Aminophylline is less potent and shorter-acting than theophylline. Its most common use is in the treatment of airway obstruction from asthma or COPD. It is used off-label as a reversal agent during nuclear stress testing. Aminophylline is a nonselective adenosine receptor antagonist and phosphodiesterase inhibitor.
It is more soluble in water than theophylline. White or slightly yellowish granules or powder, having a slight ammoniacal odor and a bitter taste. Upon exposure to air, it gradually loses ethylenediamine and absorbs carbon dioxide with the liberation of free theophylline. Its solutions are alkaline. 1 g dissolves in 25 mL of water to give a clear solution; 1 g dissolved in 5 mL of water crystallizes upon standing, but redissolves when a small amount of ethylenediamine is added. Insoluble in alcohol and in ether.
Adenosine is an endogenous extracellular messenger that can regulate myocardial oxygen needs. It acts through cellular surface receptors which effect intracellular signalling pathways to increase coronary artery blood flow, slow heart rate, block atrioventricular node conduction, suppress cardiac automaticity, and decrease β-adrenergic effects on contractility. Adenosine also antagonizes chronotropic and ionotropic effects of circulating catecholamines. Overall, adenosine decreases the heart’s rate and force of contraction, which increases blood supply to the cardiac muscle. Given specific circumstances this mechanism (which is intended to protect the heart) may cause atropine-resistant refractory bradyasystole. Adenosine’s effects are concentration-dependent. Adenosine’s receptors are competitively antagonized by methylxanthines such as aminophylline. Aminophylline competitively antagonizes the cardiac actions of adenosine at the cell surface receptors. Thus, it increases heart rate and contractility.
Precautions, contraindications and interactions
Aminophylline can lead to theophylline toxicity. Aminophylline has been found to decrease the sedative effects of propofol and decrease topiramate antiseizure action.
Aminophylline is used to reverse regadenoson, dipyridamole or adenosine based infusions during nuclear cardiology stress testing.
Some suggest aminophylline may be administered in resuscitation efforts to re-establish cardiac rhythm. However, a 2007 metanalysis concluded aminophylline offers no benefit in this scenario.
Aminophylline has shown some promise as a bodyfat reducer when used as a topical cream (sometimes referred to as "cutting gel"). Aminophylline is also a treatment option for anaphylactic shock.