Asthma Medicines

The B-adrenergic agonists available in tablet or elixir form are not for emergency use since they have slow onsets of action (up to one hour). Albuterol, terbutaline, and metaproterenol are available as oral medications. Since they are absorbed into the bloodstream in greater quantity than the inhaled form, there are greater chances of side effects. These include tremors, muscle cramps, nervousness, insomnia, and palpitations. The long-acting oral preparations of albuterol have proved useful for patients with nocturnal asthma, although the long-acting aerosol sprays that have become available also have been effective in this setting. Those patients who have difficulty using a metered-dose inhaler may benefit from the oral preparations.

Another potential advantage of oral preparations is that the medication carried in the blood may reach small bronchial tubes that may not have been reached by inhalation. These small airways are often inflamed and swollen in moderate and severe asthma and receive only a relatively small percentage of the medication inhaled. In addition, there may be thick mucus “plugs” that block the air passages. Aerosol medication may therefore be primarily distributed to the larger, more open passages which receive greater airflow on inhalation. It is conceivable, however, that medication deposited in these larger passages may be absorbed into blood vessels and reach the blood circulation, thereby eventually reaching the smaller airways.

In the asthmatic patient who does not appear to respond fully to aerosol medication, trial with an oral preparation is indicated. Peak flows or spirometry may be performed after a suitable trial of one to two weeks. If flow rates have increased and symptoms have diminished, then the oral preparation of the B2-adrenergic agonist may be used in conjunction with the aerosol. A drawback to this approach will be the greater likelihood of adverse effects from the increased absorption of the B-agonist. Of note, however, is that tolerance to these effects often develops after several days of use. Unfortunately, the elderly population with asthma may be adversely affected more than younger patients. Tremors may be especially severe in older patients. These patients are also more likely to have preexisting cardiac conditions that may increase the risk of adverse effects such as rapid or irregular heart rhythms.

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Theophylline has been used for treating bronchial asthma for nearly sixty years but is a weaker bronchodilator than the B-adrenergic agonists. Although widely used as a bronchodilator, the mechanism of its action is unclear. The most recent theories suggest an anti-inflammatory effect that is supported by the inhibition of the late phase response. Due to the controversy over its mode of action, theophylline has fallen out of favor and is no longer regarded as a first-line asthma medication comparable to the B2adrenergic agonists. As more data is obtained that firmly establishes theophylline as an anti-inflammatory agent it is likely to be regarded again as a first-line agent.

At this time theophylline may still prove useful as a second-line drug. A recent study has demonstrated that theophylline may allow patients who require high doses of inhaled corticosteroids to reduce their steroid dosages. Patients with intolerance to B-agonist side effects may find they are better able to tolerate theophylline. Its availability as an oral medication in a sustained time release form may be preferred by some patients. Dosing is usually on a twice-a-day basis, with some patients able to achieve satisfactory results from once-a-day administration. This once-a-day dose is best given in the evening and may prove extremely helpful in treating nocturnal asthma.

Sustained-Release Preparations

Large numbers of sustained-release theophylline preparations are available by prescription, but they may vary in their rate of release of medication into the bloodstream. Once a certain preparation is prescribed, adjustment of the dosage will require follow-up and blood testing. After the proper dosage is established it is advisable not to substitute one preparation for another since the substitute may not achieve the same results. There is little use for short-acting theophylline preparations since they must be given several times a day.

Intravenous Form: Aminophylline

An intravenous form of theophylline known as aminophylline is available for emergencies. In view of the faster onset of action of the B2-adrenergic agonists intravenous aminophylline would also not be considered a first-line treatment in an emergency room. Although there is some controversy concerning its effectiveness in emergencies, aminophylline’s use as a second-line agent has been established.

Obtaining a Therapeutic level

One drawback to theophylline is that a certain amount must be present to achieve an effect. This has been termed a therapeutic level (10-20 mg of the drug per liter of blood). Some patients, however, may benefit from lower levels. To achieve the therapeutic level a certain dosage must be administered. Dosing is based on the patient’s body weight and when given by mouth may require several adjustments based on blood test results before the achievement of a patient’s daily maintenance dose. When theophylline is given by mouth an effect may be achieved in approximately one hour but it may require two to three days to achieve the desired maintenance level. With intravenous administration of aminophylline a “loading dose” is usually given over thirty minutes, followed by a constant infusion. Blood levels are again required to adjust the intravenous drip. Compared to the rapidly acting B-agonists, theophylline is both weaker and slower in producing bronchodilatation. Of note, however, when theophylline is given at the same time that the patient is receiving the B-agonist, the effect of the two drugs together may be greater than when given alone.

Adverse Effects of Theophylline

Besides the above considerations, theophylline may have significant side effects, often related to high blood levels, but some patients may experience adverse effects from small dosages, including stomach and bowel upset, rapid or irregular heart beat, insomnia, nervousness, urinary frequency, and headache. Some of these effects may be prevented or reduced by avoiding caffeine, which is structurally similar to theophylline; this explains why coffee has often been noted to relieve asthma. Patients should be advised to avoid or reduce caffeine in their diets while receiving theophylline.

