It has been found from a number of studies that upon inhalation of salbutamol, peak plasma concentration of the drug occurs after a duration of approximately 3 hours. Within 72 hours, the applied dosage is normally completely excreted, through both urine and faeces. Analysis of urinary excretion data indicates that salbutamol has an excretion half-life of 3.8 hours.
Salbutamol is metabolised almost exclusively by the liver, being converted to salbutamol 4'-O-sulfate. This is then excreted through urination and defecation. After oral inhalation, 80100% of a dose is excreted via the kidney, whilst 10% may be eliminated in faeces. After oral administration, 75% of a dose is excreted in urine as metabolites, whilst 4% may be found in faeces.
Further studies into salbutamol indicate that it is capable of crossing the blood-brain barrier. Studies on rats demonstrated that salbutamol reached brain concentrations amounting to about 5% of the plasma concentrations. In structures outside the blood-brain barrier, the drug could be found in concentrations more than 100 times those in whole brain. In addition, studies on pregnant rats also revealed that salbutamol is capable of crossing the placenta. It was found that that approximately 10% of the circulating maternal drug was transferred to the foetus. The concentration in foetal lungs was comparable to maternal lungs, but foetal liver drug concentration was much lower, at 1% of maternal liver levels.