Effects of oral theophylline and oral salbutamol in the treatment of asthma

Salbutamol in the Management of Asthma: A Review

Asthma is a common inflammatory disease of the lungs. The prevalence of asthma is increasing worldwide, and the tendency indicates that the number of asthma sufferers will soar in the coming years for several reasons, in particular, the lifestyles we have adopted that expose us to risk factors. Salbutamol is the first selective short-acting β2-agonist (SABA) used as an alternative reliever in the treatment of asthma. Its therapeutic effect is based on its potent smooth muscle relaxant properties, which allow the inhibition of bronchial smooth muscle contraction and subsequent bronchodilation. Salbutamol can be administered orally, intravenously (IV), intramuscularly (IM), subcutaneously, or by inhalation. For this reason, the pharmacokinetic (PK) parameters-absorption, distribution, metabolism, and elimination-are highly diverse and, consequently, the efficacy and adverse effects also differ between each formulation. Here, we review the pharmacological profile of different salbutamol formulations, focusing on their efficacy and adverse effects for its original application, asthma.

A study of use of fixed dose combinations in Ahmedabad, India

Objective:

The aim of this study was to evaluate the pattern of fixed dose combinations (FDCs) in Ahmedabad, a city in western part of India.

Materials and Methods:

Over a period of 24 months, prescriptions were collected from 24 pharmacy stores across 6 zones of Ahmedabad city. The information was recorded in pre-formed Data Record Form after written consent from the patients (or relative (s) of the patients). The pattern of use of FDC, rationality and seasonal variation in their use were analyzed. At the end of study, results were analyzed using Chi-square test.

Results:

Out of the total 1170 prescriptions, 941 (80.3%) contained 1647 FDC formulations. The average number of FDCs prescribed was 1.41 ± 1.04 (mean ± SD). The FDCs were more frequently prescribed in the age group of 31 to 40 years (23.7%) and in males (54.4%). FDCs were most commonly prescribed by oral route (92.7%). As per drug category analysis, a higher number of FDCs containing nutritional supplements (20.2%), and those for CNS (18.1%) complaints were prescribed. A seasonal analysis showed that FDCs were commonly prescribed for respiratory complaints (23.4%), central nervous system (CNS) complaints (20.3%) and as nutritional supplements (22.4%) in winter, monsoon and summer months, respectively. Only 5.8%, 9.8% and 10.9% FDCs prescribed were included in WHO (2010), National (2011) and Gujarat State (2011) Essential Medicines Lists (EML), respectively (P < 0.0001). Irrational FDCs that are banned or FDCs containing irrational active ingredients were 1343 (81.5%) and 203 (12.3%), respectively.

Conclusion:

FDCs are widely prescribed with seasonal influence in their use. FDCs containing banned or controversial ingredients are prescribed widely.

Asthma medications and their potential adverse effects in the elderly: recommendations for prescribing

The incidence of drug-induced adverse effects is likely to increase as a result of advanced age and exposure of elderly patients to polypharmacy. Therefore, pharmacological therapy of asthma and chronic obstructive pulmonary disease (COPD) in the elderly patient can be potentially hazardous. beta(2)-agonists, administered as therapy for asthma and COPD, have recognised systemic sequelae, such as hypokalaemia and chronotropic effects, which may be life-threatening in susceptible patients. Adverse effects such as hypokalaemia can be aggravated by concomitant treatment with other drugs promoting potassium loss including diuretics, corticosteroids and theophyllines. In addition, relatively minor adverse events associated with the administration of beta(2)-agonists, such as tremor and blood pressure changes, may be of significance to the elderly patient leading to impairment in the quality of life. However, long-term treatment with beta(2)-agonists may reduce the incidence of drug-induced adverse effects as a result of beta-receptor subsensitivity. Oral and inhaled corticosteroids have been used for the treatment of acute asthma and COPD in the elderly patient. Long-term treatment with oral corticosteroids can result in serious systemic adverse effects such as suppressed adrenal function, bone loss, skin thinning and cataract formation. In contrast to beta(2)-agonists, oral corticosteroids can upregulate beta(2)-adrenoceptors and thereby potentiate the systemic sequelae of beta(2)-agonists. Hence, oral corticosteroids should be administered with caution for as short a duration as possible. Inhaled corticosteroids appear to be relatively well tolerated when administered at doses below approximately 1000 microg. However, larger doses of inhaled corticosteroids may affect hypothalamic-pituitary-adrenal function and bone turnover. In the case of inhaled corticosteroids, spacer devices, often used in older patients who cannot operate metered dose inhalers, can potentiate the systemic sequelae of both corticosteroids and beta(2)-agonists. The use of theophyllines in the treatment of COPD or chronic asthma is controversial. Theophyllines have a wide adverse effect profile and are prone to drug-drug interactions. The adverse effects may be mild or life threatening and include nausea and vomiting or sinus and supraventricular tachycardias. Therefore, theophyllines should be prescribed with extreme caution to elderly patients with asthma or COPD. In contrast, inhaled anticholinergic drugs such as ipratropium bromide and oxitropium bromide are generally safe in elderly patients and have useful bronchodilator function. Commonly reported adverse effects are an unpleasant taste and dryness of the mouth. When used as first-line therapy, anticholinergic drugs may optimise the bronchodilator effects of low-dose inhaled beta(2)-agonists in patients with chronic airflow obstruction, and hence obviate the need for higher doses.

