Influence of endogenous and exogenous effectors on the pharmacokinetics of theophylline. Focus on biotransformation

Theophylline Acetaldehyde as the Initial Product in Doxophylline Metabolism in Human Liver

Doxophylline (DOXO) and theophylline are widely used as bronchodilators for treating asthma and chronic obstructive pulmonary disease, and DOXO has a better safety profile than theophylline. How DOXO's metabolism and disposition affect its antiasthmatic efficacy and safety remains to be explored. In this study, the metabolites of DOXO were characterized. A total of nine metabolites of DOXO were identified in vitro using liver microsomes from human and four other animal species. Among them, six metabolites were reported for the first time. The top three metabolites were theophylline acetaldehyde (M1), theophylline-7-acetic acid (M2), and etophylline (M4). A comparative analysis of DOXO metabolism in human using liver microsomes, S9 fraction, and plasma samples demonstrated the following: 1) The metabolism of DOXO began with a cytochrome P450 (P450)-mediated, rate-limiting step at the C ring and produced M1, the most abundant metabolite in human liver microsomes. However, in human plasma, the M1 production was rather low. 2) M1 was further converted to M2 and M4, the end products of DOXO metabolism in vivo, by non-P450 dismutase in the cytosol. This dismutation process also relied on the ratio of NADP+/NADPH in the cell. These findings for the first time elucidated the metabolic sites and routes of DOXO metabolism in human. SIGNIFICANCE STATEMENT: We systematically characterized doxophylline metabolism using in vitro and in vivo assays. Our findings evolved the understandings of metabolic sites and pathways for methylxanthine derivatives with the aldehyde functional group.

Age-Associated Theophylline Metabolic Activity Corresponds to the Ratio of 1,3-Dimethyluric Acid to Theophylline in Mice

Age is known as one of influencing factor for theophylline (TP)-metabolizing capacity. In a previous our study, the ratio of TP and its major metabolite 1,3-dimethyluric acid (DMU) in serum (DMU/TP) is a useful index to estimate TP-metabolizing capacity, and this value markedly increased by influencing factor, such as the history of smoking. However, it is unknown whether DMU/TP values in serum reflect age-associated changes of TP-metabolizing capacity. In this study, the effect of age on the DMU/TP values in serum were investigated using mice of different age due to the limited blood sampling in human. The concentrations of TP and its metabolites in mouse serum were simultaneously measured using HPLC. As observed in human serum, serum TP concentrations were closely correlated with DMU concentration in mice, which indicates that the DMU/TP ratio is a good indicator of TP metabolic ability in mice. When TP was administered subcutaneously in 2-28-week-old mice, age-associated changes in the DMU/TP ratio in mice were observed. In conclusion, age-associated changes in TP-metabolizing capacity can be estimated by the DMU/TP ratio in serum.

Effects of ephedra water decoction and cough tablets containing ephedra and liquorice on CYP1A2 and the pharmacokinetics of theophylline in rats

Ephedra water decoction (EWD) and cough tablets containing ephedra and liquorice (maxing cough tablets, MXCT) have been used widely in the treatment of asthma. In the clinic, EWD and MXCT may be prescribed with theophylline, one of the most popular antiasthmatic drugs and a typical substrate of cytochrome P450 (CYP) 1A2. So in the present study the potential effects of EWD and MXCT on CYP1A2 activity and the pharmacokinetics of theophylline in rats were evaluated. In the in vivo CYP1A2 activity research, the rats were given oral caffeine (10 mg/kg) after a 14 day pretreatment with EWD (18 g/kg) and MXCT (0.1, 0.2 or 0.4 g/kg). Then the CYP 1A2 activity was expressed by using the caffeine metabolic ratio (CMR). The results showed that the CMR increased markedly compared with the control groups. In the pharmacokinetics experiment, the rats were given oral theophylline (10 mg/kg) after a 14 day pretreatment with EWD (18 g/kg) and MXCT (0.2 g/kg). The results showed that the AUC(0-24 h) and C(max) of theophylline were reduced markedly compared with the control groups. These results demonstrated that EWD or MXCT pretreatment obviously induced CYP1A2 activity, therefore, speeding up the metabolism of theophylline. The concomitant use of EWD or MXCT may decrease the effect of theophylline in rats.

