Toxicokinetic of HEMA in guinea pigs

Objective. Unconverted 2-hydroxyethylmethacrylate (HEMA) can be released from dental resin materials and can enter the body in humans. In the present study the uptake, distribution and excretion of ¹⁴C-HEMA applied via different routes were examined in vivo in guinea pigs.

Methods. HEMA (0.02 mmol/kg bw labelled with a tracer dose ¹⁴C-HEMA 0.3 Bq/g bw) was administered by gastric tube or by subcutaneous injection. Urine, feces, and exhaled carbon dioxide were collected for 24 h after administration. Guinea pigs were killed 24 h after the beginning of the experiment and various organs removed and ¹⁴C radioactivity measured.

Results. Low fecal ¹⁴C levels (about 2% of the dose) and urinary levels of about 15% after 24 h were noted with either route of administration. Direct measurement of exhaled CO₂ showed that about 70% of the dose left the body via the lungs. Two pathways for the metabolism of ¹⁴C-HEMA can be described. It is likely that ¹⁴C-pyruvate is formed in vivo resulting in the formation of toxic ¹⁴C-HEMA intermediates. ¹⁴C-HEMA was taken up rapidly from the stomach and small intestine after gastric administration and was widely distributed in the body following administration by each of the routes.

Conclusions. Clearance from most tissues following gastric and intradermal administration was essentially complete within one day. The peak HEMA levels in all tissues examined after 24 h were at least onemillion-fold less than known toxic levels.