Methlyxanthines

Methylxanthines

• Definition: A category of medications used in the long-term management of chronic stable asthma. Not widely used at present for COPD (Chronic Obstructive Pulmonary Disease).

Prototype and Other Medications

• Prototype Medication: Theophylline

  • Can be extended-release, offering 24-hour coverage for clients metabolizing it at a normal rate.

  • Not appropriate for individuals who metabolize medications faster, e.g., smokers.

  • Assessment: Blood levels should be assessed periodically for safety.

• Aminophylline: Preferred for intravenous administration (generic only).

Expected Pharmacologic Action

• Mechanism of Action: Methylxanthines relax smooth muscles of bronchi by blocking phosphodiesterase.

Adverse Drug Reactions

• Common Side Effects at Therapeutic Levels: Restlessness, insomnia, nausea, vomiting, diarrhea, palpitations, muscle twitching.

• Toxicity Indicators: Blood level exceeds 20 mcg/mL; life-threatening seizures, dysrhythmias may occur.

• Therapeutic Range: 10 to 20 mcg/mL.

Interventions

• Monitoring: Regular blood level checks to maintain therapeutic range and prevent delayed metabolism leading to toxicity.

• Response to Elevated Levels: Notify provider for possible dosage adjustment or to discontinue medication until a safe blood level is restored.

• Activated Charcoal: Can be given to decrease additional absorption during toxicity.

• Monitoring: Heart rate and rhythm closely during treatment.

Safety Alert

• If life-threatening cardiac dysrhythmias occur, antidysrhythmics may be necessary.

• For seizures, administer anticonvulsants and implement seizure precautions.

Administration

• Oral Administration: Base initial dose on age, weight, and metabolism.

  • Administer at prescribed intervals to maintain therapeutic blood levels.

  • Missed Dose: Do not double; follow provider's instructions.

  • Tablets: Chewable tablets must be chewed thoroughly; do not crush sustained-release or enteric-coated forms.

• Intravenous Use: Reserved for emergencies; infuse slowly at prescribed rates.

Client Instructions

• Caffeine Reduction: Advise clients to limit or eliminate caffeine to reduce CNS stimulation.

• Laboratory Tests: Encourage periodic tests to monitor medication levels.

• Adverse Effects Awareness: Provide a list of potential ADRs indicating elevated blood levels and when to notify the provider.

  • Instruct clients to stop medication and contact their provider if experiencing toxic effects (seizures, irregular heart rate).

Contraindications and Precautions

• Caution: Use in patients who smoke tobacco or marijuana.

• Drug Interactions: Clients on medications for seizure disorders, tuberculosis, peptic ulcer disease, or certain bacterial infections need dosage adjustments to prevent interactions.

Interactions

• Food and Drug Interactions:

  • Increased Risk of Toxicity: Combining with cimetidine (Tagamet), fluoroquinolones, or caffeine.

  • Decreased Blood Levels: Use of nicotine, phenobarbital, and phenytoin increases metabolism of theophylline, reducing its effect.