Introduction
Iracet XR Tablet (Extended Release) 500 mg is a drug within the pyrrolidine class that is used to treat various types of seizures stemming from epileptic disorders. It was first approved for use in the United States in 1999 and is structurally and mechanistically unrelated to other anti-epileptic drugs (AEDs). Iracet XR Tablet (Extended Release) 500 mg possesses a wide therapeutic index and little-to-no potential to produce, or be subject to, pharmacokinetic interactions - these characteristics make it a desirable choice over other AEDs, a class of drugs notorious for having generally narrow therapeutic indexes and a propensity for involvement in drug interactions.
Uses
Iracet XR Tablet (Extended Release) 500 mg is a novel anticonvulsant agent used as an adjunct medication to manage partial onset, myoclonic, and generalized tonic-clonic seizures in patients with epilepsy.
Iracet XR Tablet (Extended Release) 500 mg is indicated as an adjunctive therapy in the treatment of partial onset seizures in epileptic patients who are one month of age and older. Additionally, it is indicated as an adjunct in the treatment of myoclonic seizures in patients with juvenile myoclonic epilepsy who are 12 years of age and older, and in primary generalized tonic-clonic seizures in patients with idiopathic generalized epilepsy who are 6 years of age and older.
Iracet XR Tablet (Extended Release) 500 mg is also available as an orally dissolvable tablet that is indicated as an adjunct in the treatment of partial onset seizures in patients with epilepsy who are 4 years of age and older and weigh more than 20kg.
Associated Conditions
Pharmacodynamics
Iracet XR Tablet (Extended Release) 500 mg appears to prevent seizure activity via the selective inhibition of hypersynchronized epileptiform burst firing without affecting normal neuronal transmission, though the exact mechanism through which this occurs is unclear. The therapeutic index of levetiracetam is wide, making it relatively unique amongst other anti-epileptic medications.
Anti-epileptic drugs, including levetiracetam, may increase the risk of suicidal ideation or behaviour - patients taking levetiracetam should be monitored for the emergence or worsening of depressive symptoms, suicidal ideation, and behavioural abnormalities.
Mechanism of Action
The exact mechanism through which levetiracetam exerts its anti-epileptic effects is unclear, but is thought to be unique amongst other anti-epileptic medications. Current knowledge suggests that levetiracetam’s binding to synaptic vesicle protein 2A (SV2A) is a key driver of its action. SV2A is a membrane-bound protein that is found on synaptic vesicles and is ubiquitous throughout the CNS - it appears to play a role in vesicle exocytosis and in the modulation of synaptic transmission by increasing the available amount of secretory vesicles available for neurotransmission. Stimulation of pre-synaptic SV2A by levetiracetam may inhibit neurotransmitter release, but this action does not appear to affect normal neurotransmission. This has led to the suggestion that levetiracetam exclusively modulates the function of SV2A only under pathophysiological conditions. Iracet XR Tablet (Extended Release) 500 mg and related analogues showed a correlation between affinity for SV2A and anti-epileptic potency, further suggesting that action at this site contributes to the anti-epileptic activity of the drug.
Iracet XR Tablet (Extended Release) 500 mg has also been shown to indirectly affect GABAergic neurotransmission (despite having no direct effect on GABAergic or glutamatergic receptors) and modulate ionic currents. Similarly, levetiracetam has been shown in vitro to inhibit N-type calcium channels. How, or even if, these actions are implicated in its anti-epileptic action have yet to be elucidated.
Absorption
Iracet XR Tablet (Extended Release) 500 mg is rapidly and nearly completely absorbed following oral administration, with a reported absolute oral bioavailability of essentially 100%. Tmax is approximately 1.3 hours after dosing, and Cmax is 31 μg/mL following a single 1000mg dose and 43 μg/mL following repeated dosing. Co-administration of levetiracetam with food delays Tmax by approximately 1.5 hours and decreases Cmax by 20%.
Volume of Distribution
The volume of distribution of levetiracetam is approximately 0.5 to 0.7 L/kg.
Protein Binding
Iracet XR Tablet (Extended Release) 500 mg and its metabolites are largely unbound to plasma proteins (15,11,13
Route of Elimination
Approximately 66% of the administered dose of levetiracetam is excreted in the urine as unchanged drug, while only 0.3% of the total dose is excreted via the feces. The primary inactive metabolite of levetiracetam, L057, is also found in the urine as approximately 24% of the administered dose.
Half Life
The plasma half-life of levetiracetam is 6-8 hours and is not affected by dose or repeat administration. Half-life is increased in the elderly (by about 40%) and those with renal impairment.
Clearance
The total plasma clearance of levetiracetam is 0.96 mL/min/kg, with renal clearance comprising 0.6 mL/min/kg. The primary inactive metabolite of levetiracetam, L057, has a renal clearance of 4 mL/min/kg. Given the relatively high proportion of drug undergoing renal clearance, overall clearance of levetiracetam is reduced in patients with renal impairment.
Toxicity
The oral TDLO of levetiracetam in humans is 10 mg/kg. Symptoms of levetiracetam overdose are consistent with its adverse effect profile and may include agitation, aggression, somnolence, decreased level of consciousness, respiratory depression, or coma. There is no antidote for levetiracetam overdose, therefore management should involve general supportive measures and symptomatic treatment. Hemodialysis results in significant clearance of plasma levetiracetam (approximately 50% within 4 hours) and should be considered in cases of overdose as indicated by the patient's status.
Food Interactions
- Take with or without food. Co-administration with food slightly alters pharmacokinetics, but not to a clinically significant extent.
Dosage
Adults (≥18 years) and adolescents (12 to 17 years) weighing 50 kg or more: The initial therapeutic dose is 500 mg twice daily. This dose can be started on the first day of treatment. Depending upon the clinical response and tolerability, the daily dose can be increased up to 1,500 mg twice daily. Dose changes can be made in 500 mg twice daily increases or decrease every two to four weeks.
Pediatric population: The tablet formulation is not adapted for use in infants and children under the age of 6 years. Oral solution is the preferred formulation for use in this population. In addition, the available dose strengths of the tablets are not appropriate for initial treatment in children weighing less than 25 kg, for patients unable to swallow tablets or for the administration of doses below 250 mg. In all of the above cases, oral solution should be used.
- Monotherapy: The safety and efficacy of levetiracetam in children and adolescents below 16 years as monotherapy treatment have not been established.
- Add-on therapy: Oral solution is the preferred formulation for use in infants and children under the age of 6 years. For children 6 years and above, oral solution should be used for doses under 250 mg, for doses not in multiples of 250 mg when dosing recommendation is not achievable by taking multiple tablets and for patients unable to swallow tablets. The lowest effective dose should be used. The starting dose for a child or adolescent of 25 kg should be 250 mg twice daily with a maximum dose of 750 mg twice daily. Dosing for children 50 kg or greater is the same as in adults.
- Add-on therapy: For infants aged from 1 month to less than 6 months: The oral solution is the formulation to use in infants.
