Pharmacokinetic interactions between theophylline and other medication (Part II)

Doxofylline for Pediatric Asthma Steps 1-4. Pediatric Asthma: New Role for an Old Drug

The panoply of anti-asthma drugs for children between 6 and 18 years is not limited to those reported in the guidelines. In this review, we will re-assess the role of doxofylline, a xanthine characterized by a much higher handling than that of theophylline, as add-on treatment in pediatric asthma grade 1-4. Ten studies evaluated doxofylline in the treatment of asthma of patients non-responsive to the first-line inhaled corticosteroids. Of these, two included children and one was exclusively pediatric. According to their results, doxofylline exerts a powerful bronchodilator and anti-inflammatory activity, which can be exploited when the inhaled oral corticosteroids are not sufficient to get the desired effect of reducing symptoms. Unlike theophylline, doxofylline does not require blood testing. It can be administered together with or as an alternative to a series of other drugs considered in additional therapy.

Xanthines and Phosphodiesterase Inhibitors

Theophylline is an orally acting xanthine that has been used since 1937 for the treatment of respiratory diseases including asthma and chronic obstructive pulmonary disease (COPD). However, in most treatment guidelines, xanthines have now been consigned to third-line therapy because of their narrow therapeutic window and propensity for drug-drug interactions. However, lower than conventional doses of theophylline considered to be bronchodilator are now known to have anti-inflammatory actions of relevance to the treatment of respiratory disease. The molecular mechanism(s) of action of theophylline are not well understood, but several potential targets have been suggested including non-selective inhibition of phosphodiesterases (PDE), inhibition of phosphoinositide 3-kinase, adenosine receptor antagonism and increased activity of certain histone deacetylases. Although theophylline has a narrow therapeutic window, other xanthines are in clinical use that are claimed to have a better tolerability such as doxofylline and bamifylline. Nonetheless, xanthines still play an important role in the treatment of asthma and COPD as they can show clinical benefit in patients who are refractory to glucocorticosteroid therapy, and withdrawal of xanthines from patients causes worsening of disease, even in patients taking concomitant glucocorticosteroids.More recently the orally active selective PDE4 inhibitor, roflumilast, has been introduced into clinical practice for the treatment of severe COPD on top of gold standard treatment. This drug has been shown to improve lung function in patients with severe COPD and to reduce exacerbations, but is dose limited by a range side effect, particularly gastrointestinal side effects.

Comparative Effectiveness of 12 Treatment Strategies for Preventing Contrast-Induced Acute Kidney Injury: A Systematic Review and Bayesian Network Meta-analysis

BACKGROUND

To simultaneously evaluate the relative efficacy of multiple pharmacologic strategies for preventing contrast-induced acute kidney injury (AKI).

STUDY DESIGN

Systematic review containing a Bayesian network meta-analysis of randomized controlled trials.

SETTING & POPULATION

Participants undergoing diagnostic and/or interventional procedures with contrast media.

SELECTION CRITERIA FOR STUDIES

Randomized controlled trials comparing the active drug treatments with each other or with hydration alone.

INTERVENTION

Any of the following drugs in combination with hydration: N-acetylcysteine (NAC), theophylline (aminophylline), fenoldopam, iloprost, alprostadil, prostaglandin E₁, statins, statins plus NAC, bicarbonate sodium, bicarbonate sodium plus NAC, ascorbic acid (vitamin C), tocopherol (vitamin E), α-lipoic acid, atrial natriuretic peptide, B-type natriuretic peptide, and carperitide.

OUTCOMES

The occurrence of contrast-induced AKI.

RESULTS

The trial network included 150 trials with 31,631 participants and 4,182 contrast-induced AKI events assessing 12 different interventions. Compared to hydration, ORs (95% credible intervals) for contrast-induced AKI were 0.31 (0.14-0.60) for high-dose statin plus NAC, 0.37 (0.19-0.64) for high-dose statin alone, 0.37 (0.17-0.72) for prostaglandins, 0.48 (0.26-0.82) for theophylline, 0.62 (0.40-0.88) for bicarbonate sodium plus NAC, 0.67 (0.54-0.81) for NAC alone, 0.64 (0.41-0.95) for vitamins and analogues, 0.70 (0.29-1.37) for natriuretic peptides, 0.69 (0.31-1.37) for fenoldopam, 0.78 (0.59-1.01) for bicarbonate sodium, and 0.98 (0.41-2.07) for low-dose statin. High-dose statin plus NAC or high-dose statin alone were likely to be ranked the best or the second best for preventing contrast-induced AKI. The overall results were not materially changed in metaregressions or subgroup and sensitivity analyses.

