Pharmacokinetics of a 503B outsourcing facility-produced theophylline in dogs

Theophylline is an important drug for treatment of canine chronic bronchitis and bradyarrhythmias, but new products require validation since pharmacokinetics in dogs can vary by formulation. A new, 503B outsourcing facility-produced theophylline product (OFT) is available for veterinary use. Outsourcing facilities have many advantages over traditional compounding sources including current good manufacturing practice compliance. The purpose of this study was to establish the pharmacokinetics of OFT in dogs. Eight healthy dogs received 11 mg/kg intravenous aminophylline and 10 mg/kg oral OFT followed by serial blood sampling in a two-way, randomized, crossover design with 7-day washout. Plasma theophylline concentrations were quantified by liquid chromatography-mass spectrometry. Bioavailability, maximum concentration, time to maximum concentration, half-life and area under the curve were: 97 ± 10%, 7.13 ± 0.71 μg/mL, 10.50 ± 2.07 h, 9.20 ± 2.87 h, and 141 ± 37.6 μg*h/mL, respectively. Steady-state predictions supported twice daily dosing of the OFT, but specific dosage recommendations are hindered by lack of a canine-specific therapeutic range for plasma theophylline concentration. These findings suggest that the OFT is well absorbed and can likely be dosed twice daily in dogs, but future pharmacodynamic and clinical studies are needed to establish a definitive therapeutic range for theophylline in this species.

[Investigation of pharmacokinetics and pharmacodynamics of different doses of aminophylline in very low birth weight infants]

OBJECTIVE

To study the pharmacokinetic and pharmacodynamic features of different doses of aminophylline in very low birth weight (VLBW) infants with different postmenstrual ages, weights, and ages (in days).

METHODS

A total of 40 VLBW infants with apnea were enrolled. After an intravenous loading dose of 5 mg/kg aminophylline, they were randomized into two groups with different maintenance doses of aminophylline (1 mg/kg and 2 mg/kg, once every 8 hours). Blood concentrations of aminophylline and liver and renal functions were monitored at 8 hours, 3 days, and 7 days after the loading dose. Attacks of apnea were documented. Pharmacokinetic data of aminophylline were compared between the two groups.

RESULTS

The steady-state plasma concentration of aminophylline and plasma clearance in the 2 mg/kg group were significantly higher than those in the 1 mg/kg group (P<0.05). However, the elimination half life was shorter in the 2 mg/kg group (P<0.05). Days of apnea attacks within 7 days after birth in the 2 mg/kg group were significantly fewer than in the 1 mg/kg group (P<0.05). Aminophylline plasma clearance was positively correlated with age (in days) after birth and postmenstrual age in both groups.

CONCLUSIONS

In VLBW infants, pharmacokinetics and pharmacodynamics are different when different maintenance doses of aminophylline are given. The maintenance dose of 2 mg/kg is associated with a better effect in the treatment of apnea. Postmenstrual age and age (in days) should be considered during the adjustment of dose, and routine blood concentration monitoring should be performed.

[Investigation on pharmacokinetics of aminophylline in very low birth weight infants]

OBJECTIVE

To investigate the pharmacokinetics of aminophylline in very low birth weight infant.

METHODS

This study investigated 104 very low birth weight infants using aminophylline 5 mg/kg treating apnea who were hospitalized in our department during 2011-2012. The blood concentration of aminophylline was measured in 30 min before, 8 h and 5 d after first time loading dose, and was counterchecked every week before aminophylline withdrawal. The pharmacokinetic parameters of aminophylline were calculated and population pharmacokinetic model was established by MW/Pharm3.6 statistical analysis.

RESULTS

The average birth weight of these 104 very low birth weight infants was (1.15 +/- 0.23) kg, average gestational age was (31.19 +/- 2.50) weeks. The results of aminophylline pharmacokinetics showed: the plasma clearance was (17.88 +/- 5.61) mL/(kg x h), the apparent volume of distribution was (0.93 +/- 0.18) L/kg, the half life time was (28.6 +/- 7.59) h. The aminophylline plasma clearance was related to creatinine clearance, gestational age and days of age after birth (related coefficient was 0.68, 0.62, 0.56 respectively, P < 0.05),the apparent volume of distribution was related to birth weight (related coefficient was 0.82, P < 0.05). The population pharmacokinetics model established can predict the concentration-time curve of the patients.

CONCLUSION

The pharmacokinetics of aminophylline in very low birth weight infant was quite different from adult, which suggest blood concentration monitoring and dose adjustment for the clinical use of aminophylline in low birth weight infants.

An in-vitro comparison of controlled release aminophylline tablets: phyllocontin Continus and Pecram

It has been suggested that two controlled release preparations containing aminophylline, Phyllocontin Continus and Pecram, are clinically equivalent and are therefore interchangeable. In this study, an in-vitro evaluation of the two preparations was completed using the British Pharmacopoeia dissolution apparatus, initially using water and then an acid/buffer medium to provide a similar pH environment to that within the gastrointestinal tract. Similar release profiles were found when water was used as the dissolution medium, with very little variation between tablets within each group. Good fits were obtained for dissolution-controlled release and diffusion-controlled release models. When the acid/buffer solution was used as the dissolution medium a reduction in the rate of release was observed with Phyllocontin. It was predicted that if this was repeated in-vivo then differences in the peak plasma levels between the two formulations would be seen, although these may be masked by the other variables encountered.

Pharmacokinetics of aminophylline delivered to the small intestine and colon using remote controlled capsules

BACKGROUND

A patented remote controlled capsule (RCC) has recently been developed to provide noninvasive drug delivery to selected sites in the human gut that allows assessment of regional gastrointestinal (GI) drug absorption under a normal physiological environment. The objective of this study was to investigate the rate and extent of aminophylline absorption after site-specific delivery of the drug in the GI tract using RCC and a magnetic marker monitoring (MMM) technique.

METHODS

This study was conducted in twelve healthy male subjects, in a three-treatment, randomized, crossover manner with a 7-day washout. Eligible subjects received a 150 mg aminophylline dose through an oral administration, or via a remote controlled capsule, delivered to the small bowel or ascending colon. MMM was employed to monitor the GI transit of the RCC, and the radio-frequency signal was used to activate capsules at target sites. Blood samples were obtained at regular intervals until 24 hours post dose/activation. Plasma theophylline concentrations were measured by a TDx System Analyzer. A comparison of the PK profile with the oral dosing route of aminophylline was performed after delivery to the small bowel and colon.

RESULTS

The RCC was well tolerated in volunteers. The mean capsule activation time for the small bowel and ascending colon was 2.07 hours and 6.08 hours post dose. Aminophylline had similar absorption profiles from the small bowel compared with the stomach, with an area under the curve (AUC(t)) ratio of 92% vs. the stomach, but a lower absorption profile from the ascending colon, with an AUC(t) ratio of 47.2% vs. the stomach.

