A rare fatality attributed solely to metaxalone

Metaxalone (Skelaxin) is a prescription medication used primarily as a centrally acting skeletal muscle relaxer and is rarely implicated in drug fatalities. We present a case study involving a relatively young decedent where metaxalone is implicated as the sole agent causing death with little in the way of confounding factors. The concentration of metaxalone in hospital admission blood was determined to be 37.4 mcg/mL. In postmortem specimens the concentrations were shown to be 13.5 mcg/mL (heart blood), 4.9 mcg/mL (vitreous humor), 69.4 mcg/g (liver) and 74.0 mcg/g (brain). Additionally a blood-to-plasma (b/p) ratio was estimated using antemortem blood and serum specimens taken at the same time on the second day following admission. The b/p ratio was calculated to be 1.4 implying a higher proportion of the drug to be found in whole blood versus plasma/serum samples, an important factor which should be taken into account when comparing blood concentrations to published therapeutic ranges determined in serum/plasma.