Theophylline and gastric emptying in very low birthweight neonates: a randomised controlled trial

BACKGROUND

Theophylline treatment causes side effects such as tachycardia, hyperglycaemia, abdominal distension, and vomiting. The latter two are probably the result of delayed gastric evacuation.

OBJECTIVE

To study the effect of theophylline on gastric emptying time in preterm infants.

PATIENTS

The subjects were 18 premature neonates with a mean (SD) birth weight of 1302 (240) g and a mean (SD) gestational age of 28.7 (1.9) weeks.

MAIN OUTCOME MEASURES

In each case, gastric emptying was measured on two occasions: once when the newborns were being treated with theophylline and once when they were not. Half of the cases were randomised to receive theophylline before the initial measurement. The opposite was applied for the rest. Gastric emptying was assessed ultrasonically by measuring the change in antral cross sectional area (ACSA) at regular intervals over 120 minutes.

RESULTS

The mean (SD) ACSA half time in the newborns receiving theophylline was 52 (19) minutes compared with 37 (16) minutes in those not receiving theophylline. This difference is significant (p < 0.05).

CONCLUSIONS

Treatment with theophylline seems to delay gastric emptying in very low birthweight neonates, and this must be taken into consideration when this drug is used to treat apnoea of prematurity.

Effect of St. John's wort on the pharmacokinetics of theophylline in healthy volunteers

The objective of this study was to investigate the effect of St. John's wort (SJW, Hypericum perforatum) on the pharmacokinetics of theophylline in healthy volunteers. Twelve healthy Japanese male volunteers participated in this randomized, open-labeled, crossover study. The subjects took an SJW caplet (300 mg) three times a day for 15 days. On day 14, they received a single oral dose of 400 mg of theophylline. They took the same dose of theophylline without SJW treatment on another occasion. Plasma and urine samples were obtained during a 48-hour period after theophylline administration. Theophylline concentrations in plasma and urine, as well as the major metabolites (13U, 1U, 3X) in urine, were measured. SJW caused no significant changes in the pharmacokinetics of theophylline in plasma. SJW administration tended to increase the ratio of 1U/the total amount excreted in urine. However, no changes in the ratio of unchanged theophylline, 13U, and 3X were observed. It is unlikely that the effect of 15 days of treatment with SJW on CYPs is sufficient to cause a change in plasma theophylline concentrations.

Determination of unbound theophylline in rat blood and brain by microdialysis and liquid chromatography

To investigate the mechanism by which theophylline crosses the blood-brain barrier (BBB) and its disposition, we determined unbound theophylline in rat blood and brain using microbore liquid chromatography coupled with microdialysis. Microdialysis probes were inserted into the jugular vein and the brain striatum of male Sprague-Dawley rats. Then theophylline at dosage of 10 or 30 mg/kg was administered through the femoral vein. Theophylline and dialysates were separated using a microbore phenyl-hexyl column (150 mm x 1 mm, 5 microm). The mobile phase comprised of acetonitrile-methanol-10 mM monosodium phosphate (pH 3.0) (10:20:70, v/v/v). The UV wavelength was set at 270 nm. The concentration-response relationship was linear over a concentration range of 0.05-50 microg/ml; intra-assay and inter-assay precision and accuracy of theophylline fell within 10%. Average in vivo recoveries were 0.74 +/- 0.06 in blood and 0.27 +/- 0.07 in brain with theophylline at concentrations 1, 2 and 5 microg/ml. This biological sampling method thereby allowed the determination of theophylline levels in blood and brain tissues. The disposition of theophylline in the blood and brain tissue suggests that there was rapid exchange and equilibration between the blood and brain system. The drug-drug interaction results indicate that theophylline was able to cross BBB, but that it might not be regulated by p-glycoprotein to the pharmacokinetics of theophylline.

Evaluation of the bioavailability and pharmacokinetics of two extended-release theophylline formulations in dogs

OBJECTIVE

To evaluate the bioavailability and pharmacokinetic characteristics of 2 commercially available extended-release theophylline formulations in dogs.

DESIGN

Randomized 3-way crossover study.

ANIMALS

6 healthy adult dogs.

