Effect of orally administered dextromethorphan on theophylline- and pentylenetetrazol-induced seizures in rats

Dextromethorphan, widely used as an antitussive, has recently been shown to protect animals against maximal electroshock and excitatory amino acid (N-methyl-D-aspartate)-induced convulsions. Its protective efficacy against theophylline-induced seizures was determined in this investigation in view of the limited effectiveness of presently available anticonvulsants against this manifestation of serious theophylline intoxication. Rats were pretreated with an oral dose of dextromethorphan (50 mg/kg) or saline solution. Fifteen minutes later, the rats were infused intravenously with theophylline [approximately 11 mg/(kg.min)] until the onset of maximal seizures. Pretreatment with dextromethorphan was associated with a significant decrease in the concentrations of theophylline in the cerebrospinal fluid and serum at the pharmacologic endpoint. To further explore this unanticipated effect, a similar experiment was performed with the convulsant pentylenetetrazol (PTZ), which was infused at a rate of approximately 3.4 mg/(kg.min) until the onset of maximal seizures. Dextromethorphan-pretreated animals required a significantly larger dose of PTZ than did controls to produce the first myoclonic jerk, but a significantly smaller dose of the convulsant to produce maximal seizures. Serum and cerebrospinal fluid concentrations of PTZ at onset of maximal seizures were significantly lower in dextromethorphan-treated than in control animals. The proconvulsant activity of dextromethorphan with respect to theophylline-induced maximal seizures is similar to that of phenytoin, and is consistent with other pharmacologic evidence of such similarity.     

Anticonvulsant activity of (+)-5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine (MK-801), a substance with potent anticonvulsant,central sympathomimetic,and apparent anxiolytic properties

MK-801 prevented tonic extensor seizures in the rat induced by bicuclline with the ED₅₀ being 23 μg/kg p.o. Clonazepam, phenobarbital, diazepam, phenytoin, γ-acetylenic GABA, sodium valproate, and trimethadione were all less potent. In mice, MK-801 was likewise the most potent (ED₅₀ = 0.35 mg/kg p.o.) compound in protecting against tonic seizures induced by electroshock. Clonazepam (ED₅₀ = 0.41 mg/kg p.o.) and MK-801 (ED₅₀ = 0.67 mg/kg p.o.) were by far more potent than any of the other anticonvulsants tested versus bicuculline-elicited seizures in mice. Besides being a potent anticonvulsant, MK-801 demonstrated selectivity, since much higher doses were required in mice to block clonic convulsions produced by pentylenetetrazol (ED₅₀ = 11 mg/kg p.o.) and tonic seizures caused by strychnine (ED₅₀ > 15 mg/kg p.o.) than were needed against electroshock or bicuculline. The anticonvulsant (electroshock) effect of MK-801 in mice was unaffected by pretreating the animals with various receptor antagonists (atropine, mecamylamine, chlorpheniramine, tripelennamine, cyproheptadine, cinanserin, methysergide, cimetidine, and propranolol). MK-801 was slightly, but significantly, antagonized by methergoline, naloxone, and theophylline, whereas haloperidol and especially α-adrenoceptor blockers (prazosin, HEAT, phenoxybenzamine) markedly reduced the anticonvulsant effect of MK-801. Haloperidol was selective for MK-801, not affecting the anticonvulsant actions of phenytoin or phenobarbital. Prazosin antagonized phenytoin and phenobarbital, but to a much lesser extent than it antagonized MK-801. MK-801 is an extremely potent and selective anticonvulsant acting at least partly via a catecholaminergic mechanism.     

