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Theophylline
- indication:For the treatment of the symptoms and reversible airflow obstruction associated with chronic asthma and other chronic lung diseases, such as emphysema and chronic bronchitis.
- pharmacologypharmacology:
- mechanism: Theophylline relaxes the smooth muscle of the bronchial airways and pulmonary blood vessels and reduces airway responsiveness to histamine, methacholine, adenosine, and allergen. Theophylline competitively inhibits type III and type IV phosphodiesterase (PDE), the enzyme responsible for breaking down cyclic AMP in smooth muscle cells, possibly resulting in bronchodilation. Theophylline also binds to the adenosine A2B receptor and blocks adenosine mediated bronchoconstriction.
- toxicity: Symptoms of overdose include seizures, arrhythmias, and GI effects.
- absorprion: Theophylline is rapidly and completely absorbed after oral administration in solution or immediate-release solid oral dosage form.
- halflife: 8 hours
- roouteelimination: Theophylline does not undergo any appreciable pre-systemic elimination, distributes freely into fat-free tissues and is extensively metabolized in the liver. Renal excretion of unchanged theophylline in neonates amounts to about 50% of the dose, compared to about 10% in children older than three months and in adults.
- volumedistribution: * 0.3 to 0.7 L/kg
- clearance: * 0.29 mL/kg/min [Premature neonates, postnatal age 3-15 days] * 0.64 mL/kg/min [Premature neonates, postnatal age 25-57 days] * 1.7 mL/kg/min [Children 1-4 years] * 1.6 mL/kg/min [Children 4-12 years] * 0.9 mL/kg/min [Children 13-15 years] * 1.4 mL/kg/min [Children 16-17 years] * 0.65 mL/kg/min [Adults (16-60 years), otherwise healthy non-smoking asthmatics] * 0.41 mL/kg/min [Elderly (>60 years), non-smokers with normal cardiac, liver, and renal function] * 0.33 mL/kg/min [Acute pulmonary edema] * 0.54 mL/kg/min [COPD >60 years, stable, non-smoker >1 year] * 0.48 mL/kg/min [COPD with cor pulmonale] * 1.25 mL/kg/min [Cystic fibrosis (14-28 years)] * 0.31 mL/kg/min [Liver disease cirrhosis] * 0.35 mL/kg/min [acute hepatitis] * 0.65 mL/kg/min [cholestasis] * 0.47 mL/kg/min [Sepsis with multi-organ failure] * 0.38 mL/kg/min [hypothyroid] * 0.8 mL/kg/min [hyperthyroid]