Theophylline is a bronchodilator used to treat respiratory conditions like asthma and COPD. It works by inhibiting phosphodiesterase and antagonizing adenosine receptors to relax smooth muscle. It has a narrow therapeutic window and can cause side effects like nausea, vomiting, arrhythmias and seizures if levels are too high. Special care must be taken with dosing in children, elderly, and those with liver or kidney problems. Smoking may increase its metabolism and require higher doses to maintain therapeutic levels.

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2.  The methylxanthines (CNS stimulants)
(caffeine, theophylline and theobromine) are
mainly taken in beverages (coffee, tea, cocoa
and soft drinks) to increase alertness, and
administered in respiratory disorders.

3.  Is the prototype xanthine bronchodilator.
 A smooth muscle relaxant used for relief of
bronchospasm in certain respiratory
conditions:
 especially aminophylline a derivative of
theophylline used in asthma & COPD.
 Has a narrow therapeutic index.
 Unpredictable metabolism, propensity for drug
reactions & prominent side-effects.

4.  Has useful anti-inflammatory effects & may
increase responsiveness to corticosteroids in
pts. resistant to corticosteroids.
 Stimulant drug that may reduce sedative effects of
benzodiazepines
 An example of hydrophilic(water-soluble) drug that
may accumulate if body water decrease causing
adverse effects.

5.  2 mechanisms postulated:
 Inhibition of Phosphodiesterase (PDE), which
results in an increase in the intracellular
concentration of cAMP & enhanced extrusion of
calcium-smooth muscle relaxed
 It acts on adenosine receptors-antagonize the
effects of adenosine.
▪ Adenosine activates adenylate cyclase, which has cardiac-
depressant, bronchoconstrictor, pro-inflammatory &
platelet-aggregation-suppressant effects.

7.  Half life:
 neonates: 13-26hrs
 Children: 3-4hrs
 Tablets are formulated to optimise
absorption:
 Most provide a bioavailability of 100%.
 Peak plasma levels: 4-6hrs

8.  Should be adjusted to maintain a serum
concentration of 10–20 mg/mL.
 Doses are increased gradually over several
days while monitoring for adverse effects.
 Syrup formulation (5.33mg/mL) available for
children

9. Drug group Example Formulation Duration Usage
Theophyllines Aminophylline Slow IV
injection/infusion
Long-term
COPD
Theophylline CR tablets, syrup CR admin 2/d;
syrup 4/d
Adjunct in
severe
persistent
asthma
• In asthma, it increases cyclic AMP, inhibiting breakdown of sensitised mast
cells that stimulate release of mediators

10. DRUG
Paracetamol, caffeine, propanolol,
methadone & theophylline
Smoking increases metabolism of many
drugs, resulting in lower blood
concentrations, so higher or more
frequent drug dosing may be required.
• Metabolized by CYP1A2 in liver(& caffeine):
Cigarette induces expression of CYP1A2 thus, increases metabolism of caffeine &
theophylline & clozapine.

11.  It produces a mild diuretic effect by
increasing renal blood flow & glomerular
filtration rate and decreasing the tubular
reabsorption of sodium & water.
 Causes cerebral vasoconstriction & has been
trialled in ischaemic stroke; may induce
collateral vessels formation.

12.  Use with caution in patients with fever,
gastrointestinal or
 cardiovascular disorders, thyroid or liver
dysfunction and in
 the elderly.

13.  May promote calcium-stone formation.
 A cause of poisoning:
 Tremors & Convulsion(s)
 Hyperventilation
 Arrhythmias
 May cause profuse vomiting-hypotension.
 Nausea/Vomiting
 Abdominal pain
 Diarrhoea
 Hyperreflexia
 Headache
 Restlessness & irritability
 May induce insomnia(sleep disturbances)

14.  Sources:
 Clinical Medicine, 8th Ed., Kumar & Clarks.
 Pharmacology for Health Professionals, 4th Ed., B.
Bryant & K. Knights.
 Davidson’s Principles & Practice of Medicine, 22nd
Ed., B.Walker & I. Penman