Xanthines Beta-2 agonists

The concurrent use of xanthines such as theophylline and beta-agonist bronchodilators is a useful option in the management of asthma and chronic obstructive pulmonary disease, but potentiation of some adverse reactions can occur, the most serious being hypokalaemia and tachycardia, particularly with high-dose theophylline. Some patients may have a significant fall in serum theophylline levels if given oral or intravenous salbutamol (albuterol) or intravenous isoprenaline (isoproterenol). 

Beta2 agonists can cause hypokalaemia, particularly when they are given parenterally or by nebulisation. Xanthines such as theophylline can also cause hypokalaemia, and this is a common feature of theophylline toxicity. The potassium-lowering effects of both these groups of drugs are additive. Why some beta agonists lower serum theophylline levels is not known. 

Furukawa, C. T. (1988). Comparative trials including a beta 2 adrenergic agonist, a methyl-xanthine, and a mast cell stabilizer. Ann. Allergy 60,472-476. 

Metaproterenol (Alupent, Metaprel) [Bronchodilator/ Beta-Adrenergic Agonist] Uses Asthma reversible bronchospasm Action Sympathomimetic bronchodilator Dose Adults. Neb 0.2-0.3 mL in 2.5-3.0 mL of NS Peds. Neb 0.1-0.2 mL/kg of a 5% soln in 2.5 mL NS Caution [C, /-] Contra Tach, other arrhythmias Disp Aerosol 0.65 mg/inhal soln for inhal 0.4, 0.6% tabs 10, 20 mg syrup 10 mg/5 mL SE Nervousness, tremors (common), tach, HTN Interactions T Effects W/ sympathomimetic drugs, xanthines T risk of arrhythmias W/ cardiac glycosides, halothane, levodopa, theophylline, thyroid hormones T HTN W/ MAOIs effects W/ BBs EMS Separate additional aerosol use by 5 min fewer 3i effects than isoproterenol longer-acting monitor lung sounds before/after administration... 

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