Theophylline
·
xanthine derivative
·
treats asthma and stable COPD to relax the
bronchial smooth muscle
·
serum theophylline concentration of
10–20mg/L
·
Symptoms of theophylline toxicity
o Nausea
o Vomiting
o Gastric
irritation
o Diarrhea
o Palpitations
o Tachycardia
o Arrhythmias
o Headache
o Central
nervous system stimulation
o Insomnia
o Convulsions
·
Metabolized in the liver by CYP1A2
o Cirrhosis,
congestive heart failure, and hepatitis reduce theophylline clearance
·
Common drug interactions
o Benzodiazepines
§ theophylline
antagonizes the sedative and anxiolytic effects of benzodiazepines
o H2-receptor
antagonists
§ theophylline
concentrations are increased by cimetidine
§ famotidine,
nizatidine, and ranitidine do not interact
o Ciprofloxacin
§ theophylline
concentrations are increased
o Erythromycin
§ theophylline
concentrations are increased because theophylline clearance is reduced
o Levothyroxine
§ theophylline
concentrations are increased with hypothyroidism treatment
o Methotrexate
§ theophylline
concentrations are increased because theophylline clearance is reduced
§ might
reduce methotrexate-induced neurotoxicity and methotrexate efficacy
o Phenytoin
§ theophylline
concentrations are decreased because increases the clearance of theophylline
·
Age
o neonates
and elderly have reduced theophylline clearance
·
Smokers
o smokers
need higher theophylline doses than non-smokers
o tobacco
smoke induces CYP1A2
o smoking
cessation results in increase in serum theophylline concentrations
o reduce
theophylline dose with smoking cessation
·
Adverse effects
o risk
of QT-interval prolongation with theophylline AND citalopram or fluoxetine
together
o low
potassium, magnesium or calcium can cause QT prolongation
Source:
http://www.pharmaceutical-journal.com/learning/learning-article/theophylline-interactions/20065570.article
http://www.rxkinetics.com/manual.html