Interactions with ciprofloxacin and aminophylline toxicity

Aminophylline (and its active component, theophylline) is widely used in the treatment of asthma and chronic obstructive pulmonary disease. Although effective, toxicity is potentially serious, variations in dose requirements are common, and there is a narrow therapeutic index. In most subjects, the target range for plasma theophylline is 10-20 mg/1; however, sideeffects can occur within this range, and are common above 30-40 mg/1 [1]. Common features of toxicity are tachycardia, palpitations, nausea, vomiting, headache, insomnia, arrhythmias, and convulsions; less commonly, rhabdomyolysis and acute renal failure may supervene [1,2]. Both aminophylline and theophylline are metabolized in the liver, and drug levels are affected by hepatic impairment, smoking, alcohol, and cardiac failure [1,3]. The metabolites of theophylline are also active, and are excreted in the urine [3]. A number of commonly prescribed drugs are known to interact with the metabolism of aminophylline, many to increase plasma levels to within the toxic range. Two cases of serious aminophylline toxicity are described, one fatal, which were precipitated by the co-prescription of antibiotics. The management of aminophylline overdose is discussed, with particular respect to the input from the renal and intensive care units.