Imperatorin enhances the protective activity of conventional antiepileptic drugs against maximal electroshock-induced seizures in mice

The effects of imperatorin (8-isopentenyloxypsoralen; 9-(3-methylbut-2-enyloxy)-7H-furo[3,2-g]chromen-7-one) on the anticonvulsant activity of four conventional antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) were studied in the mouse maximal electroshock seizure model. Results indicate that imperatorin (30 and 40 mg/kg, i.p.) significantly potentiated the anticonvulsant activity of carbamazepine against maximal electroshock-induced seizures by reducing its median effective dose (ED(50)) from 10.3 to 6.8 (by 34%; P<0.05) and 6.0 mg/kg (by 42%; P<0.01), respectively. Similarly, imperatorin (40 mg/kg, i.p.) markedly enhanced the antielectroshock action of phenobarbital and phenytoin, by lowering their ED(50) values from 19.6 to 12.2 mg/kg (by 38%; P<0.05-phenobarbital) and from 12.8 to 8.5 mg/kg (by 34%; P<0.05-phenytoin) in the maximal electroshock seizure test. In contrast, imperatorin (40 mg/kg, i.p.) did not affect the protective action of valproate against maximal electroshock-induced seizures in mice. Imperatorin at lower doses of 20 and 30 mg/kg had no significant effect on the anticonvulsant activities of conventional antiepileptic drugs in the mouse maximal electroshock seizure model. Pharmacokinetic evaluation of interaction between imperatorin (30 mg/kg, i.p.) and carbamazepine (6.8 mg/kg, i.p.) revealed a significant increase in total brain carbamazepine concentration after imperatorin administration, indicating a pharmacokinetic nature of interaction between these drugs. In cases of phenobarbital and phenytoin, imperatorin (40 mg/kg, i.p.) did not alter significantly total brain concentrations of phenytoin and phenobarbital in mice, and thus, the observed interactions in the maximal electroshock seizure test between imperatorin and phenobarbital or phenytoin were pharmacodynamic in nature. The present study demonstrates that imperatorin enhanced the antiseizure effects of carbamazepine, phenobarbital and phenytoin in the mouse maximal electroshock seizure model. However, the combination of imperatorin with carbamazepine, despite its beneficial effects in terms of seizure suppression in mice, was complicated by a pharmacokinetic increase in total brain carbamazepine concentration in experimental animals. In contrast, the combinations of imperatorin with phenytoin and phenobarbital, due to their beneficial antiseizure effects and no pharmacokinetic interactions between drugs in the brain compartment of experimental animals, deserve more attention and are of pivotal importance for epileptic patients as advantageous combinations from a clinical viewpoint.     

Behavioral effects of a neurotoxic compound isolated from Clibadium surinamense L (Asteraceae)

Clibadium surinamense L, popularly known as cunambi, is a native plant from the Northern region of Brazil illegally used for predatory fishing. Previous results from our laboratory have demonstrated that the oral treatment of mice with the ethanolic extract (EE) of the leaves of the plant induced generalized tonic-clonic seizures followed by death within 30 min. The aims of the present paper were to characterize the convulsant effect of the hexanic extract (HE) of the stems and leaves of C. surinamense and, by bioguided purification, to identify the active principle and its mechanism of action. The leaves and stems were extracted with hexane (100 g/L) in Soxhlet for 36 h (yield of 2.4%), the solvent was evaporated and the powder dissolved in 1.5% saline/Tween 80. Male mice (30-35 g) treated with HE (22.5-360 mg/kg, p.o.) showed behavioral alterations consistent with CNS stimulation. The intensity and duration of the effect were proportional to the administered doses. The behavioral alterations, measured with a graded score of seizure severity, revealed that pretreatment with carbamazepine (30 mg/kg, i.p., 60 min) or phenytoin (50 mg/kg, i.p., 30 min) did not alter the HE convulsive effect. In contrast, phenobarbital (30 mg/kg, i.p., 60 min) or diazepam (2 mg/kg, i.p., 30 min) reduced the HE effect, increasing the ED(50) for clonic seizures from 64.4 to 89.8 mg/kg and 168.9 mg/kg, respectively. Purification of the HE in a silica gel column eluted with a hexane/ethyl acetate gradient yielded a single fraction with convulsant effect in which cunaniol acetate was identified by (1)H NMR as the main active compound. These results indicated that inhibition of GABAergic transmission by cunaniol acetate might be responsible for the convulsant effects of C. surinamense L in mice, but do not exclude a direct cunaniol action labilizing neuronal excitability.     

Seizures induced by theophylline and isoniazid in mice.

