Interaction of ephedrine and theophylline

Ethnobotanical and ethnomedicinal studies in Baluchi tribes: A case study in Mt. Taftan, southeastern Iran

ETHNOBOTANICAL RELEVANCE

From ancient times, the applied use of herbs has been common among indigenous people throughout the world. The present survey is a regional ethnobotanical study of Baluchi tribes living in the Mt. Taftan area, Sistan and Baluchistan Province, southeastern Iran. The aim of this study was to document all traditional knowledge and analyze the medicinal plants used in area and also to identify significant plant species for future pharmacological study.

MATERIALS AND METHODS

Local knowledge was obtained through semi structured and open interviews, in which 51 informants were interviewed. Data were analyzed with Informant Agreement Relative (IAR) and Frequency of Citation (FC) indices.

RESULTS

A total number of 106 taxa of medicinal plants were collected from ten villages from the surrounding plains and highlands of Mt. Taftan, out of 446 plant taxa collected or reported as native in the area. Most plants belong to the Irano-Turanian phytogeographical region in which Asteraceae (15%), Lamiaceae (11%), Fabaceae (8%), Rosaceae (7%), Apiaceae (7%) and Brassicaceae (5%) are those predominantly used. The regression analysis shows that families Apiaceae, Lamiaceae, Solanaceae and Rosaceae are more highly used as medicinal than species rich families such as Asteraceae and Fabaceae, which are the richest families in the Iranian flora. The highest FC was recorded for Artemisia spp. (41) and Berberis integerrima (40). The highest IAR Index was obtained for stings (0.86), followed by disorders in the circulatory system (0.7), dental problems (0.70) and injuries (0.69). Comparing our data with major ethnobotanical references in Iran revealed that medicinal applications of 34 taxa have not been cited, including Hyoscyamus malekianus, a local endemic plant using for ailments of toothache and worms. The toxicity of the endemic Semenovia suffruticosa is also reported.

CONCLUSION

As a result of this study we conclude that Taftan area harbours many plant species for which indigenous knowledge provides a background of medicinal importance. The high percentage of medicinal plants proportional to the native flora is 23.8%, compared to the world percentage of 17.1%, is an indication of the rich knowledge and relationship of isolated Baluchi tribes living in Mt. Taftan to the local flora growing in their surroundings. This rich knowledge should be highly regarded as a cultural and ethnobotanical heritage. Furthermore, ethnobotanical results show some weak interrelation between Baluchi tribes living in Iran and Pakistan, probably because of a different flora and/or unfavourable environmental conditions and perhaps local conflicts which might have reduced active cultural exchange.

Activated Charcoal Adsorption of Theophylline in Vitro

This study was initiated to evaluate the in vitro efficacy of activated charcoal as a potential agent in the treatment of acute theophylline overdoses. Two, ten, and twenty mg/ml solutions were analyzed for theophylline concentration by high-pressure cation-exchange chromatography before and after shaking with 10 g of activated charcoal. The results indicate that 1 g of activated charcoal may adsorb in vitro as much as 300 mg of theophylline. Controlled studies in humans are now indicated.

A wide variety of written forms of prescription drug information for patients are catalogued and discussed. These materials are designed to be delivered by the pharmacist, the physician or the nurse, or to serve as general reference material provided directly to consumers. Materials that describe specific prescription drugs come in the form of stickers or folded sheets directly attached to the medicine container, checklists, wallet or index card size materials, one page sheets, leaflets, brochures and booklets. The best form of patient oriented prescription drug printed material must be evaluated in the context of the goal that it is desired to achieve. Whereas shorter materials are more apt to be read, they cannot provide complete information, the rationale or explanations for the cause or prevention of therapeutic or adverse drug effects.

The importance of providing written prescription drug information to patients is indicated by the fact that many health care professionals produce or distribute these materials to augment and reinforce verbal consultation. In addition, consumer surveys indicate that written communication is a preferred source for this additional information. The examination of existing forms of written prescription drug information for patients is particularly relevant to the Food and Drug Administration (FDA). Senior officials in the FDA have announced support for the concept of written reinforcement of verbal consultation and have said that plans will be proposed for the expanded requirement of patient oriented prescription drug labeling via patient package inserts.

Avoidance of Adverse Effects during Chronic Therapy with Theophylline

Recent definition of the pharmacodynamics and pharmacokinetic characteristics of theophylline and readily available, specific assays have increased the therapeutic benefits of this drug while decreasing the risk of toxicity. Once familiarity is achieved with the various factors that can alter clearance, such as age, smoking habits, physiological abnormalities, and concurrent drug therapy, an initial dosage can be appropriately individualized. Careful product selection, the slow progressive titration of dose over nine days, and the accurate measurement and interpretation of serum theophylline concentration can prevent adverse effects and interactions. However, long-term therapy with theophylline should probably be avoided when other drugs are available for patients with cor pulmonale, liver dysfunction, congestive heart failure, migraine headaches, and seizure disorders.

