What does salbutamol do?

Salbutamol opens airways in minutes. The question is what else it does to the body.

Salbutamol (albuterol) is a beta-2 adrenergic receptor agonist. It relaxes the smooth muscle in the airway walls, which is why it relieves wheezing and shortness of breath in asthma attacks. Inhaled, it works within minutes. That much is straightforward pharmacology, and the evidence for that effect is solid.

But the story does not end there. Several lines of evidence show that salbutamol has effects the prescribing doctor may not mention. In children with acute asthma, nebulized salbutamol can cause a significant drop in blood oxygen levels: in one study, 9 of 18 children had a fall of more than 5% in arterial oxygen saturation [1]. In a larger series, oxygen saturation decreased by 2 to 6%, with the largest drops occurring 10 to 15 minutes after the dose [1]. The standard workaround is to give oxygen alongside the drug, but that masks the effect rather than preventing it.

High doses also cause metabolic effects. A case report documented salbutamol-induced lactic acidosis in a 39-year-old man treated for severe asthma: his blood lactate rose from 1.1 to 14.2 mmol/L over five hours of treatment, and his pH dropped to 7.09 [7]. The acidosis resolved after the drug was stopped. The mechanism is thought to be beta-2 stimulation of glycogenolysis and lipolysis, which increases lactate production. This is not rare in severe asthma but is rarely attributed to the drug.

A two-year randomized trial found that continuous daily use of salbutamol (four times daily, regardless of symptoms) accelerated the decline in lung function three to four times faster than using the inhaler only when needed [2]. That is for chronic use, not for occasional rescue. The study also noted that in the continuous-use group, symptoms did not correlate with FEV1 decline, meaning a patient could feel fine while their lung function was worsening silently [2]. An earlier study from the same group found the same pattern: the continuous group lost −0.072 L per year versus −0.020 L per year in the on-demand group [5].

There is also evidence that salbutamol can cross into the central nervous system through different routes depending on the species and condition, and chronic dosing can desensitize the receptor system [6]. That is well-established for beta-agonists generally: with regular use, the airway response diminishes, requiring higher doses for the same effect, and the metabolic side effects (tremor, tachycardia, hyperglycemia) become more pronounced.

On the benefit side, short-acting beta-agonists like salbutamol are effective for acute symptom relief. They reduce rescue inhaler use and improve overnight peak flow when compared to placebo [4]. But the same trial that showed benefit also found that the higher dose (100 mcg twice daily) caused palpitations requiring withdrawal in one participant, and one death occurred in a patient on maintenance prednisolone during the trial, though it was deemed unrelated [4]. The funding for that trial came from Glaxo Group Research Limited, the manufacturer [4].

A separate 24-week trial comparing a long-acting beta-agonist (salmeterol) plus steroid to a higher dose of steroid alone found that the combination allowed significantly more symptom-free days and better lung function [3]. This suggests that for some patients, a beta-agonist combined with an inhaled steroid is more effective than a steroid alone. But this design did not test salbutamol alone, and it compared a combination product (salmeterol/fluticasone, made by GlaxoSmithKline) to a different drug and device (budesonide via Turbuhaler) [3]. The question of whether the short-acting version, salbutamol, should ever be used continuously is answered by the two-year trials: it should not.

My call: salbutamol is an effective rescue drug for acute bronchospasm, but it carries a real risk of hypoxemia in children, metabolic acidosis at high doses, and accelerated lung function decline when used continuously. The risk-benefit is acceptable for occasional rescue use in symptomatic asthma, but the evidence argues strongly against daily maintenance use. Confidence: high for the acute efficacy and the continuous-use harm; moderate for the frequency of lactic acidosis, since it is documented only in case reports.