PROCEDURE

A single dose of aminophylline (11 mg x kg(-1) 15 mg x lb(-1)], i.v., equivalent to 8.6 mg of theophylline/kg 13.9 mg x lb(-1) or extended-release theophylline tablets (mean dose, 15.5 mg x kg(-1) [7.04 mg x lb9-1), PO) or capsules (mean dose, 15.45 mg x kg(-1) [7.02 mg x lb(-1)], PO) was administered to all dogs. Blood samples were obtained at various times for 36 hours after dosing; plasma was separated and immediately frozen. Plasma samples were analyzed by use of fluorescence polarization immunoassay.

RESULTS

Administration of theophylline i.v. best fit a 2-compartment model with rapid distribution followed by slow elimination. Administration of extended-release theophylline tablets and capsules best fit a 1-compartment model with an absorption phase. Mean values for plasma terminal half-life, volume of distribution, and systemic clearance were 8.4 hours, 0.546 L x kg(-1), and 0.780 mL x kg(-1) x min(1), respectively, after i.v. administration of theophylline. Systemic availability was > 80% for both oral formulations. Computer simulations predicted that extended-release theophylline tablets or capsules administered at a dosage of 10 mg x kg(-1) (4.5 mg x lb(-1)), PO, every 12 hours would maintain plasma concentrations within the desired therapeutic range of 10 to 20 microg x mL(-10.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of these single-dose studies indicated that administration of the specific brand of extended-release theophylline tablets or capsules used in this study at a dosage of 10 mg x kg(-1), PO, every 12 hours would maintain plasma concentrations within the desired therapeutic range (10 to 20 microg x mL(-1)) in healthy dogs.

[For which cases should clinicians perform blood purification in the management of acute poisoning? Clinical and pharmacological analyses]

Indications for performing blood purification such as direct hemoperfusion (DHP), hemodialysis (HD) and hemodiafiltration (HDF) in patients with acute poisoning were retrospectively analyzed. Although a quick improvement in consciousness level was achieved by an intensive treatment with DHP for three hours in 27 patients suffering from acute tranquilizer poisoning, a slow but safe recovery was surely obtained in another 111 cases who received general supportive care. The medical costs of patients treated by DHP were 2.07 times greater than those of cases treated by general supportive care. Plasma and urine concentrations of theophylline could be obtained simultaneously during the treatment by DHP. The excretion rate of DHP at 1, 2, 3 and 6 hours after starting DHP ranged from 99.4% to 96.0%. At the end of DHP, the clinical findings markedly improved and sufficient elimination from the body could be obtained. The rebound phenomenon was observed after three hours DHP in one case of acute anilin poisoning and the patient died of fatal fulminant hepatic failure at 9th hospital day. In this case, further DHP was needed. DHP is presently becoming less prevalent due to concerns over such issues as rapid metabolism and elimination efficacy in acute organophosphate and aconitine poisoning. In a case of 23-year old female who took a potentially fatal dose of 100 g of acetaminophen, blood purification was not performed and oral N acetylcysteine antidotal therapy was quite effective in order to prevent hepatic injury. The serum acetaminophen concentration was 287 microg/ml on her admission and the value fell to 28.8 microg/ml after 35 hours. These results indicate that blood purification is not always necessary because of it's poor elimination efficacy in some kinds poisoning. Nevertheless, in severe cases it was quite an effective and useful extracorporeal elimination technique for both improvement of clinical outcome and clearance of poisons. Although it is difficult to draw a definitive conclusion from this study, it is suggested that a rapid and prudent decision should be made as to perform blood purification.

Metabolic effects of caffeine in humans: lipid oxidation or futile cycling?

BACKGROUND

Caffeine ingestion stimulates both lipolysis and energy expenditure.

OBJECTIVES

Our objectives were to determine whether the lipolytic effect of caffeine is associated with increased lipid oxidation or futile cycling between triacylglycerol and free fatty acids (FFAs) and whether the effects of caffeine are mediated via the sympathetic nervous system.

DESIGN

Respiratory exchange and [1-(13)C]palmitate were used to trace lipid oxidation and FFA turnover in 8 healthy, young men for 90 min before and 240 min after ingestion of placebo, caffeine (10 mg/kg), or caffeine during beta-adrenoceptor blockade.

