INDEX theophylline

Historically, the use of xanthines has been hampered by poor aqueous solubiUty, rapid but highly variable metaboHsm, and the existance of a low therapeutic index. SolubiUty problems were partially solved by the preparation of various salt forms, eg, aminophylline. However, it was since recognized that the added base in aminophylline only increases solubiUty by increasing pH and thus does not affect the rate of absorption from the gut (65). Thus, in more recent medical practice, theophylline is commonly dispensed in anhydrous form and aminophylline is only recommended for iv adrninistration. 

Theophylline is also considered an alternative to inhaled corticosteroids for the treatment of mild persistent asthma however, limited efficacy compared to inhaled corticosteroids, a narrow therapeutic index with life-threatening toxicity, and multiple clinically important drug interactions have severely limited its use. Theophylline causes bronchodilation through inhibition of phosphodiesterase and antagonism of adenosine and appears to have anti-inflammatory and immunomodulatory properties as well.36... 

Theophylline is a non-specific phosphodiesterase inhibitor that increases intracellular cAMP within airway smooth muscle resulting in bronchodilation. It has a modest bronchodila-tor effect in patients with COPD, and its use is limited due to a narrow therapeutic index, multiple drug interactions, and adverse effects. Theophylline should be reserved for patients who cannot use inhaled medications or who remain symptomatic despite appropriate use of inhaled bronchodilators. 

Theophylline is a drug v/ith a narrov/ therapeutic index, plasma concentrations of v/hich must be maintained at 10-20 mg/L. Plasma concentrations above 20 mg/L increase the severity and frequency of adverse effects. 

Both phenytoin and theophylline have a narrow therapeutic index. 

Theophylline is a narrow therapeutic index drug with significant difference in bioavailability following oral administration. The half-life of the drug is increased by heart failure, cirrhosis and viral infections, in elderly patients, and by certain drugs, such as cimetidine, ciprofloxacin, oral contraceptives and fluvoxamine. The half-life is decreased in smokers, chronic alcoholism, and by certain drugs, such as phenytoin, rifampicin and carbamazepine. 

Severe cases may, however, require an intensified bronchodilator treatment with systemic jk-mimetics or theophylline (systemic use only low therapeutic index monitoring of plasma levels needed). Salmeterol is a long-acting in-halative P2-mimetic (duration 12 h onset -20 min) that offers the advantage of a lower systemic exposure. It is used prophylactically at bedtime for nocturnal asthma. 

Theophylline, a dimethylxanthine, causes broncho-dilation, possibly by inhibiting the enzyme phosphodiesterase in smooth muscle of the bronchioli. An other proposed mechanism of action is that of adenosine receptor antagonism. It has positive chronotropic and inotropic, CNS stimulant and weak diuretic properties. In obstructive lung disease sustained release tablets are to be preferred. Theophy-line has a narrow therapeutic index. Therapeutic plasma concentrations are between 7-15 mg/1. Theophylline undergoes N-demethylation via CYPl A2 in the liver and is eliminated in the urine as metabolites... 

Theophylline has a narrow therapeutic index and produces side effects that can be severe, even life threatening. Importantly, the plasma concentration of theophylline cannot be predicted reliably from the dose. In one study, the oral dosage of theophylline required to produce therapeutic plasma levels (i.e., between 10 and 20 pg/mL) varied between 400 and 3,200 mg/day. Heterogeneity among individuals in the rate at which they metabolize theophylline appears to be the principal factor responsible for the variability in plasma levels. Such conditions as heart failure, liver disease, and severe respiratory obstruction will slow the metabolism of theophylline. 

Geriatric Considerations - Summary Increased risk of side effects in patients with CVD and hepatic dysfunction. Theophylline has a narrow therapeutic index and is associated with numerous drug interactions. Target serum concentrations are 5-20 mg/L, with adverse effects increasing between 15-20 mg/L. Hepatic metabolism and renal excretion declines with age and the half-life of theophylline increases by 3 to 9 hours in older adults. Smoking induces theophylline metabolism therefore, if a pa-tienf sfops smoking, empiric dosage reduction may be indicated and follow serum concenfrafions closely. 

Hartleb M, Romanczyk T, Becker A, et al. (1992) The theophylline disposition after caffeine administration in liver cirrhosis an index of liver function. 

Absorption of theophylline from the gastrointestinal tract is usually rapid and complete. Some 90% is metabolised by the liver and there is evidence that the process is saturable at therapeutic doses. The tis 8 h, with substantial variation, and it is prolonged in patients with severe cardiopulmonary disease and cirrhosis. Obesity and prematurity are associated with reduced rates of elimination, whereas tobacco smoking enhances theophylline clearance by inducing hepatic P450 enzymes. Because of these pharmacokinetic factors and low therapeutic index, monitoring of the plasma theophylline concentration is necessary to optimise its therapeutic effect and minimise the risk of adverse reactions the optimum concentration range is 10-20 mg/1 (55-110 mmol/1). 

Because theophylline has a relatively narrow therapeutic index, it would be desirable to determine a dose at which the maximal and minimal concentrations at steady state will be within the therapeutic concentration range (5-15mg/L). Therefore, the 280 mg bid dose regimen is convenient and adequate to achieve Cmax and Cmin within the therapeutic range. 

Theophylline has a narrow therapeutic index, with 12-25% of overdose patients developing serious or life-threatening symptoms. Age >60 years and chronic use are risk factors for increased morbidity and mortality. 

Theophylline and polycyclic hydrocarbons in tobacco smoke (3-methylcholanthrene) represent a second type of enzyme inducer with broad induction effects. They induce CyP lA in which no change in P4go reductase occurs and a different terminal oxidase appears. After this type of induction, the clearance of tlieophylline but not that of antipyrine is increased. These substances have served as prototypes for the classification of enzyme inducers. Obviously, when patients are on a drug with a narrow therapeutic index, their dosing regimen would need to be adjusted should a known enzyme-inducing drug be added to or deleted from their therapy. 

The principal asthma therapies have all been in clinical practice since the early 1970s and before, yet their mechanisms and potential hazards in many cases remain obscure. The trend towards inhaled corticosteroids continues to raise concerns about their long-term side-effects. This has fuelled efforts to develop safer anti-inflammatory therapies, despite the advent of fluticasone, which is 100 per cent first-pass metabolized in the liver and has fewer systemic effects (Harding, 1990). Suggestions that the long-actingy 2-agonists (salmeterol, formoterol) may be anti-inflammatory appear to be unfounded, but the possibility of an antiinflammatory effect of theophylline (Ward et al., 1993) has accelerated development of selective phosphodiesterase (PDE IV) inhibitors, which may have reduced side-effects and a better therapeutic index than theophylline itself. The immunosuppressants, such as cyclosporin A which prevents expression of IL-2 and IL-2R in T cells, are limited by toxicity to a small minority of very severe corticosteroid-dependent asthmatics. 

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