Zebrafish on a chip: a novel platform for real-time monitoring of drug-induced developmental toxicity

Pharmaceutical safety testing requires a cheap, fast and highly efficient platform for real-time evaluation of drug toxicity and secondary effects. In this study, we have developed a microfluidic system for phenotype-based evaluation of toxic and teratogenic effects of drugs using zebrafish (Danio rerio) embryos and larvae as the model organism. The microfluidic chip is composed of two independent functional units, enabling the assessment of zebrafish embryos and larvae. Each unit consists of a fluidic concentration gradient generator and a row of seven culture chambers to accommodate zebrafish. To test the accuracy of this new chip platform, we examined the toxicity and teratogenicity of an anti-asthmatic agent-aminophylline (Apl) on 210 embryos and 210 larvae (10 individuals per chamber). The effect of Apl on zebrafish embryonic development was quantitatively assessed by recording a series of physiological indicators such as heart rate, survival rate, body length and hatch rate. Most importantly, a new index called clonic convulsion rate, combined with mortality was used to evaluate the toxicities of Apl on zebrafish larvae. We found that Apl can induce deformity and cardiovascular toxicity in both zebrafish embryos and larvae. This microdevice is a multiplexed testing apparatus that allows for the examination of indexes beyond toxicity and teratogenicity at the sub-organ and cellular levels and provides a potentially cost-effective and rapid pharmaceutical safety assessment tool.

Free radicals and theophylline neurotoxicity : an experimental study

Free radicals play a crucial role in health and disease and both reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been implicated in CNS effects like excitotoxicity. Theophylline, a re-emerging drug for the treatment of obstructive airway disease, has a narrow therapeutic index which precludes its safe use. The present study evaluated the possible involvement of free radicals in theophylline induced seizures in mice. Aminophylline (100-250 mg/kg) consistently induced seizures and post-ictal mortality, and conventional anticonvulsants and adenosine agonists were ineffective in antagonizing them. Further, phosphodiesterase inhibitors, per se, also did not show any significant seizurogenic potential. Pretreatments with antioxidants, ascorbic acid, alpha-tocopherol and melatonin, all dose dependently reduced seizure incidence and mortality after aminophylline, whereas, antioxidant depletion potentiated such excitotoxicity. Pretreatments with the NO synthase inhibitors, L-NAME and 7-NI blocked aminophylline seizures, whereas, the NO mimetics, L-arginine and glyceryl trinitrate, tended to potentiate this phenomenon. Sub-effective doses of aminophylline (100 mg/kg) also induced seizures when combined with subthreshold intensity of electroshock, and such seizures were similarly antagonized by the antioxidants and NO synthase inhibitors. Biochemical assay of brain homogenates showed that aminophylline seizures were associated with enhancements in brain MDA and NOx (NO metabolites) levels, whereas, SOD activity was reduced, and these changes were attenuated after melatonin and L-NAME pretreatments. The pharmacological and biochemical data are strongly suggestive of the involvement of both ROS and RNS during theophylline-induced seizures.

Possible role of free radicals in theophylline-induced seizures in mice

Theophylline is a methylxanthine bronchodilator with a narrow therapeutic index and is prone to induce seizures, the mechanisms for which are not clearly defined. Free radicals have considerable neurotoxic potential and the present study evaluated the possible involvement of these bioactive moieties in aminophylline-induced seizures in mice. Aminophylline (50-250 mg/kg) induced convulsions and mortality in mice in a dose-dependent manner. The anti-oxidants, melatonin (25-100 mg/kg) and N-actylcysteine (100 and 200 mg/kg) attenuated aminophylline seizures and mortality. Similar antagonism of aminophylline seizures was also observed after pretreatments with nitric oxide (NO) synthase inhibitors, L-NAME (3 and 10 mg/kg) and 7-nitroindazole (10 and 30 mg/kg). Further, combined treatment with otherwise sub-effective doses of melatonin and L-NAME or 7-nitroindazole produced marked protective effects against these seizures. Aminophylline-induced seizures enhanced malondialdehyde (MDA) concentrations and NO metabolite (NOx) levels in the brain homogenates of mice, and these were attenuated by melatonin and L-NAME pretreatments. The results are suggestive of the possible involvement of free radicals (reactive oxygen and reactive nitrogen species) in the convulsiogenic effects of aminophylline.

Influence of LY 300164, an AMPA/kainate receptor antagonist upon the anticonvulsant action of antiepileptic drugs against aminophylline-induced seizures in mice

LY 300164 [7-acetyl-3-(4-aminophenyl)-8,9-dihydro-8-methyl-7H-1,3-dioxazolo[4,5-h][2,3]-benzodiazepine], a novel AMPA/kainate receptor antagonist, administered intraperitoneally protected mice against aminophylline-induced seizures. At doses up to 0.5 mg/kg, which did not significantly affect the convulsant activity of aminophylline, it potentiated the protective activity of diazepam. On the other hand, LY 300164 used at the lowest protective dose of 1.0 mg/kg enhanced anticonvulsant activity of all antiepileptic drugs tested in this seizure model. However, LY 300164 neither alone nor combined with antiepileptic drugs, reduced aminophylline-induced mortality.