Isoniazid-induced seizures respond poorly to anticonvulsants but well to pyridoxine (Vitamin B6); theophylline produces difficult-to-treat seizures with substantial morbidity and mortality. Theophylline therapy depresses plasma pyridoxal-5'-phosphate (PLP), the active metabolite of pyridoxine, suggesting that theophylline-induced seizures might be amenable to treatment with pyridoxine. Our study established the dose-response relationship for convulsions due to isoniazid and theophylline in mice and determined if pyridoxine antagonized such seizures. Female CD-1 outbred mice weighing 25 to 30 g were used. Clonic seizures had clonic activity lasting 5 sec; tonic seizures had loss of the righting reflex with tonic hindlimb extension. Groups of 10 mice received single doses of 50, 100, 150, 200, 250 or 300 mg aminophylline/kg i.p. or 100, 150, 200, 250, 300 or 350 mg isoniazid/kg i.p. and were observed for seizures or death. Pyridoxine or saline with aminophylline or isoniazid were administered simultaneously. The LD50 for aminophylline was 266 mg/kg; for isoniazid it was 160 mg/kg. Doses of 150 mg aminophylline/kg or 100 mg isoniazid/kg did not induce seizures. Pyridoxine with aminophylline or isoniazid did not alter the frequency or time of onset of seizures or death. This was unexpected because pyridoxine antagonizes theophylline-induced seizures in mice and reverses isoniazid-induced seizures in humans. We found no evidence that PLP depletion in mice is a mechanism for seizures induced by isoniazid or aminophylline in a fashion similar to isoniazid in humans.     

Effect of anticonvulsant drugs on (35S)t-butylbicyclophosphorothionate binding in vitro and ex vivo

Using several concentrations of eight anticonvulsant drugs in clinical use (carbamazepine, clonazepam, phenytoin, phenobarbital, ethosuximide, primidone, sodium valproate, and D,L-gamma-vinyl GABA), we studied their abilities in vitro to displace (35S)t-butylbicyclophosphorothionate (35S-TBPS) from its binding site in a homogenate of rat brain. Thereafter ethosuximide (150 mg/kg), phenobarbital (30 mg/kg), clonazepam (0.3 mg/kg), or phenytoin (100 mg/kg) was injected intraperitoneally into rats for 16-20 days; and the effect of drug administration on 35S-TBPS binding was studied in the cortex and hippocampus ex vivo. Phenobarbital (100 microM, P less than 0.001), ethosuximide (500 microM, P less than 0.001), and phenytoin (40 microM, P less than 0.001) decreased the specific 35S-TBPS binding in vitro by 10-16%. After drug administration of phenobarbital (concentration in plasma 168 microM), the number of binding sites decreased and the binding affinity (P less than 0.05) in the cortex increased. Other anticonvulsants did not modulate 35S-TBPS binding in vitro at the concentration analogous to therapeutic plasma levels or ex vivo at the dose used. These results suggest that the use of phenobarbital may modulate the TBPS binding site, but the role of the present findings in the anticonvulsant action of phenobarbital needs to be further studied.     

Effect of YM928, a novel AMPA receptor antagonist,on seizures in EL mice and kainate-induced seizures in rats

