Inhaled Salbutamol: Effects on the Body

Inhaled Salbutamol: Effects on the Body Introduction Salbutamol is a first-choice bronchodilator drug used in the acute treatment of asthma. Asthma is a chronic respiratory disease which causes recurrent reversible airway obstruction. An asthma attack is often triggered by an immediate hypersensitivity reaction that occurs in response to an inhaled allergen, causing acute bronchospasm in the lungs. Salbutamol treats the symptoms of asthma by reversing this bronchoconstriction. It acts as a ÃŽ ²-2-adrenoreceptor agonist, and when inhaled, it binds to beta-2-adrenoreceptors in the bronchial smooth muscle of the lungs, causing the muscle to relax. This leads to dilation of the bronchioles and improved airflow. Salbutamol has been shown to cause side effects such as tachycardia, muscle tremor, an increase in systolic blood pressure and a decrease in diastolic blood pressure. When salbutamol is absorbed into the bloodstream via the lungs, it can bind to ÃŽ ²-2-adrenoreceptors present on the heart and increase the heart rate. The stimulation of beta receptors also stimulates an increase in myocardial contractility which can increase pulse pressure. Salbutamol is usually administered by inhalation of aerosol, powder or nebulised solution, although it can also be administered intravenously. A metered-dose inhaler (MDI) is normally used for aerosol administration, which provides a standard dose of salbutamol. The spray from a MDI consists of rapidly moving propellant droplets, most of which impact in the mouth and throat where salbutamol absorption is poor, and only about 10% of the inhaled drug reaches the bronchioles. 2 This proportion may be further reduced by poor inhaler coordination since many patients fail ,3 to synchronise the firing of the aerosol with inhalation. With good coordination about 15% of the dose would be expected to reach the lungs.3 Using a spacer device has proved to raise deposition of salbutamol in the lungs to levels similar to or greater than those obtained from a correctly used metered dose inhaler. (Thorax 1984;39;935-941) The spacer is a large plastic container with a mouthpiece on one end and opening at other end where MDI is attached, and is most often used by young children and the elderly. The aim of this study was to determine the acute effects of inhaled salbutamol on heart rate, pulse pressure, and peak expiratory flow rate and to compare the efficacy of salbutamol delivered by metered-dose inhaler (MDI) with that of salbutamol delivered by metered-dose inhaler attached to a spacer (MDI-spacer). The efficacy of the two methods of salbutamol delivery were analysed by comparing the bronchodilator and cardiovascular effects of salbutamol in subjects taking the MDI and MDI-spacer. Materials and Methods 18 healthy subjects were studied with an age range of 18-35 (14 females and 4 males). Salbutamol (Ventolin ®) was supplied in pressurised, metered dose inhalers (MDI). The 18 subjects were divided randomly into three groups: placebo, MDI and MDI-spacer. Subjects in the placebo group used the placebo MDI inhaler which acted as the control. Subjects in the MDI group used the salbutamol MDI. To administer a standard dose of salbutamol, they exhaled fully, and then inhaled slowly through the opening just as the drug was released from the MDI, and then held their breath for 10 seconds. [manual]. Subjects in the MDI-spacer group used a salbutamol MDI with an attached spacer device. To inhale a single dose of salbutamol, the subjects attached the MDI to the end of the spacer, breathed in deeply through the mouthpiece and then held their breath for 10 seconds [Introduction to Exp Bio] .The standard dose released with each depression of the salbutamol MDI was 0.1mg. For each subject, control readings of heart rate, pulse pressure and peak expiratory flow rate (PEFR) were taken at 3 minute intervals for 12 minutes. At 12 minutes, two successive doses of the assigned inhaler were taken (2 x 0.1mg doses= 0.2mg), immediately after which the three variables were measured. This was repeated every 3 minutes until a total dose of 0.6mg salbutamol or placebo had been administered. Heart rate was measured manually using a stethoscope and stopwatch. Diastolic blood pressure (DBP) and systolic blood pressure (SBP) were measured by using a sphyngomanometer and a stethoscope. [manual]. The pulse pressure was then calculated by subtracting the SBP from the DSB. The PEFR was measured using a Wright peak flow meter. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS), version 16.0. The data were assumed not to have a normal distribution, and the results obtained from the different groups were independent of each other. The non-paired, non-parametric Mann-Whitney-U test was therefore used to determine whether there were significant differences in any of the measured variables as a result of the salbutamol MDI, when compared to the placebo control. The test was also used to determine if there was a significant difference between the results of the MDI and MDI-spacer groups which would have been caused by the use of the spacer. For each subject, the overall change in a variable from the mean control value after a 0.6mg dose, was used to compare the results of subjects from different groups. Mann-Whitney-u test to compare results recorded for each group to see if the differences observed are significant at the 95% confidence level. A value of P