Aminophylline aggravates long-term morphological and cognitive damages in status epilepticus in immature rats

Here, we investigated whether aminophylline, an adenosine receptor antagonist used usually as a treatment for premature apnea, had synergistic effects on status epilepticus in the developing brain. On postnatal day 14 (P14), four groups of rats intraperitoneally received saline, aminophylline, lithium--pilocarpine (Li-PC), and Li-PC plus aminophylline, respectively. Subsequently, the Morris water maze task was performed at P80. The brains were then analyzed with cresyl violet stain for histological lesions and evaluated for mossy fiber sprouting with the Timm stain. No seizures were elicited in the saline-treated or aminophylline-treated rats. Both the Li-PC-treated and aminophylline plus Li-PC-treated rats exhibited seizures and there was no significant difference in mortality between the two groups. More interestingly, as in adulthood (P80), aminophylline aggravated the spatial deficits and histological damages seen in Li-PC-treated rats. In summary, this present study suggests that the use of adenosine receptor antagonists, such as aminophylline, exacerbates seizure-induced damage in the developing brain.

Proconvulsant effect of aminophylline on cortical epileptic afterdischarges varies during ontogeny

Effect of aminophylline on epileptic afterdischarges (ADs) induced repeatedly by rhythmic electrical stimulation of sensorimotor cortical area was studied in rat pups 12, 18 and 25 days old. The proconvulsant effect of aminophylline (50 and/or 100 mg/kg i.p.) was more expressed in 12- and 18-day-old rats than in the oldest group. In 12-day-old rat pups there was an enormous increase of transition of the spike-and-wave type of ADs into the second, limbic type, a situation observed only exceptionally under control conditions. A prolongation of ADs was related to this transition (limbic ADs are always longer than spike-and-wave ones). Eighteen-day-old rats exhibit this transition less frequently but a marked prolongation of spike-and-wave ADs was recorded in a part of these animals forming a pattern of status lasting some tens of minutes. Aminophylline led only to a transient prolongation of spike-and-wave ADs in the oldest group. The transition into the limbic type of ADs was seen in this age group only exceptionally what is in contrast to age-matched controls in which this transition is common. The effect of aminophylline on cortical ADs which is most marked in the youngest group changes qualitatively during postnatal development.

Lethal seizures predicted after aminophylline therapy in cocaine abusers

Mice with a history of chronic (10 days), but not acute, treatment with a non-convulsant dose of cocaine showed increased sensitivity (P<0.001) to the toxic effects of aminophylline (seizures, lethality) relative to controls even days after the cessation of cocaine treatment. The present finding suggests that individuals with a history of cocaine use may be at increased risk for convulsive and lethal complications associated with the therapeutic use of aminophylline.

Dose-finding study with nimodipine: a selective central nervous system calcium channel blocker on aminophylline induced seizure models in rats

Nimodipine, a dihydropyridine derivative central nervous system (CNS) selective calcium channel blocker was studied at four different dosage schedules in five different models of seizures in rats. At a dose of 5 mg/kg, i.p. with pretreatment time of 15 min, nimodipine significantly antagonized aminophylline (175 and 200 mg/kg, i.p.), electroshock (150 mA for 0.2 s), pentylenetetrazole (60 and 75 mg/kg, i.p.), aminophylline (100 mg/kg i.p.) + electroshock (66mA for 0.2 s), and aminophylline (100 mg/kg, i.p.) + pentylenetetrazole (40 mg/kg, i.p.) induced seizures in rats. No hemodynamic alteration was observed with this dose of nimodipine. However, 2 mg/kg, i.p. (pretreatment time of 15 min and 30 min) and 5 mg/kg, i.p. (pretreatment time of 30 min) doses of nimodipine failed to demonstrate any significant anticonvulsant effect. The study highlighted the critical role of calcium ion flux into the neurons for the genesis of seizure activity to aminophylline, electroshock, and pentylenetetrazole in rats. Furthermore, the critical dose requirement for nimodipine could be explained on the basis of its short half-life and shorter duration of protection against seizures. Therefore, nimodipine may be tried clinically as an anticonvulsant in patients who are on aminophylline because of bronchial asthma or chronic obstructive pulmonary disease, when such patients have concomitant epilepsy or other seizure prone neurological deficits or are scheduled to undergo electroshock therapy.

