A 56 year old woman is seen in her GP clinic where she reports a 7 day history of left sided back pain radiating down her left leg described as shooting in nature. She has not suffered any recent trauma. Examination reveals a positive straight leg raise but no focal neurology and no sensory deficit. She has a background of atrial fibrillation for which she is on warfarin and asthma. She has tried regular paracetamol with little improvement. What would you advise for further pain management?