Kainate-induced seizures and seizures induced by tossing stimulation in epilepsy-prone EL mice are considered as models of complex partial seizures. We used these models to evaluate the anticonvulsive effects of 2-[N-(4-chlorophenyl)-N-methylamino]-4H-pyrido[3.2-e]-1,3-thiazin-4-one (YM928), a novel -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist. In the kainate-induced seizure test in rats, wet-dog shakes (WDS) were reduced by oral administration of YM928 at doses of 7.5 mg/kg and 30 mg/kg. YM928 (15 mg/kg) reduced the number of WDS within the first 80 min, but then prolonged the time of occurrence compared with the other groups. Significant reduction in kainate-induced motor seizure was observed with 4–30 mg/kg. YM928 did not induce apparently abnormal behaviour at doses of 2–15 mg/kg but did induce sedation at 30 mg/kg. Carbamazepine (40 or 80 mg/kg), valproate (600 mg/kg), diazepam (2.5 mg/kg), and phenobarbital (20 or 40 mg/kg) exerted anticonvulsant effects against motor seizures, but only valproate, at a dose that also caused sedation, suppressed WDS. Phenytoin and ethosuximide did not show significant anti-kainate effects. In the tossing stimulation test in EL mice, i.p. injection of YM928 at 5 mg/kg or 10 mg/kg significantly increased the number of stimulations required to elicit generalized seizure. Carbamazepine (4 or 8 mg/kg), phenytoin (8 or 16 mg/kg), valproate (100–400 mg/kg), diazepam (0.5 mg/kg), phenobarbital (1.3 or 2.5 mg/kg) and ethosuximide (75–300 mg/kg) exerted significant anticonvulsant effects against these seizures. These results indicate that YM928 has anticonvulsant effects on seizure models that are characteristic of partial onset seizures in humans. YM928 is expected to have beneficial effects against human complex partial seizure with secondary generalization or temporal lobe epilepsy.     

Effects of phenytoin, phenobarbital, and valproic acid, alone and in selected combinations, on schedule-controlled behavior of rats

The present study examined the effects of phenytoin (20, 30, 40, and 50 mg/kg), phenobarbital (10, 20, 30, and 40 mg/kg), and valproic acid (80, 120, 160, and 240 mg/kg), and those of phenobarbital (10 and 30 mg/kg) combined with phenytoin (20, 30, and 40 mg/kg) or valproic acid (80, 120, and 160 mg/kg), on the lever pressing of rats maintained under fixed-ratio and interresponse-time-greater-than-t schedules of food delivery. High doses of each individual drug significantly decreased mean group response (and reinforcement) rate under the fixed-ratio schedule. No dose of an individual agent significantly affected mean group response rate under the interresponse-time-greater-than-t schedule, although high doses of phenobarbital and valproic acid significantly reduced the mean group reinforcement rate under this schedule. When given in combination, phenobarbital and phenytoin and phenobarbital and valproic acid significantly reduced response (and reinforcement) rate under the fixed-ratio schedule and reinforcement rate under the interresponse-time-greater-than-t schedule. These reductions did not significantly differ in magnitude from those predicted by an additive model of drug interaction.     

The effects of several barbiturates on lithium chloride induced taste aversion

The effects of single doses of five barbiturates on LiCl induced saccharin aversion were examined. Twenty three hour fluid deprived rats were offered a novel 0.125% saccharin solution and then were injected with either 3.0 mEq/kg LiCl or 0.9% saline. On the first test day after conditioning the animals were injected with either 60 mg/kg sodium phenobarbital, 80 mg/kg sodium barbital, 30 mg/kg sodium amobarbital, 20 mg/kg sodium secobarbital, 9 mg/kg sodium pentobarbital or 0.9% saline, 15 min prior to the drinking session. Results indicate that only 9 mg/kg pentobarbital, 60 mg/kg phenobarbital, and 80 mg/kg barbital were effective in attenuating the LiCl induced saccharin aversion on the day of administration. In addition, dipsogenic effects for only 60 mg/kg phenobarbital and 30 mg/kg amobarbital were observed in the saline treated control groups. A synergistic interaction between the effects of LiCl and sodium phenobarbital, barbital, and secobarbital was also observed. Lithium chloride plus these barbiturates resulted in a longer term aversion to saccharin than LiCl alone and no barbiturate produced saccharin aversion when administered without LiCl.     

Influence of carbenoxolone on the anticonvulsant efficacy of conventional antiepileptic drugs against audiogenic seizures in DBA/2 mice