LIMITATIONS

Patient-level data were unavailable; unable to include some treatment agents; low event rates; imbalanced distribution of participants among treatment strategies.

CONCLUSIONS

High-dose statins plus hydration with or without NAC might be the preferred treatment strategy to prevent contrast-induced AKI in patients undergoing diagnostic and/or interventional procedures requiring contrast media.

Pharmacokinetic Interactions Between Isoniazid and Theophylline in Rats

Pharmacokinetic interactions between isoniazid and theophylline were studied in male Wistar rats, 206±17 g. Concomitant oral administration of 2 × 5 mg kg−1 isoniazid accelerated slightly the disposition of theophylline (10 mg kg−1, i.v.) whereas 2 × 25 mg kg−1 isoniazid slowed it marginally. The differences in distribution volume, systemic clearance and area under the concentration-time curve (AUC) between the high and the low dose, however, were statistically significant. One week pretreatment with 10 mg kg−1 isoniazid tended towards inhibition (significant decrease of systemic clearance, increase of AUC) and 50 mg kg−1 to acceleration (decrease of half-life, mean residence time and AUC, increase of systemic clearance) of theophylline disposition. After oral pretreatment with 20 mg kg−1 theophylline, neither the kinetics of free isoniazid (50 mg kg−1, i.v.) and the amount acetylated nor the acetylation indices differed from the controls. There was no evidence that concomitant or subacute administration of different doses of isoniazid affects major metabolic pathways of theophylline or that prolonged theophylline treatment interacts with the N-acetylation capacity.

Effects of CYP inducers and inhibitors on the pharmacokinetics of intravenous theophylline in rats: involvement of CYP1A1/2 in the formation of 1,3-DMU

The types of hepatic cytochrome P450 (CYP) isozymes responsible for the metabolism of theophylline and for the formation of 1,3-dimethyluric acid (1,3-DMU) in rats in-vivo does not seem to have been studied at the dose ranges of dose-independent metabolic disposition of theophylline in rats (up to 10 mg kg(-1)). Therefore, theophylline (5 mg kg(-1)) was administered i.v. to male Sprague-Dawley rats pretreated with various inducers and inhibitors of CYP isozymes. In rats pretreated with 3-methylcholanthrene (3-MC), orphenadrine or dexamethasone (main inducers of CYP1A1/2, CYP2B1/2 and CYP3A1/2, respectively, in rats), the time-averaged non-renal clearance (CLNR) of theophylline was significantly faster than in their respective controls (1260, 42.7 and 69.0% increases, respectively). However, in rats pretreated with troleandomycin (a major inhibitor of CYP3A1/2 in rats), CLNR was significantly slower than in the controls (50.7% decrease). The 24 h urinary excretion of 1,3-DMU was increased significantly only in rats pretreated with 3-MC. The ratio of area under the curve for 1,3-DMU and theophylline (AUC1,3-DMU/AUCtheophylline) was increased significantly in rats pretreated with 3-MC (160% increase) and decreased significantly in rats pretreated with troleandomycin (50.1% decrease); however, the ratio was not increased in rats pretreated with dexamethasone. These data suggest that theophylline is primarily metabolized via CYP1A1/2, CYP2B1/2, and CYP3A1/2, and that 1,3-DMU is primarily formed via CYP1A1/2, and possibly CYP3A1/2, in rats.

