The rupee opened 18 paise lower and slipped below the 75 per US dollar mark in opening trade on Thursday after the US Fed meeting minutes signalled at the central bank’s concern over Covid-19 and its impact on economy.The local unit opened at 75 at the interbank forex market, then lost ground and touched 75.01 against the US dollar, down 19 paise over its last close of 74.82. Meanwhile, the dollar index, which gauges the greenback’’s strength against a basket of six currencies, rose 0.08% to 92.96.