A gas-chromatographic method for the determination of the antiepileptic drugs carbamazepine, phenobarbital, phenytoin and primidone in the same extract of serum is presented. Saturated ammonium sulfate solution is added to 1 ml serum, followed by extraction with chloroform. The organic phase is separated and evaporated. The residue is dissolved in 100 microliter ethylacetate/acetic acid (100 ml + 1 ml) for gas-chromatography. The gas-chromatographic determination is carried out under isothermal conditions without derivatisation, using SP 2250 DA as stationary phase for the determination of phenobarbital and phenytoin, and Dexsil 300 for the determination of carbamazepine and primidone. The coefficient of variation for the precision from day to day ranges from 4.3 to 7.5%, the recovery from 93.5 to 111%. The specificity was proven by comparison with the relative retention times of about 100 drugs. The method is compared with the corresponding EMIT-tests.
Carbamazepine is one of the most commonly prescribed antiepileptic drugs and is also used in the treatment of trigeminal neuralgia and psychiatric disorders, particularly bipolar depression. Because of its widespread and long term use, carbamazepine is frequently prescribed in combination with other drugs, leading to the possibility of drug interactions. The most important interactions affecting carbamazepine pharmacokinetics are those resulting in induction or inhibition of its metabolism. Phenytoin, phenobarbital (phenobarbitone) and primidone accelerate the elimination of carbamazepine, probably by stimulating cytochrome P450 (CYP) 3A4, and reduce plasma carbamazepine concentrations to a clinically important extent. Inhibition of carbamazepine metabolism and elevation of plasma carbamazepine to potentially toxic concentrations can be caused by stiripentol, remacemide, acetazolamide, macrolide antibiotics, isoniazid, metronidazole, certain antidepressants, verapamil, diltiazem, cimetidine, danazol and (dextropropoxyphene) propoxyphene. In other cases, toxic symptoms may result from elevated plasma concentrations of the active metabolite carbamazepine-10,11-epoxide, due to the inhibition of epoxide hydrolase by valproic acid (sodium valproate), valpromide, valnoctamide and progabide. Carbamazepine is a potent inducer of CYP3A4 and other oxidative enzyme system in the liver, and it may also increase glucuronyltransferase activity. This results in the acceleration of the metabolism of concurrently prescribed anticonvulsants, particularly valproic acid, clonazepam, ethosuximide, lamotrigine, topiramate, tiagabine and remacemide. The metabolism of many other drugs such as tricyclic antidepressants, antipsychotics, steroid oral contraceptives, glucocorticoids, oral anticoagulants, cyclosporin, theophylline, chemotherapeutic agents and cardiovascular drugs can also be induced, leading to a number of clinically relevant drug interactions. Interactions with carbamazepine can usually be predicted on the basis of the pharmacological properties of the combined drug, particularly with respect to its therapeutic index, site of metabolism and ability to affect specific drug metabolising isoenzymes. Avoidance of unnecessary polypharmacy, selection of alternative agents with lower interaction potential, and careful dosage adjustments based on serum drug concentration monitoring and clinical observation represent the mainstays for the minimisation of risks associated with these interactions.
Health insurance claims from PharMetrics Database, representing over 90 health plans between January 2000 and October 2007, were analyzed. Adult patients with epilepsy, continuously treated with carbamazepine, gabapentin, phenytoin, primidone, or zonisamide, were selected. An open-cohort design was used to classify patients into mutually exclusive periods of brand vs generic use of AEDs. Pharmacy and medical utilization were compared between the 2 periods with multivariate regression analyses. Results were stratified into epilepsy-related medical services, and stable (< or = 2 outpatient visits per year and no emergency room visit) vs unstable epilepsy. Time-to-event analyses were also performed for all services and epilepsy-related endpoints.
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We describe a simple, sensitive determination of phenobarbital, diphenylhydantoin, carbamazepine, and primidone in serum, by use of gas-liquid chromatography with temperature programming. The methylated derivatives of these anticonvulsants are well resolved, as was 5-(p-methyl-phenyl)-5-phenylhydantoin, the internal standard. The proposed procedure requires only 0.20 ml of serum and can be done in less than 30 min. The lower limit of detection for each of the drugs is 0.5 mg/liter. Analytical recoveries of drug from serum were excellent and peak height and concentration were linearly related up to twice the toxic concentration for serum.
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This solid phase enzyme immunoassay for serum phenytoin appears to be simple, precise, and accurate. It may be readily adopted in clinical laboratory for therapeutic monitoring of phenytoin level in serum.
Sixteen premature infants (mean age, 27.8 weeks) in whom apnea and bradycardia recurred despite therapeutic levels of theophylline. Six of the patients were receiving assisted ventilation.
The major established drugs used in the management of epilepsy are carbamazepine, valproic acid, phenytoin, phenobarbital, primidone, ethosuximide and benzodiazepine drugs. Carbamazepine and phenytoin are used mainly in the treatment of partial seizures and primarily or secondarily generalized tonic-clonic seizures. Valproic acid is effective against all types of seizures, but it is used most extensively in the management of generalized epilepsies. Ethosuximide is effective against absence seizures. Phenobarbital and primidone are effective against all types of seizures (except for absences) although they are less commonly used because of their sedative properties and adverse effects on cognition. Benzodiazepines are most valuable in the treatment of status epilepticus, but their long-term use is often associated with undesirable sedation and development of tolerance to their antiepileptic effect. Irrespective of the drug used, optimal clinical management requires individualization of dosage and dosing schedules based on careful evaluation of clinical response and sound knowledge of the pharmacokinetics and interaction potential of the individual compounds. Monitoring serum drug concentrations may provide a useful guide to dosage adjustments, particularly in the case of phenytoin, which shows dose-dependent kinetics within the therapeutic dosage range.
Essential tremor (ET) is the most common pathological tremor characterized by upper limb action-postural tremor (PT)/kinetic tremor (KT). There are no specific neuropathological or biochemical abnormalities in ET. The disability is consequent to amplitude of KT, which may remain mild without handicap or may become disabling. The most effective drugs for sustained tremor control are propranolol and primidone. Symptomatic drug treatment must be individualized depending on the circumstances that provoke the tremor-related disability. Broad guidelines for treatment are discussed in this review. Patients may be treated intermittently only on stressful occasions with propranolol, clonazepam, or primidone monotherapy, or an alcoholic drink. Those with persistently disabling tremor need continued treatment.