Theophylline

Question 1

Mechanism of action of theophylline

Answer 1

“Xanthine derivative”
Inhibitor of phosphodiesterase, reducing the breakdown of cAMP hence promoting bronchodilation
Relaxes smooth muscles located in airways and reduces its responsiveness to hormones/allergens

Question 2

Indications of theophylline

Answer 2

In moderate to severe asthma - as additive treatment to inhaled glucocorticoids and beta adrenergic drugs
- It is a sustained release preparation
- Long duration of action

Question 3

Therapeutic index of theophylline

Answer 3

10-20mg/l
55-110 micromol/L

To avoid toxicity, the target range in asthma is 5-15mg/L.

Question 4

Monitoring parameters for theophylline

Answer 4

• U+E’s esp K+ - depresses K+ uptake leading to hypokalaemia
• Lung function test
• Liver function - theophylline is metabolised in the liver

Question 5

Toxic side effects of theophylline

Answer 5

• Nausea and vomiting
• Diarrhoea
• Tachycardia
• Palpitations
• Nervousness
• Agitation
• Seizures
• Arrythmias

Question 6

Theophylline concentration increased in

Answer 6

• Heart failure
• Cirrhosis
• Viral infections
• In the elderly
• Drugs that inhibit its metabolism

Question 7

Theophylline concentration reduced in

Answer 7

• Smokers
• Chronic alcoholism
• Drugs that induce liver metabolism

Question 8

Theophylline and quinolones

Answer 8

Increases risk of convulsions

Question 9

Theophylline and erythromycin

Answer 9

• Interaction avoided by choosing azithromycin instead of erythromycin
• Half dose of theophylline for duration on ciprofloxacin or erythromycin or omit the morning/night time dose if dose cannot be halved
• Continue with original dose when interaction is withdrawn