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PubMed1989

Biotin transport in the human intestine: inhibition by anticonvulsant drugs.

The effect of the anticonvulsant drugs carbamazepine and primidone on the transport of biotin in the human intestine was examined with purified brush border membrane vesicles (BBMVs) and basolateral membrane vesicles (BLMVs). Both agents inhibited biotin transport in BBMV in a concentration-dependent manner. The inhibition by both carbamazepine and primidone was competitive (inhibition constant [Ki] of 4.70 and 2.25 mmol/L, respectively) and appeared to be specific because the transport of D-glucose was not affected by different concentrations of these pharmacologic agents. The transport of biotin in BLMV was not affected by carbamazepine or primidone. These results demonstrate that carbamazepine and primidone are competitive inhibitors of biotin transport in the human intestine and that the inhibitory effect is directed toward the substrate transport system at the brush border membrane of the enterocyte. These findings may relate to possible impairment of biotin status in patients on long-term therapy with anticonvulsant agents.

Anticonvulsants↗
PubMed1977

Factors influencing plasma phenobarbitone levels in epileptic patients.

1 Various statistical techniques were used to study the effects of age, sex and concurrent therapy with other anticonvulsants on the relation between plasma phenobarbitone levels and doses of (i) phenobarbtione, (ii) methylphenobarbitone or (iii) primidone, in epileptic patients. 2 Methylphenobarbitone and primidone are converted to phenobarbitone in the body. The mean doses of phenobarbitone, methylphenobarbitone and primidone which produced the same plasma phenobarbitone level (15 microgram/ml) were, respectively, 1.75,2.75 and 7.75 mg kg-1 day-1. 3 For both phenobarbitone and methylphenobarbitone dose requirement to achieve a given plasma phenobarbitone level fell progressively with age. Sex influenced the relation between plasma phenobarbitone level and phenobarbitone or methylphenobarbitone dose. Interactions were detected between primidone and both phenytoin and carbamazepine. 4 In individual patients, within the limits of dosage studied, the relation between plasma phenobarbitone level and drug dose was not rectilinear if phenobarbitone itself was taken, but was rectilinear if methylphenobarbitone was taken.

Adolescent↗
PubMed1977

The effect of anticonvulsant drugs which induce liver microsomal enzymes on derived and ingested phenobarbitone levels.

A comparison was made between the levels of derived Phenobarbitone in three groups of patients who were taking Primidone as a single drug, Primidone with Phenytoin and Primidone in combination with Phenytoin and Carbamazepine. The levels of ingested Phenobarbitone when this drug was taken as a single drug were compared with the levels when Phenobarbitone was taken in combination with Phenytoin in two other groups of patients. A significant increase in derived Phenobarbitone levels occurred when Primidone was used in combination with Phenytoin alone or with Phenytoin and Carbamazepine. The highest level occurred in a group of patients taking the three drug combination. There was no significant difference between the levels of ingested Phenobarbitone when this drug was used as single therapy or in combination with Phenytoin. We suggest that the increase in derived Phenobarbitone levels relates to the effect of Phenytoin on liver enzyme systems, and that the greater increase with triple therapy was related to the combined effect of Carbamazepine and Phenytoin on microsomal enzymes. As there was no increase in ingested Phenobarbitone levels when this drug was taken in combination with Phenytoin, we were unable to confirm previous suggestions that Phenytoin either inhibits the hydroxylation of Phenobarbitone or impairs its renal excretion.

Adolescent↗
PubMed1977

Anticonvulsants in serum, determined with a fully mechanized enzyme analyzer.

The "EMIT" enzyme immunoassay system (Syva) that involves use of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) as the enzyme label has been adapted to a fully mechanized kinetic enzyme analyzer for analysis of phenobarbital, phenytoin, and primidone. This procedure, compared with the gas-chromatographic procedure of Kupferberg [Clin. Chim. Acta 29, 283 (1970)], gave a weighted regression line--forced through the origin--of y=(1.01+/-0.04) x for phenobarbital, y=(0.95+/-0.04) x for primidone. Within-run coefficients of variation based on single determinations were 9,11, and 22% for primidone, phenobarbital, and phenytoin, respectively. Run-to-run assay CV was 6% for primidone and phenobarbital and 13% for phenytoin, based on the means of triplicate determinations of a sample with a mid-range concentration.

Evaluation Studies as Topic↗
PubMed1977

Use of saliva in therapeutic drug monitoring.