Interaction between pefloxacin and aminophylline in genetically epilepsy-prone rats

The effects of a chronic treatment with pefloxacin on aminophylline-induced seizures in genetically epilepsy-prone rat have been investigated. Two series of experiments were performed. In the first, animals received pefloxacin orally twice a day for five days, then were administered aminophylline intraperitoneally and the occurrence of seizures was evaluated. In the second series of experiments, theophylline serum concentration was evaluated in rats subject to the same experimental protocol. Pefloxacin significantly, and in a dose-dependent manner, increased the occurrence of seizure phases induced by aminophylline, but did not influence theophylline serum levels measured at different times after the injection of aminophylline. We suggest that additive neurotoxic effects of both pefloxacin and aminophylline might contribute to the increased severity of seizure score. The possible role of GABA-benzodiazepine, excitatory amino acid and purinergic mechanism, and the role of pharmacokinetic factors are discussed.

A comparative study of aminophylline- and acepifylline-induced seizures and death in the chemoconvulsion model in rats

The convulsive, pro-convulsive and lethal effects of two theophylline-containing bronchodilating agents, aminophylline and acepifylline, have been evaluated in rats. Aminophylline (theophylline ethylenediamine) caused seizures and death in a dose-dependent manner; an intraperitoneal dose of 250 mg kg-1 caused seizures and death in all rats. Intraperitoneal doses of acepifylline (theophylline ethanoate of piperazine) up to 1000 mg kg-1, however, did not cause seizure or death. Further, pre-treatment of the rats by intraperitoneal administration of a subconvulsive dose (100 mg kg-1) of aminophylline caused a significant decrease in CD50 and LD50 values for pentylenetetrazole and a significant increase in the number of positive responders (i.e. rats with a pentylenetetrazole-induced seizure score of 3 or more on a seizure scale ranging from 0 to 6) and death rate compared with those obtained for rats pre-treated with an equivalent intraperitoneal dose (140 mg kg-1) of acepifylline ('equivalent dose' referred to here denotes the theophylline content of the two preparations). The study has established the neurosafety profile of acepifylline and documents a safer alternative to aminophylline for use in asthmatics suffering from concomitant epilepsy or other seizure-prone neurological defects.

NG-nitro-L-arginine, a nitric oxide synthase inhibitor, and seizure susceptibility in four seizure models in mice

Nitric oxide may be involved in seizure phenomena even though data often seem to be contradictory. This prompted us to study the influence of nitric oxide upon electrically and chemically induced seizures. The effects of nitric oxide synthase inhibitor, NG-nitro-L-arginine (NNA), on pentylenetetrazol-, aminooxyacetic acid-, aminophylline-induced seizures or electroconvulsive shock were evaluated. NNA was applied at 1, 10 and 40 mg/ kg 0.5 and 2.0 h before chemical seizures and at 1 and 40 mg/kg 0.5 and 2.0 h prior to electroconvulsions. The nitric oxide synthase inhibitor (up to 40 mg/ kg) did not affect the susceptibility of mice to pentylenetetrazol, amino-oxyacetic acid or electroconvulsions. However, NNA significantly enhanced the convulsive properties of aminophylline when applied at 40 mg/kg, 0.5 h before the test. The CD50 value for aminophylline-induced clonus and tonus/ mortality was decreased from 233 to 191 and from 242 to 212 mg/kg, respectively. However, this pretreatment also led to a significant increase in the plasma levels of theophylline. Our results suggest that differential effects of NNA on chemically-induced convulsions might in some cases be associated with a pharmacokinetic interaction.

[The influence of selected antibiotics on the central action of aminophyllines--experimental studies]

Methylxanthines and some antibiotics can cause side effects, provoked by their central action, e.g. seizures. The epileptogenic effects of given drugs can be intensified during combined treatment, as a result of pharmacological interactions. In the present study the author investigated the influence of some commonly used antibiotics: benzylpenicillin, cefuroxime, doxycycline and amikacin upon central activity of methylxanthines in mice. The obtained results suggest, that all tested antibiotics, mainly benzylpenicillin, enhanced epileptogenicity of aminophylline in chemical seizures test. benzylpenicillin as only one among chosen antibiotics presented her own convulsant activity. During electrostimulation test, benzylpenicillin, doxycycline and amikacin intensified convulsions induced by methylxanthines. Only cefuroxime had no influence upon central action of methylxanthines in that experiments. Analysis of drugs' plasma levels, with using immunofluorescence methods, excluded pharmacokinetic interactions between them. Results of present investigation indicate, that there is a possibility of intensification of drugs' convulsant activity during combined treatment-aminophylline with some antibiotics in medical practice.

