenytoin in young adults after neurotrauma: are current practices relevant?

Anticonvulsant drugs are commonly used to treat and prevent seizures after neurotrauma. However, many physiological changes occur in the neurotrauma patient, which alter the pharmacokinetics of drugs such as phenytoin. This raises concerns relating to the dosage and monitoring of phenytoin in these patients compared with its routine use in epileptic patients. Examples of pharmacokinetic alterations within the neurotrauma patient include changes in hepatic metabolism, protein binding alterations, and disruption of the blood-brain barrier. Drug interactions and genetic factors may also contribute to pharmacokinetic variations. Many studies have reported that neurotrauma patients often present with either subtherapeutic or highly variable phenytoin serum concentrations. When phenytoin doses recommended for the epileptic patient are used in the neurotrauma patient, efficacy is limited to early posttraumatic seizures, with no effect on morbidity, mortality, or the onset of late posttraumatic seizures. This review examines the effect of neurotrauma on the pharmacokinetics of phenytoin alongside clinical outcomes and questions the current dosing and therapeutic monitoring practices within this area.

Pharmacological prophylaxis of post-traumatic epilepsy

Early and late epileptic seizures are a frequent complication of severe head traumas. The administration of anticonvulsant drugs immediately after head injury is commonly implemented as a prophylactic measure; however, there is a lack of consensus on the usefulness of prophylaxis with anticonvulsants for the prevention of late post-traumatic epilepsy (PTE). The inconsistent evidence accumulated so far from clinical studies, most nonrandomised and uncontrolled in design, and the limited knowledge of the processes underlying post-traumatic epileptogenesis, do not warrant empirical pharmacological prophylaxis with long term administration of conventional anticonvulsants. Phenytoin and phenobarbital (phenobarbitone) are used to a large extent in this indication. As a general rule, a benefit/risk analysis in individual patients should drive prophylactic drug prescription in PTE as it can have potential detrimental effects on a patient's recovery. New compounds, such as free-radical scavengers and antiperoxidants, show encouraging experimental results, but their clinical use is still very limited.

Neuropsychiatric Aspects of Traumatic Brain Injury

Traumatic brain injury (TBI) may produce a variety of neuropsychiatric problems, including impaired cognition, depression, mania, affective lability, irritability, anxiety, and psychosis. Despite the common occurrence of these symptoms following TBI, there are relatively few studies that provide clear guidance regarding management. Many symptoms (eg, irritability, affective lability, fatigue, sleep disturbance, and impaired cognition) are primarily consequences of brain injury rather than symptoms of a comorbid psychiatric disorder such as major depression. Although it is difficult to study the complicated treatments needed for such symptom complexes, we are able to recommend an approach to the evaluation and treatment of neuropsychiatric problems following traumatic brain injury. A thorough assessment of the patient is a prerequisite to the prescription of any treatment. This assessment should include a thorough developmental, psychiatric, and medication history; a detailed mental status examination; a complete neurologic examination; and quantification of neuropsychiatric symptoms using standardized and accepted inventories (eg, Neurobehavioral Rating Scale, Neuropsychiatric Inventory ). All symptoms must be evaluated in the context of the patient's premorbid history and current treatment because neuropsychiatric symptoms may be influenced by either factor or by both factors. Psychotherapy is an important component of the treatment of neuropsychiatric problems following TBI. Additionally, patients should be encouraged to become involved with local TBI support groups. When medications are prescribed, it is essential to use cautious dosing (low and slow) and empiric trials with continuous reassessment of symptoms using standardized scales and monitoring for drug-drug interactions. In general, medications with significant sedative, antidopaminergic, and anticholinergic properties should be avoided, and benzodiazepines should be used sparingly, if at all. Although patients with TBI may be particularly susceptible to adverse effects of psychopharmacologic medications, at times dosages similar to those used for the non-brain-injured psychiatric patient may be needed. When a single medication does not provide adequate relief of symptoms or cannot be tolerated at therapeutic doses, an alternative strategy is to augment the effect of one medication by using a second low-dose agent with a different mechanism of action.