Utilization Pattern and Drug Use of Traditional Chinese Medicine, Western Medicine, and Integrated Chinese-Western Medicine Treatments for Allergic Rhinitis Under the National Health Insurance Program in Taiwan

OBJECTIVES

Patients in Taiwan with allergic rhinitis seek not only Western medicine treatment but also Traditional Chinese Medicine treatment or integrated Chinese-Western medicine treatment. Various studies have conducted pairwise comparison on Traditional Chinese Medicine, Western medicine, and integrated Chinese-Western medicine treatments. However, none conducted simultaneous analysis of the three treatments. This study analyzed patients with allergic rhinitis receiving the three treatments to identify differences in demographic characteristic and medical use and thereby to determine drug use patterns of different treatments.

MATERIALS AND METHODS

The National Health Insurance Research Database was the data source, and included patients were those diagnosed with allergic rhinitis (International Classification of Diseases, Ninth Revision, Clinical Modification codes 470-478). Chi-square test and Tukey studentized range (honest significant difference) test were conducted to investigate the differences among the three treatments.

RESULTS

Visit frequency for allergic rhinitis treatment was higher in female than male patients, regardless of treatment with Traditional Chinese Medicine, Western medicine, or integrated Chinese-Western medicine. Persons aged 0-19 years ranked the highest in proportion of visits for allergic rhinitis. Traditional Chinese Medicine treatment had more medical items per person-time and daily drug cost per person-time and had the lowest total expenditure per person-time. In contrast, Western medicine had the lowest daily drug cost per person-time and the highest total expenditure per person-time. The total expenditure per person-time, daily drug cost per person-time, and medical items per person-time of integrated Chinese-Western medicine treatment lay between those seen with Traditional Chinese Medicine and Western medicine treatments.

CONCLUSIONS

Although only 6.82 % of patients with allergic rhinitis chose integrated Chinese-Western medicine treatment, the visit frequency per person-year of integrated Chinese-Western medicine ranked highest. In addition, multiple-composition medicines were used more frequently than single-composition medicines, and mar huang (Ephedra sinica Stapf) was seldom used to decrease the risk of combining medications.

Reducing drug-herb interaction risk with a computerized reminder system

Background

Traditional Chinese medicine (TCM) and Western medicine are both popular in Taiwan. Approximately 14.1% of Taiwanese residents use Western drugs and Chinese herbs concurrently; therefore, drug–herb interaction is critical to patient safety. This paper presents a new procedure for reducing the risk of drug interactions.

Methods

Hospital computer systems are modified to ensure that drug–herb interactions are automatically detected when a TCM practitioner is writing a prescription. A pop-up reminder appears, warning of interactions, and the practitioner may adjust doses, delete herbs, or leave the prescription unchanged. A pharmacist will receive interaction information through the system and provide health education to the patient.

Results

During the 2011–2013 study period, 256 patients received 891 herbal prescriptions with potential drug–herb interactions. Three of the 50 patients who concurrently used ginseng and antidiabetic drugs manifested hypoglycemia (fasting blood sugar level ≤70 mg/dL).

Conclusion

Drug–herb interactions can cause adverse reactions. A computerized reminder system can enable TCM practitioners to reduce the risk of drug–herb interactions. In addition, health education for patients is crucial in avoiding adverse reaction by the interactions.

Dispositional study of opioids in mice pretreated with sympathomimetic agents

Brain and plasma levels of morphine and codeine were determined by an assay method involving solid-phase extraction and ion-pair reversed phase HPLC. Detection was by a variable wavelength UV-detector (for codeine) and an amperometric electrochemical detector (for morphine) coupled in series. Ephedrine or phenylpropanolamine pretreatment did not interfere with the plasma disposition of morphine, evidenced by overlapping plasma concentration-time profiles. Brain opioid levels were equally unaffected by sympathomimetic pretreatment. The relative ratios of brain to plasma concentrations at the time corresponding to the respective peak anti-nociceptive activity for morphine and codeine revealed no significant differences. It is concluded that single doses of ephedrine and phenylpropanolamine do not affect the disposition of morphine and codeine in mice.

Pharmacokinetic interactions between theophylline and other medication (Part II)

Part I of this article, which appeared in the previous issue of the Journal, covered the effects or lack of effects on theophylline clearance of sympathomimetics, corticosteroids, antihistamines and other antiallergy drugs, antimicrobial agents, phenytoin, carbamazepine, barbiturates, antacids and activated charcoal. In Part II, this discussion is extended to the effects of other agents. Overall summaries, both textual and tabular, appear in Part I.