RESULTS

During fasting conditions, there were few differences in measured variables between the 3 tests. During steady state conditions (last hour of the test) after ingestion of caffeine, lipid turnover increased 2-fold (P < 0.005), and the mean (+/-SEM) thermic effect was 13.3 +/- 2.2% (P < 0.001), both of which were greater than after ingestion of placebo or caffeine during beta-adrenoceptor blockade. After ingestion of caffeine, oxidative FFA disposal increased 44% (236 +/- 21 to 340 +/- 16 micro mol/min), whereas nonoxidative FFA disposal increased 2.3-fold (455 +/- 66 to 1054 +/- 242 micro mol/min; P < 0.01). In postabsorptive conditions, 34% of lipids were oxidized and 66% were recycled. Caffeine ingestion increased energy expenditure 13% and doubled the turnover of lipids, of which 24% were oxidized and 76% were recycled. beta-Adrenoceptor blockade decreased, but did not inhibit, these variables.

CONCLUSIONS

Many, but not all, of the effects of caffeine are mediated via the sympathetic nervous system. The effect of caffeine on lipid mobilization in resting conditions can be interpreted in 2 ways: lipid mobilization alone is insufficient to drive lipid oxidation, or large increments in lipid turnover result in small increments in lipid oxidation.

EFFECTS OF Cassia auriculata AND Cardospermum halicacabum TEAS ON THE STEADY STATE BLOOD LEVELS OF THEOPHYLLINE IN RATS

The effects of concurrent administration of herbal tea prepared from dried flowers of Cassia auriculata or aerial parts of Cardospermum halicacabum and steady state serum levels of theophylline was investigated in Wistar rats. Results obtained demonstrate that a significant increase in the steady state levels of theophylline occur when this drug is administered concurrently with herbal tea prepared from either of the above plants. C. auriculata and C. halicacabum enhanced the steady state levels of theophylline by 32.5% (p < 0.02) and 48.2% (p < 0.02), respectively, when compared with the levels in animals receiving theophylline alone for the same time period. Herbal teas prepared from C. auriculata or C. halicacabum should therefore be avoided by patients treated with theophylline as these herbal teas have the potential to influence the bioavailability of the prescription drug.

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.

Low-dose theophylline in childhood asthma: a placebo-controlled, double-blind study

Regular anti-inflammatory treatment is essential in treating persistent asthma. Most commonly, inhaled corticosteroids (ICS) are used. However, especially in children, there is concern about the long-term safety of ICS such that doses should be kept to a minimum. The use of theophylline has decreased because of frequent side-effects in therapeutic doses. In adults, there have been reports about an immunomodulatory effect of low-dose theophylline. To study the clinical and immunomodulatory effect in children, 36 patients (mean age 12.5 SD 2.4 years) with moderate, persistent asthma on regular ICS were recruited into a placebo-controlled, double-blind study. After a 6-week run-in period, patients received either theophylline 10 mg/kg bodyweight or placebo for 12 weeks. Diary cards, lung function, peripheral blood lymphocyte subpopulations and serum eosinophil cationic protein (sECP) were assessed. In the treatment group, mean serum theophylline was 7.1 mg/l. There was no change in symptoms or use of rescue medication. Mean (SD) peak expiratory flow (PEF) increased from 86% (24) to 95% (18) predicted. sECP decreased from 43.2 microg/l (32.5) to 26.5 microg/l (16.9) (p = 0.02). Lymphocyte subpopulations did not change. The study failed to show a beneficial clinical or an immunomodulatory effect of theophylline when used in low doses. These results do not support a more important role of theophylline in the long-term treatment of moderate childhood asthma.

A Multi‐mechanistic Drug Release Approach in a Bead Dosage Form and In Vivo Predictions