Usefulness of the simultaneous determination of serum levels of theophylline and its metabolites in patients medicated with theophylline preparation

OBJECTIVE

Measurement of the serum level of theophylline is essential for its proper use; however, it is difficult to infer the metabolic ability of individual patients by only the serum theophylline level and to decide the appropriate medication. In this study, we simultaneously measured serum theophylline and metabolite levels in patients treated with theophylline, and investigated their usefulness.

EXPERIMENTAL

The subjects were asthma patients who visited the outpatient clinic of Respiratory Medicine, St Luke's International Hospital, between April and October 2003, and were medicated with sustained-release theophylline tablets (Theodur®). The serum level of theophylline and its metabolites was measured by HPLC in patients who gave written consent.

RESULTS

A strong correlation was noted between the serum theophylline (TP) and 1,3-dimethyluric acid (DMU) levels of 52 patients (r = 0.670), and DMU/TP was about 0.04. In a patient whose the DMU/TP was 0.216, it was recognized that metabolic ability was promoted due to a history of smoking.

DISCUSSION

In this study, it was shown that simultaneous measurement by HPLC of the serum level of theophylline and its metabolites and DMU/TP was useful to assess the metabolic ability of individual patients.

Pharmacokinetics and metabolism of natural methylxanthines in animal and man

Caffeine, theophylline, theobromine, and paraxanthine administered to animals and humans distribute in all body fluids and cross all biological membranes. They do not accumulate in organs or tissues and are extensively metabolized by the liver, with less than 2% of caffeine administered excreted unchanged in human urine. Dose-independent and dose-dependent pharmacokinetics of caffeine and other dimethylxanthines may be observed and explained by saturation of metabolic pathways and impaired elimination due to the immaturity of hepatic enzyme and liver diseases. While gender and menstrual cycle have little effect on their elimination, decreased clearance is seen in women using oral contraceptives and during pregnancy. Obesity, physical exercise, diseases, and particularly smoking and the interactions of drugs affect their elimination owing to either stimulation or inhibition of CYP1A2. Their metabolic pathways exhibit important quantitative and qualitative differences in animal species and man. Chronic ingestion or restriction of caffeine intake in man has a small effect on their disposition, but dietary constituents, including broccoli and herbal tea, as well as alcohol were shown to modify their plasma pharmacokinetics. Using molar ratios of metabolites in plasma and/or urine, phenotyping of various enzyme activities, such as cytochrome monooxygenases, N-acetylation, 8-hydroxylation, and xanthine oxidase, has become a valuable tool to identify polymorphisms and to understand individual variations and potential associations with health risks in epidemiological surveys.

Mechanism-based inhibition of human liver microsomal cytochrome P450 1A2 by zileuton, a 5-lipoxygenase inhibitor

Zileuton, a 5-lipoxygenase inhibitor, was evaluated as an inhibitor of cytochrome P450 activity in human liver microsomes. In the absence of preincubation, the racemate was found to be a weak inhibitor (IC50 > 100 microM) of phenacetin O-deethylation (POD) (CYP1A2), paclitaxel 6alpha-hydroxylation (CYP2C8), diclofenac 4'-hydroxylation (CYP2C9), (S)-mephenytoin 4'-hydroxylation (CYP2C19), bufuralol 1'-hydroxylation (CYP2D6), testosterone 6beta-hydroxylation (CYP3A4), chlorzoxazone 6-hydroxylation (CYP2E1), and bupropion hydroxylation (CYP2B6). When preincubated with NADPH-fortified human liver microsomes in the absence of substrate, zileuton (racemate) was shown to inhibit POD. The effect was NADPH-, time-, and concentration-dependent, and was characterized by a kinact (maximal rate of enzyme inactivation) and apparent KI(inhibitor concentration that supports half the maximal rate of inactivation) of 0.035 min(-1) and 117 microM, respectively (kinact/KIratio of 0.0003 min-1 microM(-1)). Preincubation-dependent inhibition of POD activity was also observed with the individual (S)-(-)- and (R)-(+)-enantiomers of zileuton [(S)-(-)-zileuton; kinact, 0.037 min(-1), KI, 98.2 microM, kinact/KIratio, 0.0004 min(-1) microM(-1); (R)-(+)-zileuton; kinact, 0.012 min(-1), KI, 66.6 microM, kinact/KIratio, 0.0002 min(-1) microM(-1)]. In addition, the inhibition of CYP1A2 was not reversed in the presence of reduced glutathione, catalase, and superoxide dismutase and was refractory to dialysis. Therefore, zileuton was characterized as a mechanism-based inhibitor of human liver microsomal CYP1A2. Mechanism-based inhibition of CYP1A2 may explain why zileuton decreases the oral clearance of antipyrine, propranolol, (R)-warfarin, and theophylline, at doses that have a minimal effect on the pharmacokinetics of (S)-warfarin, phenytoin, and terfenadine.

