Elevated peripheral levels of receptor-interacting protein kinase 1 (RIPK1) and IL-8 as biomarkers of human amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating fatal neurodegenerative disease with no cure. Receptor-interacting protein kinase 1 (RIPK1) has been proposed to mediate pathogenesis of ALS. Primidone has been identified as an old drug that can also inhibit RIPK1 kinase. We conducted a drug-repurposing biomarker study of primidone as a RIPK1 inhibitor using SOD1G93A mice and ALS patients. SOD1G93A mice treated with primidone showed significant delay of symptomatic onset and improved motor performance. One-hundred-sixty-two ALS participants dosed daily with primidone (62.5 mg) completed 24-week follow-up. A significant reduction was showed in serum levels of RIPK1 and IL-8, which were significantly higher in ALS patients than that of healthy controls (P < 0.0001). Serum RIPK1 levels were correlated positively with the severity of bulbar symptoms (P < 0.05). Our study suggests that serum levels of RIPK1 and IL-8 in peripheral can be used as clinical biomarkers for the activation of RIPK1 in central nervous system in human ALS patients. Repurposing primidone may provide a promising therapeutic strategy for ALS. The effect of primidone for the treatment of other inflammatory diseases may also be considered, since the activation of RIPK1 has been implicated in mediating a variety of inflammatory diseases including COVID-19-associated cytokine release syndrome (CRS). (ChiCTR2200060149).

Dose-dependent apoptotic and necrotic myocyte death induced by the beta2-adrenergic receptor agonist, clenbuterol

We have investigated the dose- and time-dependency of myocyte apoptosis and necrosis induced by the beta2-adrenergic receptor agonist, clenbuterol, with the aim of determining whether myocyte apoptosis and necrosis are two separate processes or a continuum of events. Male Wistar rats were administered subcutaneous injections of clenbuterol, and immunohistochemistry was used to detect myocyte-specific apoptosis and necrosis. Myocyte apoptosis peaked 4 h after, and necrosis 12 h after, clenbuterol administration. In the soleus, peak apoptosis (5.8 +/- 2.0%; P < 0.05) was induced by 10 mug and peak necrosis (7.4 +/- 1.7%; P < 0.05) by 5 mg x kg(-1) clenbuterol. Twelve hours after clenbuterol administration, 73% of damaged myocytes labeled as necrotic, 27% as apoptotic and necrotic, and 0% as purely apoptotic. Administrations of clenbuterol (10 microg x kg(-1)) at 48-h intervals induced cumulative myocyte death over 8 days. These data show that the phenotype of myocyte death is dependent on the magnitude of the insult and the time at which it is investigated. Only very low doses induced apoptosis alone; in most cases apoptotic myocytes lysed and became necrotic and the magnitude of necrosis was greater than that of apoptosis. Thus, it is important to investigate both apoptotic and necrotic myocyte death, contrary to the current trend of only investigating apoptotic cell death.

Effects of encapsulation of primidone on its oxidative metabolism in rats

The aim of this study was to evaluate the influence of primidone (PRM) nanoencapsulation on its metabolism. Suspensions of PRM powder and PRM-loaded poly-epsilon-caprolactone nanocapsules were administered orally in the same way to rats. Primidone-loaded poly-epsilon-caprolactone nanocapsules were prepared according to the interfacial deposition technique. Free PRM suspensions were obtained by addition of PRM powder to a suspension of 0.212% carboxymethylcellulose CMC 12H in water. The dose was 20 mg/kg, n = 6, for each experiment. Urinary and faecal levels of PRM and of its three major metabolites, phenylethylmalonamide (PEMA), phenobarbital (PB), and p-hydroxyphenobarbital (p-HO-PB), were determined. Concentrations were evaluated by high-performance liquid chromatography (HPLC) according to a validated analytical method. After PRM nanocapsule administration, non-metabolised PRM urinary levels were increased compared to those observed after administration of a suspension of primidone powder (43.7+/-8.8% after PRM-loaded nanocapsule and 37.7+/-8.1% after free PRM administration). For phenylethylmalonamide, no difference was observed in urinary excretion in the two cases. For two of the oxidised metabolites, PB and p-HO-PB, excretion was delayed and shortened. The amount of these oxidised metabolites was lowered from 0.95% after free PRM administration to 0.25% after PRM-loaded nanocapsule administration. No difference was noted in non-metabolised primidone excretion in faeces. These results suggest that primidone-loaded nanocapsules could be used as a vehicle for oral primidone administration in order to minimise the phenobarbital metabolic pathway.