Is combined therapy of sympathomimetics and theophylline indicated?

Bronchodilator effect and toxicity of theophylline 300 mg twice a day (R1), salbutamol 4 mg tid (R2), their combination in higher (200/4mg, R3), and lower doses (100/2mg R4), and placebo (calcium lactate 300 mg) tid (R5) were compared in 25 patients with bronchial asthma in a randomized crossover trial. Statistically significant improvement in forced expiratory volume in one second (FEV1) was observed in all the active treatment groups (R1 to R4) compared with placebo (R5). The mean improvement in FEV1 was 29.0%, 22.0%, 28.0%, 30.0%, and 0.73% in regimen R1, R2, R3, R4, and R5, respectively day 1, and corresponding improvement was 30.0%, 24.0%, 29.0%, 34.0%, and 4.4% on completion of one week therapy. On intergroup statistical comparison, mean improvement in pulmonary function test values were statistically significant or highly significant in regimens R1 to R4, as compared with placebo. However, improvement between any two regimens was not statistically significant in any of the regimens (R1-R4). Almost all the regimens were tolerated well and no patient showed major adverse reactions or cardiotoxicity necessitating withdrawal of the drug. On the other hand, minor adverse reactions were common and the high dose combination (R3) was found to have more adverse reactions than the low dose combination and either drug used alone.

Enhancement of theophylline clearance by oral albuterol

The possible effect of albuterol on theophylline clearance was studied in ten adult volunteers. Subjects received intravenous aminophylline loading dose (5.6 mg/kg), with oral albuterol (4 mg every 6 h), or inhaled albuterol (200 micrograms every 6 h), or alone (control). Theophylline levels were determined for 12-h periods. Theophylline clearance and elimination t 1/2 were calculated. Theophylline clearance was significantly higher when given with oral albuterol, in comparison with control (0.83 +/- 0.05 vs 0.73 +/- 0.06 ml/kg/min, p less than 0.02). Theophylline elimination t 1/2 was shorter with the coadministration of oral albuterol, compared with control (7.1 +/- 0.3 vs. 8.1 +/- 0.6 h, p less than 0.02). These alterations in theophylline clearance and elimination were greater in subjects who had lower control theophylline clearance. Theophylline clearance and elimination t 1/2 recorded with inhaled albuterol were not significantly different from control values. Coadministration of oral albuterol and theophylline resulted in enhancement of theophylline clearance, particularly in subjects with initially slow theophylline elimination. Such patients may require theophylline dosage adjustment as a result of this interaction.

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.