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.

Drug metabolism and drug interactions in the elderly

In the elderly concomitant use of several drugs (polypharmacy) is very common. Thus, the risk for drug interactions might be increased in this population. Since most drugs are hepatically eliminated by various metabolic pathways, liver function has to be considered as an additional factor modifying drug response. This chapter focuses on the hepatic mechanisms of interactions, especially on various inhibitors and inducers of the most important cytochrome P450 isoenzymes involved in drug metabolism. In addition, age-dependent changes in liver function are addressed. Based on pharmacokinetic results with different probe drugs, some inconsistencies in this area are discussed. The most important metabolic drug-drug interactions are independent of the age of the patients. However, since elderly patients consume a greater proportional share of drugs, they represent a population at risk for interactions. Awareness of this clinical problem may help to diminish those risks.

Effect of alosetron on theophylline pharmacokinetics

AIMS

To examine the potential for alosetron to alter the pharmacokinetics of theophylline by inhibiting its metabolism, as suggested by in vitro and in vivo effects on CYP1A2 activity.

METHODS

Ten healthy female volunteers received theophylline 200 mg twice daily alone for 8 days and with alosetron 1 mg twice daily for 15 days in this randomized, placebo-controlled, two-way-crossover study.

RESULTS

Alosetron had no significant effect on theophylline plasma concentrations (Cmax approximately 9 microg ml(-1), AUC approximately 90 microg ml(-1) h) or oral formation clearance of three major metabolites produced via CYP1A2: 3-methylxanthine, 1-methylurate and 1,3-dimethylurate (5, 7 and 16 ml min(-1), respectively). Concomitant administration of alosetron and theophylline was well tolerated.

CONCLUSIONS

The absence of a clinical drug interaction involving inhibition of theophylline metabolism by alosetron was not predicted by in vitro and in vivo metabolic probe data.

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.

Lack of Pharmacokinetic Interaction between Moxifloxacin, a Novel 8-Methoxyfluoroquinolone, and Theophylline

OBJECTIVE

To investigate the plasma and urinary pharmacokinetics, safety and tolerability of theophylline and moxifloxacin after single and repeated doses of either compound administered alone or concomitantly with the other.

DESIGN

This was a randomised, multiple-dose, period-balanced, 3-way crossover study in healthy volunteers.

PARTICIPANTS

12 nonsmoking healthy volunteers, 21 to 30 years of age were included in this study.

METHODS

The investigational medications, all given orally, were as follows: treatment A, moxifloxacin 200mg alone; treatment B, theophylline 400mg alone; treatment C, theophylline 400mg plus moxifloxacin 200mg. Each drug or combination was given twice daily on days 2 to 4 of the 5-day study period and as single morning doses on days 1 and 5. The study periods were separated by 1-week washout intervals. The plasma and urinary pharmacokinetics of moxifloxacin and theophylline were characterised after the first (morning of day 1) and eighth (morning of day 5) doses.