Simultaneous determination of primidone and its three major metabolites in rat urine by high-performance liquid chromatography using solid-phase extraction

A new high-performance liquid chromatographic method for simultaneous determination of primidone (PRM) and of its three major metabolites, phenobarbital (PB), p-hydroxyphenobarbital (p-HO-PB) and phenylethylmalonamide (PEMA), in rat urine, was developed. After acid hydrolysis, these compounds were extracted from urine by means of a Bond Elut Certify LRC column with good clean-up. The extracts were chromatographed on a C18 reversed-phase column using isocratic elution at 40 degrees C, with UV detection at 227 nm. The limit of detection was 0.5 mg/ml for the four compounds. Good linearity (r2>0.99) was observed within the calibration ranges studied: 37.4-299.3 microg/ml for PRM, 26.4-211.2 microg/ml for PB, 12.5-100.2 microg/ml for p-HO-PB and 12.1-97.0 microg/ml for PEMA. Repeatability was in the range 3.1-6.8%. This method constitutes a useful tool for studies on the influence of various parameters on primidone metabolism.

Phenobarbital, drug metabolism, and human cancer

To investigate the possible influence of anticonvulsant treatment on cancer risk, a nested case-control study of 104 lung cancers, 18 bladder cancers, and 322 cancer-free controls was conducted. The background for the study was previous observations among 8004 epileptics in Denmark with a significantly high risk for lung cancer and a significantly low risk for bladder cancer. Cigarette smoking appears to explain the lung cancer excess but not the low risk for bladder cancer, another tobacco-related disease. Information was abstracted on 94 and 95% of the cases and controls, respectively. Lung cancer was not associated with any anticonvulsant drug, but bladder cancer was inversely related to use of phenobarbital (PB). The apparent protective effect of PB was further evaluated in a study of rats given 4-aminobiphenyl (ABP), a bladder carcinogen. The levels of 4-aminobiphenyl adducts in hemoglobin and in bladder and liver DNA were significantly lower in rats given PB prior to 4-aminobiphenyl, compared to controls. These studies suggest that PB may induce drug-metabolizing enzymes of the liver that deactivate bladder carcinogens found in cigarette smoke and provide clues to the role of activation and detoxification of carcinogens in humans.

Urinary metabolites of phenobarbitone, primidone, and their N-methyl and N-ethyl derivatives in humans

1. Phenobarbitone (1) and three of its N-alkyl derivatives, and primidone (10) and four of its N-alkyl derivatives, were orally administered separately to two human volunteers. Total urine was collected for approximately 2 weeks following each dose, and the drugs and their metabolites were assayed by g.l.c.-mass spectrometry. 2. Recoveries in the phenobarbitone series increased from approximately 40% to approximately 50% as alkylation of (1) increased. There was a linear relationship between the extent of p-hydroxylation and the lipophilicity (log P) of the substrates. The increased total recovery was largely attributable to increased p-hydroxylation. 3. Urinary recoveries in the primidone series decreased from approximately 80% for (10) to approximately 30% for its diakyl derivatives, despite a slight increase in p-hydroxylation with increasing alkylation (and increasing lipophilicity). The decreased recovery was mainly the result of decreased urinary excretion of the drug.

The disposition of primidone in elderly patients

1. The pharmacokinetics and metabolism of primidone at steady-state were studied in 10 elderly patients aged 70-81 years and eight control subjects aged 18-26 years. 2. Primidone half-lives and clearance values (mean +/- s.d.) were similar in the elderly and in the young (12.1 +/- 4.6 vs 14.7 +/- 3.5 h and 34.8 +/- 9.0 vs 33.2 +/- 7.2 ml h-1 kg-1 respectively. 3. The serum concentrations of the metabolites phenylethylmalonamide (PEMA) and phenobarbitone relative to those of parent drug were higher in the elderly than in the young, the difference being significant (P less than 0.01) in the case of PEMA. 4. The renal clearances of primidone, phenobarbitone and PEMA were moderately decreased in the elderly but this reduction was statistically significant only for PEMA. Elderly patients excreted a reduced proportion of unchanged primidone and an increased proportion of PEMA in urine. 5. Ageing is associated with a greater accumulation of PEMA, which is unlikely to have a major clinical significance.

