Erasing all its initial gains, the Sensex at the Bombay Stock Exchange had dropped 46 points, or 0.2 percent, to 18,638, in afternoon trade, a short while ago.But earlier in the morning, the Sensex had opened 44 points, or 0.2 per cent higher, at 18,727, on mild buying interest by investors, amid mixed regional bourses. The Sensed had lost almost 220 points in the last two trading sessions.Stock markets in Japan, China, Hong Kong, South Korea and Singapore were trading mixed.