Management of Asthma

Elimination of the causative agents from the environment of an allergic asthmatic is the most successful means available for treating this condition.

Desensitization or immunotherapy with extracts of the suspected allergens has enjoyed widespread favor, but controlled studies are limited and have not proved it to be highly effective.

Drug Treatment:

The drugs used in the treatment of asthma may be grouped conveniently into five categories, beta-adrenergic agonists, methylxanthines, flucocorticids, mast cell stabilizing agents and anticholinergics. Inhibitors of mediator synthesis and mediator receptor antagonists are currently undergoing clinical trials.

Adrenergic Stimulants:

The drugs in this category consist of the catecholamines, resorcinols, and saligenins. These agents are analogues and produce airway dilation through stimulation of beta receptors with the resultant formation of cyclic AMP.

They also decrease the release of mediators and improve mucociliary transport. The catecholamines in widespread clinical use are epinephrine, isoproterenol, isoetharine, rimiterol and hexopenaline.

The last two are not available in the United States. As a group, these compounds are short acting and effective only by inhalational or parenteral routes.

Epinephrine and isoproterenol are not beta selective and have considerable chronotropic and inotropic cardiac effects. Epinephrine also has substantial alpha stimulating effects.

The usual dose is 0.3 to 0.5 ml of a 1:1000 solution administered subcutaneously. Isoproterenol is devoid of alpha activity and is the most potent agent of this group. It is usually administered in a 1:2000 solution by inhalation.

Isoetharine is the most beta selective compound of this class, but it is a relatively weak bronchodilator. It is employed as an aerosol and supplied as a 1 percent solution. The pharmacologies of hexoprenaline and rimiterol are similar to that of isoetharine.

The commonly used resorcinols are metaproterenol, terbutaline, and fenoterol, and the most widely known saligenin is albuterol, or salbutamol.

With the exception of metaproterenol, these drugs are highly selective for the respiratory tract and virtually devoid of significant cardiac effects except in high doses.

Their major side effect is tremor. They are active by all routes of administration and because their chemical structures allow them to bypass the metabolic processes used to degrade the catecholamines.

Their effects are long lasting, exceeding 6 h in many studies. Differences in potency and duration between agents can be eliminated by adjusting doses and administration schedules.

Inhalation is the preferred route of administration because it increases the bronchial selectivity of these drugs and allows maximal bronchodilation to occur with fewer side effects.

This is true not just in maintenance therapy but also during the treatment of severe acute obstruction. In the past it was fashionable to treat episodes of severe asthma with intravenous sympathomimetics such as isoproterenol.

This approach no longer appears justifiable. Isoproterenol infusions clearly can induce myocardial damage, and even the beta selective agents such as terbutaline and albuterol when given intravenously offer no advantages over the inhaled route.

For maintenance therapy, long acting theophylline compounds are available and are usually given twice per day or once daily. The dose is adjusted on the basis of the clinical response with the aid of serum theophylline levels.

Single dose administration in the evening may reduce nocturnal symptoms. In contrast to the large number of oral compounds, aminophylline is the only compound available for intravenous use.

The recommendations for intravenous therapy in children aged 9 –16 and young adult smokers not currently receiving theophylline products are as follows: A loading dose of 6 mg is given followed by an infusion of 1.0 mg er hour for the next 12 h and then 0.8 mg per hour thereafter.

The most common side effects of theophylline are nervousness, nausea, vomiting, anorexia and headache. At plasma levels greater than 30 ml, there is a risk of seizures and cardiac arrhythmias.

Cromolyn sodium and nedocromil sodium are not bronchodilators. Their major therapeutic effects are inhibition of degranulation of mast cells, thereby preventing the release of the chemical mediators of anaphylaxis.

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