Antiasthmatic therapy in children

The availability of more and better medications for asthma contrasts with reports of an increasing frequency of hospitalization and fatalities. An understanding of the pathophysiology of the disease, its variations in clinical patterns, and the therapeutic potential of the available options for treatment in this overview of asthma management provides a basis for addressing this paradox. A scheme for matching the therapeutic options to the clinical pattern of the disease is presented with comments on the delivery of health care to asthmatic patients. Results of outcome from comprehensive asthma management programs are described.

Salbutamol induced hypokalaemia: the effect of theophylline alone and in combination with adrenaline

1. We have previously shown that salbutamol induced hypokalaemia, like adrenaline induced hypokalaemia, is the result of stimulation of a membrane bound beta 2-adrenoreceptor linked to Na+/K+ ATPase. We have also demonstrated that adrenaline induced hypokalaemia is potentiated by therapeutic concentrations of theophylline. 2. In a single-blind study of 14 normal volunteers, we infused salbutamol in doses used in clinical practice and examined the effects of the addition of theophylline alone or combined with (-)-adrenaline on plasma potassium levels, heart rate and blood pressure. The combinations studied were (i) salbutamol + vehicle control adrenaline infusion + placebo theophylline; (ii) salbutamol + vehicle control adrenaline infusion + theophylline; (iii) salbutamol + adrenaline + theophylline. 3. In a randomised, balanced placebo controlled design oral slow release theophylline or placebo was given for 9 days. Subjects were studied twice on the active limb (days 7 and 9) and once on the placebo limb (day 9) and the procedure was identical on each of the 3 study days except for the solutions administered. 4. Theophylline increased salbutamol induced hypokalaemia and in some individuals profound hypokalaemia (less than 2.5 mmol l-1) was observed with these relatively low doses of salbutamol and theophylline. Adrenaline did not further increase the magnitude of the fall in potassium observed. Combining theophylline with salbutamol increased the tachycardia resulting from the salbutamol infusion. Salbutamol infusion caused a fall in diastolic and rise in systolic blood pressure on all 3 study days and this was not altered by either theophylline or adrenaline alone or together.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between rate and extent of absorption of oral theophylline from Uniphyl brand of slow-release theophylline and resulting serum concentrations during multiple dosing

The relationship between a standardized assessment of rate and extent of absorption of slow-release theophylline and serum concentrations during multiple dosing was examined in eight healthy adult volunteers. Each subject received single doses of a reference theophylline solution in addition to single and multiple doses of Uniphyl, a "once-a-day" theophylline formulation, administered after an overnight fast and after a large breakfast. Extent of absorption was similar during single and multiple dosing but was significantly greater when dose was taken after breakfast; 68 +/- 7% (mean +/- SEM) and 61 +/- 4% of administered doses were absorbed during single and multiple dosing, respectively, when breakfast was withheld, whereas 83 +/- 4% and 86 +/- 4% of administered doses were absorbed when single and multiple doses, respectively, followed breakfast. Observed mean serum concentrations during multiple dosing approximated values predicted from the single-dose study; mean peak serum concentrations averaged more than twice the tough for both predicted and observed values after both fasting and postprandial administration. These data demonstrate incomplete absorption of theophylline from Uniphyl with greater extent of absorption when Uniphyl is taken after food. The study also provides further documentation that characterization of rate and extent of absorption from single doses permit prediction of the mean serum concentration-time profile during multiple dosing at defined rates of theophylline elimination. This provides the potential to anticipate fluctuations in serum concentrations at clinically relevant elimination rates that deviate from the mean of samples typically used for study.

Addition of terbutaline to optimal theophylline therapy. Double blind crossover study in asthmatic patients

The efficacy and side effects of oral or inhaled terbutaline were examined in 13 mild-to-moderate asthmatic patients (ages 12 to 71 years) on maintenance theophylline (levels 10 to 25 micrograms/ml). In a crossover design, each patient received for two weeks oral terbutaline, 5 mg qid, inhaled terbutaline, 400 micrograms qid, or identical placebo tablets or metered-dose inhalers. Prior to each double-blind period, terbutaline was given for two weeks to ensure development of beta-adrenergic subsensitivity. Home-monitored peak flows and need for supplementary bronchodilators were significantly improved with both oral and inhaled terbutaline, but only the inhaled drug significantly decreased symptoms. Long-term terbutaline, either oral or inhaled, added to maintenance theophylline improved the patients' pulmonary function. The inhaled drug also improved the patients' clinical status as reflected by asthma symptom scores and need for extra bronchodilator. Combining terbutaline with theophylline did not produce evidence of cardiotoxicity.