Lack of effect of aciclovir on metabolism of theophylline and expression of hepatic cytochrome P450 1A2 in rats

There is an interesting clinical report indicating that aciclovir, which is mainly excreted into urine, decreases the systemic clearance of theophylline by inhibiting cytochrome P450 (CYP) 1A2-mediated metabolism. In this study, we investigated the effect of aciclovir on the metabolism of theophylline, and on the activity and expression of hepatic CYP1A2 in rats. Theophylline (10 mg/kg) was injected intravenously into rats treated with two different dosages of aciclovir. When theophylline was simultaneously administered with aciclovir (50 mg/kg), the systemic clearance of theophylline and metabolic clearance of its major metabolites, 1-methyluric acid and 1,3-dimethyluric acid, were unchanged. In place of theophylline, when 1-methyl-3-propylxanthine (2.5 mg/kg), which is almost metabolized by CYP1A2 in rats, was coadministered intravenously with aciclovir (50 mg/kg), the pharmacokinetics of 1-methyl-3-propylxanthine was also unchanged. When theophylline was administered to rats pretreated with repeated intraperitoneal injections of aciclovir (25 mg/kg twice daily for 3 d), no significant differences in the systemic clearance of theophylline and its metabolic clearance to 1-methyluric acid and 1,3-dimethyluric acid were observed between the control and aciclovir-treated rats. This dosage of aciclovir did not change the activity of 7-ethoxyresorufin O-dealkylation, which is represented as CYP1A2 activity. In Western blot analysis, no significant change in the protein levels of hepatic CYP1A2 was observed between the control and aciclovir-treated rats. The present study suggests that aciclovir has no effect on the pharmacokinetics and metabolism of theophylline and on the activity and expression of hepatic CYP1A2 in rats.

Clinical Pharmacology of Cilomilast

Chronic obstructive pulmonary disease (COPD) is a multicomponent, chronic inflammatory disease of the lungs with systemic complications. The majority of the inflammation occurs in the peripheral airways and lung parenchyma. It is a progressive disease, leading to disability and eventual death, despite conventional therapy. Inflammatory activity can be reduced by increasing intracellular cyclic adenosine-3',5'-monophosphate (cAMP) through inhibition of phosphodiesterase (PDE) IV, the principal PDE isoenzyme within pro-inflammatory cells, including eosinophils, mast cells, macrophages, lymphocytes, neutrophils and epithelial cells. PDE IV inhibition also has other effects, including relaxation of airway smooth muscle, suppression of smooth muscle mitogenesis and modulation of excitatory activity in pulmonary nerves. Cilomilast is a systemically available, second-generation, selective PDE IV inhibitor. It retains the therapeutic activity of the first-generation PDE IV inhibitors but lacks their profound emetic effect. Cilomilast is the first drug to demonstrate a reduction of tissue cells considered central to the ongoing inflammatory process (macrophages and CD8+ lymphocytes) in patients with stable COPD. Cilomilast is completely absorbed following oral administration and has negligible first-pass metabolism. It exhibits linear pharmacokinetics, with low between-subject variability. Cilomilast is highly protein bound (99.4%), but this binding is concentration-independent at clinically relevant doses, and it has a small volume of distribution at steady state (17L). Plasma clearance (approximately 2 L/h) is almost entirely metabolic, through multiple parallel pathways. Its terminal elimination half-life is approximately 6.5 hours and steady state is rapidly achieved with twice-daily administration. The most abundant metabolite, formed by the action of cytochrome P450 2C8, has <10% of the activity of the parent molecule. Cilomilast pharmacokinetics in COPD patients were consistent with those in healthy subjects. Smoking, age and ethnicity had no clinically relevant effects. Total plasma cilomilast pharmacokinetic parameters did not change significantly with renal or hepatic impairment, but concentrations of unbound cilomilast increased with declining renal or hepatic function. Cilomilast had no clinically relevant interactions with a range of drugs likely to be coadministered to patients with COPD, with the exception of erythromycin where concurrent administration with cilomilast was associated with an increased incidence of gastrointestinal adverse events, a pharmacodynamic interaction predicted by their secondary pharmacology. Nausea was the principal adverse reaction seen in healthy subjects taking cilomilast, but this was reduced by administration with food or by use of simple dose-escalation regimens. Cilomilast has not shown a propensity for any of the serious cardiac or neurological adverse effects associated with theophylline. Cilomilast exhibits favourable and predictable pharmacokinetics, has few clinically relevant drug-drug interactions and has demonstrated effects on measures of inflammation of potential benefit in the treatment of COPD. It is generally well tolerated and has not generated safety concerns in any clinical study.

