Theophylline Flashcards
Therapeutic Index
10-20mg/L
NARROW
Plasma protein binding
40%
LOW
Describe the metabolism
90% metabolised in liver via CYP450
Describe elimination
90% metabolised
10% via kidney unchanged (urine)
FIRST ORDER KINETICS
VARIABLE rates
What factors affect clearance?
age, illness, thyroid function, smoking, diet, drugs
INTERACTIONS
SSRIs, quinolone antibiotics, allopurinol, erythromycin, cimetidine
SMOKING
Which BTS step introduces theophylline - in which form?
STEP 3: SR theophillyne
STEP 4 as an add-on
Theophylline structure
PURINE derivative
similar to caffeine
Indications
chronic asthma
severe asthma
COPD
Define SUSTAINED RELEASE TABS
modified tabs to release drug at a predetermined rate -> achieve constant drug serum conc
Advantages of SR tabs
Avoid toxicity Prolonged half life & efficacy Control of drug plasma levels ONE DAILY DOSE - enhances patient compliance Relieve morning symptoms of asthma
Compare distribution or oral & IV theophylline
ORAL: follows one compartment model (simple)
IV: follows PK of a 2 compartment model
Effects of theophylline
reduces inflammation
enhances effects of B2-agonists & corticosteroids
Mechanism
AFFECTS MANY PATHWAYS & MEDIATORS
Side effects
NON-SPECIFIC