Update on the pharmacodynamics and pharmacokinetics of theophylline

Theophylline has emerged as a major prophylactic agent for controlling the symptoms of chronic asthma, but it provides little if any relief of pulmonary symptoms caused by irreversible chronic airways obstruction. Although in vitro it inhibits phosphodiesterase and antagonizes adenosine receptors, theophylline's mechanism of action in asthma is unknown. Often, 10 to 20 micrograms/ml is used as the range of serum concentrations where there is the greatest likelihood of obtaining maximal benefit safely. Slow-release products have the potential to provide more stable serum concentrations with longer dosing intervals. However, clinically important differences in rate and sometimes extent of absorption exist between the 15 formulations sold under 29 brand names in this country. In patients with more rapid elimination, few products have sufficiently slow absorption to allow twice-daily use. Often these formulations must be administered every eight hours to prevent breakthrough in asthmatic symptoms despite promotional claims to the contrary. In patients with slower elimination, differences among products are unlikely to be clinically important with 12-hour dosing intervals. Current products approved for "once-a-day" dosing are clinically inadequate because of erratic absorption or excessive serum concentration fluctuations. Moreover, food induces dose dumping of potentially toxic amounts of theophylline from Theo-24, greatly increases the extent of absorption of theophylline from Uniphyl, decreases extent of absorption from Theo-dur-Sprinkle capsules, but has no clinically important effect on Theo-Dur tablets, Theobid, Slo-Bid, or Somophyllin-CRT. The effects of food or other factors that alter gastrointestinal physiology on theophylline absorption are unknown for most other products.

Theophylline use: an overview

Four critical issues related to theophylline are addressed: What is theophylline? Why use it? How should it be used? Who should receive it? Theophylline is a methylated xanthine with established clinical benefit as maintenance therapy for chronic asthma. In fact, evolution of our knowledge of the pharmacodynamics and pharmacokinetics of theophylline has made this drug the most effective nonsteroidal prophylactic used for chronic asthma. Theophylline has the potential for serious toxicity at excessive serum concentrations. Nonetheless, its major justification for use today, when so many other asthma medications have become available, is because of the high degree of efficacy that can be attained with appropriate use. The optimal likelihood of maximal safe effect is attained with maintenance of serum concentrations within the 10 to 20 micrograms/ml therapeutic range. Dosage should be individualized by clinical titration, guided by measurement of serum concentrations, and continued only if well tolerated; selection of appropriate products and dosing intervals permits maintenance of acceptably stable serum concentrations. Asthma in patients only intermittently symptomatic, regardless of severity, is probably best treated by intervention measures with inhaled bronchodilators, supplemented when necessary by short-term use of oral corticosteroids, rather than by long-term maintenance therapy. Theophylline therapy in patients with obstructive pulmonary disease other than asthma should generally be highly selective and based on clearly demonstrable clinical benefit.

Cromolyn sodium: a review

Cromolyn is a white crystalline powder which is poorly absorbed from the gastrointestinal tract. Its therapeutic value lies in its functions as an inhaled or topically applied agent. Cromolyn has been approved in the United States for asthma therapy since 1973. It was marketed at that time as a drug to reduce the corticosteroid requirements of severe asthmatics. It clearly did not live up to that claim. Initial enthusiasm for cromolyn was replaced by disillusionment. In the last few years, investigators have taken another look at cromolyn and have a renewed interest in it. Cromolyn's mechanisms of action remain only partially understood. It appears to block allergic mediator release from certain mast cells. It may also decrease bronchial hyperreactivity. The frequency of drug toxicity at customary dosages is extremely low. Adverse effects tend to be mild, short-lived and without sequelae. Currently, cromolyn is a first line therapy for mild to moderate asthma requiring chronic treatment. It is also of proven efficacy in the treatment of allergic rhinitis, allergic conjunctivitis and vernal keratoconjunctivitis.

Volume of distribution of theophylline in acute exacerbations of reversible airway disease. Effect of body weight

The literature is unclear as to whether theophylline loading doses should be based on total body weight (TBW) or ideal body weight (IBW). The objective of this study was to determine the most appropriate body weight for estimation of volume of distribution (Vd) in calculating theophylline loading dose in patients with acute bronchospasm. Fifty-four adult patients with acute bronchospasm requiring intravenous (IV) theophylline therapy were entered into the study. Patients were randomized into three theophylline loading dose groups based on (1) TBW, (2) IBW, and (3) adjusted body weight (ABW). Initial serum theophylline concentrations were used to determine an IV loading dose to reach a plasma concentration of 12 to 15 micrograms/ml. Percent prediction error was used to determine the appropriateness of each dosing group. Volumes of distribution were also determined for each group. There was a statistically significant difference at p less than 0.01 in the percent prediction error when patients in the TBW group were compared to the IBW and ABW groups. A statistically significant difference in the Vd was observed between the TBW and IBW group (p less than 0.01). We conclude that IBW is more appropriate than TBW or ABW for determining theophylline loading dose in patients with acute bronchospasm.

