MetanxSide Effects - XML FEED - Medications.com http://www.medications.com/se/Metanx Recent side effects for Metanx Neck pain, upper arm pain, lower back (kidney area) pain both sid Sun, 24 Feb 2008 14:44:01 -0500 http://www.medications.com/effect/view/27458 Neck pain, upper arm pain, lower back (kidney area) pain both sides. The neck pain feels like something to do with arteries. The arm pain is an aching feeling in the upper arm muscles. Back pain is a lower backache. http://www.medications.com/effect/view/27458