CONCLUSIONS

The proprietary of the RCC and MMM technique offer the opportunity to obtain data on the intestinal absorption of a drug in humans under noninvasive conditions. Aminophylline is rapidly and efficiently absorbed from the small bowel. While colonic absorption was limited by the poor water condition although effective absorption was observed from the ascending colon. This provides an opportunity for rational development of modified-release formulations as well as alternative dosage forms.

Novel chronotherapeutic rectal aminophylline delivery system for therapy of asthma

The aim of this study was to develop a new chronotherapeutic pharmaceutical preparation as a sustained-release suppository for prevention and therapeutic use against bronchial asthma in the early morning. Sustained-release hollow-type (SR-HT) suppositories using sodium alginate (Alg-Na), sodium polyacrylate (PANa) or polyacrylate-PANa co-polymer (PA-PANa) as gelling polymers (gel agent) were prepared and pharmaceutical characteristics of these suppositories were investigated. Type A SR-HT suppositories comprised a suppository shell prepared with oleaginous base and containing aminophylline only or aminophylline with Alg-Na or PANa in the cavity (hollow space). Type B SR-HT suppositories comprised a suppository shell prepared with oleaginous base and gel agent (30%), with aminophylline in the hollow space. In drug-release studies, the acrylate polymer-containing suppositories showed linearity of delayed release rate, providing significantly decreased the highest concentration of theophylline in plasma (C(max)) and delayed the time required to reach C(max) (t(max)) and the mean residence time (MRT) after rectal administrated in rabbits. In particular, suppositories containing PA-PANa maintained significantly higher theophylline concentrations than control suppositories at 12h after rectal administration. Furthermore, histopathological examination indicated that these suppositories using acrylate polymers did not result in rectal lesions. The SR-HT suppository, particularly using PA-PANa as a gel agent, may thus be useful against nocturnal symptoms of asthma. In this study, we confirmed new formulation of sustained-release suppository for chronotherapy of theophylline using oily base material in combination with polymer such as PA-PANa. The hollow-type suppository containing oleaginous base and hydrophilic polymer in the shell could be useful device for rectal administration of various drugs with prolongation of plasma concentration.

Pharmacokinetics of intraperitoneally instilled aminophylline, terbutaline and tobramycin in pigs

INTRODUCTION

Venous catheters are sometimes difficult or even impossible to insert and may also be associated with serious complications. This study was carried out to investigate whether intraperitoneal administration of drugs may be an alternative to the intravenous route in patients with limited vascular access.

MATERIALS AND METHODS

Three drugs commonly in use in clinical practise, aminophylline, terbutaline and tobramycin, were administered to pigs intravenously and intraperitoneally in small volumes. Serum concentrations were analysed over a period of 6 h and pharmacokinetic key variables for each drug were calculated.

RESULTS

Aminophylline (theophylline), terbutaline and tobramycin were absorbed from the peritoneal space and into systemic circulation. For theophylline, the concentration/time profiles after intraperitoneal and after intravenous administration were almost identical, and the intraperitoneal bioavailability was calculated to 0.94. For terbutaline and tobramycin, the intraperitoneal absorption was delayed without any initial peak. Moreover, the intraperitoneal bioavailability was lower than for theophylline (0.71 and 0.65, respectively).

CONCLUSION

The pharmacokinetic properties after intraperitoneal administration differed among the three drugs, but the results are encouraging and provide a basis for further investigation in humans.

Reliability of salivary theophylline in monitoring the treatment for apnoea of prematurity

OBJECTIVE

To evaluate the reliability of salivary levels of theophylline in monitoring therapy of apnoea of prematurity.

STUDY DESIGN

Aminophylline was administered intravenously in 13 infants with apnoea, in a loading dose of 5 mg/kg and maintenance dose of 3 mg/kg, every 8 h. The patients were divided into two groups according to their postconceptional age (PCA): group A, of infants with small PCA (32.8+/-2.0 weeks; n=6 cases), and group B, infants with higher PCA (37.1+/-0.8 weeks; n=7 cases).

RESULTS

A total of 57 paired samples of serum and saliva were obtained in all 13 infants. The mean serum level of theophylline was 7.8+/-5.8 microg/ml and the ratio between serum and salivary concentration of theophylline was 1.53+/-0.28. A strong correlation between the serum and salivary concentration of theophylline (r=0.973) was found. Infants with small PCA had significant higher serum concentration of theophylline than those with higher PCA (10.6 vs 5.3 microg/ml; P=0.0002). The difference between the mean ratios of serum/salivary theophylline levels in the two groups was low (1.44 vs 1.62; P=0.0155).

CONCLUSION

The strong correlation of theophylline in serum and in saliva recommends the salivary levels as a reliable method for monitoring the treatment of apnoea of prematurity.

[Studies on drug release from aminophylline konjac glucomannan matrix tablet]

OBJECTIVE

In vitro aminophylline release from matrix tablets with konjac glucomannan (KGM) were studied to elevate the feasibility of KGM used as carrier materials to prepare matrix tablets.

METHOD

KGM hydrophilic matrix tablets were prepared by direct compression method with aminophylline as the model drug. The effects of test methods, pH values, ionic strength of dissolution media and rotation speeds on drug release were studied by in vitro dissolution experiment.

RESULT

The MDT value tested by Paddle method was less than that tested by Basket method (P < 0.05). Among the rate of drug release in different dissolution media, distillded water is the fastest, pH 6. 8 PBS is the second, 0.1 mol x L(-1) HCL is the slowest. MDT increased with increasing the ionic strength of dissolution media (P < 0.05). MDT decreased with increasing the rotation speed, but the rate of drug release did not increase when the rotation speed was more than 100 r x min(-1) (P > 0.1). The mechanism of drug release were diffusion and erosion.

CONCLUSION

KGM can be used in sustained delivery systems as a good candidate of hydrophilic polymer.

Pharmacokinetic and pharmacodynamic interactions of aminophylline and topiramate in the mouse maximal electroshock-induced seizure model

The aim of this study was to determine the influence of acute (single) and chronic (twice daily for 14 consecutive days) treatments with aminophylline (theophylline(2).ethylenediamine) on the anticonvulsant potential of topiramate (a broad-spectrum antiepileptic drug) in the mouse maximal electroshock-induced seizure model. Additionally, the effects of acute and chronic administration of aminophylline on the adverse effect potential of topiramate were assessed in the chimney test (motor performance). To evaluate pharmacokinetic characteristics of interaction between topiramate and aminophylline, total brain concentrations of topiramate and theophylline were estimated with fluorescence polarization immunoassay technique. Results indicate that aminophylline in non-convulsive doses of 50 and 100 mg/kg (i.p.), both in acute and chronic experiments, markedly attenuated the anticonvulsant potential of topiramate by raising its ED(50) value against maximal electroconvulsions. Aminophylline at a lower dose of 25 mg/kg did not affect significantly the ED(50) value of topiramate in the acute experiment, but the drug markedly increased the ED(50) value of topiramate during the chronic treatment in mice. Only, aminophylline at 12.5 mg/kg, in both acute and chronic experiments, did not affect the antielectroshock action of topiramate in mice. Moreover, aminophylline at a dose of 100 mg/kg had no impact on the adverse effect potential of topiramate in the chimney test. Pharmacokinetic evaluation of total brain concentrations of topiramate and theophylline revealed that topiramate significantly increased total brain theophylline concentrations following both acute and chronic applications of aminophylline. Conversely, aminophylline did not alter total brain concentrations of topiramate in mice. Based on this preclinical study, one can conclude that aminophylline attenuated the antiseizure action of topiramate in the mouse maximal electroshock-induced seizure model and the observed interaction between drugs was both pharmacokinetic and pharmacodynamic in nature.