A prospective clinical study of theophylline safety in 3810 elderly with asthma or COPD

A large-scale prospective study was conducted in 3810 Japanese elderly (> or =65 years old) patients with asthma or chronic obstructive pulmonary disease (COPD) who had been treated with sustained-release theophylline tablets (THEODUR) at a dose of 400 mg/day for 1-6 months, in principle. Among 3798 protocol-complying patients (mean age: 73.8 +/- 0.10 years, 1997 with COPD), 261 theophylline-related adverse events were observed in 179 (4.71%) patients. The 5 most frequently observed adverse events were "nausea" (40 episodes, 1.05%), "loss of appetite" (22 episodes, 0.56%), "hyperuricemia" (16 episodes, 0.42%), "palpitation" (15 episodes, 0.39%), and "increased alkaline phosphatase" (11 episodes, 0.28%). No convulsions were reported. Six patients had serious adverse events. The incidence of theophylline-related adverse events was higher in patients with hepatic disease (odds ratio: 1:1.81) and in patients with arrhythmia (odds ratio: 1:1.88). Blood drug concentration measurements in 736 patients indicated that the drug levels were < or =15 microg/ml in 641 patients (87.1%), and no correlation was noted between dose and theophylline-related adverse events. These results suggest that sustained-release theophylline can be used safely in elderly patients with asthma or COPD.

Effect of levofloxacin on theophylline clearance during theophylline and clarithromycin combination therapy

OBJECTIVE

To report a case of decreased theophylline clearance by the addition of levofloxacin in a patient receiving theophylline and clarithromycin.

CASE SUMMARY

A 59-year-old Japanese man who was receiving theophylline for emphysema experienced stimulation, insomnia, and tachycardia due to theophylline toxicity after clarithromycin and levofloxacin were added to the regimen. The combination of these agents resulted in a decrease in theophylline clearance to approximately 60% of the initial value obtained while the patient was receiving theophylline alone. The adverse effects disappeared after the dosage was reduced and the theophylline serum concentration decreased; however, there was no change in theophylline clearance. After discontinuation of levofloxacin, the theophylline serum concentration decreased, and theophylline clearance returned to the initial level even though clarithromycin was continued.

DISCUSSION

Levofloxacin is believed not to influence the clearance of theophylline, although some new fluoroquinolones have been reported to do so. This case indicates that levofloxacin and clarithromycin inhibited theophylline metabolic pathways catalyzed by both CYP1A2 and CYP3A4 and resulted in the decrease in theophylline clearance. The clearance of theophylline, therefore, is not influenced by clarithromycin alone.

CONCLUSIONS

Careful monitoring is required when levofloxacin is prescribed for patients who are taking clarithromycin with theophylline.

Apparent decrease in population clearance of theophylline: implications for dosage

BACKGROUND

Having observed in recent years that the theophylline dose requirements needed to attain peak serum concentrations of 10 to 20 micrograms/ml infrequently reached previously described mean values, we hypothesized that a downward shift in the range of dose requirements had occurred among patients with asthma.

STUDY DESIGN

We examined dosage requirements needed to attain peak serum concentrations of 10 to 20 micrograms/ml in all patients with chronic asthma treated with theophylline by the Pediatric Allergy and Pulmonary Clinic at the University of Iowa from 1990 to 1994 (n = 300) and at the Pediatric Pulmonary Clinic at the University of Florida from 1992 to 1995 (n = 93). We then compared these doses to previous dose requirements from 1978 to 1983 determined in the same manner.

RESULTS

Despite similar mean peak serum concentrations during both time periods (14 micrograms/ml), mean theophylline dosage requirements during the period of this study were approximately 25% lower among all age groups than those previously observed (p < 0.001). There were no significant differences in mean dosage requirements between the Iowa and Florida patients in any age group examined.

CONCLUSIONS

Theophylline dose requirements needed to attain serum concentrations of 10 to 20 micrograms/ml have decreased significantly from those on which current dosing recommendations are based. This suggests a decrease in mean clearance of the population.