[Effect of beta 2-adrenergic agonists on neurotoxic action of aminophyllines]

The purpose of the present investigation was to evaluate whether the beta 2-adrenergic agonists affect the pharmacodynamics and pharmacokinetics of aminophylline-induced seizures. Adult male Albino Swiss mice were treated i.p. with salbutamol, fenoterol or terbutaline and 30 min. later they received i.p.aminophylline. During 90 min. observation clonic and tonic seizures and also mortality of mice were registered. Moreover the influence of beta 2-adrenomimetics on electroshock-induced seizure threshold (CS 50) and on plasma aminophylline concentration was estimated. It was found that pretreatment with salbutamol, fenoterol and terbutaline decreased the ED 50 (for clonic and tonic seizures) and LD 50 of aminophylline. Fenoterol decreased but terbutaline increased the CS 50 in mice. Only terbutaline elevated significantly the plasma concentration of aminophylline. The data indicate that concomitant treatment with beta 2-adrenergic agonists together with aminophylline increase the risk of aminophylline-induced seizures. Thus plasma monitoring of aminophylline concentration could be used in all patients treated simultaneously with beta-2-adrenergic agonists and aminophylline.

Pyridoxine as therapy in theophylline-induced seizures

Theophylline-induced seizures have significant morbidity and mortality and are difficult to treat. Theophylline therapy for asthma has been observed to depress plasma pyridoxal 5'-phosphate (PLP) levels which may decrease gamma-aminobutyric acid (GABA) synthesis and thereby contribute to seizures. We hypothesized that treatment with pyridoxine might prove beneficial in theophylline-induced seizures. One hundred thirty-nine mice were injected with 250 mg theophylline/kg ip and 89 mice were injected with 250-750 mg pyridoxine/kg ip as treatment. Decreased rates of seizure (42 vs 70%, p < 0.002) and death (29 vs 56%, p < 0.002) were observed. Six New Zealand White rabbits were given 115 mg theophylline/kg iv over 50 min followed by treatment with an iv bolus of 115 mg pyridoxine/kg, with subsequent continuous drip infusion of 230 mg/kg over 50 min. Serum theophylline levels and plasma PLP levels showed significant negative correlation prior to pyridoxine infusion with a mean peak theophylline level of 182 micrograms/ml and a mean low PLP level of 64 nM/L. Electroencephalogram (EEG) tracings were obtained before infusions, during theophylline infusion and during pyridoxine infusion. All 6 rabbits developed abnormal EEGs during theophylline infusion and all 6 rabbit EEG patterns returned to baseline during treatment with pyridoxine. These findings suggest that pyridoxine may partially reverse theophylline-induced central nervous system toxicity.

Synthesis, toxicological, pharmacological, and bronchodilating activity in vitro of some xanthineacetic acid derivatives

The possibility of the preparation of some ester derivatives of dimethylxanthines from 1-theobromine- and 7-theophylline acetic acids and 7-(2-hydroxyethyl)-theophylline by DCC/DMAP-mediated esterification under mild conditions was studied. The structures of the compounds synthesized and by products isolated were demonstrated by microanalyses, UV-, IR-, and 1H NMR data. Acute toxicity assessment of the compounds on mice showed that compounds 4, 5, 6, and 7 are less toxic than aminophylline. A pharmacological study of the in vitro broncholytic effect (IC50 and pD2 values) of the derivatives and aminophylline showed that the new compound 4 (1,2,3,6-tetrahydro-1,3-dimethyl-2,6-dioxo-7H-purine-7-acetic acid 2-(1,2,3,6-tetrahydro-1,3-dimethyl-2,6-dioxo-7H-purin-7-yl)ethyl ester) has a strong bronchodilating effect on serotonine- and acetylcholine-induced spasm in guinea pig trachea. The same compound does not influence barbiturate-induced hypnosis and locomotor activity, unlike to the effect of the aminophylline, used as a reference substance.

Aminophylline exhibits convulsant action in rats during ontogenesis

Aminophylline-induced seizures were studied in 166 male albino rats in five age groups--7, 12, 18, 25 and 90 days old. Aminophylline injected in doses from 150-350 mg/kg i.p. elicited both minimal, clonic and major, i.e. generalized tonic-clonic seizures during the 60-min observation period. The pattern of minimal seizures did not change during development; major seizures exhibited changes in proportion to their three phases--running, tonic and clonic phases. Dependence on the dose of aminophylline was observed in the incidence of major seizures as well as in shortening of latencies of both types of seizures. More marked convulsant effects of aminophylline in 7-, 12- and 18-day-old rat pups than in older animals might be due to pharmacokinetic as well as pharmacodynamic factors.

