Objective To study the pharmacokinetics and relative bioavailability of tetramethylpyrazine longcirculating liposomes and tetramethylpyrazine conventional liposomes in rats. Methods 12 rats were randomly divided into two groups. Single dose of tetramethyl-pyrazine long-circulating liposomes and tetramethylpyrazine conventional liposomes were intravenously administrated to the rats respectively. The tetramethylpyrazine concentration in plasma was determined by HPLC,and the pharmacokinetic parameters were cal...