Pharmacokinetics of Theophylline in Guinea Pig Tears

It is well recognized that the theophylline (TP) concentration in human tears correlates well with the free TP concentration in human plasma. However this correlation was found only in a very narrow range of concentrations of TP, and pharmacokinetic analysis of TP in tears has not been carried out for a wide range of concentrations of TP. The aims of this investigation were to develop a simple kinetic model for TP in guinea pig plasma (total [Cf+b] and free [Cf]), cerebrospinal fluid (CSF) [C](CSF) and tears [C](T), and to examine whether [Cf], [Cf+b] and [C](CSF) can be predicted from [C](T) using the resulting kinetic parameters. [Cf+b], [Cf], [C](CSF) and [C](T) were determined by GC/EI-SIM following bolus i.v. injection of TP in doses of 10, 50 and 100 mg/kg into guinea pigs. The wide range of concentrations of [Cf+b] could be quantitatively described by a two-compartment model with non-linear elimination kinetics and individual volume distribution of TP at each dose. [C](T) and [C](CSF) were analyzed using passive diffusion models with and without the pH-partition theory, respectively. The value of [Cf] could be predicted from the value of [C](T). Thus, the measurement of [C](T) which can be collected non-invasively would be a useful method for the therapeutic drug monitoring of TP.

[Study on evaluation index of acupoint transdermal administration--drug delivery coefficient]

OBJECTIVE

To investigate the correlation of skin electric resistance changes with the blood drug content in acupoint transdermal administration, and to establish an new evaluation index for drug delivery efficiency through acupoints.

METHODS

Twenty-four rabbits were randomly divided into an observation group and a control group. In the observation group, aminophylline was administrated through "Feishu" (BL 13), "Geshu" (BL 17) and "Danzhong" (CV 17) which are commonly used for treatment of bronchial asthma, and the control group through sham-points on the back. The skin resistance and plasma aminophylline content were determined after application of aminophylline to the points, and their changes with time were observed. The ratio of Css/Rss at stability was defined as delivery coefficient (DC) which reflects the efficiency of delivering drug at acupoints and sham acupoints.

RESULTS

Both the plasma aminophylline and the skin resistance value tended to steady about 6-8 h after application of aminophyiophylline. The DC in the acupoints was higher than that in the sham-acupoints (P < 0.01). And there was significant difference as DC of the "Feishu"was significant difference (BL 13) and "Danzhongas DC of the "Feish" (BLCV 17) compared with that of "Geshu" (BL 17) (P < 0.01).

CONCLUSION

The bigger the DC is, the higher the efficiency of drug delivery is; the efficiency of drug delivery through acupoints is higher than that through sham-acupoints.

Dog Colonoscopy Model for Predicting Human Colon Absorption

PURPOSE

This study was conducted to develop and validate a dog colon model that predicts colon permeability in humans.

METHODS

The following compounds were studied: Class 1 highly soluble (HS)/highly permeable (HP): aminophylline, propranolol, CP-409092; Class 2 LS/HP: nifedipine; trovafloxacin, sertraline; Class 3 HS/LP: azithromycin, atenolol, CP-331684, CP-424391; Class 4 LS/LP: CJ-13610. Administration to dogs was made 30 cm cranial to the anal sphincter with a lubricated Schott Model VFS-5 flexible endoscope. The bioavailability of the compound following the colon administration in dogs, relative to the same formulation administered orally (relative bioavailability), was determined.

RESULTS

Except for atenolol, a small hydrophillic molecule, the relative bioavailability from administration to the colon of the dog correlated well with the following compound properties: high solubility and high, passive permeability > high solubility, low permeability > low solubility, high, passive permeability approximately low solubility, low permeability.

CONCLUSION

The dog colon model is proposed as a surrogate for human intubation studies when the controlled release candidate falls in BCS Classes 2 (LS/HP), 3 (HS/LP), and 4 (LS/LP). However, no human intubation or dog colon studies are required for Class 1 (HS/HP), as these compounds are likely to be well absorbed from the colon.

Pharmacokinetics of theophylline in diabetes mellitus rats: induction of CYP1A2 and CYP2E1 on 1,3-dimethyluric acid formation

Pharmacokinetic parameters of theophylline and one of its metabolites, 1,3-dimethyluric acid (1,3-DMU), were compared after intravenous and oral administration of aminophylline, 5mg/kg as theophylline, to diabetes mellitus rats induced by alloxan (DMIA) or streptozotocin (DMIS), and their respective control rats. In DMIA and DMIS rats, expression of CYP1A2 and 2E1 increased approximately three times. Theophylline was metabolized to 1,3-DMU by CYP1A2 and 2E1 in rats. Hence, it was expected that formation of 1,3-DMU increased in DMIA or DMIS rats. This was proven by the following results. First, after intravenous administration of theophylline, the AUC of 1,3-DMU was significantly greater in DMIA (110% increase) or DMIS (47.4% increase) rats. Second, the AUC of theophylline was significantly smaller in DMIA (26.1% decrease) or DMIS (30.1% decrease) rats because of significantly faster time-averaged total body clearance in DMIA (34.8% increase) or DMIS (42.7% increase) rats. Third, based on in vitro hepatic microsomal studies, intrinsic 1,3-DMU formation clearances were significantly faster in DMIA (20.4% increase) or DMIS (30.7% increase) rats than respective control rats. Similar results (AUC values of theophylline and 1,3-DMU) were also obtained after oral administration.

In vitro methods for the evaluation of drug availability from suppositories: comparison between biological and artificial membranes

Drug availability from suppositories is currently evaluated in vitro by means of a model consisting of a dialysis tube (porous membrane) or isolated biological membrane (animal rectum). We propose a new alternative in vitro method to determine drug availability from suppositories consisting of an artificial membrane soaked with n-octanol, coupled with a filter paper sheet soaked with phosphate buffer. This method provides for an integrated hydro-lipophilic simulation of the biological membrane, including the mucus layer adhering to the rectal mucosa. By simply using the porous membrane, the amount of drug released varied directly according to its solubility for formulations with lipophilic excipients. For formulations with hydrophilic excipients, drugs with low/intermediate solubility in water showed increased availability in comparison to lipophilic excipients. The in vitro rat rectum model provided overall results that were similar to those obtained with the porous membrane method, although the percentage values of AUC were lower. The new model of in vitro simulated absorption produced a degree of drug availability that was lower in comparison to both previous methods. However, the simulated model appeared to give a pattern of drug availability closer to that of the model of in vitro rat rectum. The new in vitro artificial model thus appears to be useful in suppositories preformulation studies, allowing for an estimate of drug availability and the choice of the most adequate excipient.