RESULTS

At steady state, the plasma pharmacokinetics of theophylline for treatments B and C proved equivalent in terms of maximum concentration (Css(max)) and bodyweight- and dose-normalised Css(max) lestimated true ratio 96%, 90% confidence interval (CI) 87 to 105%] and also in terms of area under the concentration-time curve from 0 to 12 hours (AUCss(tau)) and normalised AUCss(tau) (ratio 95%, 90% CI 85 to 107%); the median times to Cmax(tmax) were also similar (5.0 and 6.0 hours for treatments B and C, respectively). The plasma pharmacokinetics of moxifloxacin for treatments A and C were equivalent with respect to Css(max) (estimated true ratio 109%, 90% CI 97 to 123%) and AUCss(tau) (ratio 104%, 90% CI 100 to 108%); the median tmax values were also similar (0.5 and 1.0 hour for treatments A and C, respectively). The treatments were well tolerated.

CONCLUSIONS

Moxifloxacin - in contrast to some older quinolones - does not interact pharmacokinetically with theophylline, confirming preclinical results on the absence of cytochrome P450-mediated metabolism.

Effect of age on the profile of alkanes in normal human breath

Ethane and pentane in breath are markers of oxidative stress, produced by ROS-mediated lipid peroxidation of n-3 and n-6 polyunsaturated fatty acids (PUFAs), but little is known about other n-alkanes in normal human breath. We investigated the spectrum of alkanes in normal human alveolar breath, and their variation with age. Fifty normal humans were studied (age range 23-75, median 35). Volatile organic compounds (VOCs) in alveolar breath were captured on sorbent traps and assayed by gas chromatography and mass spectroscopy. Alveolar gradients (concentration in breath minus concentration in ambient room air) of alkanes were determined. C4-C20 alkanes were observed in breath and room air. Their mean alveolar gradients were negative from C4 to C12 and positive from C13 to C20. The mean alveolar gradients of four alkanes (C5-C8) were significantly less negative in the older subjects (p < 0.05). There were no significant differences between males and females. Normal human breath contained a spectrum of alkanes which may include new markers of oxidative stress. The mean rate of clearance (via cytochrome p450) exceeded the mean rate of synthesis (by ROS-mediated oxidative stress) for C4-C12 alkanes, while synthesis was greater than clearance for C13-C20 alkanes. The elevated alkane profile in older subjects was consistent with an age-related increase in oxidative stress, though an age-related decline in alkane clearance rate may have contributed.

Influence of gatifloxacin, a new quinolone antibacterial, on pharmacokinetics of theophylline

The influence of gatifloxacin, a new quinolone antibacterial, on the pharmacokinetics of theophylline (TP) was studied in five healthy adult male volunteers. After 200 mg of TP in sustained-release preparation was administered twice daily for 4 consecutive days, the same dose of TP and 200 mg of gatifloxacin were administered concurrently to the subjects twice daily for 5 consecutive days. Comparison of the pharmacokinetic parameters on day 4 of TP alone, and days 3 and 5 of co-administration revealed no significant differences in the maximum concentrations (Cmax), areas under the serum concentration-time curve (AUC0-12), total body clearances, and the amounts and proportions of TP and its metabolites in urine. One subject, however, showed 55% and 44% increases in Cmax and AUC0-12, respectively, on day 5 of co-administration relative to values on day 4 of TP alone. Thus, co-administration of gatifloxacin seemed to have little effect on the pharmacokinetics of TP. Further studies will be necessary to clarify the pharmacokinetic interaction between quinolones and TP, and it is recommended that, when both gatifloxacin and TP are administered, the background of the patients, such as their age, liver and cardiac functions, and other concomitant medications, be considered.

Effect of indinavir on the single-dose pharmacokinetics of theophylline in healthy subjects

The effect of multiple doses of indinavir on the pharmacokinetics of a single dose of theophylline was investigated in 16 healthy male subjects using a randomized, double-blind, placebo-controlled, parallel-group study design. On days 1 and 7, all of the subjects received a single oral 250 mg dose of theophylline. From days 2 to 7, the subjects received orally administered 800 mg doses of indinavir or a matched placebo every 8 hours. On day 7, theophylline and indinavir (or a placebo) were coadministered. The geometric mean AUC(0-24 h) of theophylline increased 18% when coadministered with indinavir compared to when theophylline was administered alone. This small increase in AUC(0-24 h), although considered statistically significant, did not meet the prespecified criterion for clinical significance. The geometric mean Cmax of theophylline, when coadministered with indinavir, was within 8% of theophylline when administered alone. The mean tmax (+/- SD) value for theophylline, when coadministered with indinavir (0.9 +/- 0.5 h), was comparable to that observed for theophylline alone (1.0 +/- 0.5 h). In conclusion, the administration of multiple doses of indinavir followed by a single dose of theophylline did not appear to result in a clinically significant pharmacokinetic interaction for theophylline.