Carbenoxolone, the succinyl ester of glycyrrhetinic acid, is an inhibitor of 11beta-hydroxy steroid dehydrogenase and gap junctional intercellular communication. It is currently used in clinical treatment of ulcer diseases. Systemic administration of carbenoxolone (1-40 mg/kg, intraperitoneally (i.p.)) was able to produce a dose-dependent decrease in DBA/2 audiogenic seizure severity score. Glycyrrhizin, an analogue of carbenoxolone inactive at the gap-junction level, was unable to affect audiogenic seizures at doses up to 30 mg/kg. In combination with conventional antiepileptic drugs, carbenoxolone, 0.5 mg/kg, i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. This effect was not observed after the combination of glycyrrhizin (10 mg/kg, i.p.) with some conventional antiepileptic drugs. The degree of potentiation induced by carbenoxolone was greater for diazepam, felbamate, gabapentin, phenobarbital and valproate, less for lamotrigine, phenytoin and carbamazepine. This increase was associated with a comparable impairment in motor activity; however, the therapeutic index of combined treatment of antiepileptic drugs with carbenoxolone was more favourable than the combination with glycyrrhizin or saline. Since carbenoxolone did not significantly influence the total and free plasma levels of diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital, valproate and carbamazepine, pharmacokinetic interactions are not likely. However, the possibility that carbenoxolone can modify the brain clearance of the anticonvulsant drugs studied may not be excluded. In addition, carbenoxolone did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, carbenoxolone showed an additive anticonvulsant effect when administered in combination with some classical anticonvulsants, most notably diazepam, felbamate, gabapentin, phenobarbital, and valproate, implicating a possible therapeutic relevance of such drug combinations.     

Topiramate potentiates the antiseizure activity of some anticonvulsants in DBA/2 mice

Topiramate (1-50 mg/kg, intraperitoneally (i.p.)) was able to antagonize audiogenic seizures in DBA/2 mice in a dose-dependent manner. Topiramate at dose of 2.5 mg/kg i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. The degree of potentiation induced by topiramate was greatest for diazepam, phenobarbital and valproate, less for lamotrigine and phenytoin and not significant for carbamazepine and felbamate. The increase in anticonvulsant activity was associated with a comparable increase in motor impairment. However, the therapeutic index of the combination of all drugs+topiramate was more favourable than that of antiepileptics+ saline, with the exception of carbamazepine or felbamate+topiramate. Since topiramate did not significantly influence the total and free plasma levels of the anticonvulsant drugs studied, we suggest that pharmacokinetic interactions, in terms of total or free plasma levels, are not probable. However, the possibility that topiramate can modify the clearance from the brain of the anticonvulsant drugs studied cannot be excluded. In addition, topiramate did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, topiramate showed an additive effect when administered in combination with some classical anticonvulsants, most notably diazepam, phenobarbital, lamotrigine, phenytoin and valproate.     

The anticonvulsant effects of diazepam and phenobarbital in prek1ndled and kindled cortical seizures

The effects of various doses of diazepam (0.5–4 mg/kg) and phenobarbital (15–60 mg/kg) were determined on prekindled (focal) and kindled (generalized) cortical seizures in the same rats. Only high sedating doses of diazepam or phenobarbital reduced the elicited afterdischarge duration (ADD) and behavioral response in the prekindled focal cortical seizure. Against the kindled seizure, both diazepam and phenobarbital showed a marked and statistically significant increase in effectiveness in all but the smallest doses tested. The ADD of the kindled cortical seizures was reduced to prekindled lengths by diazepam (1–4 mg/kg) or phenobarbital (30–60 mg/kg). The increased anticonvulsant effectiveness found in this study is similar to previous findings with diazepam and phenobarbital against prekindled and kindled amygdaloid seizures, but stands in contrast to findings with prekindled and kindled pentylenetetrazol seizures.     

Pharmacokinetics of phenytoin following intravenous and intramuscular administration of fosphenytoin and phenytoin sodium in the rabbit.

