When a client with chronic obstructive pulmonary disease is taking theophylline also receives ciprofloxacin (Cipro), which of the following interactions would occur?
A. Cipro Toxicity
B. Ineffectiveness of ciprofloxacin
C. Theophylline toxicity
D. Ineffective theophylline
Correct Answer: C. Theophylline toxicity
Theophylline toxicity may occur because the action of theophylline is increased when given with Ciprofloxacin. Theophylline has an extremely narrow therapeutic window. Theophylline toxicity occurs when serum theophylline levels surpass the levels in the therapeutic range. This can occur by intentional overdose or unintentionally when metabolism and/or clearance of theophylline is altered due to certain physiological stressors.
Option A: There is no such thing as Cipro toxicity. Toxic doses of theophylline can be as low as 7.5 mg/kg. When taken orally, 80% to 100% of theophylline is absorbed in the gastrointestinal tract. Peak serum levels can occur from 30 to 120 minutes for immediate release formulations. Sustained-release formulations have peak levels between 6 and 10 hours.
Option B: One mechanism is that theophylline blocks adenosine receptors, which has both therapeutic and toxic effects such as bronchodilation, tachycardia, cardiac arrhythmias, seizures, and cerebral vasoconstriction. At larger doses, theophylline inhibits phosphodiesterase causing increased cyclic adenosine monophosphate resulting in increased levels of adrenergic activation and catecholamine release.
Option D: In theophylline toxicity, epinephrine levels can be 4- to 8-times higher than normal, and norepinephrine concentrations can be 4- to 10-times higher than normal. Increased catecholamine concentrations have a variety of adverse effects such as cardiac arrhythmias, metabolic acidosis, hyperglycemia, and hypokalemia. Chronic theophylline toxicity can occur when there is an accumulation of the drug due to metabolism being overwhelmed or inhibited. It can also occur when clearance is decreased.