Our previous study has successfully prepared a combination of immediate release, enteric coated, and controlled release (CR) beads and mathematically modeled in vitro drug release characteristics of the combination based on the release profiles of individual beads. The objectives of the present study are to evaluate the combination and individual beads in vivo and to mathematically model in vivo drug input characteristics of the combination based on the in vivo input of individual beads. Beagle dogs were used as an animal model, and theophylline as a model drug. In vivo percent drug absorbed at different times (input function) after administration of a capsule bead dosage form was calculated using the Wagner-Nelson deconvolution method using intravenous injection of theophylline in each dog as a reference. The in vivo input functions of individual beads were each fitted to appropriate mathematical equations. The in vivo input function of the bead combination dosage form was calculated based on the individual mathematical equations (expected), and verified experimentally in vivo (experimental). The results showed that all bead dosage forms behave in vivo as defined in vitro. Enteric coated beads significantly delay the time to reach the maximum concentration of drug (tmax=4.9 h) compared to uncoated immediate release beads (2 h). The lag time of enteric coated beads is 1.1 h. CR beads showed both longer tmax (6 h) and mean residence time (MRT=9.7 h) compared to the uncoated immediate release beads (tmax=2 h and MRT=7.1 h) as designed in vitro. The in vivo input functions for the three individual beads can be fitted to equations as a function of square root of time. The combined bead dosage form showed tmax of 2.4 h and MRT of 7.9 h. The experimental and expected in vivo input profiles agreed to within +/- 12% (residues at individual data points). Our results suggest that the drug input function of a combined multi-mechanism oral dosage form can be predicted from the in vivo performance of individual formulations using the dog as an in vivo model.

Theophylline treatment may adversely affect the anoxia-induced erythropoietic response without suppressing erythropoietin production

OBJECTIVE

To investigate the influence of theophylline on erythropoiesis in chronic obstructive pulmonary disease (COPD) and explore the potential underlying mechanisms.

METHODS

We evaluated the haematological parameters and erythropoietin (EPO) values in 38 COPD patients, 18 of which had been treated with theophylline (8 mg/kg daily) for at least 1 year, and the other 20 had never received this drug; 38 sex- and age-matched healthy volunteers served as controls. We further studied the development of BFU-E (bursts forming units of erythrocyte precursors) -derived colonies in semisolid methylcellulose cultures in blood samples from 7 patients randomly selected from both groups. In addition, we studied the effects of theophylline on the erythroid cell development by adding this agent to erythroid cell cultures from 6 healthy volunteers at various concentrations.

RESULTS

Haemoglobin values were found to be significantly lower in COPD patients treated with theophylline than in those untreated ( P<0.05). Both groups of patients exhibited significantly higher haemoglobin values than normal subjects ( P<0.01 and P<0.001 for treated and untreated patients, respectively). Serum EPO levels did not differ among the three studied groups. Unlike untreated patients and controls, the serum of the theophylline-treated patients produced a significant growth inhibition of erythroid bursts ( P<0.05); the in vitro use of theophylline showed a concentration-dependent inhibition ( P<0.001).

CONCLUSION

Our findings confirm the decrease of red cell production, which occurs following administration of theophylline, exclude the possibility of decreased EPO synthesis and suggest a direct inhibitory action of theophylline on erythropoiesis.

In vitro removal of therapeutic drugs with a novel adsorbent system

BACKGROUND/AIMS

Substances in the middle molecular weight range have been shown to play a significant pathogenetic role in as diverse disorders as end-stage renal disease and multiple organ failure. To overcome the limitations in the amount removed by hemofilters, new sorbents with a high biocompatibility are actively being developed. Furthermore, biocompatible sorbents by their nonspecific adsorptive behavior could have great impact on detoxification treatment in exogenous intoxications. We performed an in vitro evaluation of a newly developed highly biocompatible sorbent cartridge (Betasorb((R))), examining its adsorptive capacity concerning therapeutic drugs.

METHODS

Uremic blood spiked with a range of therapeutic drugs was recirculated for 2 h in an in vitro hemoperfusion circuit containing a Betasorb device for hemoperfusion. The drug concentrations before and after the passage of the cartridge were measured, and the total amount removed was calculated.

RESULTS

The sorbent showed effective removal of glycopeptide antibiotics, digoxin, theophylline, phenobarbital, phenytoin, carbamazepine, and valproic acid. Moderate removal could be demonstrated for tacrolimus and cyclosporine A; aminoglycosides were removed to a small extent only.

CONCLUSION

Betasorb hemoperfusion shows a potent adsorptive capacity concerning therapeutic drugs (except aminoglycosides) and could be of major value in the treatment of intoxications. On the other hand, drug monitoring and possible adjustments are necessary during Betasorb hemoperfusion to maintain the therapeutic ranges of the drugs in blood.

