Ive been using tincture of merthiolate for over a week on a wound and today i accidentally swallowed a drop. chances of toxicity?

Unlikely: Tincture of merthiolate has different ingredients depending on where and when it was made. The over-the-counter version now likely uses benzalkonium chloride as its active ingredient. In general, one must look at the active ingredient to see if there is any need to worry. That said, eating one drop of an over-the-counter skin antiseptic in the US is unlikely to do anything bad.