Aminophylline: exploring cardiovascular benefits versus medical malcontent

Although aminophylline/theophylline has been relegated to third- and fourth-line status in the cardiopulmonary armamentarium, its use in specific pathophysiologic states, especially those of cardiac etiology, can be of significant benefit. The consulting clinician should maintain an awareness of its potential as adjunctive therapy in cases of atrioventricular block, cardiac arrest, heart failure, and bradyarrhythmias in particular. It should not yet be shelved as an archaic agent.

Effect of acute aminophylline administration on diaphragm function in high cervical tetraplegia: a case report

Theophylline has been shown to have beneficial effects on phrenic nerve and diaphragm activation. This case report involves a C5-C6 chronic tetraplegic patient with acute respiratory failure and ventilator dependence. IV aminophylline was administered in increasing doses (2 mg/kg, 4 mg/kg, and 6 mg/kg) over the course of 1 day. Diaphragm surface electromyography (sEMG), measures of respiration (tidal volume, minute ventilation, and frequency), and serum theophylline levels were captured. Diaphragm sEMG activity increased by a maximum of 50% at therapeutic levels. The rapid shallow breathing index dropped from 112 to 86. The subject was successfully weaned from ventilatory support. We conclude that administration of aminophylline facilitated weaning from ventilatory support in this tetraplegic patient.

Study on the effect of food on the absorption of theophylline

BACKGROUND

The pharmacokinetics of theophylline under fasting and normal meal have been widely studied, but that of Euphyllin Retard in Chinese subjects has not been reported. Since various food-induced absorption changes occur with sustained-release theophylline, it is of interest to study the food effect (especially Chinese food) on this drug product.

METHODS

A total of 10 non-smoking healthy male volunteers were involved in the study with a 2-period crossover comparison. They were randomly divided into 2 groups. In the first phase study, group A took a single dose of 350 mg Euphyllin Retard (theophylline-ethylenediamine formulation, containing 255 anhydrous theophylline) under fasting condition. Group B took the same dose with breakfast. Blood samples were collected before and during the 36 hours following administration of the drug. For the second-phase study after 2 weeks, the group A acted as fasting group and group B as non-fasting group. The difference in the absorption of theophylline with fasting versus non-fasting administration was assessed using pharmacokinetic parameters derived from a serum theophylline concentration (STC) vs time curve.

RESULTS

The means of maximum drug concentration (Cmax), unextrapolated area under the concentration vs time curve (AUC) from time 0 to 24 hours (AUCun), extrapolated AUC from time 0 to infinity (AUCex), and terminal elimination rate constant (Kel) were higher in the non-fasting group. The fasting group showed a more delayed time to maximum concentration (Tmax). The mean of half-life (T50%) was slightly higher in fasting group. In comparing each of the variables, no statistically significant differences were demonstrated between the 2 modes of administration except Cmax.

CONCLUSION

Food increases the rate but not the extent of the absorption of Euphyllin Retard, and one should be aware of the possibility of unwanted side effects caused by high peak concentration. There were wide variations in serum drug levels among individuals, so serum theophylline level monitoring is necessary for an optimal effect. This study was performed in a limited number of normal healthy subjects and the same result is yet to be in asthmatic patients and a larger population of normal subjects.

Effect of some convulsants on the protective activity of loreclezole and its combinations with valproate or clonazepam in amygdala-kindled rats

Loreclezole (5 mg/kg) exerted a significant protective action in amygdala-kindled rats, reducing both seizure and afterdischarge durations. The combinations of loreclezole (2.5 mg/kg) with valproate, clonazepam, or carbamazepine (applied at their subprotective doses) also exhibited antiseizure effect in this test. However, only two first combinations occurred to be of pharmacodynamic nature. Among several chemoconvulsants, bicuculline, N-methyl-D-aspartic acid and BAY k-8644 (the opener of L-type calcium channels) reversed the protective activity of loreclezole alone and its combination with valproate. On the other hand, bicuculline, aminophylline and BAY k-8644 inhibited the anticonvulsive action of loreclezole combined with clonazepam. The results support the hypothesis that the protective activity of loreclezole and its combinations with other antiepileptics may involve potentiation of GABAergic neurotransmission and blockade of L-type of calcium channels.

Effects of acute renal failure induced by uranyl nitrate on the pharmacokinetics of intravenous theophylline in rats: the role of CYP2E1 induction in 1,3-dimethyluric acid formation

In rats with acute renal failure induced by uranyl nitrate, the hepatic microsomal cytochrome P450 (CYP) 2E1 and CYP3A23 increased 2-4- and 4-times, respectively, CYP2C11 decreased to 80% of control, but the levels of CYP1A2 and CYP2B1/2 were not changed. It has been reported that theophylline was metabolized to 1,3-dimethyluric acid by CYP1A2 and CYP2E1 and 1-methylxanthine via CYP1A2, which was metabolized further to 1-methyluric acid via xanthine oxidase in rats. Hence, it was expected that the formation of 1,3-dimethyluric acid would show an increase in rats with renal failure as a result of induction of CYP2E1. The pharmacokinetics of theophylline were compared in control rats and rats with renal failure after intravenous administration of aminophylline, 5 mg kg(-1) as theophylline. In rats with renal failure, the plasma concentrations of theophylline were considerably lower and the resultant total area under the plasma concentration-time curve from time zero to time infinity (AUC(0- infinity )) of theophylline was significantly smaller (2,200 vs 1,550 microg min mL(-1)) compared with control rats. In rats with renal failure, the plasma concentrations of 1,3-dimethyluric acid were considerably higher and the resultant AUC(0-6 h) of 1,3-dimethyluric acid was significantly greater (44.4 vs 456 microg min mL(-1)) compared with control rats. Moreover, the AUC(0-6 h, 1,3-dimethyluric acid)/AUC(0- infinity, theophylline) ratio increased from 2.02% in control rats to 29.4% in rats with renal failure. The in-vitro intrinsic 1,3-dimethyluric acid formation clearance was significantly faster in rats with renal failure (734 vs 529 10(-6) mL min(-1)) compared with control rats using hepatic microsomal fraction. The results led us to conclude that in rats with uranyl nitrate-induced renal failure after the administration of aminophylline, 5 mg kg(-1) as theophylline, there was an increase in the formation of 1,3-dimethyluric acid as a result of an increase in CYP2E1 expression.

Investigation of solid-state reactions using variable temperature X-ray powder diffractometry. II. Aminophylline monohydrate

PURPOSE

The object of this investigation was to demonstrate the utility of X-ray powder diffractometry (XRD) to study the kinetics of a complex pharmaceutical solid-state reaction wherein the reactant, product and intermediate phases were all simultaneously quantified.