Effect of tamoxifen on the pharmacokinetics of theophylline in rats

The effect of tamoxifen on the pharmacokinetics of theophylline was investigated in male Sprague-Dawley rats. The oral administration of tamoxifen at a dose equal to 40 mg kg-1 48 h before the intravenous injection of theophylline 10 mg kg-1, significantly (P < 0.05) increased the clearance of theophylline by 39%, with no apparent effect on the volume of distribution. As a consequence, the elimination half-life of theophylline was significantly (P < 0.05) shortened in the tamoxifen-treated rats (3.56 +/- 0.39 h vs 5.25 +/- 0.48 h) as well as its mean residence time (5.04 +/- 0.60 h vs 7.50 +/- 0.75 h). Although these data cannot be directly extrapolated to the clinical situation, they provide experimental support to suggest that more attention should be paid to the potential risk of pharmacokinetic interactions in the presence of tamoxifen.

Controlled study of the putative interaction between famotidine and theophylline in patients with chronic obstructive pulmonary disease

The effects of famotidine (80 mg per day), cimetidine (1600 mg per day), and placebo on theophylline pharmacokinetic parameters in chronic obstructive pulmonary disease (COPD) patients were compared. This was an open-label, randomized, three-period cross-over study, in which each subject first underwent a seven-day theophylline washout period, and thereafter received three single intravenous doses of theophylline (5 mg/kg infused over 30 minutes) during the study. Each of the experimental treatments was administered orally every 12 hours for a total of 9.5 days (19 doses). Theophylline was infused after the 17th dose of each treatment. Fourteen serial blood samples were collected before the start of each infusion, and for 30 hours after the end of each infusion. Plasma samples were assayed for theophylline, pharmacokinetic parameters were estimated, and treatment effects on each parameter were compared. Fourteen COPD patients completed all three periods of the investigation. Famotidine treatment had virtually no effect on any of theophylline's pharmacokinetic parameters. In contrast, cimetidine treatment significantly altered every pharmacokinetic parameter of theophylline as follows: Cimetidine decreased theophylline geometric mean CL from 2.74 L/h to 2.07 L/h (P < .001), and prolonged theophylline harmonic mean half-life from 6.6 to 9.6 hours (P < .001) and mean residence time from 10.8 to 15.0 hours (P < .001). Cimetidine treatment slightly increased theophylline volume of distribution by approximately 10%, and that change also was statistically significant (P = .032). The authors conclude that the treatment effects of cimetidine on theophylline pharmacokinetic parameters were in accord with those reported by others, and that famotidine treatment had no effect on any of theophylline's pharmacokinetic parameters in COPD patients.

Prevention of drug absorption in simulated theophylline overdose

1. The effects of emesis, gastric lavage and oral activated charcoal on theophylline absorption were compared in healthy volunteers. 2. One of four regimes (ipecacuanha-induced emesis, gastric lavage, oral activated charcoal and no treatment) was randomly chosen one hour after a simulated overdose with sustained-release theophylline on four separate occasions in twelve healthy volunteers. 3. Syrup of ipecacuanha produced emesis in all twelve volunteers but only seven vomited any tablets. Gastric lavage yielded tablets in only one volunteer. 4. The mean systemic availabilities (areas under the concentration-time curves relative to control) of theophylline for ipecacuanha-induced emesis, gastric lavage and charcoal, were 107.1%, 101.1% and 16.9%, respectively. 5. Oral activated charcoal was thus highly effective, while gastric lavage and emesis were ineffective in preventing theophylline absorption. Activated charcoal is potentially the most effective first-line treatment for acute overdosage with sustained-release theophylline tablets.