Metabolic studies with phenobarbitone, primidone and their N-alkyl derivatives: quantification of substrates and metabolites using chemical ionization gas chromatography-mass spectrometry

Metabolic studies with phenobarbitone, primidone and some of their N-alkyl derivatives required the concurrent assay of any mixture of these substrates (twelve compounds) and their major metabolites (an additional twenty-two compounds) in urine. The method described in the present report met this requirement by incorporating two complementary derivatization techniques into a gas chromatographic-mass spectrometric (GC-MS) assay procedure. Following hydrolysis of conjugates with beta-glucuronidase, urine samples were extracted with ethyl acetate (3 X 5 ml). The combined extracts were dried over sodium sulphate, divided into two equal portions, and the solvent was removed. One residue was derivatized by propylation using 1-iodopropane with base catalysis. The other residue was silylated using methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide. The derivatives in each case were analysed by GC-MS, using temperature-programmed packed-column GC and chemical ionization MS. Mass spectra were acquired over an appropriate mass range, and peak areas for the compounds of interest were determined from specific mass chromatograms. Satisfactory precision, accuracy, specificity and sensitivity were obtained for all analytes. All compounds produced satisfactory derivatives by at least one procedure; twelve compounds could be analysed by both techniques. The method illustrates the utility of chemical ionization GC-MS for the simultaneous quantitative analysis of multiple related analytes in complex biological samples.

Primidone and essential tremor

To clarify whether primidone itself, and not only its metabolite phenobarbitone, suppresses essential tremor, the effect of a high single dose of primidone was tested. Of 11 patients, 8 showed a reduction of their tremor by 54%-69% for up to 28 h. The serum concentration of primidone was as expected, whereas those of the metabolites phenyl-ethyl-malonamide and phenobarbitone were very low. The tremor suppression can thus be considered to be an effect of primidone. Three of the 11 patients did not show a reduction of tremor.

Effect of primidone in somatic and germ cells of mice

Primidone, an anti-convulsant drug, was tested in mice for mutagenicity in somatic cells by the micronucleus test and in germ cells by the sperm-head abnormality assay. Mice were treated orally with the drug at doses of 4.37, 8.75 and 13.11 mg/mouse. The results indicate that the drug is capable of inducing mutations both in somatic and germ cells of mice.

Nursing interventions for anticonvulsant drug interactions

The management of epilepsy or seizure disorder commonly includes drug therapy. Optimal treatment may involve single-drug regimens, but multiple agents are often required. Although any pharmacological agent can be involved in a drug interaction, anticonvulsants are often implicated. As more drugs are prescribed for the patient, the potential for drug interactions increases. This article reviews the background of anticonvulsant drug interactions, the most common interactions encountered, and nursing interventions useful in monitoring potential interactions. Suggestions for nursing research are given.

Carbamazepine drug interactions

Carbamazepine (CBZ) is commonly prescribed as an anticonvulsant or for the pain of trigeminal neuralgia. The potential for clinically important drug interactions exists because CBZ may induce the hepatic metabolism of other drugs or, conversely, other drugs may induce or inhibit the metabolism of CBZ. Studies and case reports demonstrate that CBZ may accelerate the metabolism of phenytoin, phenobarbital (PB), primidone, valproic acid, and warfarin. Likewise, phenytoin, PB, and primidone may increase the hepatic metabolism of CBZ. Inhibition of the metabolism of CBZ has been caused by triacetyloleandomycin, erythromycin, propoxyphene, isoniazid, and cimetidine. Future investigations will document the clinical significance of the CBZ interactions as well as reveal new interactions.

Poor correlation between single-dose data and steady-state kinetics for phenobarbitone, primidone, carbamazepine and sodium valproate in children during monotherapy. Possible reasons for the lack of correlation

An investigation was performed to determine the relationship between the serum drug concentration/dose ratio at 24 hours following a first dose and that at steady-state for phenobarbitone, primidone (as phenobarbitone and as primidone), carbamazepine and sodium valproate, in order to assess the utility of this method in clinical practice. The drugs were given as monotherapy to 63 children for the treatment of epilepsy or febrile convulsions. The correlation between concentration/dose ratios, instead of between serum concentrations, was investigated with the aim of allowing the use of variable doses. The correlation coefficients were: r = 0.30 for phenobarbitone; r = 0.05 for phenobarbitone derived from primidone; r = 0.38 for primidone; r = 0.19 for carbamazepine; and r = 0.52 for sodium valproate. None of these correlation coefficients differed statistically from 0. These low correlation coefficients contrast with the acceptable results found by other authors for other drugs, indicating that several factors may have a greater influence on this correlation than earlier investigations suggest. The poor correlation obtained emphasises the need for clinical verification of mathematical models based on theoretical considerations which do not always apply in practice.

Phenylethylmalonamide serum levels in patients treated with primidone and the effects of other antiepileptic drugs

Data are presented for the serum levels of 2-ethyl-2-phenylmalonamide (PEMA) in patients receiving anticonvulsant medication. Statistical analysis of these data indicates that the serum level of PEMA, which is a metabolite of primidone, is affected not only by the dose of primidone but also by the serum levels of other prescribed anticonvulsant drugs. In particular, phenobarbitone is shown to be a major perturbation upon the PEMA serum level.

