Within a few years, doctors may have a new tool to help assess the severity of asthma, so patients can take more accurate doses of inhaled corticosteroid medication.
That tool is a machine that measures exhaled nitric oxide. The amount of nitric oxide in exhaled air is a marker for asthma, and increasing levels of nitric oxide indicate the illness is getting worse.
While asthma treatments have advanced significantly, it isn't always easy for doctors to know how much medication a patient needs. If too little is given, serious asthma exacerbations can result; if too much, the asthma may be controlled but the patient may experience unnecessary side effects.
"Because of the lack of a good tool for establishing the best dose of steroids, they are usually prescribed in a general range," explains Dr. Aaron Deykin, a pulmonologist at Brigham and 'Women's Hospital in Boston. "For some this may be too low, but for many others, it may be too much."
Researchers assessed 46 asthmatic using the exhaled nitric oxide test and compared them with a group of 48 people whose asthma was assessed using conventional tools, such as symptom report, peak flow and pulmonary function testing.
All of the volunteers had been using inhaled corticosteroids. Based on the results of the nitric oxide test or conventional measurements, the researchers adjusted the dose of the inhaled corticosteroids until the optimum dose for controlling asthma symptoms was achieved. Once the optimal dose was achieved, the volunteers were followed for 12 months.
The final average daily dose of fluticasone, the inhaled corticosteroid used in this study, was 370 micrograms (mcg) for the nitric oxide group compared with 641 mcg for the conventional group-a difference of more than 40%.
While the rates of asthma exacerbations were less than one per patient per year, according to the study, the nitric oxide group averaged 45% fewer exacerbations than the conventional group.
"Nitric oxide measurements are a major step forward in assessing asthma," says study co-author Dr. D. Robin Taylor, a professor of respiratory medicine at the Dunedin School of Medicine in New Zealand, "In our lab in New Zealand, [nitric oxide measurements] are now used routinely and provide very important information to the clinician. They help us to get a clearer picture of the extent of airway inflammation in the bronchial tubes and, until now, that has not been possible," she says
She describes the nitric oxide test as a simple breathing test, similar to the breathalyzer test used to measure the amount of alcohol in the blood.
"This paper shows that using [the exhaled nitric oxide] test, which is quite simple for the patient to perform, you can safely adjust the dose of steroid," Deykin agrees.
The benefit for people who have asthma is that they can use lower doses of the steroid, and hopefully, experience fewer side effects. "Asthma can be well maintained, despite using a much lower dose of inhaled steroid. Nitric oxide measurements allowed the dose to be adjusted safely and appropriately," Taylor says.
Taylor cites two significant limitations to using nitric oxide measurements. First, they may not be useful for all types of asthma, and, second, the test is unreliable in smokers.
Deykin points out that not all insurance companies will reimburse the patient for the test. Also, he says, the devices can be difficult to maintain and are still expensive (approximately $30,000). However, according to Taylor, at least two companies are working on making portable, less costly machines that should be available within three years.