Children and Theophylline

One disturbing but controversial side effect has been noted in children. A possible adverse effect on learning and behavior has been raised by some studies. There are conflicting results with additional studies that have not demonstrated these effects. At this time, theophylline should be used with caution in young children. Careful monitoring for changes in behavior patterns and learning must be performed.

Overdosage

In excessive or toxic dosages, theophylline may cause nausea, vomiting, irregular heart rhythms, and seizures. Theophylline should never be used without direction and supervision from the physician. Fatalities have been reported in asthmatics who have overused over-the-counter asthma medications that contain theophylline. These arc preparations should be withdrawn to avoid toxic reactions.

Drugs That Interact with Theophylline

Another important consideration when patients receive theophylline is the potential for drug interaction. This interaction may result in higher blood levels or toxicity from theophylline. One major group of drugs that can interact with theophylline are certain antibiotics, including erythromycin, clarithromycin, ciprofloxacin, levafloxacin, and olfloxacin. In addition, a widely prescribed stomach medication, cimetadine (Tagamet), may also interact with theophylline. One of the anti-leukotrienes, zileuton (Zyflo) has also been found to interact with theophylline. Fortunately, many other antibiotics and stomach medications, and anti-leukotrienes, are compatible with theophylline. In instances where one of the drugs that may interact with theophylline must be given, a reduction in the theophylline dosage may be made in order to avoid toxicity. A simple rule is to cut in half the total daily dose whenever receiving one of the above medications. It is vital to monitor blood levels in that situation.

Factors That Affect Theophylline Breakdown

Other factors may contribute to slower breakdown or clearance of theophylline, such as age, liver disease, and heart disease. Elderly patients have been found to clear theophylline more slowly. Patients with diseases of the liver as well as those with congestive heart failure have also been found to have slower metabolism of theophylline. In these groups, lower dosages of theophylline should be given.

Some drugs may accelerate clearance of theophylline from the body. Cigarette and marijuana smokers are often found to clear theophylline more rapidly than nonsmokers and may need their dosages increased. TWo medications used for epilepsy, phenytoin (Dilantin) and phenobarbital, may also increase breakdown of theophylline.

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Beta-Agonists

Since asthma is characterized by narrowing of bronchial tubes caused by tightening of bronchial wall muscle, treatment has traditionally focused on reversing this process, which is called bronchodilatation. The medications that produce this effect are bronchodilators. At this time the most effective bronchodilators are the Bzadrenergic agonists. These drugs are all derivatives of epinephrine which has effects on both the heart (termed beta-I) and lung (beta-2). Epinephrine is an important hormone produced in the body by the adrenal gland but has been synthesized in the laboratory. The B2-adrenergic agonists have been developed to be “selective” stimulants of lung structures, avoiding unwanted effects on the heart and blood vessels such as high blood pressure and palpitations. Their effects are produced through nerve endings called receptors located within the lungs. One such B2-receptor is located in the muscle layer that surrounds the bronchial tube. With the administration of these agents and stimulation of the receptor the bronchial wall muscle relaxes, producing bronchodilatation.

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Inhaled Corticosteroids

With greater emphasis being placed on the inflammatory nature of bronchial asthma, the anti-inflammatory agents have achieved greater importance in treatment. The most effective anti-inflammatory agents are corticosteroids, limited to oral or injectable forms until relatively recently, when an inhalation form became available. The topically active inhaled steroids have radically changed and improved the treatment of bronchial asthma. Patients who would have previously been dependent on oral steroids with serious lifetime consequences have been able to be maintained on the spray with virtually no side effects. Those patients with milder forms of asthma but who overuse bronchodilator drugs have been able to decrease their consumption of these agents, reducing the adverse effects of these drugs and perhaps avoiding fatal attacks.

How They Work

Corticosteroids reduce inflammation in the bronchial tubes. Steroids prevent the late phase response and reduce bronchial hyperresponsiveness. The inhaled corticosteroids (bec1omethasone dipropionate, triamcinolone acetonide, flunisolide, budesonide, fluticasone) are “topically active” and achieve their effect on the surface of the bronchial lining. Many of these same agents are used as creams or ointments for skin conditions. If you visualize the lining of the bronchial tube in asthma to be red and inflamed, then the application of the steroid spray is not unlike applying a steroid cream to a skin rash. The results may be a dramatic reduction in inflammation and irritability.

It must be emphasized that for corticosteroids to be effective they must be administered regularly. Tho often patients may abandon a steroid inhaler before it has a chance to work. Compared to the B-adrenergic agonists, corticosteroids do not have an immediate effect and cannot rapidly reduce symptoms. For this reason patients may stop this important medication before it has had an adequate trial. Remember that the primary purpose of corticosteroid sprays is prevention. If used correctly these agents may provide long-term control over asthma. Another major benefit of the regular use of inhaled corticosteroid sprays is the reduced need for B2-agonists, which is extremely important in view of the detrimental effects noted from overusing B2-adrenergic agents.

