Methylxanthines: Asthma & COPD Management

• Methylxanthines are used in the long-term management of chronic stable asthma, but are not recommended for COPD.

Prototype and Other Medications

• The prototype methylxanthine is theophylline, which can be extended release for 24-hr coverage.
• Individuals who metabolize medications quickly may not be suitable for extended-release theophylline.
• Blood levels of theophylline should be assessed periodically for safety.
• Aminophylline is the preferred methylxanthine for IV administration.

Expected Pharmacologic Action

• Methylxanthines relax smooth muscles of the bronchi by blocking phosphodiesterase.

Adverse Drug Reactions

• At therapeutic levels, methylxanthines have few side effects.
• When blood levels exceed the therapeutic level, CNS stimulation can cause restlessness and insomnia.
• Other adverse effects include nausea, vomiting, diarrhea, palpitations, and muscle twitching.
• Toxic levels can cause life-threatening seizures and dysrhythmias.
• The therapeutic level of theophylline is 10 to 20 mcg/mL with toxicity occurring at levels greater than 20 mcg/mL.

Interventions

• Monitor blood levels of clients receiving methylxanthines to maintain a therapeutic level.
• Notify the provider if medication levels rise to adjust the dosage or discontinue the medication.
• Administer activated charcoal to decrease absorption.
• Monitor heart rate and rhythm.
• Antidysrhythmics may be necessary for life-threatening cardiac dysrhythmias.
• Initiate anticonvulsant therapy and seizure precautions if a seizure occurs.

Administration

• Administer methylxanthines orally.
• Base the initial dose on age, weight, and factors affecting metabolism and excretion.
• Give methylxanthines at prescribed intervals to maintain a therapeutic blood level.
• Do not double the next dose if a dose is missed.
• Chewable tablets should be chewed thoroughly, while sustained-release or enteric-coated preparations should not be crushed or chewed.
• Intravenous administration is reserved for emergencies and must be infused slowly at the prescribed dosage.

Client Instructions

• Reduce or eliminate caffeine intake.
• Have periodic laboratory testing of medication levels.
• Report adverse drug reactions indicating high blood levels to the provider.
• Stop taking the medication and notify the provider immediately if seizures or irregular heart rate occur.

Contraindications and Precautions

• Use cautiously in patients who smoke tobacco or marijuana.
• Clients taking medications for seizure disorders, tuberculosis, peptic ulcer disease, or bacterial infections need to be aware of medication interactions and adjust dosages.
• Metabolic rates are affected by age, medications, disease, and smoking.

Interactions

• Cimetidine and fluoroquinolones increase the risk of toxicity.
• Caffeine increases methylxanthine levels.
• Nicotine, phenobarbital, and phenytoin decrease blood levels of theophylline.
• Cimetidine increases the risk for methylxanthine toxicity.

Question and Answer

• The client who drinks two cups of coffee each morning needs further instruction because caffeine can increase CNS stimulation and raise theophylline levels, potentially leading to toxicity.

Methylxanthines like theophylline are used for long-term asthma management but not COPD. Theophylline relaxes bronchial smooth muscles. High levels can cause CNS stimulation, nausea, and serious issues like seizures.