Asthma sympathomimetics

Ephedra distachya L. China 1-ephedrine, 1-methylephedrine, 1-norephedrine, methylephedrine, d-pseudoephedrinem, d-N-methy lpseudoephedrine. 30-3133 This herb is toxic. Treat asthma, sympathomimetic action, relieve headache, body ache, and coughing, lower fever by increasing perspiration. 

Sympathomimetics (drugs that mimic the sympathetic nervous system) are used primarily to treat reversible airway obstruction caused by bronchospasm associated with acute and chronic bronchial asthma, exercise-induced bronchospasm, bronchitis, emphysema, bronchiectasis (abnormal condition of the bronchial tree), or other obstructive pulmonary diseases. 

Derivatives of phenylethanolamine substituted by a phenolic hydroxyl on the para position have been known for some time to exhibit 0-adrenergic agonist activity. As a consequence of this property, the compounds have proven useful as bronchodilators for the treatment of asthma (see Chapter 3). Since such sympathomimetic drugs tend to have undesired activity on the cardiovascular system in addition to the desired activity on the bronchii, considerable work has been devoted to the preparation of compounds that would show selectivity for the adrenergic receptors (02> that predominate in the lung. Attachment of the side chain to a heterocyclic aromatic phenol has been one avenue that has shown promise for achieving this selectivity. 

Bronchodilators. Narrowing of bronchioles raises airway resistance, e.g in bronchial or bronchitic asthma Several substances that are employed as bronchodilators are described elsewhere in more detail P2-sympathomimetics (p. 84, given by pulmonary, parenteral, or oral route), the methylxanthine theophylline (p. 326, given parenterally or orally), as well as the parasympatholytic ipratropium (pp. 104, 107, given by inhalation). 

Sympathomimetics Accor6 ng to the National Asthma Education and Prevention Program s Expert Panel Report II, long-acting 2-agonists (eg, salmeterol) are used... 

Metaproterenol (Alupent, Metaprel) [Bronchodilator/Beta Adrenergic Agonist] Uses Asthma rev ible bronchospasm Action Sympathomimetic bronchodilator Dose AduUs. Inhal 1-3 inhal q3-4h, 12 inhal max/24 h wait 2 min between inhal PO 20 mg q6-8h Peds. Inhal 0.5 mg/kg/dose, 15 mg/dose max inhaled q4-6h by neb or 1-2 puffs q4-6h PO 0.3-0.5 mg/kg/dose... 

The sympathomimetic or adrenergic or adrenomimetic drugs mimic the effects of adrenergic sympathetic nerve stimulation. These are the important group of therapeutic agents which may be used to maintain blood pressure and in certain cases of severe bronchial asthma. 

One of the most important uses of sympathomimetic drugs is in the therapy of bronchial asthma. This use is discussed in Chapter 20. Nonselective drugs (epinephrine), -selective agents (isoproterenol), and B2-selective agents (albuterol, metaproterenol, terbutaline) all are available for this indication. Sympathomimetics other than the 32-selective drugs are now rarely used because they are likely to have more adverse effects than the selective drugs. 

The drugs most used for management of asthma are adrenoceptor agonists, or sympathomimetic agents (used as "relievers" or bronchodilators) and inhaled corticosteroids (used as "controllers" or anti-inflammatory agents). Their basic pharmacology is presented in detail elsewhere (see Chapters 9 and 39). In this chapter, we review their pharmacology relevant to asthma. 

The sympathomimetic agents that have been widely used in the treatment of asthma include epinephrine, ephedrine, isoproterenol, and albuterol, and other l32-selective agents (Figure 20-4). Because epinephrine and isoproterenol increase the rate and force of cardiac contraction (mediated mainly by receptors), they are reserved for special situations (see below). 

The 32-selective adrenoceptor agonist drugs, particularly albuterol, are the most widely used sympathomimetics for treatment of the bronchoconstriction of asthma at present (Figure 20-4). These agents differ structurally from epinephrine in having a larger... 

Epinephrine Nonselective and agonist Bronchodilation plus all other sympathomimetic effects on cardiovascular and other organ systems (see Chapter 9) Anaphylaxis, asthma, others (see Chapter 9) rarely used for asthma (B 2-selective agents preferred) Aerosol, nebulizer, or parenteral see Chapter 9... 

During the acute phase of thyrotoxicosis, B-adrenoceptor blocking agents without intrinsic sympathomimetic activity are extremely helpful. Propranolol, 20-40 mg orally every 6 hours, will control tachycardia, hypertension, and atrial fibrillation. Propranolol is gradually withdrawn as serum thyroxine levels return to normal. Diltiazem, 90-120 mg three or four times daily, can be used to control tachycardia in patients in whom blockers are contraindicated, eg, those with asthma. Other calcium channel blockers may not be as effective as diltiazem. Adequate nutrition and vitamin supplements are essential. Barbiturates accelerate T4 breakdown (by hepatic enzyme induction) and may be helpful both as sedatives and to lower T4... 

Metaproterenol (Alupent, Metaprel) [Bronchodilator/ Beta-Adrenergic Agonist] Uses Asthma reversible bronchospasm Action Sympathomimetic bronchodilator Dose Adults. Neb 0.2-0.3 mL in 2.5-3.0 mL of NS Peds. Neb 0.1-0.2 mL/kg of a 5% soln in 2.5 mL NS Caution [C, /-] Contra Tach, other arrhythmias Disp Aerosol 0.65 mg/inhal soln for inhal 0.4, 0.6% tabs 10, 20 mg syrup 10 mg/5 mL SE Nervousness, tremors (common), tach, HTN Interactions T Effects W/ sympathomimetic drugs, xanthines T risk of arrhythmias W/ cardiac glycosides, halothane, levodopa, theophylline, thyroid hormones T HTN W/ MAOIs effects W/ BBs EMS Separate additional aerosol use by 5 min fewer 3i effects than isoproterenol longer-acting monitor lung sounds before/after administration... 

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