Effects of pregnancy on antiepileptic drug utilization

Pregnancy is associated with characteristic changes in the disposition of antiepileptic drugs; recent findings on this aspect of drug utilization are presented. In one study involving 48 pregnancies, the mean level-dose ratio of phenytoin decreased by 34%. In another study of 111 patients, phenytoin clearance increased gradually over the first 32 weeks of pregnancy and reached twice the preconception value. In two studies with phenobarbital, levels tended to decrease, although this effect was less pronounced than for phenytoin. Similarly for primidone, pregnancy had little effect on steady-state levels; however, levels of phenobarbital formed from primidone exhibited large decreases during pregnancy followed by increases after delivery. This effect was quite consistent. Carbamazepine clearance tended to increase to a relatively small extent. Limited data indicate that valproate levels decrease by 30 to 40% during pregnancy. The mechanisms responsible for these effects have not been elucidated and possibly include decreased bioavailability or compliance, increased metabolic clearance, or decreased plasma protein binding. Since the patient at risk of an increase in seizure frequency cannot be identified prior to conception, therapeutic monitoring is imperative during and after pregnancy.

Interactions between anticonvulsants and other commonly prescribed drugs

Many drug interactions can be demonstrated, but only a few are so clinically significant that they necessitate adjusting drug dosages. The same drug combination may produce changes of variable extent or direction in different individuals. The reasons for this variability include genetic control of the rate and inducibility of drug metabolism, and environmental factors such as contact with chemicals. Among antimicrobial agents, chloramphenicol may cause accumulation of phenytoin (PHT) and phenobarbital (PB), and isoniazid may cause PHT, carbamazepine (CBZ), and primidone (PRM) to accumulate. Erythromycin may cause accumulation of CBZ. Among anti-ulcer agents, antacids may reduce PHT concentration while cimetidine may cause accumulation of PHT, CBZ, and diazepam (DZP). Salicylates displace strongly binding drugs such as PHT, DZP, or valproate (VPA) from the binding sites in plasma proteins, which may lead to some decline of the total plasma level with an increase in the unbound drug percentage. Conversely, anticonvulsants may influence the dosage requirements of oral anticoagulants by inducing their metabolism. Failures of oral contraceptives have been attributed to anticonvulsants in some patients. Probably the most predictable interaction that necessitates dosage adjustment is accumulation of PB caused by VPA. Intentional inhibition of PRM metabolism by nicotinamide serves as an example of attempts to utilize an interaction for improved therapeutic effect.

Single-dose kinetics of primidone in acute viral hepatitis

The pharmacokinetics of primidone (PRM) after oral administration of a single 500 mg dose was studied in 7 patients with acute viral hepatitis and 7 healthy control subjects. The elimination half-life and the apparent clearance of unchanged PRM in the patients were 18.0 +/- 3.1 h and 42 +/- 14 ml X h-1 X kg-1, respectively (mean +/- SD) and did not differ significantly from the values in the controls (half-life 17.0 +/- 2.4 h; clearance 35 +/- 8 ml X h-1 X kg-1). The metabolite phenylethylmalonamide (PEMA) was detected in the serum of all normal subjects within 2-24 h. By contrast, serum levels of this metabolite were undetectable (less than 2 mumol/1) in all but one of the patients. Serum levels of phenobarbital (PB) remained below the limit of detection (less than 2 mumol/1) in all subjects. The findings indicate that accumulation of PRM with its attendant toxicity is unlikely to occur in epileptic patients who develop acute viral hepatitis, despite evidence that the metabolism of the drug is affected by this condition. The possibility of impaired conversion to PB and its implications are discussed.

Studies on the intracerebral metabolism of anticonvulsant drugs--I. Perfusion of primidone through the isolated brain of the rat

Primidone and phenobarbital (each 85 nmoles/ml were separately perfused through the isolated brain of the rat. After 5 min of perfusion similar amounts of primidone and phenobarbital were taken up into the brain; for both drugs the concentration ratio between brain and perfusion medium was about 0.2. However, after 2 hr of perfusion the mean concentration ratio for primidone was about 0.55; for phenobarbital it was about 0.9 thus indicating a better uptake of phenobarbital. In two regions (hypophysis, mesencephalon) the concentration of phenobarbital was significantly higher than in perfusion medium. During 2 hr of perfusion of primidone, substantial quantities of phenobarbital and PEMA were formed amounting to 1400 pmoles for each metabolite. The highest concentration of the metabolites was found in septum, hypothalamus, hypophysis and mesencephalon. The in situ metabolism of primidone in the intact brain was demonstrated for the first time.