METHODS

Aminophylline monohydrate (I) decomposed to anhydrous theophylline (III) either directly or through an intermediate (anhydrous aminophylline, II). The reaction kinetics were studied isothermally at several temperatures ranging from 65 to 100 degrees C. By measuring the intensities of the XRD peaks unique to I, II and III, it was possible to simultaneously quantify the 3 phases during the entire reaction.

RESULTS

Assuming that all the reaction steps follow first-order kinetics. the three equations describing the concentrations of I, II and III as a function of time, were derived. By fitting the experimental data to these equations, it was possible to obtain the rate constants for the three reaction steps. The rate constants were obtained at different temperatures and were used to draw Arrhenius type plots from which the activation energies were determined. At lower temperatures (< 80 degrees C). the concentration of the intermediate phase, i.e., II, was low throughout the reaction while at higher temperatures (> 90 degrees C), there was rapid formation and accumulation of II during the early stages of the reaction. These differences could be attributed to the fact that k1 (I --> II) had a more pronounced temperature dependence than k2 (I --> III) and k3 (II --> II). The XRD results were confirmed with isothermal thermogravimetry.

CONCLUSIONS

Variable temperature XRD is a powerful tool to probe reaction kinetics in crystalline pharmaceuticals since it permits simultaneous quantification of multiple solid phases.

[Preparation and evaluation of press-coated aminophylline tablet using crystalline cellulose and polyethylene glycol in the outer shell for timed-release dosage forms]

In an attempt to achieve chronopharmacotherapy for asthma, press-coated tablets (250 mg), which contained aminophylline in the core tablet in the form of low-substituted hydroxypropylcellulose (L-HPC) and coated with crystalline cellulose (PH-102) and polyethylene glycol (PEG) at various molecular weights and mixing ratios in the amounts of PH-102 and PEG as the outer shell (press-coating material), were prepared (chronopharmaceutics). Their applicability as timed-release (delayed-release) tablets with a lag time of disintegration and a subsequent rapid drug release phase was investigated. Various types of press-coated tablets were prepared using a tableting machine, and their aminophylline dissolution profiles were evaluated by the JP paddle method. Tablets with the timed-release characteristics could be prepared, and the lag time of disintegration was prolonged as the molecular weight and the amount of PEG, for example PEG 500,000, in the outer shell were increased. The lag time of disintegration could be controlled by the above-mentioned method, however, the pH of the medium had no effect on disintegration of the tablet and dissolution behavior of theophylline. The press-coated tablet (core tablet:aminophylline 50 mg, L-HPC and PEG 6000; outer shell:PH-102:PEG = 8:2 200 mg) with the timed-release characteristics was administered orally to rabbits for an in vivo test. Theophylline was first detected in plasma more than 2 h after administration; thus, this tablet showed a timed-release characteristics in the gastrointestinal tract. The time (tmax) required to reach the maximum plasma theophylline concentration (Cmax) observed after administration of the press-coated tablet was significantly (p < 0.05) delayed compared with that observed after administration of aminophylline solution in the control experiment. However, there was no difference in Cmax and area under the plasma theophylline concentration-time curve (AUC0-->24) between the press-coated tablet and aminophylline solution. These results suggest that the press-coated aminophylline tablet (with the timed-release characteristic) offers a promising forms of theophylline chronotherapy for asthma.

Theophylline metabolism after cardiac surgery

The effect and metabolism of theophylline administration after cardiac surgery has never been reported. Two series of 2-hour intravenous aminophylline administrations (3 mg/kg/h) were conducted in 10 adult patients on the operative day (acute phase) and on the 4th or 5th postoperative day (recovery phase). Both blood and urine samples were collected for 24 hours after dosing. Heart rate increased in both phases, but the cardiac index increased with the decrease of diastolic blood pressure only in the acute phase (p < 0.05). Plasma concentration levels of theophylline tended to be slightly higher in the acute phase, and renal clearance increased in the recovery phase (p < 0.05). The urinary ratio of 3-methylxanthine to theophylline was significantly higher in the acute phase (p < 0.05). This suggests that cytochrome P4501A2 is partially activated rather than depressed and that N-demethylation is promoted more than hydroxylation immediately after surgery.

Biopharmaceutical characterization of oral theophylline and aminophylline tablets. Quantitative correlation between dissolution and bioavailability studies

Considering the narrow therapeutic index of theophylline and the low range between the safe and toxic serum concentrations of this drug, the study of its pharmacokinetic properties is necessary. However, considering the time consuming and expensive in vivo tests, quantitative correlation between in vivo bioavailability and in vitro dissolution tests can be used routinely in quality control tests of these drug products to predict the in vivo pharmacokinetic parameters. For this reason healthy human volunteers were used for in vivo studies and serum samples were analyzed by a fluorescence polarization immunoassay analysis (FPIA) method. The results showed that an open one compartmental model could best describe the pharmacokinetic properties of orally administered theophylline and aminophylline tablets. Linear regression analysis by least-square method showed a good correlation between some in vivo and in vitro parameters obtained from dissolution studies by rotating basket and paddle methods. D(30)% (percentage of drug dissolved in vitro after 30 min) and F(0.5)% (drug absorbed in vivo after half an hour calculated by Wagner-Nelson equation) showed best correlation (r=0. 99036). C(max) (maximum serum concentration) of this drug also correlates well with t(25%) (time required to dissolve 25% of the drug). The calculated correlation coefficients could best predict the actual values of some pharmacokinetic parameters; AUC(0-->infinity), AUC(0-->1), F(0.5)% and C(max).

Usefulness and safety of theophylline injection form (Theodrip) for the treatment of acute asthma

The effects of the speed of intravenous infusion on the pharmacokinetics of theophylline were studied in 9 healthy volunteers (Ex I). Subjects were intravenously administered either six 4.8 mg/kg theophylline (Theodrip, Nikken Chemicals Co., Ltd., Japan) or three matching placebo injections (4.8 ml/kg physiological saline) for 30 min (Step I) or for 15 min (Step II). In Steps I and II, Cmax was 10.8 +/- 1.1 and 10.8 +/- 0.8 micrograms/ml, respectively. These Cmaxs were concentrations yielding therapeutic effects in patients with acute asthma. Next, comparative pharmacokinetics between theophylline (Theodrip) and aminophylline were examined by a crossover method in 16 healthy volunteers (Ex II). The 90% confidence limits of the differences of mean values were within 80-120% and were 92.8-100.1% for Cmax, 99.7-105.3% for t1/2 and 100.2-104.4% for AUC. Thus, we concluded that the pharmacokinetics of the plasma theophylline after intravenous administration of Theodrip (theophylline at 4.8 mg/kg) were bioequivalent to those of aminophylline (6.0 mg/kg) for 30 min. In Ex I and II, no subjects had adverse effects and in Ex I no influence on ECG was seen. In addition, the convenience of Theodrip was compared with that of ampules of aminophylline among nurse volunteers (Ex III). The times required for set-up of Theodrip were significantly shorter than those of aminophylline ampules. On the other hand, the adverse reactions to aminophylline resulting from hypersensitivity reactions to its ethylenediamine component have been reported. Theodrip consists of 200 mg theophylline and 200 ml physiological saline in a plastic bag. Therefore, Theodrip, which does not contain ethylenediamine, is expected to have less adverse effects and be easier to handle than aminophylline.