Search for an antidote to electroconvulsion and lethality in aminophylline-sensitized mice

Diazepam (10 mg/kg i.p.) or MK-801 (0.25 mg/kg i.p.) offered complete protection against corneal electroshock (30 mA x 0.2 s)-induced tonic seizures and lethality but failed to protect from aminophylline (150 mg/kg i.p.) + electroshock (15 mA x 0.2 s)-induced tonic seizures and lethality in mice. The diazepam (2.5 mg/kg i.p.) and MK-801 (0.25 mg/kg i.p.) combination completely protected the mice from aminophylline + electroshock-induced seizures and lethality. Sodium valproate (500 mg/kg i.p.) protected the mice from electroshock (30 mA) per se and aminophylline + electroshock (15 mA)-induced seizure and lethality. The present study established the neurosensitizing potential of a single, non-convulsive dose of aminophylline for electroconvulsion due to subthreshold intensity electroshock and demonstrated the prophylactic efficacy of sodium valproate and the synergistic therapeutic potential of diazepam and MK-801 combination against such seizure attacks.

Effect of preperfusion of lead and aminophylline on digoxin cardiotoxicity

An attempt has been made to investigate the cardiotoxicity of an interaction of Lead acetate (LA), Aminophylline (APH) and Digoxin (DGN), employing an isolated frog heart preparation. While DGN-Cardiotoxicity was potentiated by LA-preperfusion, it was antagonized by APH-preperfusion as revealed by data reflecting the mean DGN perfusion time (Sec) and mean DGN exposure (microgram/10 mg heart weight) for cardiac arrest. In an experimental group involving interaction of LA, DGN and APH, preperfusion of APH has significantly diminished but not fully abolished LA-induced potentiation of DGN-cardiotoxicity. On the other hand, perfusion of APH after LA resulted not only in annulment of LA-induced potentiation but also in an eventual residual protective effect of APH. It was striking that simultaneous preperfusion of APH and LA led to exacerbation of LA-induced potentiation. The results of this interaction study involving two widely prescribed cardioactive drugs, are considered to be of immense pharmaco-toxicological interest.

Effect of aminophylline on transpulmonary passage of venous air emboli in pigs

Aminophylline has been shown to dramatically reduce the filtering capacity of the lung in dogs during venous air embolism. Similarities have been pointed out between the cardiovascular and respiratory systems of the pig and of humans. We therefore wanted to find out whether aminophylline also modifies the transpulmonary spillover of microbubbles to the arterial circulation of the pig. Twenty-eight pigs were anesthetized with pentobarbital sodium and mechanically ventilated. Aminophylline was injected intravenously into 10 of the pigs before the introduction of air bubbles into the right ventricle, while the other 18 pigs served as controls. A transesophageal echocardiographic probe was used to detect eventual air bubbles in the left atrium or in the aorta. Pigs received either air infusion, at rates varying from 0.05 to 0.20 ml.kg-1.min-1, or calibrated microbubbles, 5-300 microns diam. We found that aminophylline-treated pigs did not show any change in spillover incidence compared with controls. Furthermore, in both groups the spillover during continuous air infusion seemed to be a preterminal event, because the pigs had very low arterial pressure when arterial bubbles were observed. Finally, there was an increase in mean pulmonary arterial pressure from 18 +/- 3.4 to 26 +/- 2.2 (SD) mmHg (n = 4, P less than 0.01) in aminophylline-treated pigs after a bolus injection of microbubbles (less than or equal to 50 microns, total volume less than 0.5 ml). Our results suggest that aminophylline does not modify the transpulmonary passage of microbubbles in this porcine model. In addition, it would seem that the pulmonary circulation of the pig is sensitive to very small volumes of air, when injected as microbubbles.

Diazepam-atenolol combination antagonizes aminophylline-induced convulsions and lethality in mice

The present study was undertaken to identify protective drugs against aminophylline (240 mg/kg i.p.)-induced convulsions and lethality in mice. Diazepam (10 mg/kg) and valproic acid significantly prevented the convulsions, but were not effective in preventing mortality. Phenytoin, atropine, carbamazepine and atenolol were ineffective in protecting against convulsions and death. Ketamine gave partial protection against convulsions, but was not effective in preventing mortality. Diazepam (10 mg/kg) and atenolol (5 mg/kg) administered together gave total protection against convulsions and death. These results show that aminophylline-induced convulsions are relatively resistant to antiepileptic drugs, and that a combination of diazepam and a beta-blocker (atenolol) has potential as an anti-aminophylline agent.

Adenosine receptor antagonism accounts for the seizure-prolonging effects of aminophylline

The mechanism of action of aminophylline in prolonging seizures was tested in amygdala-kindled rats. Aminophylline prolonged the afterdischarge duration of kindled seizures. This seizure-prolonging action of aminophylline was strongly antagonized by the adenosine A1 agonist cyclohexyladenosine and partially antagonized by the benzodiazepine partial agonist RO 15-1788. However, the specific benzodiazepine antagonist CGS 8216 did not affect the seizure-prolonging action of aminophylline. Also, the potent anticonvulsant effect of diazepam on kindled seizures, which was completely antagonized by CGS 8216, was unaffected by aminophylline. Furthermore, a range of benzodiazepine inverse agonists, GABA antagonists, phosphodiesterase inhibitors and xanthines did not prolong afterdischarge durations. These results demonstrate that the seizure-prolonging action of aminophylline is due to block of A1 adenosine receptors since it is prevented by adenosine A1 agonists.