Specific Agents

The inhaled corticosteroids, their brand names, and the forms that are available. Beclomethasone dipropionate, triamcinolone acetonide, budesonide, fluticasone propionate, and flunisolide are available in the United States. Budesonide (Pulmicort Thrbuhaler) and fluticasone propionate (Flovent Rotadisk) are now available in multidose DPI dispensers. These two agents have only recently been introduced into the United States.

Dosage and Administration

Inhaled corticosteroids may be given in varying dosages depending on individual patients. A common starting dose would be between 100 and 400 micrograms (l1g) per day. High doses (600-2000 ug) may be necessary for control of severe asthma. Inhaled corticosteroids are best given on a twice-a-day basis.

Current information suggests that the inhaled corticosteroids are not equivalent on a per puff or microgram (u.g) basis. Fluticasone propionate appears to be the most potent agent in laboratory studies. Although these laboratory studies appear to correlate with increased effectiveness in patients, direct comparison of the five agents is lacking. The delivery systems used to administer inhaled corticosteroid may affect the effectiveness of the specific medication. For example, when budesonide is administered as a DPI (Thrbuhaler), twice the amount of medication is delivered when compared to the MDI. Budesonide is only available in the DPI form in this country. Fluticasone propionate is available in three dosages (44, 110, and 220 u.g per puff) which allows increased flexibility in adjusting the appropriate dosage for the individual patient.

“High-Dose” Sprays

In view of the large number of sprays needed on a daily basis, “high-dose” sprays have been made available with up to 250 u.g per puff of corticosteroid. These inhalers allow patients with stable asthma to be maintained on as little as two puffs twice a day.

Adverse Effects and How to Prevent Them

The primary side effect of inhaled corticosteroids is development of a yeast infection known as candidiasis in the mouth or throat. With large numbers of puffs from the “low-dose” inhaler or the use of the “high-dose” preparation, there is a greater risk of this infection. This is a local infection and the rare instances of its spreading outside the mouth have typically occurred in patients with lowered immunity who took no precautionary steps. Several preventive steps can be taken to avoid the infection, including rinsing the mouth and spitting after spraying. If unable to rinse the patient may simply drink, flushing residual medication away from the mouth and throat. Passage through the digestive tract leads to rapid breakdown of the drug but rinsing is still preferred. Another extremely helpful step in administering inhaled steroid aimed at reducing the risk of yeast infection is a spacer. This simple device improves delivery of the steroid to the lung as well as reducing the amount likely to be deposited in the mouth and throat. Triamcinolone acetonide (Azmacort) incorporates a spacer in its MDI.

If candidiasis is discovered, treatment should be given promptly, consisting usually of an antifungal agent (nystatin, clotrimazole) prepared as an oral suspension or as a lozenge. It is rare that development of an oral yeast infection will recur and prompt discontinuation of inhaled steroids. In patients with recurrent yeast infection a switch to another anti-inflammatory agent such as cromolyn sodium or nedocromil is indicated.

Another infrequent side effect of inhaled steroids is an effect on the voice. This uncommon effect is usually noted as hoarseness and may be alleviated with a spacer and by a temporary reduction in dosage. Patients who complain of changes in voice should have a careful examination of the vocal cords to ensure that there is no other explanation for the abnormality.

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The B-agonists were developed in the 1940s, with isoproterenol the first of the class. Like epinephrine (adrenaline) this agent has both beta-1 and beta-2 effects. Isoetharine was one of the first”selective”B2-adrenergic agonists introduced in the United States and it was followed by metaproterenol. With the development of selective B2-adrenergic agonists there is no place for the use of nonselective agents that have significant stimulatory effects on the heart and circulation. Further research has produced more potent and longer-acting selective agents.

For the Acute Asthmatic Attack: Short-Acting Agent

Several selective B2-adrenergic agonists are available for use. These agents are available as aerosol sprays delivered by metered-dose inhalers (MDIs), aerosol solution to be delivered by nebulization, dry powders for inhalation (DPI), short and long-acting tablets, and as syrups flavored for children. In the acute asthmatic attack the treatment of choice for prompt relief of symptoms is the administration of a short-acting B2-adrenergic agonist. B2-adrenergic agonists (albuterol, metaproterenol, pirbuterol, terbutaline, fenoterol, and bitolterol) have a rapid onset of action (within minutes) with a duration of action of four to six hours. The recommended dosage is two puffs every six hours as needed. These medications differ in potency as well as how fast they begin to work and when their peak effect is reached. There are also differences in how long the effect of the drug lasts. Fenoterol has never been made available in the United States. Its extremely rapid onset of action may have contributed to its overuse and it has been implicated in cases of fatal asthma in New Zealand. Table 1 lists the B2-agonists by generic and brand name as well as the types of preparations that are available.

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