Food induced changes in theophylline absorption from a once-a-day theophylline product

Food-drug interactions

Interactions between food and drugs may inadvertently reduce or increase the drug effect. The majority of clinically relevant food-drug interactions are caused by food-induced changes in the bioavailability of the drug. Since the bioavailability and clinical effect of most drugs are correlated, the bioavailability is an important pharmacokinetic effect parameter. However, in order to evaluate the clinical relevance of a food-drug interaction, the impact of food intake on the clinical effect of the drug has to be quantified as well. As a result of quality review in healthcare systems, healthcare providers are increasingly required to develop methods for identifying and preventing adverse food-drug interactions. In this review of original literature, we have tried to provide both pharmacokinetic and clinical effect parameters of clinically relevant food-drug interactions. The most important interactions are those associated with a high risk of treatment failure arising from a significantly reduced bioavailability in the fed state. Such interactions are frequently caused by chelation with components in food (as occurs with alendronic acid, clodronic acid, didanosine, etidronic acid, penicillamine and tetracycline) or dairy products (ciprofloxacin and norfloxacin), or by other direct interactions between the drug and certain food components (avitriptan, indinavir, itraconazole solution, levodopa, melphalan, mercaptopurine and perindopril). In addition, the physiological response to food intake, in particular gastric acid secretion, may reduce the bioavailability of certain drugs (ampicillin, azithromycin capsules, didanosine, erythromycin stearate or enteric coated, and isoniazid). For other drugs, concomitant food intake may result in an increase in drug bioavailability either because of a food-induced increase in drug solubility (albendazole, atovaquone, griseofulvin, isotretinoin, lovastatin, mefloquine, saquinavir and tacrolimus) or because of the secretion of gastric acid (itraconazole capsules) or bile (griseofulvin and halofantrine) in response to food intake. For most drugs, such an increase results in a desired increase in drug effect, but in others it may result in serious toxicity (halofantrine).

Evaluation of the mechanical destructive force in the stomach of dog

Orally administered dosage forms receive a destructive force in the gastrointestinal (GI) tract due to peristalsis. In this study, the destructive force was measured with a 'destructive force-dependent release system' (DDRS). DDRS is a press-coated tablet with an extremely brittle outer layer composed of highly hydrophobic Teflon(R) powder, which is molded with a weak compression force. Teflon(R) powder forms a porous but water-impermeable layer around the core tablet. A marker drug contained in the core tablet is released only when the tablet receives a force larger than its pre-determined crushing strength. A comparison of the physiological conditions in the GI tract of dogs with those of humans, including the destructive force against tablets in the stomach, helps us to understand their difference in bioavailability of oral dosage forms. With DDRS, it is possible to evaluate the destructive force of both human and dog stomach using the same method. Therefore, the destructive force data from human and dog can be directly compared. The destructive force in the dog stomach was evaluated to be 3.2 N, which was considerably stronger than that of humans.

A unique dosage form to evaluate the mechanical destructive force in the gastrointestinal tract

The purpose of this study was to prepare tablets that could evaluate the destructive force in the gastrointestinal (GI) tract. Many factors are known to affect in vivo drug release from oral dosage forms. There is still relatively little information on the mechanical destructive force in the GI tract. Press-coated tablets with an extremely brittle outer layer were developed using a unique, highly hydrophobic Teflon powder that could be shaped with weak compression force. A marker drug contained in the tablets was released only when the tablets received a force larger than its predetermined crushing strength. We referred to this type of tablet as a 'destructive force dependent release system' (DDRS). A total of nine healthy, male subjects were orally administered the tablets under fed and/or fasting conditions. Tablets with a predetermined crushing strength of 1.50 N were crushed by all of the four subjects who took them under fed conditions and two of the five subjects under fasting conditions. Tablets with a crushing strength of 1.89 N were crushed by two of the six subjects who took them under fed conditions and none of the five subjects under fasting conditions. The range of mechanical destructive force in the human stomach was obtained.

