Theophyllines

Question 1

1) What class of drug are theophylline and aminophylline?

2) What are the 3 main effects of these drugs?

Answer 1

1) Methylxanthines.

2) Vasodilatation, anti-inflammatory and immunomodulatory.

Question 2

Name the 4 possible mechanisms of action of Methylxanthines.

Answer 2

1) Inhibition of phosphodiesterase enzymes.
2) Adenosine receptor antagonism.
3) Activation of histone deacetylases.
4) Increased diaphragmatic activity and reduced fatigue.

Question 3

1) What 2 pharmacokinetic properties have led to theophylline being produced in modified release preparations?
2) Why are different formulations of theophylline not readily interchangeable?
3) How is theophylline metabolised?

Answer 3

1) Unpredictable absorption and variable plasma half-life.
2) Because theophylline has a narrow therapeutic index and different formulations vary in their release characteristics.
3) By CYP450 enzymes in the liver.

Question 4

1) How should patients taking regular theophylline be monitored?
2) Name 3 drugs that might precipitate theophylline toxicity.

Answer 4

1) By measuring blood theophylline levels.

2) Ciprofloxacin, erythromycin, clarithromycin, fluconazole and ketoconazole.

Question 5

List the 5 main groups of important adverse effects to theophylline.

Answer 5

1) GI upset ( N&V&D)
2) CNS stimulation (insomnia, irritability, dizziness, headache, seizures - at high concentrations).
3) Hypotension from peripheral vasodilation.
4) Hypokalaemia, especially after acute administration
5) Cardiac stimulation produces various arrhythmias.