theophylline

Theophylline is a methylxanthine drug used as a bronchodilator in the management of asthma and chronic obstructive pulmonary disease (COPD). It is a derivative related to caffeine and theobromine. The therapeutic effects arise from inhibition of phosphodiesterase enzymes, which increases intracellular cyclic adenosine monophosphate (cAMP), and from antagonism of adenosine receptors. This combination promotes smooth muscle relaxation in the airways and may have anti-inflammatory effects.

Administration and pharmacokinetics: Theophylline can be given orally or by intravenous infusion as the salt aminophylline. It has a narrow therapeutic index and requires monitoring of plasma concentrations. Typical target levels are about 5–15 micrograms per milliliter. The drug is mainly metabolized in the liver by cytochrome P450 enzymes (notably CYP1A2) and is excreted renally. Half-life varies with age, liver function, and smoking status: roughly 8 hours in non-smokers, longer in children or liver disease, and shorter in smokers due to enzyme induction.

Clinical use and safety: Theophylline is now less commonly used as a bronchodilator because of toxicity risk and drug interactions. It may be employed as add-on therapy in selected cases of chronic asthma or COPD when other treatments are insufficient or unavailable. Because of the risk of adverse effects, dosing is individualized and regular blood monitoring is recommended. Common side effects include nausea, vomiting, tremor, headaches, and palpitations; toxicity can cause tachyarrhythmias, seizures, and severe CNS effects.

Drug interactions and monitoring: Several drugs and factors alter theophylline levels. Macrolide antibiotics (e.g., erythromycin, clarithromycin), certain fluoroquinolones, and cimetidine can raise levels and toxicity risk. Smoking induces metabolism and lowers levels; rifampin, phenobarbital, and phenytoin also reduce levels. Caffeine-containing products can augment adverse effects. Regular monitoring of serum levels and clinical status is essential.