We measured the concentrations of phenobarbital, phenytoin, primidone, ethosuximide, antipyrine, and caffeine in paired samples of saliva and plasma by gas chromatograph-mass spectrometer-computer (GC/MS/COM) and enzyme immunoassay. Mixed saliva was collected for the antipyrine and caffeine studies, parotid saliva for the phenobarbital, primidone, ethosuximide and phenytoin studies. The saliva/plasma (S/P) ratios (by weight) obtained by GC/MS/COM were: phenobarbital, 0.31-0.37; phenytoin, 0.11; ethosuximide, 1.04; antipyrine, 0.83-0.95; caffeine, 0.55. The S/P ratio obtained by enzyme immunoassay were: phenobarbital, 0.32; phenytoin, 0.12; primidone, 0.85. The concentrations of phenytoin, primidone, ethosuximide and antipyrine in saliva correspond to the free fraction of the drug in plasma. When we analyzed samples containing phenobarbital or phenytoin (plasma or saliva) by both techniques, we found that the enzyme immunoassay values were generally higher than GC/MS/COM values, suggesting that the metabolites as well as the parent drug were measured in the immunoassay.

Antipyrine↗
PubMed1978

Therapeutic monitoring of anticonvulsant drugs in psychiatric patients: rapid, simultaneous gas-chromatographic determination of six commonly used anticonvulsants without interference from other drugs.

A simple, sensitive and precise gas-chromatographic method for simultaneous extraction, derivatization and determination of methsuximide, ethosuximide, diphenylhydantoin, carbamazepine, phenobarbital and primidone in the presence of other drugs has been described. The method is especially useful for drug monitoring in patients on multiple anticonvulsant therapy while also on combination therapy with psychotropic drugs. It overcomes the analytical interferences between mephenytoin and phenobarbital; methsuximide and primidone; kemadrin and primidone; cholesterol and primidone; prolixin, haldol and other drugs; encountered in other methods using underivatized, trimethylsilylated or methylated drugs. As little as 0.5 microgram/ml of a drug can be determined and if needed the method can be scaled down to 0.3 ml plasma. The method yielded recoveries of 97-103% with standard deviations of 0.7-1.8. For a constant check of the precision, an internal quality control using daily analysis of a sample from a frozen plasma pool supplemented with known concentrations of the anticonvulsants was used. The method is suitable for use in routine clinical laboratory.

Anticonvulsants↗
PubMedDate not supplied

Simultaneous rapid HPLC determination of anticonvulsant drugs in plasma and correlation with EMIT.

A method is presented for measuring simultaneously five anti-convulsants (primidone, ethosuximide, phenobarbital, carbamazepine and diphenylhydantoin) in serum and plasma by high-performance liquid chromatography (HPLC) using alphenal (5 - allyl - 5 - phenyl - barbituric acid) as the internal standard. All five drugs are separated from each other and, in the case of primidone, from its metabolie, 2 - phenyl - 2 - ethyl - malondiamide. Total HPLC time for the separation is seven minutes. The chromatography is performed on a C-8 reverse phase column with a mobile phase consisting of acetonitrile/phosphate buffer (35/65) at 25 degrees C. The eluted drugs are detected at 220 nm and quantitated from their peak heights relative to that of the internal standard. The lower limits of detection for each drug is 200 ng per ml for primidone, 1000 ng per ml for ethosuximide, 200 ng per ml for phenobarbital, 100 ng per ml for carbamazepine and 200 ng per ml for diphenylhydantoin. Analytical recoveries for the five drugs ranged from 97 to 107 percent. Correlation of results for 187 specimens by enzyme-immunoassay (emit) was 0.981 for primidone, 0.827 for ethosuximide, 0.975 for phenobarbital, 0.889 for carbamazepine and 0.990 for diphenylhydantoin. In the HPLC assay, ethotoin was found to interfere with phenobarbital and phensuximide with carbamazepine.

Anticonvulsants↗
PubMed1981

Clinical evaluation of the new compound diphenylsilanediol for ani-epileptic efficacy and toxicity.

