Half of SCDF's 30 ambulances (15 ambulances), will be randomly assigned, equipped and trained to carry the new medication (Penthrox). The other half (15 ambulances), will be trained and equipped with IM tramadol. Allocation will be on a per station level. After 6 months, the two separate cohort of ambulances will cross over to administer Penthrox and Tramadol and respectively. This is done in order to minimize any potential patient selection bias and ambulance crew operator bias arising in the two 6-monthly time periods.