Coronary vascular lesions in dogs treated with phosphodiesterase III inhibitors

A treatment-related coronary arteriopathy has been observed in the dog following the oral or intravenous administration of 4 potent phosphodiesterase type III inhibiting inodilators at high multiples of their ED50 for periods from 1 day to 6 months. A fifth compound of a similar pharmacological class exhibited limiting toxicity at low multiples of its ED50 and this compound failed to induce coronary arterial lesions. The earliest treatment-related findings observed were medial hemorrhage and necrosis with focal breaks in the internal elastic lamina. Later changes, observed from day 9 onwards, included intimal thickening consisting of smooth muscle proliferation with a mucoid ground substance, variable and inconsistent inflammatory changes involving one or more arterial tunics and adventitial hemorrhage, fibrosis and neovascularization. The changes were restricted to the coronary arteries including the extramural and intramural branches. The distribution of lesions varied from widespread, multifocal involvement of both coronary arterial systems to focal lesions with no obvious site of predilection. Induction of this lesion may involve changes in coronary flow and pressure as a result of an exaggerated pharmacological response to this class of compound. The susceptibility of other species (rat, cynomolgus monkey, or pig) to this effect has been investigated with no treatment-related arteriopathy being observed.

Inhibition of aminophylline-induced convulsions in mice by antiepileptic drugs and other agents

Common antiepileptic drugs and agents affecting different neurotransmitter systems were studied against aminophylline (280 mg/kg i.p.)-induced convulsions in mice. All drugs and agents were administered i.p. Diazepam and phenobarbital antagonized the whole seizure pattern and the respective ED50 values for the clonic phase were 3.5 and 62 mg/kg. Valproate at 500 mg/kg protected fewer than 50% of mice against the clonic phase. The remaining antiepileptics (acetazolamide, up to 1,000 mg/kg; carbamazepine and diphenylhydantoin, up to 50 mg/kg; ethosuximide, 500 mg/kg and trimethadione, 400 mg/kg) were totally ineffective in this respect. Propranolol (up to 20 mg/kg), baclofen (20 mg/kg), gamma-hydroxybutyric acid (300 mg/kg), aminooxyacetic acid (20 mg/kg), clonidine (up to 0.2 mg/kg), ketamine (30 mg/kg), atropine (20 mg/kg), papaverine (50 mg/kg) and L-phenylisopropyladenosine (2 mg/kg) did not affect the clonic phase either. Only antagonists of N-methyl-D-aspartic acid excitation, 2-amino-5-phosphonopentanoic acid and 2-amino-7-phosphonoheptanoic acid afforded protection against aminophylline-induced clonic seizure activity. The results show that aminophylline convulsions are relatively resistant to antiepileptic drugs and suggest that antagonists of excitatory transmission are potential antiaminophylline drugs.

Lack of arrhythmogenicity of isoflurane following administration of aminophylline in dogs

Induction of halothane anesthesia after aminophylline administration may cause ventricular arrhythmias. Isoflurane may be as effective a bronchodilator as halothane. This study was designed to determine whether induction of isoflurane anesthesia after intravenous aminophylline is arrhythmogenic in dogs. One group of six dogs was anesthetized with 1.5% isoflurane in the absence of aminophylline. Three additional groups of six dogs were given intravenous aminophylline 10, 25, or 50 mg/kg, respectively, followed 3 min later by 1.5% isoflurane. No arrhythmias occurred after aminophylline and isoflurane at any time in any animal. In contrast to halothane, induction of isoflurane anesthesia after aminophylline is safe and does not cause cardiac arrhythmias.

Neonatal apnea, xanthines, and necrotizing enterocolitis

This study evaluates the relationship of xanthine treatment of premature apnea and NEC in a bowel ischemia model. The superior mesenteric artery was occluded for 1.0 minute in 82 wheanling rats. Group I (n = 41) were untreated controls. Group II (n = 21) received aminophylline (AMPH) 40 mg/kg I.P., 4 hr and immediately prior to clamping. Animals were evaluated for bowel infarction, perforation, and mortality at 7 days. In 20 additional rats (10 per group) bowel was evaluated by scanning electron microscopy (EM) at timed intervals (5 and 30 min). Ischemic bowel occurred in 25 of 41 (60%) controls (18 (43%) with necrosis; 7 (17%) with perforations) and 19 of 21 (90%) rats with AMPH (15 (70%) had necrosis; 4 (19%) perforations). Mortality was 60% (controls) and 90% (AMPH) respectively (p less than .05). On EM, AMPH enhanced bacterial overgrowth however actual mucosal damage appeared similar. Following ischemia, AMPH has an adverse effect on the bowel. Use of AMPH in prematures at risk for NEC is questioned.