Clinical pharmacokinetics of vasodilators. Part II

Stimulating cardiac beta 1-adrenoceptors with oxyfedrine causes dilatation of coronary vessels and positive inotropic effects on the myocardium. beta 1-adrenergic agonists increase coronary blood flow in nonstenotic and stenotic vessels. The main indication for the use of the phosphodiesterase inhibitors pamrinone, mirinone, enoximone and piroximone is acute treatment of severe congestive heart failure. Theophylline is indicated for the treatment of asthma, chronic obstructive pulmonary disease, apnea in preterm infants ans sleep apnea syndrome. Severe arterial occlusive disease associated with atherosclerosis can be beneficially affected by elcosanoids. These drugs must be administered parenterally and have a half-life of only a few minutes. Sublingual or buccal preparations of nitrates are the only prompt method (within 1 or 2 min) of terminating anginal pain, except for biting nifedipine capsules. The short half-life (about 2.5 min) of nitroglycerin (glyceryl trinitrate) makes long term therapy impossible. Tolerance is a problem encountered with longer-acting nitric oxide donors. Knowledge of the pharmacokinetic properties of vasodilating drugs can prevent a too sudden and severe blood pressure decrease in patients with chronic hypertension. In considering the administration of a second dose, or another drug, the time necessary for the initially administered drug to reach maximal efficacy should be taken into account. In hypertensive emergencies urapidil, sodium nitroprusside, nitroglycerin, hydralazine and phentolamine are the drugs of choice, with the addition of beta-blockers during catecholamine crisis or dissecting aortic aneurysm. Childhood hypertension is most often treated with angiotensin-converting enzyme (ACE) inhibitors or calcium antagonists, primarily nifedipine. Because of the teratogenic risk involved with ACE inhibitors, extreme caution must be exercised when prescribing for adolescent females. The propagation of health benefits to breast-fed infants, combined with more women delaying pregnancy until their fourth decade, has entailed an increase in the need for hypertension management during lactation. Low dose hydrochlorothiazide, propranolol, nifedipine and enalapril or captopril do not pose enough of a risk of preclude breastfeeding in this group. The most frequently used antihypertensive agents during pregnancy are methyldopa, labetalol and calcium channel antagonists. Methyldopa and beta-blockers are the drugs of choice for treating mild to moderate hypertension. Prazosin and hydralazine are used to treat moderate to severe hypertension and hydralazine, urapidil or labetalol are used to treat hypertensive emergencies. The use of overly aggressive antihypertensive therapy during pregnancy should be avoided so that adequate uteroplacental blood flow is maintained. Methyldopa is the only drug accepted for use during the first trimester of pregnancy.

Effect of terbinafine on theophylline pharmacokinetics in healthy volunteers

Twelve healthy volunteers were enrolled in an open-label, randomized, crossover study. Subjects received single doses of theophylline (5 mg/kg) with and without multiple-dose terbinafine, and 11 blood samples were collected over 24 h. The study phases were separated by a 4-week washout period. Theophylline serum data were modeled via noncompartmental analysis. When the control phase (i.e., no terbinafine) was compared to the treatment phase (terbinafine), theophylline exposure (the area under the serum concentration-time curve from time zero to infinity) increased by 16% (P = 0.03), oral clearance decreased by 14% (P = 0.04), and half-life increased by 24% (P = 0.002). No significant changes in other theophylline pharmacokinetic parameters were evident.

Effect of combination therapy with ciprofloxacin and clarithromycin on theophylline pharmacokinetics in healthy volunteers

Five adults completed this four-way randomized crossover study to compare the effects of oral treatment with ciprofloxacin, clarithromycin, and a combination of the two drugs on theophylline pharmacokinetics. The area under the concentration-time curve for theophylline during combination therapy was not different from that for ciprofloxacin alone. Beta error may explain this finding, but any real effect from combination treatment appears to be clinically unimportant.