Adverse reactions and interactions with theophylline

Despite the trend towards newer therapeutic agents, theophylline continues to play a major role in the treatment of reversible airway obstruction. Clinical use of the drug is complicated by a relatively narrow therapeutic range and a large pharmacokinetic variability between patients. Generally, however, theophylline toxicity is foreseeable and preventable. Most cases can be attributed to either inadvertent or intentional overdosing of the drug. Age, disease state and drug interactions are other factors which may contribute to its toxicity. Nausea, vomiting and tachycardia are common signs of mild theophylline toxicity; seizures, ventricular arrhythmias and hypotension are life-threatening manifestations of severe toxicity which may respond poorly to standard therapy. Although serum theophylline concentration correlates with toxicity in a general fashion, life-threatening adverse reactions are not readily predictable from the drug concentration alone. Treatment of theophylline toxicity primarily involves supportive care along with gastric lavage and administration of activated charcoal to facilitate drug removal. The early use of haemoperfusion may be life-saving in cases of severe toxicity.

Management of asthma and chronic airflow limitation. Are methylxanthines obsolete?

After almost 50 years as first-line drugs in the management of asthma and COPD, methylxanthines have been largely superceded by inhaled adrenoceptor agonist and anticholinergic bronchodilators which are more potent and far less toxic. Accumulating evidence indicates that intravenous theophylline contributes side effects, but is rarely of benefit in acute exacerbations of asthma or COPD. In the maintenance therapy of asthma, first-line therapy is dose-optimized inhaled steroids, reducing the need for bronchodilators. Inhaled adrenoceptor agonists are second line medications, anticholinergic aerosols third line, and theophylline, if needed at all, may fulfill a minor systemic steroid-sparing function in severe asthmatics on maximum doses of the inhaled medications. In the maintenance therapy of some patients with COPD, theophylline sometimes may be useful but these responders should be identified by objectively establishing therapeutic benefit. Since many patients have side effects from the methylxanthines, while their therapeutic benefit over and above dose-optimized inhaled therapy is marginal, their continued almost routine use in the management of reversible airflow obstruction is hard to justify, although this class of drugs may be useful in selected patients in whom both subjective and objective benefit can be demonstrated. In COPD, theophylline may improve exercise capacity in some patients by still incompletely understood mechanisms probably unrelated to bronchodilation.

Avoiding asthma fatalities in family practice

Epidemics of sudden death in patients with asthma are more likely to result from inadequate realization of severity and insufficient or inappropriate drug therapy than from toxic drug reactions. The authors review management in children and adults involving step-by-step addition of different classes of drugs according to the severity and persistence of the asthma.

Influence of food on bioavailability from two controlled-release granules of theophylline

The bioavailability and absorption pattern of theophylline from Theolong granule and Theodur-G were studied in five healthy volunteers both in fasting conditions and after taking two different meals. In all the subjects, no dose-dumping effect was observed with a standard- or a fat-rich breakfast on these preparations. Postprandial administration delayed the absorption of theophylline and a fat-rich breakfast significantly reduced the area under the curve (AUC0-26) for both preparations. The mean AUC decreased by 14.0% for the former and 19.7% for the latter when the fat-rich breakfast was administered. Intake of a standard breakfast resulted in a decrease in the AUC0-26 by 10.6% for Theolong granules but there was little effect observed with the Theodur-G granules.

Food interactions with sustained-release theophylline preparations. A review

Currently, theophylline is being used predominantly as sustained-release capsules or tablets. In the mid-seventies the first preparations for use with a dosage interval of 12 hours (twice-daily preparations) were introduced. Since 1983, theophylline preparations that can be given with an interval of 24 hours (once-daily preparations) have become available. The release of theophylline from some of these products can be influenced (either increased or decreased) by concomitant intake of food. With some preparations the composition of the meal (especially the fat content) has an influence on the degree of effect. The consequence may be an effect on the rate of absorption or on the amount absorbed, or both simultaneously. This could result in an unexpected shift of the plasma theophylline concentration. Such a shift is therapeutically undesirable, because theophylline has a fairly narrow therapeutic range. A review is given of those food interactions with the sustained-release theophylline preparations, both twice-daily and once-daily products, that are currently on the world market. Special attention is paid to the specific (bio)pharmaceutical characteristics of the different products, and to the influence of the composition and timing of the meals. For each preparation the effect of food on the following pharmacokinetic parameters is discussed: area under the plasma concentration-time curve, peak plasma drug concentration and time to reach this peak. Where possible, the results for both adults and children are discussed. There are indications that children are more susceptible to food-effects than adults. The regulatory aspects are mentioned briefly. Clinically important effects of food have been observed with the following twice-daily products: 'Theo-Dur Sprinkle', 'Theolair SR' (= 'Nuelin SR') and 'Theograd'. Pronounced effects could have an even greater impact with once-daily preparations, as the total daily dose will be given at a single time. A particularly sudden release of a major part of the dose ('dose-dumping') may result in toxic plasma concentrations. Among these products, clinically important effects in children have been reported with 'Theo-24' and 'Uniphyl'.