Changes in primidone/phenobarbitone ratio during pregnancy and the puerperium

Plasma concentrations of primidone and its metabolite phenobarbitone were monitored in 9 pregnant epileptic patients treated with primidone (and in 3 cases other antiepileptic drugs) given at constant doses throughout pregnancy and the puerperium. Phenobarbitone plasma concentrations were monitored in another 6 patients given phenobarbitone itself. A trend towards increasing primidone plasma concentrations during the second quarter of pregnancy was evident in all patients, with a concomitant significant decrease in primidone-derived phenobarbitone plasma concentrations. A trend towards a lowering of plasma concentrations of phenobarbitone administered as such was confirmed. These results suggest the usefulness of a careful monitoring of primidone and primadone-derived phenobarbitone during pregnancy and the puerperium. Discrepancies of findings with primidone and phenobarbitone are discussed in view of the possible mechanism involved.

Anticonvulsant effect of primidone in the gerbil. Time course and significance of the active metabolites

The anticonvulsant effect of primidone was determined in gerbils, in which seizures were elicited by a blast of compressed air, over the time range of 30 min to 18 h after oral administration. ED50s remained fairly constant from 1 to 12 h after administration: 46-73 mumol/kg with the minimal value at 6 h. Of the metabolites, phenobarbital was maximally effective at 2 h after administration (ED50 35 mumol/kg), whereas phenylethylmalondiamide (PEMA) only had a weak anticonvulsant effect (ED50 1.55 mmol/kg at 2 h). By determination of primidone and its active metabolites in plasma and brain at 1, 4 and 12 h after administration of the respective ED50s, it could be shown that unchanged primidone is mostly responsible for the anticonvulsant effect of the first hours, but, at 12 h, only phenobarbital could be detected in both tissues. PEMA could not be detected in brain. From the effective brain concentrations at different times it could be calculated that primidone and phenobarbital have the same anticonvulsant potency on a molar base in the gerbil. The concentrations necessary to control seizures in this model were considerably lower than those needed to suppress convulsions in maximal seizure models in mice and rats.

[Comparative study of the levels of anticonvulsants and their free fractions in venous blood, saliva and capillary blood in man]

There is a good correlation for the six anticonvulsants studied in mono and polytherapy in human serous and capillary blood. Blood can be taken either at the vein, or at the finger. The ratio free fraction and saliva/serous blood has given for phenobarbital 0.65 (0.52 - 0.83) and 0.30 (0.21 - 0.46), pH 5.9 - 7.5, phenytoin 0.11 (0.10 - 0.11) and 0.12 (0.08 - 0.23), primidone 0.81 (0.74 - 0.83) and 1.03 (0.88 - 1.11), carbamazepine 0.22 (0.20 - 0.26) and 0.37 (0.30 - 0.50), ethosuximide 0.99 (0.81 - 7.01) and 0.95 (0.90 - 1.30), and less than 0.10 for valproate levels. In certain conditions, saliva may have a considerable place in drug monitoring.

Identification of p-hydroxyprimidone as a minor metabolite of primidone in rat and man

Urine specimens from rats and humans who received single doses of primidone (PRM) have been investigated by GC/MS procedures. In addition to the previously documented metabolites of PRM, a small chromatographic peak was encountered which had a mass spectrum suggesting a hydroxy-PRM derivative. Synthesis of p-hydroxy-PRM from PRM was effected; the para isomer was separated from unwanted isomers by preparative HPLC. The PMR spectrum of the synthetic compound proved the position of the hydroxy substituent to be para. This compound had identical GC retention time and an almost identical mass spectrum with that obtained in the urinary extracts. Para-hydroxy-PRM was therefore confirmed as a new, minor metabolite of PRM in rat and man.

Coma and crystalluria: a massive primidone intoxication treated with haemoperfusion

The present paper describes a patient who was in danger of dying from a massive primidone overdose. She was comatose, hypotensive and in acute renal failure with crystalluria. Because of her clinical condition and high plasma primidone level (209 mg/l) haemoperfusion was instituted. Both the calculated drug clearances and the remarkable improvement in the patient's clinical condition suggest that haemoperfusion was very effective.

[Primidone kinetics and analysis of its interactions with the major antiepileptic drugs]

In 5 volunteers, after single oral administration of 10 mg/Kg of primidone (PRM) plasmatic concentration of the drug has been monitored during 24 hours. PRM plasma half life was found longer than in previous reports. It was however confirmed that its metabolite phenobarbital (PB) is not present in the blood for at least 48 hours. Moreover 166 patients under long term PRM treatment were investigated as to the influence of phenytoin (DPH) and carbamazepine (CBZ) on the PB serum levels. It was found that patients in therapy with PRM + DPH showed a better relationship between PRM oral dose and PB plasma level and also between oral dose and plasma level of DPH than in patients in monotherapy with PRM or DPH, whereas these effects were not evident in patients taking PB + DPH.

