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).