A controlled clinical trial of the anti-epileptic efficacy and toxic side effects of diphenylsilanediol was conducted on 24 client-owned epileptic dogs. Data obtained from an abbreviated procedural treatment program indicated that diphenylsilanediol compared favorably with primidone as an anti-epileptic compound, but had limiting toxic side effects to the liver, pancreas, and possibly to other tissues. There was a mean reduction of 60.7% in seizure frequency in 15 epileptic dogs treated with diphenylsilanediol when compared with their pretreatment frequency. There was a mean reduction of 55.6% in seizure frequency in 9 spileptic control dogs treated with primidone. Samples of blood obtained from the dogs in the program on the 4th, 8th, 12th, 24th, and 36th weeks of treatment were examined for complete blood cell count, blood urea nitrogen, liver function, and pancreatic function. Toxic side effects were not seen among the primidone-treated control dogs, with the exception of occasional dose-related drowsiness. Among the diphenylsilanediol-treated dogs, 3 developed liver disease, 2 developed definite pancreatic changes, and 2 showed evidence of bone marrow suppression. Four dogs died during treatment with diphenylsilanediol, whereas no deaths occurred during the same interval of primidone therapy.

Animals↗
PubMed1987

Monomeric serum calcitonin and bone turnover during anticonvulsant treatment and in congenital hypothyroidism.

Decreased basal and calcium-stimulated calcitonin serum levels have been found in children with congenital hypothyroidism and in those receiving anticonvulsant drugs. The purpose of our investigation was to confirm these results using a new technique for calcitonin measurement and to study the effect on bone turnover. Calcitonin serum levels were measured with two different antibodies before and after a low-dose Ca infusion in patients receiving phenytoin, primidone, carbamazepine, or valproate and in patients with congenital hypothyroidism receiving L-thyroxine. In comparison with control values, basal and Ca-stimulated extractable calcitonin, representing the monomeric and biologically active form of the hormone, were moderately decreased in patients with epilepsy receiving phenytoin and primidone, and severely decreased in patients with hypothyroidism. Ca and bone metabolism were normal, except for an elevated renal threshold for phosphate (indicating phosphate conservation) in patients receiving phenytoin and primidone, and increased fasting urinary excretion of Ca and hydroxyproline (indicating increased bone resorption) in patients with hypothyroidism. The secretory capacity of the C cells for monomeric calcitonin is decreased in children receiving treatment with some, but not all, anticonvulsant drugs, and lacking in patients with hypothyroidism. Patients with calcitonin deficiency may be prone to osteopenia if the tendency to increased osteoclastic activity is aggravated by secondary hyperparathyroidism in patients with epilepsy receiving phenytoin and primidone or by inappropriate thyroid replacement therapy in patients with hypothyroidism.

Adolescent↗
PubMed1985

[Pharmacologic principles in the treatment of epilepsy in the dog and cat].

The pharmacokinetics of antiepileptic drugs used for the treatment of human epilepsies is reviewed for dogs and cats. In dogs, especially phenobarbital and primidone must be regarded as useful drugs for chronic treatment on account of their elimination rate and bioavailability. Phenytoin, carbamazepine, valproic acid and benzodiazepines are eliminated so rapidly that a therapeutic value cannot be expected. In cats, phenytoin, phenobarbital, valproic acid and diazepam must be regarded as suited for chronic treatment, but there is a definite lack of clinical experience. Phenobarbital and primidone are useful for treatment of clonic-tonic generalized seizures (grand mal) in dogs. The effect of primidone depends mostly on its metabolite phenobarbital. Since primidone, given in high dosage for longer periods of time, gives rise to liver damage, phenobarbital is regarded as the drug of first choice. A status epilepticus may be treated by i.v. injection of diazepam, clonazepam, phenytoin or lidocaine. In cats with grand mal, treatment with daily doses of about 1 mg/kg diazepam may be tried. It proved effective for longer time periods without development of tolerance. There is no reliable clinical experience with other drugs in this species.

Animals↗
PubMed1981

[Effect of anticonvulsants on convulsions induced by kynurenine, quinolinic acid, strychnine and corazole].

Benzobarbital, primidone, phenobarbital, phynytoin and trimethadionum (in order of decreasing activity) were moderately effective against DL-kynurenine (50 micrograms, i. c. v.)-induced seizures in SHR albino male mice. Diazepam was ineffective even in doses of 15 and 25 mg/kg. Against seizures induced by quinolinic acid (5 micrograms, i. c. v.) anticonvulsants, particularly primidone and phenytoin, were more effective than against kynurenine-induced seizures. Diazepam was slightly effective in high doses of 7-15 mg/kg. Primidone and benzobarbital in doses used (10-50 mg/kg) were ineffective against strychnine and pentylenetetrazol. Selective efficacy of primidone and benzobarbital in this model of seizures suggests that kynurenine and quinolinic acid could be involved in the grand mal fits in epileptic patients.