[Monitoring therapy by analysis of the drug concentration of saliva]

The distribution of a drug between blood and saliva depends on its physicochemical properties, e.g. binding to plasma proteins, apparent dissociation constant and lipid solubility. The clinical value of measuring salivary drug concentrations in therapeutic drug monitoring is demonstrated using anticonvulsant therapy in children as an example. For carbamazepine and phenytoin there is a close and constant saliva/serum ratio over a wide range of concentrations, which is influenced by the salivary flow rate only to an insignificant degree. Salivary concentrations of carbamazepine account for about 40%, of phenytoin for about 10% of the serum concentrations. In contrast, salivary levels of primidone and phenobarbital are significantly influenced by the rate of saliva flow. In resting saliva primidone levels slightly exceed those in serum and fall significantly below the corresponding serum values during forced stimulation of salivary flow. For phenobarbital in resting saliva the mean saliva/serum ratio is 0.3 and increases significantly during forced stimulation. Provided the conditions of sample collection are standardized saliva is suitable for monitoring primidone and phenobarbital therapy, too.

Drug interactions with valproic acid

Valproic acid undergoes drug-drug interactions with most of the commonly used anticonvulsants. Since it possesses a wide range of indications, concomitant use with other anticonvulsants, and hence interactions, are not infrequent. Many of these interactions are reciprocal and may have important therapeutic consequences. Valproate acts as a protein binding displacer and/or metabolic inhibitor with respect to a number of other anticonvulsants (phenobarbitone, primidone, phenytoin). Inhibition of metabolism would, in most instances, result in a decrease of the dose requirements of the affected drugs. Valproate is a low clearance drug primarily eliminated by metabolism. Its metabolism is highly inducible by some of the major anticonvulsants (e.g. carbamazepine, phenytoin). Valproate is also highly protein bound in plasma and thus is displaced by salicylates and free fatty acids. However, displacement alone, unlike induced metabolism, should not affect the drug's dose-response relationship.

Anticonvulsants during pregnancy and lactation. Transplacental, maternal and neonatal pharmacokinetics

Few data are available on placental transfer of anticonvulsants during early pregnancy. Nevertheless, it has been demonstrated that at this early stage of gestation, considerable amounts of phenytoin, primidone/phenobarbitone and carbamazepine as well as some of their metabolites are already present in fetal tissues. Potentially reactive metabolites of anticonvulsants can be formed by the fetal liver and accumulate in some organs. At term, most anticonvulsants are present in neonatal plasma in concentrations similar to those in maternal plasma. Valproic acid, on the other hand, can accumulate in fetal blood, for still unknown reasons. Elimination by the neonate is variable and is dependent on several factors, such as clinical state, pre- or perinatal enzyme induction, absorption of the drugs and their plasma protein binding. Neonatal acquisition of anticonvulsants via breast-feeding does not seem to be harmful for the neonate. In the case of phenobarbitone, however, the drug may accumulate in nursing neonates to levels approaching or even exceeding those of their mothers. Significant drug levels can also build up in neonates and infants nursed by carbamazepine- and ethosuximide-treated mothers. This review contains relevant pharmacokinetic data on anticonvulsant drugs widely used during pregnancy and the neonatal period. The differences between pregnant and non-pregnant adults as well as between neonates and older age groups are emphasized. Some pharmacokinetic data are correlated with clinical manifestations, such as seizure frequency, neonatal depression and withdrawal symptoms.

Interactions between primidone, carbamazepine, and nicotinamide

The effect of nicotinamide on the conversion of primidone to phenobarbital was studied in mice and in three epileptic patients. In mice, 200 mg per kilogram of nicotinamide increased the half-life of primidone by 47.6%, and the conversion to phenobarbital and phenylethylmalonamide was decreased by 32.4% and 14.5%, respectively. Nicotinamide also decreased the conversion of primidone to phenobarbital in patients. The dose of nicotinamide correlated directly with the primidone-phenobarbital ratio (r = 0.861, p less than 0.01). Nicotinamide also increased carbamazepine levels in two patients treated with this drug. The data demonstrate that nicotinamide inhibits metabolism of primidone in mice and metabolism of primidone and carbamazepine in humans. This probably occurs by inhibition of cytochrome P-450 by nicotinamide.