Pharmacokinetic study of theophylline in dogs after intravenous administration with and without ethylenediamine

Aminophylline (ethylenediamine salt of theophylline) and Theodrip, a new formulation of theophylline developed by Nikken Chemicals, are drugs for the treatment of acute bronchial asthma in injectable form. The present study was conducted using dogs to first confirm the bioequivalence of the two injectable forms containing theophylline and aminophylline and to secondly clarify the influence of the rate of venous infusion on the pharmacokinetics of theophylline in plasma. The following results were obtained: 1) Pharmacokinetic parameters of plasma theophylline after an intravenous bolus injection were close to those after the dosing of aminophylline in dogs by a crossover method. Thus, the 95% confidence limits of mean value differences of Cmax, t1/2 and AUC between the two injection forms were in the range of -3.16-4.28%, -6.19-7.28% and -7.23-5.28%, respectively. These results indicate the bioequivalence between theophylline and aminophylline in dogs from a pharmacokinetic point of view as well as the lack of influence of ethylenediamine on the pharmacokinetics of theophylline. 2) After the intravenous bolus injection (30 sec) and the 15-min constant rate infusion of theophylline to dogs, the plasma concentrations of theophylline were 27.37 +/- 3.67 micrograms/ml and 18.34 +/- 2.32 micrograms/ml immediately after the completion of administration, respectively. It is notable that in humans the former concentration level has been observed to frequently cause adverse effects, whereas the latter was in the safe range. Consequently, the 15-min constant rate infusion did not result in the rapid increase in the plasma theophylline concentrations and was superior to the bolus injection from the viewpoint of maintaining the safety plasma concentrations. In conclusion, to avoid hypersensitivity due to ethylenediamine and the adverse effects caused by high plasma concentrations of theophylline, it was considered that constant rate infusion of theophylline to the venous is preferable in the clinical setting.

Aminophylline in the treatment of fluid overload

OBJECTIVE

Aminophylline has not been studied as an adjunct diuretic in critically ill children. Our purpose was to evaluate its use in the treatment of fluid overload in these patients.

DESIGN

Open, controlled clinical trial.

SETTING

Pediatric intensive care unit.

PATIENTS

Study subjects ranged from 2-46 months of age, were fluid overloaded, and were receiving a continuous infusion of furosemide (> or =6 mg/kg/day). Patients with hemodynamic instability or liver dysfunction were excluded.

INTERVENTIONS

A single dose of aminophylline (6 mg/kg) was given after establishing baseline values. There were no additional diuretics or changes in vasoactive agents during the study.

MEASUREMENTS AND MAIN RESULTS

Urine output, creatinine clearance, and sodium and potassium excretion were measured before and after administration of the aminophylline bolus. Heart rate and mean arterial pressure (mm Hg) were recorded hourly. Urine output increased by >80% (p < .01) during the first 2 hrs after administration of the aminophylline bolus and then returned to baseline by 4 to 6 hrs. The change in urine output is consistent with the pharmacokinetics of aminophylline. Heart rate and mean arterial pressure exhibited a change of <10% from baseline.

CONCLUSIONS

These results suggest that aminophylline is an effective adjunct to furosemide in increasing diuresis in critically ill children with fluid overload. The increased diuresis can be accomplished without increased risk if drug levels are adequately monitored.

Biodegradable cross-linked prodrug of the bronchial dilator Vephylline. 2. Kinetics and quantum chemical studies on the release mechanism

Experimental thermodynamics studies and quantum chemical reaction path calculations on the hydrolytic degradation of Poly-vephyllinemalate microspheres in acidic and basic media were performed. It was possible to make a conclusion on the release mechanism of free Vephylline as follows: a hydrolytic cleavage of the ester bonds between molecular fragments of R,S-malic acid takes place and leads to a soluble oligoester fraction. Then, further hydrolysis of the ester bonds between the xanthine fragment and R, S-malic acid leads to the release of Vephylline as free base. The hydrolytic process takes place in acidic solution with rapid degradation of the ester bonds between the malic acid monomers and by far slower degradation of the ester bonds between the malic acid and Vephylline. In basic solution both steps of the hydrolysis are fast processes leading to a complete release of free Vephylline within 1 h. The process of Vephylline release is under entropic control. The experimental results are well correlated to the results obtained after kinetics investigation and after AM1 quantum chemically calculated energy barriers in the reaction path leading to the tetrahedral intermediates of the hydrolytic reactions. This conclusion is in good accordance with an indirect study on the release mechanism of Vephylline from its polymeric prodrug, paying attention to the biological response, reported previously.

Pharmacokinetics of theophylline metabolites in 8 Chinese patients

AIM

To study theophylline metabolites pharmacokinetics in patients after a therapeutic dose.

METHODS

Eight adult patients with mild bronchial asthma and normal liver function were infused aminophylline intravenously (6.6 mumol.kg-1). The plasma concentrations of theophylline and its 4 metabolites: 1,3-dimethyluric acid (DMUA), 3-methylxanthine (3-MX), 1-methyluric acid (MUA), and the intermediate 1-methylxanthine (1-MX) were monitored by HPLC throughout 24 h.

RESULTS

The plasma concentration of DMUA was the highest one among the 4 metabolites. 3-MX showed the slowest elimination rate. The plasma concentration of 1-MX throughout a 24-h period showed that there was a picking up of 1-MX (from 0.04 mumol.L-1 to 1.05 mumol.L-1) in the next morning.

CONCLUSION

The formation of DMUA was the main metabolites. During night there was an accumulation of 1-MX.

[Brain perfusion changes after head trauma assessed by cerebral SPECT with aminophylline test]

Tomographic cerebral blood flow SPECT scanning using Tc-99m-HMPAO was performed before and after i.v. administration of aminophylline in 36 patients between 6 months to 11 years after closed head trauma. Asymmetries of brain perfusion were found in 34 patients, normal rCBF distribution in 2 patients. Bi-focused asymmetries on the presumed line: trauma-contra coup were seen in 64% of the patients. In 70.4% of the patients with brain perfusion asymmetries the CT scan was normal. The aminophylline test improved the perfusion in 42% of the patients, indicating preserved perfusion reserve. Persistence of brain perfusion alterations after head trauma exists. Aminophylline test may be useful in the assessment of brain perfusion reserve in post-traumatic focus. Brain perfusion SPECT scans may be useful for medico-legal purposes.

Design and evaluation of layered diffusional matrices for zero-order sustained-release

New layered matrix systems designed for zero-order sustained release are presented. The devices consist of a hydrophobic middle layer and press-coated hydrophillic and/or hydrophobic barrier layer(s). The systems overcome the inherent disadvantage of non-linear release associated with diffusion-controlled matrix devices by providing additional releasing surface with time to compensate for the decreasing release rate. The in vitro release of pseudoephedrine hydrochloride as a model compound from the matrices was examined. Modulation of release from a selected matrix containing aminophylline was evaluated in a crossover study using nine beagle dogs. Preliminary in vitro/in vivo correlation was also studied. The systems described in this paper can potentially be scaled up to commercial production.

