asthma - bronchodilator Xanthine drugs

Question 1

Give an example of an oral Xanthine drug

Answer 1

Theophylline (1,3-dimethylxanthine)

Question 2

Give an example of an Xanthine drug administered via slow IV injection followed by infusion

Answer 2

Aminophyline (theophylline ethylendiamine)

Question 3

What is the clinical use of Xanthine drugs, when are they used?

Answer 3

They are used in addition to steroids in patients non-responsive to β2-adrenoceptor agonists and in patients with acute severe asthma

Question 4

What is the mechanism of action of Xanthine drugs?

Answer 4

mechanism still unclearthought to be

• phosphodiesterase inhibitor,Increasing cAMP / cGMP levels, leading to smooth muscle relaxation
• Interaction with G proteins
• Antagonism of adenosine receptors (explains cardiac side effects)
• Stimulate CNS / respiratory centres

Question 5

What is the therapeutic window for side effects of Xanthine drugs?

Answer 5

• 30-100 μmol/L = therapeutic benefit
• > 110 μmol/L = adverse effects
• > 200 μmol/L = significant adverse effects

Question 6

What are the CNS side effects of Xanthine drugs?

Answer 6

insomnia
nervousness
seizures

Question 7

What are the CVS side effects of Xanthine drugs?

Answer 7

palpitations
tachycardia
dysrhythmia (most likely with aminophylline)

Question 8

Pharmacokinetics -

What enzyme metabolizes Theophylline, and where is this enzyme found?

Answer 8

metabolized by P450 enzymes in liver

Question 9

What drug induces P450 enzymes and thus reduces the action of theophylline?

Answer 9

carbamazepine

Question 10

What drug iinhibits P450 enzymes and thus increases the action of theophylline?

Answer 10

clarithromycin

Question 11

When is clarithromycin used therapeutically?

Answer 11

To treat chest infections in asthmatic patients