Clinical pharmacokinetics of beta-agonists

The beta-agonists have found wide clinical use as racemic mixtures for 20 years, but information on their pharmacokinetics is not comprehensive. They are well absorbed orally, but have low systemic availability due to extensive first-pass sulphation. When administered by inhalation, very little of the administered dose reaches the lungs, but the small amount that does produces effective bronchodilatation. Plasma protein binding of most beta-agonists is negligible, and there is substantial extravascular distribution of the administered dose. Elimination of intravenous drug is predominantly renal, whereas oral doses are mostly eliminated by biotransformation. Renal clearance correlates with creatinine clearance; therefore, dose reduction should be considered if renal function is impaired, such as in the elderly or in cardiac failure. The elimination half-life of most beta-agonists is relatively short, and pharmacokinetics are independent of dose and duration of treatment. Differences in the pharmacokinetics of the enantiomers are evident. There is very large variation in pharmacodynamic response for a given plasma beta 2-agonist concentration among different subjects, and as treatment proceeds in an individual subject. Therefore, in most cases therapeutic response and side effects are more useful for the monitoring of beta 2-agonist treatment than measurement of plasma drug concentrations. The pharmacokinetics of beta 2-agonists are not greatly altered in pregnancy although these agents cause a marked reduction in maternal renal function. Placental transfer is relatively rapid, and side effects are observed in fetus and neonate. Elimination may be somewhat faster in children (8 to 15 years) than in young adults. Asthma does not appear to influence the pharmacokinetics of beta 2-agonists; the only recorded drug interaction of clinical significance is an increase in theophylline clearance by intravenous isoprenaline (isoproterenol). Controlled release oral preparations do not reduce side effects, but may improve compliance due to less frequent dosing. The application of pharmacokinetic principles may improve the clinical usage of beta-agonists, at least when they are used in premature labour and in cardiac failure.

Increased theophylline clearance in asthmatic patients due to terbutaline

The pharmacokinetic mechanism of the theophylline-terbutaline interaction has been studied. Sustained release theophylline 200-400 mg b.d. was given with placebo or terbutaline 2.5 mg t.d.s. to six adult asthmatic patients. Terbutaline decreased the serum trough theophylline levels from 8.1 to 7.3 micrograms/ml, improved daily the clinical score from 1.51 to 1.26 and increased the peak expiratory flow rate from 316 to 370 l/min. In a single dose study following the chronic therapy, it was shown that there was no change in the peak theophylline concentration or in the timing of the peak, but the t1/2 was reduced from 9.0 to 7.5 h, and the systemic clearance was increased from 20.2 to 24.8 ml.h-1.kg-1. Thus, terbutaline reduced the serum theophylline concentration by increasing its systemic clearance.

Acute effects of short-term subcutaneous terbutaline on theophylline disposition

Theophylline and subcutaneous terbutaline are frequently used concurrently in the management of acute asthma. Recent evidence demonstrating a reduction in theophylline serum concentrations during concomitant oral terbutaline therapy prompted our evaluation of subcutaneous terbutaline's effect on theophylline pharmacokinetics. Using a randomized, placebo controlled, crossover design, the disposition of a single oral theophylline dose (7 mg/kg) was studied in eight healthy, adult males before and after repeated subcutaneous administration of terbutaline (0.25 mg). Two-way analysis of variance revealed no significant difference in elimination rate constant (ke), area under the concentration-time curve (AUC), or apparent oral clearance (CL/F) of theophylline following terbutaline administration. These results indicate that subcutaneous administration of terbutaline does not alter the pharmacokinetics of single, oral doses of theophylline in adults.

Treatment of acute asthma. Is combination therapy with sympathomimetics and methylxanthines indicated?

The role of bronchodilator regimens combining a sympathomimetic and a methylxanthine in the treatment of acute exacerbations of asthma remains controversial. This report describes the outcome of 157 emergency room visits for asthma in which patients were randomly assigned to single-drug therapy with intravenous aminophylline, subcutaneous epinephrine, or inhaled isoproterenol or to one of three regimens combining a sympathomimetic and a methylxanthine. The increase in one-second forced expiratory volume after one hour of treatment with the two-drug combinations (0.79 +/- 0.07 liter) was significantly greater than for epinephrine alone (0.57 +/- 0.08 liter; p less than 0.05) but did not differ significantly from that occurring with therapy with isoproterenol alone (0.72 +/- 0.09 liter; p = NS). This disparity reflects the greater bronchodilation effected by isoproterenol as a single agent than by epinephrine, in the dosing schedules and routes of administration chosen. Among patients presenting with severe airflow obstruction (one-second forced expiratory volume 35 percent or less of normal), the bronchodilator response to isoproterenol alone was 0.88 +/- 0.14 liter versus 0.51 +/- 0.11 for epinephrine alone (p less than 0.05). It is concluded that the observed benefit derived from use of combination therapy depends on the dosage and potency of the particular sympathomimetic to which a methylxanthine is added, and on the severity of the airflow obstruction at presentation.