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.

Electrogenic ion transport along the human duodenum in childhood

BACKGROUND

To find reliable sites to study the effects of different secretagogues on electrogenic ion secretion, we investigated the secretion pattern in different parts of duodenum.

METHODS

Histologically normal routine intestinal biopsy specimens from children were mounted in a modified Ussing chamber. The secretory responses to prostaglandin E2 (PGE2), aminophylline, dibutyryl cyclic adenosine 5'-monophosphate (cAMP), and acetylcholine (ACh) were studied with continuous measurements of the potential difference. Tissue resistance and generated current were calculated.

RESULTS

ACh induced secretion in the whole of duodenum, although the secretory response was augmented distally. PGE2 and cAMP induced significant secretion only in the distal duodenum.

CONCLUSIONS

The ACh-induced, calcium-mediated, electrogenic secretion was expressed along the whole duodenum, whereas the cAMP-mediated secretion was only seen in the distal part. The fully expressed electrogenic chloride secretion was only seen at or distal to the duodenojejunal flexure. Our study shows that it is important to carefully define the localization of physiologic studies performed in the duodenum.

Increased theophylline metabolism in the menstrual phase of healthy women

BACKGROUND

We previously reported on a Japanese woman with premenstrual asthma whose serum theophylline concentration was lower before the onset of her menstrual period. We evaluated the clearance of theophylline in each phase of her menstrual cycle and found an increase in clearance in the premenstrual and menstrual phases.

OBJECTIVE

This study was designed to investigate whether changes in theophylline clearance may occur with the menstrual cycle in nonasthmatic women.

METHODS

Aminophylline, 250 mg, was infused intravenously for 45 minutes, and the clearance of theophylline was calculated in seven healthy, ovulatory women on days 1 or 2, 10, and 20 or 25 of the menstrual cycle. The serum concentration of theophylline was determined with an enzyme immunoassay (homogeneous).

RESULTS

Theophylline clearance was significantly higher and its half-life was significantly shorter in the menstrual phase than in the follicular phase.

CONCLUSION

The metabolism of theophylline, and consequently, its clearance were increased in healthy women around the onset of menses. Clinicians must therefore consider the menstrual variation in theophylline metabolism when prescribing this drug to female patients.

The pharmacologic effects of recombinant, human colony-stimulating factors and their modulation by theophylline

STUDY OBJECTIVES

To investigate the effect of colony-stimulating factors (CSFs) on drug metabolism using theophylline as a substrate (phase I), and to evaluate the influence of theophylline on endogenous serum cytokine concentrations (phase II).

DESIGN

Open-label, prospective study.

SETTING

The bone marrow transplant unit of a tertiary university teaching hospital.

PATIENTS

Thirty-seven women with breast cancer (28 phase I, 9 phase II).

INTERVENTIONS

Patients received aminophylline 0.58 mg/kg either as a 30-minute intravenous infusion before receiving recombinant CSFs or after several days of CSF therapy, just before high-dose chemotherapy (phase I) or as a continuous intravenous infusion after bone marrow transplantation (phase II).

MEASUREMENTS AND MAIN RESULTS

Clearance of theophylline was significantly higher after CSF administration (0.76 vs 0.99 ml/min/kg, p = 0.019). Continuous infusion of aminophylline resulted in elevations of serum macrophage-CSF and interleukin 6.

CONCLUSIONS

Administration of CSFs before autologous bone marrow transplantation for priming progenitor cells may alter drug metabolism. Studies should be conducted to evaluate the potential effects of CSFs on the disposition of chemotherapeutic agents.

Kinetics of theophylline in apnea of prematurity in small for gestational age babies

OBJECTIVES

To study the pharmacokinetics of theophylline and its correlations to pharmacodynamic effects in apnea of prematurity in small for gestational age babies.

DESIGN

Prospective case control study.

SETTING

Level III Neonatal Intensive Care Unit.

SUBJECTS

Ten small for gestational age (SGA) babies and 10 gestation matched appropriate for gestational age (AGA) babies with recurrent apnea of prematurity.

METHODS

All babies were investigated to exclude secondary causes of apnea. 5 mg/kg of aminophylline loading dose followed by 2 mg/kg as maintenance dose every 8 hourly intravenously was used. The trough and peak levels of theophylline were assessed on different days of therapy. Clinical monitoring was done for the efficacy and toxicity of the drug. Analysis was done using unpaired Student's 't' test and the correlation between plasma theophylline levels of different days was performed by using ANOVA.

RESULTS

The therapeutic drug levels were achieved within 24 hours in all babies. The SGA babies showed 25% higher drug levels as compared to AGA babies. The mean trough plasma theophylline levels ranged from 8.15 +/- 1.59 to 12.37 +/- 1.54 micrograms/ml in SGA babies while in AGA babies they ranged from 6.26 +/- 1.93 to 9.96 +/- 1.96 micrograms/ml in first 8 days of therapy. The mean peak levels in SGA babies ranged from 11.91 +/- 1.84 to 17.13 +/- 1.63 micrograms/ml and in AGA babies ranged from 8.17 +/- 1.84 to 13.02 +/- 1.48 micrograms/ml. Twenty per cent SGA and AGA babies each developed clinical toxicity though toxic drug levels were found in 50% SGA and 30% AGA babies.

CONCLUSION

There is a need to modify dosage schedule for these babies.

Properties controlling the diffusion and release of water-soluble solutes from poly(ethylene oxide) hydrogels: 3. Device geometry

The diffusive release from hydrogels can be determined by both composition and geometry. This paper presents a theoretical and experimental comparison of the release characteristics of proxyphylline in water-swollen slabs, spheres, and cylinders of a urethane cross-linked poly(ethylene oxide). Contrary to general conventional wisdom it was found that practically cylinders and spheres, which have considerable potential advantages for oral delivery, can provide good 'anomalous' rates for which the 'exponent of release' into water from the dry xerogels is c. 0.8 compared with 1.0 for zero order. An exponent of 0.94 was found for release into water from 'larger' xerogel flat slabs thus confirming that these configurations can provide essentially constant delivery formulations from which the active agent cannot be 'dumped'. For up to 40% total drug release, the theoretical release profiles were essentially of identical form for all three geometries in the swollen state and, as expected in theory and practice, showed an exponent for release of close to 0.5. However, the experimental release of proxyphylline was found to be more sustained from swollen spheres of these polymers than theory would predict. The half life times for release were further extended by approximately two and a half times for the initially dry devices compared with the initially swollen ones.

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.

