Uni-Guaifen 600/300Side Effects - XML FEED - Medications.com http://www.medications.co.uk/se/Uni-Guaifen+600%2F300 Recent side effects for Uni-Guaifen 600/300 Guaifen with Bromfed caused a very high heart rate. I took it onc Mon, 27 Aug 2007 13:29:55 -0400 http://www.medications.co.uk/effect/view/23225 Guaifen with Bromfed caused a very high heart rate. I took it once. The doctor did a EKG and determined the heart waveforms looked normal but really fast. Over 160bps when it slowed enough to count. I was given something to slow the heart. It took 3 days http://www.medications.co.uk/effect/view/23225