The measurement of theophylline in human serum or plasma using gas chromatography and isotope dilution-mass spectrometry (GC-IDMS) taking other substituted xanthines into consideration

A method is described which uses a combination of gas chromatography and isotope dilution-mass spectrometry (GC-IDMS) to determine the concentration of theophylline (1,3-dimethyl xanthine) in human plasma or serum samples. The effects of similar substituted xanthines - namely theobromine (3,7-dimethyl xanthine), paraxanthine (1,7-dimethyl xanthine) 1,3-dimethyl-7-(2-hydroxyethyl) xanthine (internal standard HPLC) and caffeine (1,3,7-trimethyl xanthine) were tested to confirm the specificity of the method. The derivatisation of all xanthines was performed with N-methyl-N-trimethylsilyl trifluroacetamide (MSTFA). The internal standard used was 2-(13)C ,1,3-(15)N2-theophylline. The extraction and derivatisation procedures were examined in detail and optimised stepwise during the development of the method. High-performance liquid chromatography (HPLC) was used for comparison.

Effects of long-term theophylline exposure on recovery of respiratory function and expression of adenosine A1 mRNA in cervical spinal cord hemisected adult rats

Our lab has previously shown that when administered acutely, the methylxanthine theophylline can activate a latent respiratory motor pathway to restore function to the hemidiaphragm paralyzed by an ipsilateral C2 spinal cord hemisection. The recovery is mediated by the antagonism of CNS adenosine A1 receptors. The objective of the present study was to assess quantitatively recovery after chronic theophylline administration, the effects of weaning from the drug, and the effects of the drug on adenosine A1 receptor mRNA expression in adult rats subjected to a C2 hemisection. Rats subjected to a left C2 hemisection received theophylline orally for 3, 7, 12, or 30 days and were classified as 3D, 7D, 12D, or 30D respectively. Separate groups of 3D animals were weaned from drug administration for 7, 12, and 30 days before assessment of respiratory recovery. Additional groups of 7D and 12D animals were also weaned from drug administration for 7 and 12 days prior to assessment. Sham-operated controls received theophylline vehicle for similar periods. Quantitative assessment of recovered respiratory activity was conducted under standardized electrophysiologic recording conditions approximately 18 h after each drug application period. Serum theophylline analysis was conducted at the end of electrophysiologic recordings. Adenosine A1 receptor mRNA expression in the phrenic nucleus was assessed with in situ hybridization and immunohistochemistry. Chronic theophylline induced a dose-dependent effect on respiratory recovery over a serum theophylline range of 1.2-1.9 microg/ml. Recovery was characterized as respiratory-related activity in the left phrenic nerve and expressed as a percentage of activity in the homolateral nerve in noninjured animals under similar recording conditions. Recovered activity was 34.13 +/- 2.07, 55.89 +/- 2.96, 74.78 +/- 1.93, and 79.12 +/- 1.75% respectively in the 3D, 7D, 12D, and 30D groups. Theophylline-induced recovered activity persisted for as long as 30 days when drug administration was stopped and serum levels of the drug were virtually undetected. Furthermore, recovered activity in 3D and 7D animals increased significantly as a function of duration of weaning. Adenosine A1 receptor mRNA expression was not significantly changed by theophylline administration. It is concluded that recovery of respiratory function in C2-hemisected rats induced by chronic theophylline is unrelated to adenosine A1 receptor mRNA expression. Recovered activity persists even when drug administration has been stopped. The significance of our results is that in the clinical application of theophylline to improve respiratory impairment, intermittent drug administration may be sufficient to engender and maintain the therapeutic benefits of the drug.

Determination of theophylline clearance after cimetidine infusion in critically ill patients

The potential for continuous infusion of cimetidine to affect the clearance of aminophylline was assessed in 18 critically ill patients treated for bronchospasm. This was a pharmacokinetic drug-drug interaction study in which the subjects were administered aminophylline as a continuous infusion at low doses (mean 10.8 mg/hr). Subjects were started on cimetidine (50 mg/hr) 24 hours post aminophylline drip and remained on it for 48 hours. Theophylline clearance was determined right before and 48 hours after starting cimetidine. There were no significant differences in theophylline clearance before and after infusion of cimetidine (P >.05). Based on our findings, cimetidine does not seem to affect the clearance of low doses of theophylline in critically ill patients.

Effect of daidzein on CYP1A2 activity and pharmacokinetics of theophylline in healthy volunteers

OBJECTIVE

To examine the potential effect of daidzein on CYP1A2 activity and on the pharmacokinetics of theophylline by inhibiting its metabolism.

