Chimeric double-stranded nucleic acid

A pharmaceutical composition which comprises a double stranded nucleic acid complex comprising a first nucleic acid strand annealed to a second nucleic acid strand, wherein:

• (i) the first nucleic acid strand hybridizes to a transcription product of a target gene to modify the expression of the target gene by a non-RNase H-dependent antisense effect, wherein the first nucleic acid strand comprises
• (a) consecutive DNA nucleotides, modified DNA nucleotides, nucleotide analogs and/or modified nucleotide analogs which have a sequence complementary to the transcription product and can hybridize to the transcription product, and
• (b) the total number of the nucleotides, modified nucleotides and nucleotide analogs is 12 to 25 nucleotides, and
• (ii) the second nucleic acid strand comprises
• (a) consecutive RNA nucleotides or modified RNA nucleotides which have a sequence complementary to the first nucleic acid, and
• the second nucleic acid strand comprises
• (b) one or more modified nucleotides, nucleotide analogs and/or modified nucleotide analogs located on 5′ terminal side of the consecutive RNA nucleotides or modified RNA nucleotides, and/or
• (c) one or more modified nucleotides, nucleotide analogs and/or modified nucleotide analogs located on 3′ terminal side of the consecutive RNA nucleotides or modified RNA nucleotides.