Phenytoin: an inhibitor and inducer of primidone metabolism in an epileptic patient

The interaction between primidone and phenytoin was studied in an epileptic patient treated with primidone only and primidone plus phenytoin for 3 months. Plasma and urine levels of drugs and metabolites were monitored daily by GC and GC-MS. The addition of phenytoin to the regimen increased steady-state plasma levels of phenobarbitone and phenylethylmalonamide (PEMA), metabolites of primidone, and decreased levels of primidone and unconjugated p-hydroxyphenobarbitone (p-OHPB), a metabolite of phenobarbitone. After withdrawal of phenytoin, plasma phenobarbitone and primidone levels slowly returned to previous steady-state levels, PEMA rapidly decreased to lower levels than before, and p-OHPB levels rose rapidly. Urinary excretion of primidone and its metabolites paralleled the changes in their plasma levels after the addition of phenytoin but the percentage of unconjugated p-OHPB in urine was unchanged during the course of the study. In conclusion phenytoin initially induces the conversion of primidone to PEMA and phenobarbitone, although each to a different extent, but it appears to inhibit the hydroxylation of phenobarbitone. Thus, two apparently contradictory phenomena seem to be involved in the primidone-phenytoin interaction. The net effect is an enhanced increase in plasma phenobarbitone levels.

Pharmacokinetics of primidone elimination by uremic patients

The hemodialyzability of primidone was investigated in four patients on long-term hemodialysis. Primidone, 500 or 250 mg, was given orally 2 hours before hemodialysis. Blood and dialyzate samples were collected periodically during the 4-hour dialysis and measured by gas-liquid chromatography and high-performance liquid chromatography for primidone. Dialysis clearance calculated by the instantaneous dialyzate method averaged 97.7 ml/min, which is considerably greater than the metabolic clearance of 30 ml/min for the drug. The extraction efficiency of the hollow-fiber dialyzers averaged 40.2 pr cent for plasma samples. A mean of 31.7 per cent of the administered dose of primidone was removed during hemodialysis. The half-life was 5.1 hours in our patients during hemodialysis, a nearly two-thirds reduction of the 13.9-hour half-life calculated in uremic patients. Because of the reduction in elimination half-life, greater dialysis clearance than metabolic clearance, high extraction efficiency, and significant drug removal during dialysis, we conclude that primidone is dialyzable.

Pharmacokinetics of phenylethylmalonamide (PEMA) in normal subjects and in patients treated with antiepileptic drugs

The pharmacokinetics of phenylethylmalonamide (PEMA), a major metabolite of primidone, were investigated following administration of single oral doses (400 mg) to six normal subjects and six patients receiving chronic treatment with antiepileptic drugs. Peak serum PEMA levels were usually attained with 2-4 h after intake. The oral bioavailability estimated on the basis of the recovery of unchanged drug in the urine of normal subjects was at least 80%. Half-life values ranged from 17 to 25 h in normal subjects and from 10 to 23 h in the patients. No statistically significant difference in any of the calculated kinetic parameters could be found between the two groups. The data indicate that PEMA is readily absorbed from the gastrointestinal tract and that it is eliminated predominantly unchanged in the urine of man.

On P-chlorphenylalanine interference with phenobarbital formation from primidone

Premedication with PCPA antagonized in rats the anticonvulsant activity of Primidone and of other drugs against seizures evoked by electroshock. Only in the case of Primidone, however, the anticonvulsant activity could not be re-established by increasing the dosage. Our investigations have shown that PCPA caused a strong inhibition of the conversion of Primidone to phenobarbital, both in vivo and in vitro.

Diphenylhydantoin and primidone in tears

Diphenylhydantoin (PHT) and primidone (PRM) were determined by the EMIT technique in the plasma, tears, saliva, and CSF of epileptic patients. Results indicate for PHT that tear values are more strictly correlated than are the saliva values to plasma and CSF concentrations. As for PRM, the data obtained show great interindividual variability of concentration in the different body fluids--in agreement with the wide range of both protein binding and half-life of this drug.

Primidone kinetics: effects of concurrent drugs and duration of therapy

Primidone (PRM) kinetics was examined in two groups of adult seizure patients: (1) 10 newly diagnosed in whom only PRM was used, the monotherapy (MT) group, and (2) nine in whom PRM was added to other antiepileptics, the combination therapy (CT) group. Time-concentration data were obtained after an initial dose of 250 mg and during subsequent steady-state periods. PRM elimination was slower (p less than 0.05) after the initial dose in MT patients (half-life (t 1/2) = 15.2 hr, apparent clearance = 35 ml/hr/kg) than in CT patients (t 1/2 = 8.3 hr, clearance = 51 ml/hr/kg). PRM metabolites, phenobarbital and phenylethylmalonamide, appeared much earlier in CT patients. Continued PRM exposure in MT patients was accompanied by an increase in apparent clearance in three of seven patients, but no change in four of seven. In four CT patients in whom other antiepileptics were withdrawn there was a decrease in apparent clearance (61.4 to 29.9 ml/hr/kg) no rates in the range of MT patients. PRM kinetics is influenced by concurrent antiepileptic drugs and by duration of PRM therapy.