Theophylline QID, TID, BID and now QD? A report on 24-hour dosing with slow-release theophylline formulations with emphasis on analyses of data used to obtain Food and Drug Administration approval for Theo-24

Dosing intervals for slow-release theophylline preparations depend on the rate of formulation absorption, the rate of patient elimination, and clinically acceptable fluctuations in serum concentration. Three products, two new to the United States market, have received approval by the Food and Drug Administration (FDA) for 24-hour dosing claims. Data submitted to the FDA for Theo-24 (Searle) suggest slow but incomplete absorption in single-dose studies, and multiple-dose studies confirm incomplete absorption relative to plain theophylline tablets. Fluctuations in serum concentration expressed as a percentage of the trough value at steady state with Theo-24 given once daily in the morning ranged from 48 to 1371% among 18 subjects; 13 of the 18 had greater than 100% fluctuation, which is the upper limit for fluctuations that can stay within the 10- to 20-micrograms/ml therapeutic range. Among another 18 subjects with somewhat slower and less variable rates of elimination, fluctuations ranged from 40-168% at steady state, with 4 of 18 greater than 100% during daily dosing with Theo-24; all subjects had fluctuations less than 100% (39-92%) when they were given Theo-dur tablets every 12 hours. Theo-dur tablets have also received FDA approval for once daily administrations, but only 1 of 14 subjects in a submitted study had fluctuations less than 100% and thus was able to stay within the therapeutic range. No data were available on the absorption of Uniphyl, also approved for once-daily dosing, but large fluctuations in serum concentration are apparent from advertisements for the European product Uniphyllin, and are also suggested by presentations on Uniphyl at a recent scientific meeting. Current standards for receiving FDA approval for 24-hour dosing appear to be inconsistent with the pharmacodynamics and pharmacokinetics of theophylline and fail to consider the greater risks from variability in absorption when a single, large daily dose is taken.

Albuterol: an adrenergic agent for use in the treatment of asthma pharmacology, pharmacokinetics and clinical use

Albuterol is a long-acting beta 2-adrenergic receptor-selective drug that relaxes airway smooth muscle. It is currently available in the United States in oral and metered-dose inhaler forms. Nebulizer solutions and parenteral preparations are likely to be marketed here in the future. The chemical modifications that make albuterol beta 2-selective also promote oral bioavailability and increased duration of action by decreasing sensitivity to degradative enzymes. Albuterol can also produce undesirable dose-related effects: metabolic effects including decreased levels of plasma potassium, phosphate, calcium and magnesium; increased levels of plasma glucose, insulin, renin, lactate and ketones; peripheral vasodilation and perhaps some direct cardiac stimulation resulting in decreased systemic and pulmonary vascular resistance, increased pulse pressure and tachycardia; and skeletal muscle tremor. These side effects are most common with parenteral administration and much less prominent with aerosol administration, which yields lower systemic concentrations. Limited pharmacokinetic data suggest a long distribution phase, a terminal half-life of 3-8 hours, and 10-20% oral bioavailability. Aerosolization of albuterol or a similar agent with a compressed-air nebulizer appears to be best first-line management of the patient with acute dyspneic asthma, but appropriate preparations for this kind of therapy are currently missing from the United States market. Intravenous albuterol has also been employed in acutely dyspneic patients, but produces more side effects than carefully administered intravenous theophylline, is impaired by lack of sufficient pharmacokinetic information to guide dosing, and is of uncertain efficacy in the asthmatic with respiratory failure. However, it appears to lack the potentially life-threatening side effects that can result when theophylline is used carelessly . In the ambulatory patient, aerosolized albuterol (or a similar agent) administered by metered-dose inhaler is an excellent agent for treatment as needed and/or for prevention of acute bronchospasm triggered by exercise or other predictable cause. Advantages include a high degree of efficacy, rapid onset and long duration of effect, and minimal side effects. Regularly scheduled administration of albuterol by metered-dose inhaler is a widely used and effective maintenance medication for patients requiring long-term prophylactic therapy. However comparisons of the ability of this regimen and the other common maintenance regimens (cromolyn and theophylline) to control chronic symptoms of asthma are needed.

