Beta-agonist bronchodilators

Beta-agonist bronchodilators + Potassium-depleting drugs Hypoloilaemia... 

Halothane is known to cause arrhythmias and it has been suggested that it may increase susceptibility to the adverse cardiac effect of beta-agonist bronchodilators, which can cause arrhythmias. Note that beta agonists such as terbutaline are sympathomimetics (see Table 24.1 , (p.879)), like adrenaline (epinephrine), which has also been shown to cause arrhythmias in the presence of halothane (see Anaesthetics, general + Inotropes and Vasopressors , p.99). 

When anaphylactic reactions do occur in patients taking beta blockers, it may be preferable to use a beta-agonist bronchodilator such as isoprena-line rather than adrenaline (epinephrine). Glucagon, which has inotropic and chronotropic actions that are only minimally antagonised by beta blockers, may also be effective in reversing anaphylactoid shock in patients taking beta blockers. ... 

Direct stimulators of beta-1 and beta-2 receptors (beta-agonist bronchodilators) ... 

The interaction between phenylephrine and the MAOIs is dealt with elsewhere (see MAOIs orMMAs + Sympathomimetics Phenylephrine , p. 1148). Consider also MAOIs or RIMAs + Sympathomimetics Beta-agonist bronchodilators , p.ll46 and Inotropes and Vasopressors Dopamine + Selegiline , p.893, for dosing advice with when dopamine is given to patients taking MAOIs. 

Non-cardioselective beta blockers (e.g. propranolol, timolol) should not be used in asthmatic subjects because they may cause serious bronchoconstriction, even if given as eye drops. Non-car-dioselective beta blockers oppose the bronchodilator effects of beta-agonist bronchodilators, and higher doses may be required to reverse bronchospasm. Even cardioselective blockers (e.g. atenolol) can sometimes cause acute bronchospasm in asthmatics. However, cardioselective beta blockers do not generally inhibit the bronchodilator effect of beta-agonist bronchodilators. 

No adverse pharmacodynamic interaction normally occurs between beta-agonist bronchodilators and cardioselective beta blockers. This has been demonstrated in studies with ... 

Beta-agonist bronchodilators + Potassiunn-depleting drugs... 

The concurrent use of salbutamol (albuterol) or terbutaline and theophylline can cause an additional fall in serum potassium levels, and other beta2 agonists will interact similarly. See Theophylline -i- Beta-agonist bronchodilators , p.l 174. 

The concurrent use of xanthines such as theophylline and beta-agonist bronchodilators is a useful option in the management of asthma and chronic obstructive pulmonary disease, but potentiation of some adverse reactions can occur, the most serious being hypokalaemia and tachycardia, particularly with high-dose theophylline. Some patients may have a significant fall in serum theophylline levels if given oral or intravenous salbutamol (albuterol) or intravenous isoprenaline (isoproterenol). 

Severe bronchoconstriction and reduction in respiratory function can result. Patients with severe hyperreactivity of the airways can experience bronchoconstriction at a dosage as low as 0.025 mg/ml (0.125 cumulative units). If severe bronchoconstriction occurs, reverse immediately by administration of a rapid-acting inhaled bronchodilator (beta-agonist). 

FIGURE 26-1 Mechanism of action of beta agonists on respiratory smooth muscle. Beta agonists facilitate bronchodilation by stimulating adenyl cyclase activity, which in turn increases intracellular cyclic AMP production. Cyclic AMP activates protein kinase, which appears to add an inhibitory phosphate group to contractile proteins, thus causing muscle relaxation and bronchodilation. 

Isoetarine is a beta-adrenoceptor agonist bronchodilator given orally in a modified-release formulation (SED-13, 363) (SEDA-21, 184). It is slightly more beta2-selective than isoprenaline but has a beta-blocking metabolite. 

Emphysema is treated by using bronchodilators such as anticholinergic and beta agonists (ipratropium bromide, theophylline) to open the airway by relaxing muscles around the bronchi. Corticosteroids are used to reduce the inflammation that is associated with emphysema. 

Enantiomer Preparations of Inhaled Drugs. There has been much interest in the differences in effects of enantiomers of many medications, and beta agonist adrenergic bronchodilators have received much attention. Evidence suggests that the (R)-enantiomer of albuterol is mainly responsible for bronchodilation while the (S)-enantiomer may stimulate airway reactivity. Data suggest, however, that after aerosol delivery, the systemic absorption for (R)-albuterol is faster than for (S)-albuterol and that, conversely, the lung retention of (S)-albuterol is longer, which may be detrimental [29]. The extent to which enantiomers will displace racemic preparations is not yet determined. 

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