The purpose of this study was to evaluate and compare plasma phenytoin concentration versus time profiles following intravenous (i.v.) and intramuscular (i.m.) administration of fosphenytoin sodium with those obtained following administration of standard phenytoin sodium injection in the rabbit. Twenty-four adult New Zealand White rabbits (2.1 +/- 0.4 kg) were anaesthetized with sodium pentobarbitone (30 mg/kg) followed by i.v. or i.m. administration of a single 10 mg/kg phenytoin sodium or fosphenytoin sodium equivalents. Blood samples (1.5 ml) were obtained from a femoral artery cannula predose and at 1, 3, 5, 7, 10, 15, 20, 30, 45, 60, 90, 120, 180, 240 and 300 min after drug administration. Plasma was separated by centrifugation (1000 g; 5 min) and fosphenytoin, total and free plasma phenytoin concentrations were measured using high performance liquid chromatography (HPLC). Following i.v. administration of fosphenytoin sodium plasma phenytoin concentrations were similar to those obtained following i.v. administration of an equivalent dose of phenytoin sodium. Mean peak plasma phenytoin concentrations (Cmax) was 158% higher (P = 0.0277) following i.m. administration of fosphenytoin sodium compared to i.m. administration of phenytoin sodium. The mean area under the plasma total and free phenytoin concentration-time curve from time zero to 120 min (AUC(0-120)) following i.m. administration was also significantly higher (P = 0.0277) in fosphenytoin treated rabbits compared to the phenytoin group. However, there was no significant difference in AUC(0-180) between fosphenytoin and phenytoin-treated rabbits following i.v. administration. There was also no significant difference in the mean times to achieve peak plasma phenytoin concentrations (Tmax) between fosphenytoin and phenytoin-treated rabbits following i.m. administration. Mean plasma albumin concentrations were comparable in both groups of animals. Fosphenytoin was rapidly converted to phenytoin both after i.v. and i.m. administration, with plasma fosphenytoin concentrations declining rapidly to undetectable levels within 10 min following administration via either route. These results confirm the rapid and complete hydrolysis of fosphenytoin to phenytoin in vivo, and the potential of the i.m. route for administration of fosphenytoin delivering phenytoin in clinical settings where i.v. administration may not be feasible.     

The anticonvulsant effects of diazepam and phenobarbital in prekindled and kindled seizures in rats

The effects of various doses of diazepam (0.5–4 mg/kg) and phenobarbital (7.5–60 mg/kg) were determined on prekindled and kindled amygdaloid seizures in the same rats. Diazepam was ineffective against the prekindled focal seizures, but demonstrated profound and statistically significant control of the kindled seizures. In the kindled state, diazepam reduced the afterdischarge duration and seizure rank score to prekindled levels. Only the largest sedating dose of phenobarbital produced a reduction of both prekindled afterdischarge duration and seizure rank score. Against the kindled seizure, phenobarbital showed a marked and statistically significant increase in effectiveness in all but the smallest dose tested. The afterdischarge duration of kindled seizures was reduced to prekindled levels by 15–60 mg/kg of phenobarbital, while seizure rank score was reduced to prekindled levels by 30 and 60 mg/kg phenobarbital. The effects of two doses of diazepam (0.5 and 2.5 mg/kg) and phenobarbital (7.5 and 30 mg/kg) were tested against prekindled and kindled pentylenetetrazol (PTZ)-induced seizures. Preliminary work with 3 doses of pentylenetetrazol (30, 40 and 60 mg/kg) demonstrated that repeated doses of 30 mg/kg readily kindled seizures without the significant mortality seen with larger doses. Both diazepam and phenobarbital were less effective against seizures kindled with 30 mg/kg pentylenetetrazol compared to prekindled seizures. The comparative lack of effect that was seen with diazepam and phenobarbital against the pentylenetetrazol kindled seizure at doses associated with control of the kindled amygdaloid seizure may reflect an underlying difference in the pathogenesis of kindling between these seizure models. Further, the lack of suppression of the prekindled amygdaloid afterdischarge duration by large doses of diazepam, in contrast to large doses of phenobarbital, may also reflect differences between the mechanisms of action of these two drugs. This paradigm provides a model for testing the effectiveness of anticonvulsants during the progressive development of various epileptogenic seizures.     