A clinical and pharmacokinetic basis for the selection and use of slow release theophylline products

In order to achieve the greatest chance for maximum benefit from theophylline in the management of chronic asthma, the serum concentration should be maintained in the therapeutic range of 10 to 20 micrograms/ml. Conventional rapid release formulations produce excessive fluctuations in serum concentrations that can result in variability in clinical response between doses. In contrast, slow release formulations have the potential to achieve relatively constant serum concentrations with 12-hour dosing intervals, thus providing around-the-clock stabilisation of the hyper-reactive airways that characterise chronic asthma. Furthermore, the decreased frequency of dosing with these formulations can improve patient compliance. However, significant differences in rate and extent of absorption exist between the available formulations. Single-dose bioavailability studies comparing a slow release product with an oral solution or plain uncoated tablet in a crossover design permit examination of the rate and extent of absorption. Comparison of a slow release product with an oral reference following multiple doses at steady-state permits examination of the extent but generally not rate of absorption. The mean fraction absorbed-time profile, calculated from a modification of the Wagner-Nelson equation, is a process-independent method of comparing rates of absorption of different products after single doses. A prospective study in 14 children with chronic asthma has demonstrated that this modified equation, when rearranged to iteratively solve for serum concentrations, can accurately predict steady-state serum concentrations for different dosing intervals in patient populations with different rates of elimination. When slow release products are compared in this manner at 8- or 12-hour dosing intervals for patients with slow elimination, clinically relevant differences between brands are not apparent. However, in patients with rapid elimination, i.e. children, cigarette smokers, and 25% of non-smoking adults, application of this method shows that only some formulations (i.e. 'Slo-Bid Gyrocaps' and 'Theo-Dur', which is also marketed under different brand names names such as 'Sustaire', 'Pulmi-Dur' and 'Theolin Retard') can maintain serum concentrations within the therapeutic range for an entire 12-hour dosing interval. More rapidly absorbed slow release products must be administered at 8-hour dosing intervals in patients with rapid elimination, despite promotional claims to the contrary. Current products promoted for once-a-day administration are clinically inadequate because of incomplete and erratic absorption, and/or excessive serum concentration fluctuations.(ABSTRACT TRUNCATED AT 400 WORDS)

Theophylline. A "state of the art" review

Theophylline is a bronchodilator and respiratory stimulant that is effective in the treatment of acute and chronic asthma, Cheyne-Stokes respirations, and apnea/bradycardia episodes in newborns. It is also used as an adjunct in the treatment of congestive heart failure and acute pulmonary edema, but it has no established efficacy in patients with chronic irreversible airways obstruction. Benefits and risks from theophylline relate directly to serum concentration, which is a function of both dose and elimination characteristics of the drug in an individual patient. When used to treat acute symptoms, an initial loading dose based on a mean volume of distribution is required to rapidly obtain maximum bronchodilator effect. Because of large interpatient differences in elimination, constant intravenous infusion rates for continued therapy must be guided by monitoring serum theophylline concentration at intervals until a steady-state serum concentration is reached within the 10-20 micrograms/ml therapeutic range. Intravenous, oral or rectal solutions and plain uncoated tablets are appropriate for acute therapy, while reliably absorbed slow-release formulations offer therapeutic advantages for the management of chronic asthma, particularly in patients with rapid elimination. Dosage for long-term therapy is determined by starting with low doses that allow virtually complete acceptance of the medication followed by gradual increases, if tolerated, at three day intervals until mean age-specific doses are reached. Subsequent adjustment in dosage regimens are then based upon serum concentration measurements. Most clinical laboratories now measure theophylline, and newer systems have been developed to provide emergency results within minutes at a reasonable cost. In cases of theophylline poisoning, the drug must be rapidly removed to prevent life-threatening toxicity. When serum concentrations are in excess of 60 micrograms/ml charcoal hemoperfusion dialysis may be indicated, even in the absence of obvious signs of toxicity.

Comparison of orally administered metaproterenol and theophylline in the control of chronic asthma

The efficacy of metaproterenol (orciprenaline) and theophylline given orally at currently recommended doses was examined in 34 children with chronic asthma using a randomized double-blind cross-over evaluation of four weeks' duration for each active regimen. No serious adverse effects were seen with either medication, but tremor occurred more frequently with metaproterenol (P less than 0.01). No significant differences were observed in the frequency of nausea, vomiting, headache, or insomnia (P greater than 0.05). Symptoms of wheezing, coughing, exercise intolerance, and interference with sleep were more frequently associated with the oral metaproterenol regimen; completely asymptomatic days occurred 50% more frequently in association with theophylline therapy (P less than 0.01). Mean peak flows, performed twice daily during each of the four-week study periods, were 86 and 92% of predicted for metaproterenol and theophylline, respectively (P less than 0.05). Pulmonary function decreased significantly less with theophylline than with metaproterenol among those who completed six minutes of treadmill exercise during both regimens (P less than 0.05). Corticosteroids, used for acute symptoms that failed to respond to the addition of inhaled metaproterenol, were required in four patients during both regimens, in ten patients only during the metaproterenol regimen, and in one patient only during the theophylline regimen (P less than 0.02). Thus, theophylline therapy was associated with fewer adverse effects, fewer symptoms of asthma, better pulmonary function, better exercise tolerance, and less requirements for corticosteroids than was treatment with metaproterenol.