METHODS

The experiment was conducted in a single-blind, placebo-controlled, parallel study. The caffeine metabolic ratio (CMR) used as an indicator of CYP1A2 function was completed at baseline and after daidzein or placebo co-administration. A single dose of 100 mg theophylline was taken by all 20 volunteers on day 3. Thereafter, volunteers were allocated for one of two regimens. One group received 200 mg daidzein twice daily for 10 days. The other group received placebo. On day 12, the test group received 200 mg daidzein with 100 mg theophylline; the parallel group received 100 mg theophylline with placebo.

RESULTS

The baseline value of CMR between test group and control group did not show a difference (P=0.215). The percentage decrease in CMR ranged from -50% to 20%, with an average value of -19.8+/-19.7%. The percentage decrease in test group was statistically significant (P=0.009), and no significant changes were shown in the control group (t=0.12, P=0.914). By comparing the pharmacokinetic parameters of theophylline before and after daily treatment with daidzein, the effect of daidzein on the metabolism of theophylline was evident. Comparing the kinetics parameters of theophylline of day 1 (without co-medication) with those of day 12 (10-day daidzein), the AUC(0-48), AUC(0- infinity ), C(max) and t(1/2) were significantly increased by 33.57+/-21.75% (CI, 1.21-1.46, P< 0.05), 33.77+/-21.45% (CI, 1.20-1.46, P<0.05), 23.54+/-16.93% (CI, 1.23-1.52, P< 0.05) and 41.39+/-45.92% (t=-3.19, P=0.011), respectively. The pharmacokinetic parameters of theophylline within the placebo group showed no statistically significant difference (P >0.05).

CONCLUSIONS

Daidzein, a principal isoflavone in soybean, in higher doses may inhibit CYP1A2 activity in vivo, and physicians should be aware of potential drug-food interactions.

Reversal of acute tacrolimus-induced renal vasoconstriction by theophylline in rats

OBJECTIVE

To determine whether theophylline, a nonselective adenosine receptor antagonist and phosphodiesterase inhibitor, reverses the acute declines in renal blood flow and glomerular filtration rate induced by high-dose tacrolimus in rats.

DESIGN

Prospective, randomized, placebo-controlled experimental study.

SETTING

University-based basic science research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

After mechanical ventilation and instrumentation under isoflurane and nitrous oxide anesthesia, animals received either tacrolimus 0.5 mg/kg intravenously or vehicle and 1 hr later either theophylline 4 mg/kg intravenously or vehicle.

MEASUREMENTS AND MAIN RESULTS

By using radiolabeled microspheres, renal blood flow was measured in three groups: control (n = 5), tacrolimus plus vehicle (n = 6), and tacrolimus plus theophylline (n = 6) at four time points-baseline and 60, 75, and 90 mins after tacrolimus or vehicle (the latter two time points being 15 and 30 mins after theophylline or vehicle, respectively). Whole blood tacrolimus and serum theophylline concentrations were measured. In a separate group of animals, by using (51)Cr-EDTA, glomerular filtration rate was measured in two groups: tacrolimus plus vehicle (n = 5) and tacrolimus plus theophylline (n = 5) at baseline and over two consecutive 20-min time periods beginning 61 mins posttacrolimus. Urine flow rate also was measured. Following tacrolimus, both renal blood flow and glomerular filtration rate declined in parallel by approximately 33% and 50% from baseline after 75 and 90 mins, respectively (p <.05 by two-way repeated-measures analysis of variance). Theophylline completely reversed these tacrolimus-induced decreases in renal blood flow and glomerular filtration rate. Urine flow rate also increased in response to theophylline.

CONCLUSIONS

Low-dose theophylline reverses tacrolimus-induced declines in renal blood flow and glomerular filtration rate observed in an acute model of tacrolimus toxicity. Theophylline's effect in chronic toxicity remains to be determined.

