Theophylline Flashcards
1
Q
Range
A
Therapeutic Range: 10 to 20mg/L (55 to 110micromol/L)
(although a plasma theophylline concentration of 5 to 15mg/L may still be effective) Loading doses may be required
2
Q
Monitoring
A
Serum potassium, plasma theophylline concentration
Plasma-theophylline concentration is measured 5 days after starting oral treatment and at least 3 days after any dose adjustment
HEPATIC METABOLISM
3
Q
Warning signs
A
- Toxicity e.g. vomiting (may be intractable), agitation, restlessness, dilated pupils, sinus tachycardia, hyperglycaemia, severe hypokalaemia may develop rapidly, haematemesis, convulsions, cardiac arrhythmias
- Symptoms of uncontrolled asthma (cough, wheeze, tight chest)
- Frequent courses of antibiotics and/or oral corticosteroids
4
Q
Action and interaction
A
- Advise patient to report immediately to a doctor if any warning signs occur
- Inform the patient of potential interactions with theophylline and the need to check with a pharmacist or doctor before taking any new medication (including OTC, prescribed or herbal medicines)
- Advise patient to inform their GP before stopping or starting smoking
- Emphasise the importance of maintaining on the same brand of medicine and recommend that the patient always checks when collecting their medicine from a pharmacy and when taking the medicine; the rate of absorption from modified-release preparations can vary between brands
Interactions
- Potentially serious hypokalaemia may result from beta2 agonist therapy. Caution required in severe asthma, because this effect may be potentiated by concomitant use of theophylline, corticosteroids, and diuretics as well as hypoxia. Plasma potassium should be monitored in severe asthma
- Increased plasma concentrations with diltiazem, cimetidine, ciprofloxacin, erythromycin, oestrogens, fluvoxamine, verapamil
- Possible increased risk of convulsions when theophylline given with quinolones
- Reduced plasma concentrations with carbamazepine, primidone, phenobarbital and phenytoin, ritonavir