Enhancement of cardiotoxic effects of beta-adrenergic bronchodilators by aminophylline in experimental animals

To examine the cardiotoxic interaction between beta-adrenergic bronchodilators and theophylline, we tested the effects of isoproterenol or bitolterol alone and in combinations with aminophylline in experimental animals, both electrocardiographically and histologically. The sc LD50 values for isoproterenol in 4- to 5-month-old, 500-600 g (heavy) and 1.5- to 2-month-old, 150-200 g (small) male Sprague-Dawley rats were 0.6 mg/kg and 1300 mg/kg, respectively, and values for bitolterol were 4 mg/kg and greater than 1800 mg/kg, respectively. Results of the electrocardiographic studies in heavy rats, using the calculated LD20 dosage of isoproterenol with or without pretreatment of aminophylline, demonstrated that both mortality and the arrhythmia-inducing effect of isoproterenol were significantly potentiated by aminophylline but only mortality was increased in small rats. Aminophylline also potentiated the electrocardiographic effects of 1/40 of the LD50 dosage of isoproterenol in heavy rats but did not enhance the effects of bitolterol at this dose level. Potentiation of the arrhythmogenic effect of isoproterenol was also observed in rabbits. The severity of the myocardial lesions produced by isoproterenol or bitolterol in heavy rats was significantly enhanced by aminophylline. The heavy rat appears to be a sensitive model for studying the interaction of these classes of drugs.

Caffeine- and aminophylline-induced seizures

The epileptogenicity of caffeine and aminophylline was studied in rats. Intraperitoneal administration of caffeine produced an immediate excitation and seizures followed by an encephalopathy. A progression from encephalopathy to seizures was observed following aminophylline administration. During the development of behavioral seizures, the EEGs showed a progression from fast activity isolated or bursts of spikes and/or sharp waves to full-blown epileptiform discharges. A wide spectrum of cardiac arrhythmias was observed during and following the seizures. Epileptiform activities ranging from isolated or bursts of spikes and/or sharp waves to continuous epileptiform discharges were observed following local application of the drugs to the cerebral cortex.

Oral sustained-release aminophylline in medical inpatients: factors related to toxicity and plasma theophylline concentrations

1 Consecutive medical inpatients expected to benefit from a theophyllinate were treated with sustained-release aminophylline in a protocol conforming with ordinary practice. Of 16 patients, five had toxicity with aminophylline 450 mg daily, and a further three with 900 mg daily. Toxicity was serious in three patients. 2 Toxicity was significantly less common in cigarette smokers, and was related to higher plasma theophylline concentrations. However, there was a large overlap between concentrations associated with toxicity (as low as 9 micrograms/ml) and the accepted therapeutic range (5-20 micrograms/ml). Most patients with toxicity had theophylline levels within the therapeutic range. 3 For the same dose of aminophylline there was sevenfold variation between patients in plasma theophylline, with higher concentrations in non-smokers, infrequent alcohol users, older patients, those with left ventricular failure and those with lower serum transaminases. There variables could not be separated completely because of the small number of observations. 4 A nomogram for aminophylline dosage or monitoring of serum theophylline levels would have prevented little of the toxicity observed in these patients, although these measures would ensure that therapeutic concentrations were attained, and might prevent life-threatening toxicity.

Arrhythmogenic effects of aminophylline during halothane anesthesia in experimental animals

Arrhythmogenic effects of aminophylline (theophylline ethylenediamine) during halothane anesthesia have been reported but have not been related to serum theophylline levels. This study was designed to determine the arrhythmogenicity of therapeutic and toxic serum theophylline levels during halothane anesthesia. The study consisted of three parts. In part 1 (induction) six dogs were anesthetized for 15 minutes with 1% halothane in air and then given intravenous aminophylline, 50 mg/kg. In part 2 (maintenance) eight dogs were anesthetized for 2 hours with 1% halothane and then given intravenous aminophylline, 10 mg/kg. In part 3, after four additional hours of steady-state 1% halothane anesthesia, additional intravenous aminophylline, 25 mg/kg, was given to these eight animals. Three of six dogs in part 1 had arrhythmias following aminophylline, with serum theophylline levels ranging from 48 to 66 mg/L. No dog in part 2 had arthythmias following the 10 mg/kg dose of aminophylline, with serum theophylline levels of 14 to 23 mg/L. Six of eight dogs in part 3 had arrhythmias shortly after aminophylline, 25 mg/kg, with serum theophylline levels of 36 to 72 mg/L. Aminophylline administration after prolonger 1% halothane anesthesia appears free from arrhythmogenic effects if serum theophylline levels remain near the therapeutic range (10 to 20 mg/L). Aminophylline administration resulting in high serum theophylline levels (above 36 mg/L) causes ventricular arrhythmias when aminophylline is given during induction or maintenance of 1% halothane anesthesia. Arrhythmias usually (89%) begin with 5 minutes of aminophylline administration, and these arrhythmias always resolve spontaneously within 2 minutes of onset.