Effect of age and sex on theophylline clearance in young subjects

The joint effects of age and gender on theophylline plasma clearance (Clp) were assessed using an analysis of covariance technique. Data from several literature sources and from our laboratory were collated for this analysis with only non-smoking subjects aged 1.3 to 30.0 years considered. The values of Clp exhibited markedly greater variability in the younger subjects, necessitating development of a weighted linear least-squares program to fit the data. The data exhibited a linear decrease in Clp with increasing age regardless of sex. A gender influence was evident over the age range of 4 to 20 years. Male Clp values tended to be higher than those of females over this age interval [25.5 ml/hr/kg higher (31%) at 4 years and 12.5 ml/hr/kg higher (22%) at 20 years]. These differences are statistically significant, and since they represent a divergence of greater than 20%, may be clinically significant as well. The statistical technique employed may be of value in future pharmacokinetic studies for the examination of multiple effects on pharmacokinetic parameters.

Two novel methods for the determination of CYP1A2 activity using the paraxanthine/caffeine ratio

Cytochrome P450 1A2 (CYP1A2) plays an important role in drug metabolism. Provocation with caffeine is used to estimate CYP1A2 activity, but in most tests a long period of caffeine abstinence has to be taken into account. We compared two novel methods with the currently applied test. The pharmacokinetic (PK) parameters of caffeine and paraxanthine were estimated in eight caffeine-taking healthy volunteers by fitting serum concentration-time data to a two-compartment PK model. Then a three-step approach was followed. Step 1: The caffeine administration regimens of three provocation methods, which differ by their periods of abstinence, together with the PK parameters of each volunteer, were entered in a PK simulation program and the molecular ratio of the paraxanthine/caffeine concentration (P/C molratio) of each method was estimated for the individual volunteers. Step 2: For each method a relationship for the population between the caffeine clearance (Clc) and the corresponding P/C molratio was empirically established. Step 3: The true caffeine clearance (Clc tr) of each volunteer, as found by fitting the individual PK curve, was compared for all three methods with the clearance estimated from the individual P/C molratio using the relationship of step 2. The predictive values for Clc of the three methods did not differ significantly from Clc tr. For the three methods the values for bias were 6.7, 4.3 and 3.1%, respectively and for precision they were 12.3, 20.6 and 17.8%. We conclude that the two novel methods of caffeine provocation show good predictive performance for Clc when compared with the conventional method. Abstaining from caffeine for a long period is not necessary to estimate CYP1A2 activity (using the P/C molratio) accurately.

Paraxanthine/caffeine ratio: as an index for CYP1A2 activity in polycyclic aromatic hydrocarbons exposed subjects

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and originate from incomplete combustion process of organic materials. These compounds are bioactivated to reactive metabolites which bind covalently to DNA and subsequently initiate carcinogenesis. PAHs have been well established as an enzyme inducer of cytochrome P450 (CYP) such as CYP1A1 and CYP1A2. Caffeine is primarily metabolized by CYP1A2 to paraxanthine, so it has been used as a specific probe for assessing CYP1A2 activity. The purpose of this study was to compare CYP1A2 activity in female subjects that were automobile exhaust exposed and non-automobile exhaust exposed using serum paraxanthine/caffeine ratio as an index. Each subject took a 180 mg single oral dose of caffeine solution. Blood samples were collected before and 5 hours after caffeine intake. Serum samples were separated by centrifugation and stored at -20 degrees C until analysis by high performance liquid chromatography (HPLC). Carbon monoxide (CO) level in blood was also detected using spectrophotometer. The results showed that serum paraxanthine/caffeine ratio in exposed subjects was significantly higher than non-exposed subjects (mean +/- SE of 0.45 +/- 0.05 and 0.33 +/- 0.03, respectively; p < 0.05). CO level in exposed subjects was also significantly higher than non-exposed subjects (mean +/- SE of 4.03 +/- 0.21 and 3.01 +/- 0.18, respectively; p < 0.05).

CONCLUSION

Paraxanthine/caffeine ratio, as an index for CYP1A2 activity, can be used to determine PAHs exposure. Automobile exhaust exposed subjects demonstrated significantly higher CYP1A2 activity than that of the non-exposed subjects. Exposed subjects have a possibly higher risk of chemical carcinogenesis.