A practical guide to interactions involving theophylline kinetics

A practical guide to the drug interactions involving theophylline kinetics is presented. The text is classified into three categories--pharmacokinetics, pharmacodynamics, and miscellaneous drug interactions. In the discussion of pharmacokinetics, interactions are classified according to site; in vitro, intestinal, metabolic, protein binding, and renal mechanisms are considered. The pharmacodynamic section concentrates on possible additive effects of theophylline and other commonly used bronchodilators, while in the miscellaneous section, discussion is devoted to those interactions involving allergic skin testing and changed results of commonly used assay methods for theophylline. Increased awareness of possible interactions should lead to a more critical approach to theophylline prescribing, particularly in those cases where an unexpected therapeutic effect (or theophylline serum concentration) is obtained during the treatment of asthmatic patients.

Effects of oral theophylline combined with oral and inhaled beta-2-adrenostimulants in asthmatics

The acute ventilatory, cardiovascular and tremorogenic effect of a high oral dose of terbutaline (5 mg) was compared with that of half the dose (2.5 mg) combined with 280 mg anhydrous theophylline orally in the randomized, double-blind, cross-over study in eight asthmatics. After 120 min, when steady-state bronchodilation was achieved, five terbutaline inhalations (1.25 mg terbutaline sulphate) were added to both treatment regimens. The mean maximum plasma concentration of theophylline was then 7 micrograms/ml (39 mumol/l). Inhalation of a beta 2-adrenostimulant had a very good additional effect without increasing side effects in these patients with good inhalation technique. The oral low-dose combination gave significantly better bronchodilation than the high dose of terbutaline alone and caused significantly less tremor. Although the combination only had an additive bronchodilating effect, it may offer important clinical advantages. If the patient cannot use the metered dose aerosol, an oral low dose combination should be preferred to a single high dose of either theophylline or beta 2-adrenostimulants. In patients with good inhalation technique but not controlled by inhalation from a metered dose aerosol alone, a combination of oral theophylline and terbutaline in "sub-optimal" dose and an inhaled beta 2-agonist in individually titrated optimal dose gave a maximal bronchodilating effect with minimum side effects.

Effect of erythromycin on theophylline kinetics

The effect of erythromycin base on theophylline kinetics was studied in eight informed, nonsmoking, adult males who received a 15-min infusion of theophylline (aminophylline) 5 mg/kg, prior to (control) and after (experimental) a 7-day course of 1 gm daily erythromycin base (E-Mycin). Each subject acted as his own control. Multiple serum samples were collected for 24 hr after each dose and were analyzed for theophylline by high-pressure liquid chromatography. The mean +/- SD pharmacokinetic parameters for each phase of study were as follows: apparent volume of distribution (L/kg) 0.45 +/- 0.05 (control), 0.41 +/- 0.05 (experimental); clearance (ml . min/kg) 0.83 +/- 0.17 (control), 0.60 +/- 0.11 (experimental); elimination half-life (hr) 6.65 +/- 1.88 (control), 8.10 +/- 1.58 (experimental). Erythromycin significantly affected the elimination half-life and clearance of theophylline (p less than 0.05). The apparent volume of distribution was unaffected (p greater than 0.05). Therefore patients being administered theophylline appear to be at added risk for the development of toxicity when erythromycin is added to the therapeutic regimen.

The value of maintenance theophylline in steroid-dependent asthma

We examined the value of maintenance theophylline at serum concentrations of 10 to 20 micrograms per milliliter in a placebo-controlled, randomized, double-blind trial of 33 children with steroid-dependent chronic asthma. Patients were free of all symptoms 63 +/- 6 per cent of the days (mean +/- S.E.M.) when taking theophylline as compared with 42 +/- 6 per cent when taking placebo (P < 0.01). Inhaled metaproterenol was required twice as often with placebo (P < 0.01), and additional daily corticosteroids were needed more than three times as often with placebo (P = 0.02). Daily peak flow measurements improved with theophylline (P < 0.01) as did monthly spirometric measurements and residual volume measured by plethysmography. Theophylline was associated with a 50 per cent increase in the number of patients able to complete an exercise test (P = 0.01) and with a smaller decrease in forced expiratory volume in one second among patients completing the exercise (P < 0.02). We conclude that maintenance bronchodilator therapy with theophylline can provide clinically important benefit for patients with chronic steroid-dependent asthma.

