As an effective bronchodilator, theophylline causes relaxation of bronchial smooth muscle by blocking adenosine receptors. This action decreases airway resistance and increases airflow to the lungs.
Oral theophylline decreases the frequency and severity of asthma attacks and is indicated as maintenance therapy for chronic asthma. This drug's long duration of action in the sustained release form makes it an appropriate medication for patients with nocturnal attacks. Although intravenous theophylline is available, this route is used only in emergencies due to the risk of fatal cardiovascular reactions.
Since this medication causes CNS stimulation, an elevated theophylline blood level between 20-25 mcg/mL may cause insomnia.
A theophylline blood level between 20-25 mcg/mL may cause restlessness. Avoid giving theophylline with caffeine to prevent excess CNS excitation that may exacerbate the restlessness.
Theophylline toxicity, which typically presents with drug plasma levels about 30 mcg/mL, may cause arrhythmias such as ventricular fibrillation. Administering lidocaine (see Picmonic "Lidocaine") may help control severe cardiac dysrhythmias.
Theophylline toxicity, which typically presents with drug plasma levels about 30 mcg/mL, may cause seizures. Administering IV diazepam may help decrease seizure activity.
Since theophylline has a narrow therapeutic range, the dosage of this drug must be carefully managed in relation to the patient's plasma levels. If the patient presents with symptoms indicating a mild reaction (i.e., nausea, vomiting, diarrhea, insomnia, and restlessness), the medication should be stopped immediately before more serious symptoms associated with toxicity occur (i.e., ventricular fibrillation, convulsions). Drugs such as phenobarbital, phenytoin, and rifampin decrease the effects of theophylline by inducing hepatic drug-metabolizing enzyme production. Medications such as cimetidine and ciprofloxacin inhibit hepatic function and cause increased theophylline plasma levels.
Monitoring theophylline plasma levels is necessary to ensure therapeutic effects and avoid toxicity. Most patients tolerate theophylline blood levels between 5-15 mcg/mL. Theophylline plasma levels of 20-25 mcg/mL may cause mild reactions, while a blood level above 30 mcg/mL may lead to severe adverse effects.
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