Pharmacokinetics of an ultralong sustained-release theophylline formulation when given twice daily in elderly patients with chronic obstructive pulmonary disease: monitoring implications

The steady-state pharmacokinetics of an ultralong sustained release formulation of theophylline (Unilong) twice daily (bid) in elderly hospitalized patients suffering from chronic obstructive pulmonary disease (COPD) have been studied in order to establish guidelines for monitoring. The study was carried out in 37 patients (33 men), aged 60-87 years. Samples were collected from 0 to 12 h after the morning dose on day 9 of treatment with 250 mg bid (n=25) or 375 mg bid (n=12). Considerable variability in apparent clearance (range 0.33-1.49 ml/min per kg of ideal body weight), Css(min)/D (range 0.28-1.86), Css(max)/D (range 0.65-2.33) and (Css(max)-Css(min))/Css(avg) (range 0.18-0.80) was observed. There was no significant correlation between the patient's age and apparent clearance within this elderly population. The concentration-to-dose ratio and the relationship between the steady-state plasma concentration at different times during the dosage interval and Css(avg) are described. It is concluded that the interpatient variability in peak-trough fluctuation of this formulation was higher than that described in healthy volunteers by other investigators, and that the apparent clearance did not decrease with age within this elderly population with COPD. The importance of theophylline monitoring is emphasized and rules to estimate Css(avg) and Css(5h) from Css(0h) when only a single sample obtained before the morning dose is available are given.

Effect of a divided caffeine dose on endurance cycling performance, postexercise urinary caffeine concentration, and plasma paraxanthine

This study compared the effects of a single and divided dose of caffeine on endurance performance and on postexercise urinary caffeine and plasma paraxanthine concentrations. Nine male cyclists and triathletes cycled for 90 min at 68% of maximal oxygen uptake, followed by a self-paced time trial (work equivalent to 80% of maximal oxygen uptake workload over 30 min) with three randomized, balanced, and double-blind interventions: 1) placebo 60 min before and 45 min into exercise (PP); 2) single caffeine dose (6 mg/kg) 60 min before exercise and placebo 45 min into exercise (CP); and 3) divided caffeine dose (3 mg/kg) 60 min before and 45 min into exercise (CC). Time trial performance was unchanged with caffeine ingestion (P = 0.08), but it tended to be faster in the caffeine trials (CP: 24.2 min and CC: 23.4 min) compared with placebo (PP: 28.3 min). Postexercise urinary caffeine concentration was significantly lower in CC (3.8 micro g/ml) compared with CP (6.8 micro g/ml). Plasma paraxanthine increased in a dose-dependent fashion and did not peak during exercise. In conclusion, dividing a caffeine dose provides no ergogenic effect over a bolus dose but reduces postexercise urinary concentration.

Isozyme-specific induction of low-dose aspirin on cytochrome P450 in healthy subjects

OBJECTIVE

This study was designed to define the effect of low-dose aspirin administration on the activity of cytochrome P450 (CYP) in normal human subjects.

METHODS

Aspirin, 50 mg daily, was given for 14 days to 18 nonsmoking healthy male volunteers. A modified 5-drug cocktail procedure consisting of caffeine, mephenytoin, metoprolol, chlorzoxazone, and midazolam was performed to simultaneously assess in vivo activity of CYP1A2, CYP2C19, CYP2D6, CYP2E1, and CYP3A, respectively. The activities were assessed on 4 occasions including at baseline, after 7 and 14 daily doses of aspirin, and at 7 days after discontinuation of aspirin. Concentrations of parent drugs and corresponding metabolites in biologic samples were assayed by reversed-phase HPLC.

RESULTS

Both 7-day and 14-day aspirin intake increased the activity of CYP2C19 significantly, as indicated by 4-hydroxymephenytoin urinary recovery (P <.001). Induction of low-dose aspirin on CYP2C19 was time-dependent. CYP3A activity indices increased moderately but significantly by both 7-day and 14-day aspirin treatment (P <.05), but the percentage changes in CYP3A activity indices were not significant. Low-dose aspirin had no effect on CYP1A2, CYP2D6, and CYP2E1 in vivo activity by either 7-day or 14-day treatment.

CONCLUSIONS

The effect of low-dose aspirin on CYPs was enzyme-specific. Both 7-day and 14-day low-dose aspirin induced the in vivo activities of CYP2C19 but did not affect the activities of CYP1A2, CYP2D6, and CYP2E1. The effect of low-dose aspirin on CYP3A activity awaits further confirmation. When low-dose aspirin is used in combination with drugs that are substrates of CYP2C19, doses of the latter should be adjusted to ensure their efficacy.