Performance of a new automated substrate-labeled fluorescence immunoassay system evaluated by comparative therapeutic monitoring of five drugs

The analytical performance of a new automated substrate-labeled fluorescence immunoassay system (Ames TDA/Optimate) was evaluated by comparative therapeutic drug monitoring of carbamazepine, phenobarbital, phenytoin, theophylline, and quinidine. Using Optimate, the coefficients of variation of the within- and between-run variability in the lower therapeutic range were 4.8 and 4.7%, respectively, for carbamazepine (by high-performance liquid chromatography (HPLC): 4.3 and 8.2%), 4.5 and 7.2%, respectively, for phenytoin (by gas-liquid chromatography (GLC): 1.9 and 6.2%), 2.4 and 2.9%, respectively, for phenobarbital (by GLC: 11.4 and 14.7%), 3.2 and 4.6%, respectively, for theophylline (by HPLC: 7.2 and 12.5%), and 3.0 and 22.8%, respectively, for quinidine (by fluorometry: 3.0 and 4.2%). Stored calibration curves in connection with a normalization factor could be used for at least 4 weeks for the measurement of human specimens. Linear regression analysis of parallel therapeutic drug level monitoring demonstrated good agreement between the Optimate (y) and comparative technique (x) for each drug. The corresponding expressions for carbamazepine are y = 0.85x + 0.49 (r = 0.09, n = 44), for phenobarbital y = 0.99x + 0.75 (r = 0.98, n = 45), for phenytoin y = 0.97x - 0.35 (r = 0.99, n = 50), for theophylline y = 1.0x + 0.43 (r = 0.99, n = 44), and for quinidine y = 0.94x + 0.11 (r = 0.96, n = 32).(ABSTRACT TRUNCATED AT 250 WORDS)     

Anticonvulsant activity of some 4-aminobenzamides

A series of 4- aminobenzamides of some simple primary and secondary amines were prepared and evaluated for anticonvulsant effects. The compounds were tested in mice against seizures induced by electroshock and pentylenetetrazole ( metrazole ) and in the rotorod assay for neurologic deficit. For those N-alkyl amides tested, 4-amino-N- amylbenzamide (6) was the most potent against maximal electroshock seizures (MES): ED50 = 42.98 mg/kg; however, the N- cyclohexylbenzamide (8) showed the greatest protective index (PI = TD50/ED50), 2.8. The introduction of a second aromatic ring produced more potent compounds, with d,l-4-amino-N-(alpha-methylbenzyl)-benzamide (12) showing the highest level of activity. This compound has an anti-MES ED50 of 18.02 mg/kg in mice when administered intraperitoneally (ip) and a TD50 of 170.78 mg/kg (PI = 9.5) in the same species. These data compare quite favorably with those for phenobarbital and phenytoin in the same assays.     

Role of cocaethylene in toxic symptoms due to repeated subcutaneous cocaine administration modified by oral doses of ethanol.

The present study investigated the toxicity of repeated subcutaneous cocaine administrations combined with oral doses of ethanol, and discussed the role of the toxic metabolite cocaethylene. Subcutaneous cocaine (70 mg/kg) was given to male ICR mice at 45 min after an oral administration of either ethanol (maximum 3 g/kg) (cocaine-ethanol group; n = 50) or saline control (cocaine group; n = 30), once per day, for up to 5 days. In the combined cocaine-ethanol group, the total frequency of death was significantly increased (86%) as compared to the cocaine group (40%). In both administration groups, regardless of the day of death, "late" deaths characterized by the late and unexpected onset of fatal symptoms could be differentiated from "early" deaths on the basis of the survival time after the last cocaine injection, the drug concentrations in the tissues at the time of death, and/or the observed physical disorders. In the combined cocaine-ethanol group, a late death group with survival times exceeding 12 hr and two early death groups could be differentiated, based on the presence or absence of cocaethylene and the different types of clinical symptoms. In the early death group in which cocaethylene could be detected, the volume of ethanol ingested was not significantly different from the late death group with large ethanol consumption and slow exacerbation of the respiratory and locomotive symptoms. Furthermore, the severity of the cocaine-induced seizures was also similarly decreased by ethanol. In the other early death group in which cocaethylene could not be detected, the volume of ethanol ingested was significantly lower than in the late death group, and seizures as severe as in the cocaine-only group were observed.     