Influence of chronic aminophylline on antielectroshock activity of diazepam and aminophylline-induced convulsions in mice

The effects of chronic administration of aminophylline (AMPH; 50 mg/kg, twice daily for 14 consecutive days) were studied on both antielectroshock efficacy of diazepam (DZP) and convulsive activity of AMPH in mice. AMPH injected acutely at a dose of 50 mg/kg significantly reduced anticonvulsant action of DZP elevating ED50 from 10.9 (control) to 15.9 mg/kg (p < 0.01). After the administration of AMPH for 3 days, ED50 value was still higher compared with control. Chronic treatment with AMPH resulted in further increase of ED50 of DZP, which was 20.2 mg/kg, and this elevation was significant not only when compared with saline-treated animals, but also with acute and 3-day administration of the xanthine (p < 0.01, 0.05, and 0.001, respectively). Therefore, no tolerance to this AMPH-mediated effect was found, and even an enhancing influence was observed. On the other hand, chronic treatment with AMPH decreased convulsive activity of AMPH elevating ED50 for induction of clonic seizures from 218 to 252 mg/kg (p < 0.01). The remaining seizure parameters were unaffected. Furthermore, in both cases pharmacokinetic interactions were excluded, at least in terms of total plasma levels of the drugs. The results suggest that the mechanisms governing AMPH-induced reversal of the anticonvulsant efficacy of DZP qualitatively differ from those underlying AMPH-induced convulsions. Moreover, these data support the claim that AMPH should be avoided in patients suffering from different types of epilepsy.

The design of oral sustained-release theophylline dosing after conversion from intravenous to oral therapy

We studied the design of oral sustained-release theophylline dosing after conversion from constant aminophylline infusion. Twelve children with bronchial asthma (9 boys and 3 girls) were evaluated in this study. Each patient received a constant intravenous administration of aminophylline for 4-10 days. Three hours after conversion from constant aminophylline infusion, they received oral sustained-release theophylline twice daily at 12-hour intervals. Blood samples were obtained at least once during the aminophylline infusion, just before conversion from the aminophylline infusion, and 0, 3 and 6 hours, and 4-5 days after administering oral theophylline. Pharmacokinetic parameters were estimated using the serum theophylline concentrations that were obtained during constant aminophylline infusion. These estimates of pharmacokinetic parameters were used to predict the serum theophylline concentrations during oral theophylline therapy. Predicted serum theophylline concentrations using individual pharmacokinetic parameters were fitted with actual measured values in this study. When switching a patient from intravenous aminophylline to sustained-release oral theophylline, the use of Bayesian analysis of serum theophylline concentration values obtained during intravenous therapy works well in predicting serum theophylline concentrations and in determining oral dosages that maximize the drug's effectiveness.

Adequacy of recommended aminophylline loading doses in children

The adequacy of a loading dose of aminophylline 6 mg/kg i.v. in hospitalized pediatric patients with reactive airway disease was studied. Children six months to 14 years of age were studied to determine their serum theophylline concentrations after they were given an aminophylline loading dose of 5-7 mg/kg i.v. and to see whether they had to receive additional bolus doses. Bolus doses were infused over 20-30 minutes and were followed by a continuous infusion. Additional bolus doses were administered if the patient's serum theophylline concentration and clinical condition indicated they were necessary. Data from two separate phases of the study were combined for analysis. Phase 1 was designed for estimating population pharmacokinetic values. Some 72% of the 64 patients studied had subtherapeutic serum theophylline concentrations (< 10 mg/L) within 5.5 hours of the loading dose, and 78% required at least one additional bolus dose. Males had significantly lower serum theophylline concentrations than females; of the patients with subtherapeutic concentrations, 67% were males. Patients five years of age or younger were more likely than older children to have subtherapeutic theophylline concentrations. A 6-mg/kg loading dose of i.v. aminophylline did not produce adequate serum theophylline concentrations or eliminate the need for a second bolus dose in most pediatric patients with acute exacerbations of asthma.

Kinetics of absorption of a new once-a-day formulation of theophylline in the presence and absence of food

Two three-way crossover studies were done to characterize the drug release characteristics of Monospan (3M Pharmaceuticals, St. Paul, MN) capsules, a new once-a-day theophylline formulation. In the first study, 22 healthy males received single 450-mg doses of Monospan in the presence and absence of a high-fat breakfast; the same dose of Somophyllin (Fisons, Rochester, NY) immediate-release liquid was given to fasted subjects as a reference. The second study involved 29 healthy males given a single dose of 900 mg of Monospan in the presence and absence of the same high-fat meal; Theo-24 (G. D. Searle and Co., Skokie, IL) capsules were given to fasted subjects as a reference. The results of both studies showed that food did not affect the absorption of theophylline from Monospan; peak concentration, to and area under the serum concentration-time curve were all unchanged. The absorption rates were similar with both strengths and dietary conditions and showed that theophylline was absorbed slowly from Monospan at a constant rate (approximately 3.2%/h) over 24 h. Absorption continued past 24 h, and the extent of absorption from Monospan compared with that from each reference averaged 88% or higher. A good correlation (r > 0.980) was observed for Monospan between the amount absorbed in vivo and the amount released in the in vitro dissolution test, a result that demonstrates the precise rate control of Monospan. We conclude that Monospan is a suitable once-a-day formulation that can be taken without regard to food.

Individualizing aminophylline doses in premature infants using bioelectrical impedance: a non-invasive approach

The role of bioelectrical impedance (BI) in estimating the pharmacokinetics and, therefore, individualized doses, of aminophylline in preterm infants (gestational age 26-35 weeks) was assessed in a two-phase study. Multiple regression analysis in the first group of neonates (phase I, n = 19) identified resistance, reactance, weight and length as optimal predictors of distribution volume (adjusted R2 = 0.84, coefficient of variation (CV) = 10.17%), and length2/impedance and postconceptual age as predictors of clearance (adjusted R2 = 0.74, CV = 26.73%). Application of these models to an independent group (phase II, n = 20) generated doses which satisfactorily achieved target theophylline loading and steady-state (SS) 'peaks' of 10 micrograms/mL and SS 'troughs' of 7.7 +/- 0.6 micrograms/mL. A better understanding of specific criteria and limitations of the impedance technique in neonates is necessary in order to refine BI measurements.

Effect of mexiletine on elimination and metabolic conversion of theophylline and its major metabolites in rats

In an attempt to clarify the possible mechanism of the interaction between theophylline (TP) and mexiletine (ME), the elimination kinetics and in vitro metabolism of TP and its metabolites were investigated in rats. The plasma elimination of TP, 1,3-dimethyluric acid (1,3-DMU) and 1-methyluric acid (1-MU) was significantly delayed by the intravenous (i.v.) administration of ME. The oral administration of ME also decreased the elimination rate of TP to the same extent as the i.v. dosing. The in vitro metabolic experiment showed that ME significantly inhibited the metabolic conversion of TP to 1,3-DMU and, 1,3-DMU to 1-MU, and slightly inhibited the conversion of TP to 3-methylxanthine, these processes being mediated by microsomal enzymes, with no inhibition of xanthine oxidase. Our results indicated that ME could inhibit the metabolic conversion of TP and its metabolite in rat, as reported in man.