Circadian variation in theophylline absorption during chronic dosing with a slow release theophylline preparation and the effect of clock time of dosing

1. Eight volunteers were given seven doses of 200 mg of slow release theophylline at either 11.00 h and 23.00 h (regimen 1) or 17.00 h and 05.00 h (regimen 2). At the time of the sixth dose (60 h) hourly blood sampling was started and continued for 24 h. After at least 1 week volunteers crossed over to the other regimen. 2. Volunteers retired to bed at 23.00 h and arose after the 07.00 h sample during both regimens. 3. During regimen 1 there was a marked rise in mean tmax from 3.3 h after dosing at 11.00 h to 9.3 h after dosing at 23.00 h (P less than 0.001). There was also a fall in AUC(0,12) from 89.9 mg l-1 h after dosing at 11.00 h to 79.0 mg l-1 h after dosing at 23.00 h. There was no difference in mean Cmax values. 4. During regimen 2 these circadian changes were abolished with mean values after both dosing times lying between those observed during regimen 1. 5. A marked delay in absorption occurs at night and cannot be explained by food intake.

Comparison between steady state pharmacokinetics and effects of two once-daily, slow-release theophylline formulations in nocturnal asthma

The effects on bronchoconstriction, on non-specific bronchial hyperreactivity (nBH), and the pharmacokinetics at steady state of two theophylline preparations, controlled release (CR) capsules (Riker Pharmaceuticals) and UnixanR tablets (Pharmacia) were compared in patients with nocturnal asthma. Doses were individualised with the intention of achieving plasma trough concentrations greater than 8 micrograms/ml with CR-capsules. The same dose of the two formulations was taken in the morning during two 2-week periods in a randomised, double-blind, cross-over design. During a 24 h hospital study day at the end of the two periods, pulmonary function tests, blood samples, and bronchial histamine challenges were performed. Eleven patients completed the study. Doses were median 15 mg/kg (range 10-20). FEV1 and PEF were statistically significantly better (p less than 0.05) 24 h after dosing (08:00) with CR-capsules. No statistically significant changes in nBH were demonstrated. Despite no significant differences in extents of absorption, the plasma theophylline concentration fluctuations were significantly less (p less than 0.001) during treatment with CR-capsules. We found CR-capsules superior to Unixan in pharmacodynamics 24 h after dosing and in pharmacokinetics with equal bioavailability. In nocturnal asthma the pharmacodynamic differences may be eliminated with evening dosing. No statistically significant changes in nBH were observed.

Sustained-release theophylline and nocturnal asthma, once-daily and unequal dosing schedules

Many asthmatic patients experience aggravation of symptoms overnight resulting in disruption of their sleep. Sustained-release theophylline represents at this time a major bronchodilator medication which possesses a sufficient duration of activity to avert the nocturnal breathing distress of asthma. Circadian rhythm-adapted theophylline schedules consisting of unequal dosing--more or all the drug taken in the evening--have proven efficacious in clinical investigations for certain patients. Although the kinetic behavior of some formulations is affected by food, the circadian rhythm-adapted schedules represent a significant step forward toward the goal of optimizating sustained-release theophyllines for patients who experience nighttime symptoms.

Food interactions with once-a-day theophylline preparations: a review

At present, theophylline is used predominantly as sustained-release dosage forms. Since the mid-seventies many such products have been introduced and have found huge application for use with a dosage interval of 12 hr ('twice-a-day' preparations). Since 1983 theophylline has also been available as preparations that can be given with an interval of 24 hr ('once-a-day' preparations). The release of theophylline from sustained-release dosage forms can be influenced (either increased or decreased) by concomitant intake of food. Obviously, ultra-slow-releasing products are most vulnerable to food effects. With some preparations the composition of the meal, especially its fat content, determines the degree of the food effect. The effect of meal timing and content on once-a-day theophylline preparations must be known since rather large doses are ingested all at a single time. If food can alter the release of theophylline in an unexpected manner from ultra-slow preparations, drug effectiveness may be impaired if release is inhibited or toxicity might result if sudden release of drug occurs. Herein, information about food interaction with once-a-day theophylline preparations is reviewed as this topic is important both for clinicians as well as those concerned with chronopharmacologic investigations of such medications.