Effects of phenobarbital in combination with phenytoin or valproic acid on the delayed-matching-to-sample performance of pigeons

The present study examined the effects of phenobarbital (5, 10, 20, and 40 mg/kg), phenytoin (2.5, 5, 7.5, and 15 mg/kg), and valproic acid (40, 60, 80, and 120 mg/kg), and those of phenobarbital (10 and 20 mg/kg) in combination with phenytoin (2.5, 5, and 7.5 mg/kg) or valproic acid (40, 60, and 80 mg/kg), on the delayed-matching-to-sample performance of pigeons. In general, high doses of each individual drug reduced accuracy. Drug combinations also reduced accuracy relative to control values. Reductions in accuracy produced by drug combinations were very similar in magnitude to those predicted by a response-addition model of drug interaction.     

The influence of intravenous cimetidine dosage regimens on the disposition of theophylline

The influence of the method of cimetidine administration on theophylline disposition was studied in nine healthy, cigarette smoking male volunteers. The treatment phases consisted of: A) theophylline alone, B) theophylline plus intermittent cimetidine therapy (300 mg IV every 6 hr), and C) theophylline in combination with continuous infusion cimetidine (50 mg/hr). Theophylline (4.8 mg/kg) was administered intravenously as aminophylline over 30 minutes during each treatment phase. During study phases B and C subjects received 48 hours of cimetidine therapy beginning 24 hours prior to theophylline dosing. Blood samples for determination of theophylline concentrations were collected serially over 24 hours. Serum theophylline concentrations were determined in duplicate using fluorescence polarization immunoassay (Abbott Diagnostic TDx). The average age of the subjects was 27.4 +/- 4.7 years, and the individual smoking histories ranged from 0.5 to 1.5 packs per day (average 0.89 +/- 0.33). The mean (+/- SD) body weight was 79.1 +/- 8.2 kg and all subjects were within 20% of their ideal body weight. Theophylline pharmacokinetic parameters were determined using noncompartmental analysis. ANOVA for repeated measures and Tukey's multiple comparison test were used for statistical analysis. The mean (+/- SD) theophylline clearance for each of the treatment groups was: 1.4 +/- 0.4, 1.2 +/- 0.3, and 1.2 +/- 0.2 ml/min/kg for phases A, B and C, respectively. Cimetidine decreased the clearance of theophylline, however, theophylline clearance was not statistically different between regimens B and C. Thus, the method of cimetidine administration (intermittent versus continuous infusion) did not influence the magnitude of the drug-drug interaction.     

Effect of felbamate and its combinations with conventional antiepileptics in amygdala-kindled rats

We investigated the effect of felbamate, administered singly and in combination with carbamazepine, phenobarbital, phenytoin or clonazepam, on various behavioral and electrographic correlates of seizures in amygdala-kindled rats. Felbamate (5 or 10 mg/kg) significantly increased afterdischarge threshold, shortened seizure and afterdischarge durations but remained without effect on seizure severity. Furthermore, the combination of felbamate (2.5 mg/kg) with carbamazepine (7.5 mg/kg; both drugs at their subeffective doses), was associated with the reduction in seizure severity and afterdischarge duration. In relation to the afterdischarge duration, the antiseizure potency of felbamate and carbamazepine, in combination, was comparable with that of carbamazepine (10 mg/kg) administered alone. Neither carbamazepine (7.5 and 10 mg/kg) nor felbamate (2.5-10 mg/kg) affected seizure severity, whereas the combined administration of felbamate (2.5 mg/kg) with carbamazepine (7.5 mg/kg) led to significant reduction in seizure severity from the fifth to the third stage of Racine's scale. Among the conventional antiepileptic drugs evaluated in this study, only valproate (100 mg/kg) and clonazepam (0.1 mg/kg) exerted similar action on seizure severity. However, the combinations of felbamate (2.5 mg/kg), with subeffective doses of valproate, phenobarbital, phenytoin or clonazepam, were not associated with any protective action. As blood and brain felbamate and carbamazepine concentrations were unaffected, a pharmacokinetic interaction can be excluded and a pharmacodynamic interaction concluded. These data suggest that felbamate and carbamazepine, administered in combination, may be useful in patients with drug-resistant partial epilepsy.