Antigen-induced bronchial anaphylaxis in actively sensitized guinea-pigs: anti-anaphylactic effects of sodium cromoglycate and aminophylline

1 The inhibitory effects of sodium cromoglycate (SCG) and aminophylline on antigen-induced bronchial anaphylaxis in guinea-pigs, actively sensitized according to different regimens, were examined. 2 SCG (1 mg/kg administered intravenously) reduced the anaphylactic response in animals sensitized with 1 microgram ovalbumin (OA) together with A1(OH)3 100 mg, and challenged at 14 and 40 days after sensitization. If higher doses of antigen (10 micrograms OA together with A1(OH)3 or 5 mg OA on day 0 plus 10 mg OA on day 2) were used for sensitization, the protective effect of SCG was found only in animals tested 14 days after sensitization. 3 A low dose of aminophylline (0.3 mg/kg) that was without a direct bronchodilator effect when tested against a histamine (4 micrograms/kg)-induced bronchospasm, produced an anti-anaphylactic effect. The anti-anaphylactic effect of aminophylline varied slightly with the way the animals were immunized and the time at which they were tested. 4 It is concluded that bronchial anaphylaxis in guinea-pigs sensitized with low doses of ovalbumin is a suitable model for the evaluation of anti-anaphylactic properties of drugs.

The interaction of erythromycin and theophylline in the asthmatic dental patient

Possible interaction of erythromycin with theophylline is a problem in the dental treatment of asthmatic patients. This interaction can be circumvented by using other antibiotics or adjusting the dose of theophylline.

Clinical and metabolic features of overdosage with Amesec

A 23-year-old woman ingested 2g. amylobarbitone, 10.4g. aminophylline and 2g. ephedrine. She was deeply unconscious, hypothermic, and went on to have supraventricular and ventricular dysrhythmias, convulsions and haematemesis. During the last convulsion she aspirated vomitus and died. The peak plasma concentration of amylobarbitone was 19mg. per l. and those of ephedrine and theophylline were 13 times higher than accepted therapeutic levels. During the course of the poisoning marked hypokalaemia (1.8mmol./l.) and hyperinsulinaemia (greater than 240mU./l.) were found in conjunction with mild hyperglycaemia (9.6mmol./l.) and elevation of free fatty acid levels (1860mumol./l.). The mechanism of these changes is discussed.

Combination bronchodilators: antagonism of airway smooth muscle contractions in vitro

The component drugs of fixed-dose combination bronchodilators may interact in a synergistic manner to antagonize airway contractions. To examine this hypothesis, combinations of ephedrine (E) and theophylline (Th) or salbutamol (S) and theophylline were tested for their ability to relax contracted guinea-pig airway smooth muscle in vitro. The combination bronchodilator effect was compared to the summed effects of the component drugs given individually (i.e. a theoretical additive response, Ta). Relaxation responses to combination bronchodilators were considered less-than-additive if significantly less than Ta, additive if non-significant and greater-than-additive or synergistic if the values were significantly greater than Ta. It was found that the E-Th combinations interacted primarily in an additive fashion to relax contractions induced by histamine, acetylcholine and 5-hydroxytryptamine at concentrations that produced one-half maximal contractile response (ED50). Similarly S-Th combinations interacted in an additive manner to reverse histamine and acetylcholine contractions. In the case of both E-Th and S-Th combinations, the drugs were more effective in reducing the smooth muscle contractions when given during rather than prior to the response. It may be concluded that beta-sympathomimetics and methylxanthines when combined do not interact in a synergistic fashion to produce relaxation of contracted airway smooth muscle.

The relation of product formulation to absorption of oral theophylline

To assess the potential for therapeutic problems related to the bioavailability of oral theophylline preparations, we examined the rate and extent of absorption for various formulations in adult volunteers. Absorption of theophylline from a solution or from uncoated tablets was rapid and complete. Three of six sustained-release formulations were more slowly, but still completely and consistently, absorbed. Absorption of the other three sustained-release formulations appeared to be more erratic and less complete. Serum concentration-time curves during multiple eight-hour dosing were simulated for the bioavailable preparations. With three sustained-release formulations it was predicted that fluctuations in serum theophylline concentrations between doses would decrease, as compared with uncoated tablets, to a clinically important extent, particularly in children, in whom elimination of theophylline is generally rapid.