Pharmacokinetics of primidone and its active metabolites in the dog

In dogs, the metabolism of primidone and the pharmacokinetics of the drug itself as well as its metabolites phenobarbital and phenylethylmalonic acid diamide (PEMA) was followed after single oral doses of 30 mg/kg (0.14 mmole/kg). Primidone was rapidly absorbed, so that maximal serum concentrations were reached after 2 hr, the concentration fell then with a half-life averaging 5 hr in Beagles and 10 hr in Mongrels. PEMA appeared in plasma with a ka of 0.003--0.005 min-1, reached maximal concentrations after about 6.5 hr in Beagles and 12 hr in Mongrels. The elimination half-life averaged 7.5 hr in Beagles and 14 hr in Mongrels. After single oral doses, phenobarbital could only be detected in low concentrations in some Beagles. Phenobarbital had an elimination half-life of 32 +/- 4.8 hr in Beagles and of 70 +/- 16 hr in Mongrels. During continued treatment with daily doses of 30--50 mg/kg primidone, steady-state concentrations of about 15 micrograms/ml (65 nmole/ml) were reached after 6--8 days, the PEMA concentrations showed rather pronounced fluctuations around average values of 8--10 micrograms/ml (39--49 nmole/ml), whereas the concentrations of primidone mainly remained below 5 micrograms/ml (23 nmole/ml). In mice, the anticonvulsant potency of the 3 drugs was determined: Elevations of the electroconvulsant threshold by 40 V were produced by 0.01 mmole/kg of phenobarbital, 0.017 mmole/kg of primidone or 0.37 mmole/kg of PEMA. Taking the anticonvulsant potency of the 3 drugs into consideration, phenobarbital is responsible for more than 85% of the total anticonvulsant activity during continued medication of primidone. The penetration of primidone and its metabolites into the cerebro-spinal fluid was followed: phenobarbital reached steady state levels already after 1--1.5 hr, primidone and PEMA not before 2.5 hr. The concentrations in CSF roughly corresponded to the free drug in plasma. On account of the similarities in metabolism and pharmacokinetics of primidone in dog and man, the former species seems to be a suitable model in epilepsy research. Differences between both species are most pronounced in the Beagle.

Primidone metabolism in renal insufficiency and acute intoxication

Primidone (PRIM) is metabolized into phenobarbital (PB) and phenylethylmalonamide (PEMA). During anticonvulsant therapy with PRIM under normal conditions PB represents by fat the largest portion of the total concentration of all three components (PRIM + PB + PEMA). In combined therapy with diphenylhydantoin (DPH), and during chronic PRIM overdosage, the relative concentration of PB is even higher. A case of renal insufficiency while on PRIM therapy and a case of acute PRIM intoxication are presented. In both cases PRIM and PEMA are elevated while PB is relatively low. The mechanisms involved in this phenomenon are discussed. Excluding young children with chronic PRIM overdosage, and the endogenous and exogenous intoxication described here, a relative PB concentration below 40% indicates a lack of patient compliance if a steady treatment schedule has been maintained for at least 3 weeks.

Flow-dependent salivary primidone levels in epileptic children

In 36 epileptic children treated with primidone alone or in combination with additional anticonvulsants, salivary drug levels were compared in resting (I) and in flow-stimulated (II) saliva and were related to the corresponding serum levels. Primidone levels in saliva I and saliva II were highly correlated (r = 0.97) but were significantly (p less than 0.001) lower in saliva II; the mean difference was -38%. Serum primidone levels were highly correlated to salivary primidone levels both in saliva I (r = 0.92) and in salvia II (r = 0.91). A significant negative correlation could be established between the salivary flow rate and the saliva/serum ratio of primidone, especially in saliva I (r = 0.61; p less than 0.001). The mean saliva I/serum ratio was 1.115, reflecting drug accumulation in resting saliva. The reason primidone accumulates remains unclear. When salivary flow was stimulated, the mean saliva/serum ratio decreased to 0.7, indicating the development of a drug concentration slope from blood to saliva. This is explained by the limited permeation of the drug through cellular membranes due to its rather low lipid solubility. From the data it can be concluded that saliva is suitable for monitoring primidone levels provided the conditions of sample collection are standardized.

Carbamazepine levels in pregnancy and lactation

An epileptic patient whose seizures were controlled with carbamazepine and primidone was followed throughout pregnancy and lactation. Blood levels of primidone decreased during pregnancy and rose postpartum requiring dosage adjustments. Pharmacologically insignificant amounts of the drug were detected in breast milk. A review of the literature revealed 94 infants exposed to carbamazepine in utero and no evidence to date that this drug carries a teratogenic risk.