The objective of the investigators pilot study is to assess the pharmacokinetic profile of two corticosteroid drugs, prednisone and prednisolone, in children who present to the pediatric emergency department with an asthma exacerbation. The investigators hypothesis is that the pharmacokinetic profile in this population will be similar to healthy children and adults.

The standard of practice in treating children with asthma exacerbations is to give corticosteroid drugs early in the course of the exacerbation. These drugs decrease symptoms, provide faster time to recovery and improve of quality of life. However, there is 100% variability in a child's response to corticosteroids at a standard dose which is based on primarily on adult studies. The pharmacokinetic analysis or the process by which a drug is metabolized by the body is the first step to determine the proper dose.

Patients between the ages of 2 and 16 years with asthma exacerbations will be recruited from the pediatric emergency department. After the patients get the drugs, blood samples will be drawn over 8 hours to get the following parameters: maximum concentration reached in the body, the time for the drug to be eliminated from the body, how long the drug stays in the body, how much of the drug is found in the urine after it is given, and concentration of metabolites or breakdown products in urine and blood. These are the parameters needed to make the pharmacokinetic profile and is the first step towards appropriate dosing of these two medications for asthma exacerbations in children.

Inclusion Criteria:

• patients aged 2 to 16 years
• acute asthma exacerbation requiring an oral corticosteroid (either prednisone or prednisolone)
• any "reactive airways disease" treated like asthma

[Asthma is defined as at least 2 wheezing episodes and/or the patient has been treated with beta agonist and/or inhaled, oral or intravenous corticosteroids for the recurrent episodes of wheezing in the past] [Acute asthma exacerbation is defined as wheezing episode with any of the following symptoms: tachypnea, dyspnea, use of accessory muscles, or an increased need for short acting beta agonist prior to presentation to PED]

Exclusion Criteria:

• any systemic corticosteroid use within 1 week of presentation to PED
• use of any other corticosteroid apart from oral prednisone or prednisolone for the current acute asthma exacerbation
• bronchiolitis
• underlying chronic medical condition other than asthma (ie: cystic fibrosis, nephrotic syndrome, epilepsy, etc)
• liver impairment (including elevated transaminases)
• renal impairment
• primary or secondary immunodeficiences
• concomitant immunosuppressive medication use
• IVIG use within 4 weeks
• need for assisted ventilation

children between the ages of 2 and 16 years who present to the tertiary care pediatric emergency department in London, Ontario with an asthma exacerbation