  A-122 pnictides (A an alkaline earth element) possess striped
antiferromagnetic states of orthorhombic (OR) symmetry and nonmagnetic states
of tetragonal (T) symmetry. Based on total energy calculations, we show that
the T = 0K pressure-driven transition from OR to T states occurs at a pressure,
$P_H$, where the tetragonal enthalpy drops below the orthorhombic. The OR state
remains metastable up to a higher pressure, $P_M$ > $P_H$. We find anomalies in
magnetism and orthorhombicity as $P \rightarrow P_M$, and a trend towards
elastic instability.