Prevention of drug absorption in simulated theophylline overdose

To assess the effectiveness of oral activated charcoal and catharsis in preventing theophylline absorption, 12 healthy subjects, aged 20-35 years, received 3 x 200 mg sustained-release theophylline tablets and 16 radio-opaque placebo tablets on six occasions. On each occasion, they received either no treatment (control) or one of five treatments. Treatments were a) oral activated charcoal (Carbomix): 50 g at 1 h, 25 g at 5 h and 9 h; b) sorbitol 70%: 150 mL at 1 h; c) activated charcoal: 50 g at 6 h, 25 g at 10 h and 14 h; d) sorbitol 70%: 150 mL at 6 h; e) charcoal commencing at 6 h plus sorbitol at 6 h (i.e. a combination of treatments c and d). Plasma theophylline concentrations were measured and all stools collected over 36 h to assess placebo tablet recovery by radiography. Charcoal administration at 1 h was 91.2% effective in preventing theophylline absorption and at 6 h was 57.3% effective, while combined charcoal and catharsis at 6 h was 63.3% effective. Sorbitol-induced catharsis at 1 h and 6 h did not reduce theophylline absorption despite greater tablet recovery. Oral activated charcoal may be the most effective treatment for sustained-release theophylline overdose, with maximum benefit when administered soon after an overdose, though later administration might still be of value. Sorbitol catharsis is of no benefit either alone or in combination with charcoal.

Pharmacokinetic optimisation of asthma treatment

Asthma is generally managed with bronchodilator therapy and/or anti-inflammatory drugs. Guidelines now advocate selection of drugs and pharmaceutical formulations (long-acting vs short-acting, inhaled vs systemic) on the basis of disease severity. Theophylline has a narrow therapeutic margin. Clearance is highly variable and plasma concentrations should be monitored to avoid the occurrence of plasma concentration-related adverse effects. The rate of absorption of theophylline differs depending on the sustained release formulation administered. Some products do not provide sufficient plasma drug concentrations for therapeutic efficacy over a 12-hour period, particularly in patients with high clearance rates (e.g. children and patients who smoke). Administration of drugs via inhalation offers several advantages over systemic routes of administration (e.g. adverse effects are decreased). Inhalation is now advocated as first-line therapy. Aerosol medications available for the treatment of asthma are beta 2-agonist (including the newer long-acting agents such as salmeterol), corticosteroids, anticholinergic drugs, sodium cromoglycate (cromolyn sodium) and nedocromil. To reach the airways, aerosolised particles should be 1 to 5 microns in diameter. Particles of this size can be produced by nebuliser for continuous administration or by metered-dose inhaler and drug powder inhaler for unit dose medication. For efficient use of the metered-dose inhaler, slow inhalation and actuation must be coordinated. However, efficacy and convenience can be improved when spacer devices are used. Furthermore, spacer devices lessen the oropharyngeal adverse effects of inhaled corticosteroids. Dry powder inhalers are more easily used by children and elderly patients than metered-dose inhalers. Regardless of the device used, a maximum of 10% of the inhaled dose reaches the airways. The rest of the dose is swallowed and absorbed through the gastrointestinal tract. Most inhaled drugs have low oral bioavailability, either because of a high first-pass metabolism (beta 2-agonists and glucocorticoids) or because of lack of absorption (sodium cromoglycate). Sulphation of beta 2-agonists occurs in the wall of the gastrointestinal tract and extensive metabolism of inhaled corticosteroids occurs in the liver. Low bioavailability of the swallowed fraction contributes to reduced adverse effects. The pharmacokinetic properties of an inhaled drug are of interest. The fraction of the dose absorbed through the lung has the same disposition characteristics as an intravenous dose, and the swallowed fraction has the same disposition as an orally administered dose. However, for many drugs, pharmacokinetic data after inhalation are limited and cannot be used as a criteria for selection of therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of tocainide on theophylline metabolism

The effect of 5 days of oral tocainide (400 mg every 8 h) on the kinetics of theophylline given as a single 5 mg kg-1 i.v. infusion over 30 min was investigated in eight healthy male nonsmokers. Treatment with tocainide decreased the plasma clearance of theophylline from 37.5 +/- 6.9 (mean +/- s.d.) to 33.7 +/- 5.0 ml kg-1 h-1 (difference -3.8, 95% CI, -1.7 to -5.9; P = 0.004) and increased its terminal elimination half-life from 9.7 +/- 2.5 to 10.4 +/- 2.1 h (difference 0.7, 95% CI, 0.2 to 1.2; P = 0.011). Tocainide decreased the formation clearances of 3-methylxanthine and 1-methyluric acid, but the formation clearance of 1,3-dimethyluric acid was unaltered. These data indicate that tocainide exerts a modest inhibitory effect on theophylline metabolism. The magnitude of this change is substantially smaller than that reported to be produced by mexiletine.