Animals↗
PubMed1981

Valproic acid and its metabolites: placental transfer, neonatal pharmacokinetics, transfer via mother's milk and clinical status in neonates of epileptic mothers.

The pharmacokinetics of valproic acid (VPA) and several metabolites were measured in 11 epileptic mothers and their 12 newborns. VPA was found in higher concentrations in cord serum than in maternal serum [(factor 1.7 +/- 0.6; (n = 6)]. VPA was excreted in the neonates with a mean half-life of 47 +/- 15 hr (n = 8) which is approximately 4 times the mean value found in adult epileptics. Maternal comedication (primidone and phenytoin) resulted in slightly reduced half-lives. The transplacental kinetics of the two main VPA metabolites in blood were similar to those of VPA. The very low levels of VPA in mother's milk (3% of maternal serum concentrations) suggest apparent safety of breast feeding. The [13C]aminopyrine breath test indicated neonatal hepatic enzyme activities which were slightly above those of unexposed neonates, but much below those of neonates which had been exposed to primidone and phenytoin in utero. Six of eight neonates exposed to VPA-monotherapy, but only one exposed to primidone or phenytoin comedication, developed an icterus neonatorum. A number of minor anomalies (four to eight per child) were observed, particularly hernias, diastasis of musculus rectus abdominis and weak abdominal walls. Two children were microcephalic and in another four children the head circumferences were below the 10th percentile. Significant withdrawal symptoms were not observed. Also hypoplasia of the nails and phalanges and facial dysmorphism associated with the "fetal hydantoin syndrome" did not occur in VPA-exposed children except in one case in which primidone had been administered as comedication.

Abnormalities, Drug-Induced↗
PubMed1982

Fluorescent immunoassay for determining antiepileptic drug concentrations: clinical usefulness.

The need for rapid and accurate antiepileptic drug measurement in blood is well established. A substrate-labeled fluorescent immunoassay (FIA) has been developed that can measure phenobarbital, phenytoin, primidone, and carbamazepine in serum. To our knowledge, the primidone and carbamazepine assays have not previously been tested in a field trial. We compared FIA and the well-established antiepileptic drug immunoassay technique EMIT for the quantitation of both carbamazepine and primidone. In our hands, the FIA method compared favorably with the EMIT method for accuracy and reliability but is somewhat more time consuming. This method has the advantage of being more sensitive, however, and requires only a finger-stick blood sample. Because of this and the simplicity of the equipment required, the FIA system should also be relatively inexpensive to set up and to operate.

Anticonvulsants↗
PubMed1991

Quantitative comparison of barbiturates in essential hand and head tremor.

The tremorolytic effects of primidone and phenobarbital in essential tremor of hands and head were compared in a double-blind, placebo-controlled trial. Quantitative measurements of tremor were obtained in 15 patients by means of an accelerometric method. Only primidone proved to be superior to placebo in reducing hand tremor, suggesting that its tremorolytic effectiveness is largely dependent on the parent drug rather than its metabolite phenobarbital. Head tremor tended to improve only in three out of six patients with both primidone and phenobarbital, but, likely due to the small number of affected patients, the effect failed to reach statistical significance.

Aged↗
PubMed1978

Serotonin metabolism with idiopathic grand mal seizures.

Serotonin was determined in platelets of 140 patients with idiopathic mal seizures. According to anticonvulsive therapy these patients were divided into the following five groups: no medication, Diphenylhydantoin, Diphenylhydantoin calcium, Primidon, and combination of various of the anticonvulsants mentioned. The results obtained in the entire group of patients as well as in the various subgroups were compared with those of a group of healthy persons without therapy. In addition the various subgroups were compared to each other. There were significantly reduced serotonin values in the patients with idiopathic grand mal seizures as well as in each of its various groups as compared with the values obtained in healthy persons. Furthermore, significantly higher values were observed in the patients receiving primidone as compared with those receiving no anticonvulsants, Diphenylhydantoin, and a combination of various anticonvulsants. Our results taken together with those reported in the literature point to the possibility that a special imbalance in the cerebral neurotransmitter system, including a deficiency of serotonin, may represent a pathogenetic factor for idiopathic grand mal seizures. In addition, this investigation indicates that primidone elevates serotonin in platelets of patients with grand mal seizures.

Blood Platelets↗
PubMed1989

The treatment of severe action myoclonus.

