Asthma patients were able to reduce their inhaled steroid drugs by a net 40 per cent when their dosages were tailored using a new type of breath test.
Doctors at present adjust patients' intake of drugs such as Flixotide - which prevent asthma breathlessness and wheezing - mainly based on their reports of symptoms.
But the breath-testing machine, which measures exhaled nitric oxide, has proven more effective, say Otago University researchers.
The results of the study, the first to show the machine can be used to improve asthma care, are published today in a leading American journal, the New England Journal of Medicine.
They reduce with inhaled steroid treatment, but rise again when asthma worsens.
By measuring nitric oxide, the machine assesses inflammation in the breathing tubes of the lungs, allowing doctors to adjust the dosage of inhaled steroid.
"Our study showed that we can use nitric oxide measurements to take some of the guesswork out of deciding how much treatment to give patients with asthma," said Professor Taylor.
"In some cases, using nitric oxide results meant that the treatment dose could be reduced substantially, in some cases to almost zero.
The machines, available since 1998, had reduced in price, now costing about US$5000 ($7059).
Professor Taylor said all public hospitals ought to have one, but only several did - including two in Auckland hospitals.
He said that inhaled steroids were safe, but carried a degree of side-effect risk at high doses, over 1000 mcg a day of Flixotide or its equivalents.
The president of Asthma New Zealand, Allen Liang, said the breath-testing method was useful but the cost of administering each test may prove prohibitive.
Dr Wong said research showed that people taking steroids through puffers had a very small chance of experiencing bone thinning, or osteoporosis.