Chromosome aberrations induced by clinical medicines

Inducibility of chromosome aberrations of cultured mammalian cells was examined on 11 clinical medicines which are used for a long term mainly in the field of internal medicine. P-aminosalicilic acid, isonicotinic acidhydrazid, streptomycin A, hydralazine hydrochloride methimazole and theophylline induced definite increase of chromosome aberrations. Among them P-aminosalicilic acid was a little weak in its effect. The effects of rifamycin SV, aminophylline and isosorbide dinitrate were judged as suspicious, because only a slight increase of the aberrations were caused. Reserpine and propylthiouracil induced little chromosome aberrations. Effective concentrations of these medicines in our chromosome test were compared with their maximum blood concentrations in clinical use in human quoted from the published papers. Their ratios by isonicotinic acid hydrazid, streptomycin A, methimazole, theophylline and issorbide dinitrate were very high and those by others were relatively low. Because p-aminosalicilic acid, rifamycin SV, hydralazine hydrochloride and aminophylline were positive or suspicious in our chromosome test, further pursue for the safety evaluation seems necessary.

Role of alpha- and beta-adrenergic activation in ventricular fibrillation death of corticoid-pretreated rats

Death in ventricular fibrillation was induced consistently in desoxycorticosterone acetate-pretreated rats by the beta-adrenergic agonist isoproterenol but not by norepinephrine or epinephrine, both of which possess alpha- as well as beta-adrenergic activity. Aminophylline, which enhances beta-adrenergic activity, and phenoxybenzamine, an alpha-receptor blocking agent, were used to study the roles of alpha- and beta-adrenergic stimulation in the production of ventricular fibrillation. With the addition of aminophylline, both norepinephrine and epinephrine produced death in ventricular fibrillation, and the existing cardiotoxicity of isoproterenol was potentiated. Similarly, in the presence of phenoxylbenzamine, doses of norepinephrine and epinephrine that had been well tolerated became lethal. Internventions that favor beta-adrenergic preponderance, either by enhancing beta-effects or by blocking protective alpha-adrenergic activation, apparently increase the arrhythmogenic propensity of norepinephrine and epinephrine in steroid-pretreated rats. The similarity of some forms of stress to the experimental protocol of chronic steroid treatment followed by acute catecholamine exposure is discussed.

Comparative toxicity of caffeine and aminophylline (theophylline ethylenediamine) in young and adult rats

The toxicity of aminophylline and caffeine was studied in adult and 2-day-old rats following a single subcutaneous injection of the respective drug. Following the injection of high doses of either methylxanthine, adult rats developed convulsions, tremors, lethargy and licking of lips. In adult rats, the LD50 of caffeine and aminophylline was the same after 24 h and after 1 week of observation: caffeine 265 mg/kg, and aminophylline 202 mg/kg (theophylline base 172 mg/kg). In young rats, the LD50 was greater when the observation was carried out for 1 week than at 24 h after the injection; at 24 h: caffeine 220 mg/kg, and aminophylline 169 mg/kg (theophylline base 144 mg/kg); at 1 week: caffeine 155 mg/kg, and aminophylline 140 mg/kg (theophylline base 119 mg/kg). Young rats failed to gain weight at a normal rate after administration of either methylxanthine. The greater toxicity of both methylxanthines in newborn animals may be at least partly due to the extremely slow elimination of theophylline and caffeine in the neonate.

Toxicity and tissue distribution of aminophyline in neonatal and adult mice and rats

The LD50 of aminophylline in adult mice differed from young mice and rats of both ages, in which the values were remarkably similar (Table 1). With the exception of fat, which had lower concentrations in all groups, tissue concentrations after a 4 mg/kg rectal dose of aminophylline in the 10-day-old animals ranged from 10-20 microng/g as compared to 4-10 microng/g in the adults (Table 2). To evaluate preferential distribution, an analysis of tissue to blood concentration ratios was made. All ratios approximated 1.0 except fat which had a ratio of 0.1-06. The neonates of each species had significantly higher tissue to blood ratios for brain, heart, small intestine, skeletal muscle, and fat (P less than 0.05). Brain to plasma and brain to blood ratios were very similar ranging from 0.4-1.3 in adults versus 0.8-1.7 in neonates. Consideration of the time course indicated a trend toward unit, with the overall ratio in both groups being 1.15 at 2 hr. However, at all earlier time periods the ratios were clearly higher in neonates. Administration of aminophylline intraperitoneally to produce serum concentrations of theophylline far in excess of the 10-20 microng/ml considered to be safe and effective in clinical use did not decrease bilirubin levels in young or old Gunn rats (Fig. 1).