Ten patients with severe disabling myoclonus were treated with clonazepam, sodium valproate, primidone and piracetam alone, or in different combinations. Electrophysiological assessment indicated a cortical origin for the myoclonus in every case. Considerable improvement of myoclonus was achieved with combinations of these drugs in all patients, but this was not possible with monotherapy. In one patient two drugs were necessary (clonazepam and piracetam); in the others more than two drugs were required. The combination of sodium valproate, clonazepam and primidone (3 patients), or piracetam, clonazepam and primidone (3 patients), or the four drugs together (3 patients) was necessary to provide substantial relief of myoclonus. Such polytherapy generally was tolerated well. The benefits of treatment continued for more than 1 year in all cases, although progressive underlying pathology often caused other increasing disability.

Adolescent↗
PubMed2003

Benefits and risks of pharmacological treatments for essential tremor.

Essential tremor can cause significant functional disability in some patients. The arms are the most common body part affected and cause the most functional disability. The treatment of essential tremor includes medications, surgical options and other forms of therapy. Presently there is no cure for essential tremor nor are there any medications that can slow the progression of tremor. Treatment for essential tremor is recommended if the tremor causes functional disability. If the tremor is disabling only during periods of stress and anxiety, propranolol and benzodiazepines can be used during those periods when the tremor causes functional disability. The currently available medications can improve tremor in approximately 50% of the patients. If the tremor is disabling, treatment should be initiated with either primidone or propranolol. If either primidone or propranolol do not provide adequate control of the tremor, then the medications can be used in combination. If patients experience adverse effects with propranolol, occasionally other beta-adrenoceptor antagonists (such as atenolol or metoprolol) can be used. If primidone and propranolol do not provide adequate control of tremor, occasionally the use of benzodiazepines (such as clonazepam) can provide benefit. Other medications that may be helpful include gabapentin or topiramate. If a patient has disabling head or voice tremor, botulinum toxin injections into the muscles may provide relief from the tremor. Botulinum toxin in the hand muscles for hand tremor can result in bothersome hand weakness and is not widely used. There are other medications that have been tried in essential tremor and have questionable efficacy. These drugs include carbonic anhydrase inhibitors (e.g. methazolamide), phenobarbital, calcium channel antagonists (e.g. nimodipine), isoniazid, clonidine, clozapine and mirtazapine. If the patient still has disabling tremor after medication trials, surgical options are usually considered. Surgical options include thalamotomy and deep brain stimulation of the thalamus. These surgical options provide adequate tremor control in approximately 90% of the patients. Surgical morbidity and mortality for these procedures is low. Deep brain stimulation and thalamotomy have been shown to have comparable efficacy but fewer complications have been reported with deep brain stimulation. In patients undergoing bilateral procedures deep brain stimulation of the thalamus is the procedure of choice to avoid adverse effects seen with bilateral ablative procedures. The use of medication and/or surgery can provide adequate tremor control in the majority of the patients.

Adrenergic Agonists↗
PubMed1991

Formation of active metabolites of anticonvulsant drugs. A review of their pharmacokinetic and therapeutic significance.

All of the commonly used anticonvulsants drugs, except possibly primidone, are cleared from the human body mainly by metabolism. The metabolites of phenytoin, phenobarbital and ethosuximide have so far not been shown to possess significant pharmacological activity. However, carbamazepine-10,11-epoxide, derived from carbamazepine, has anticonvulsant activity comparable with that of its progenitor, while oxcarbazepine, a new anticonvulsant congener of carbamazepine, is essentially a prodrug for its 10-hydroxy derivative. Valproic acid forms numerous metabolites through a variety of pathways; 2-en valproic acid, a beta-oxidation derivative, probably contributes to its anticonvulsant action, though the extent of the contribution is uncertain. Another metabolite, 4-en-valproic acid, has been considered a possible hepatotoxin and teratogen. N-Methyl-phenobarbital and primidone, though both anticonvulsants in their own right, are metabolised to phenobarbital, which probably mediates much of their antiseizure effect. Primidone also yields the weaker anticonvulsant phenylethylmalonamide. The various benzodiazepine anticonvulsants form numerous metabolites, some of which possess both antiseizure and other forms of pharmacological activity. As yet, there is little understanding of how best to interpret simultaneous plasma concentration measurements of anticonvulsant drug and its active metabolite (or metabolites) in the clinical situation, and the possible roles of anticonvulsant metabolites in the idiosyncratic toxicity of these drugs remain largely unexplored.

Anticonvulsants↗