How to fetch data from database textbox when combox value is selected in datagridview

When I choose a value from a datagridview combo box , I want to fetch data from the database into a datagridview textbox. See in the image when I choose any medicine name that unitprice should be fetched from the database. How can that be done?

             SqlConnection con = new SqlConnection(connection string);

            con.Open();

            SqlDataAdapter adp = new SqlDataAdapter("select quantity,unitprice,totalprice from stock where medicinename='" + dataGridView1.Columns[0].ToString() + "' ", con);
            DataSet ds = new DataSet();
            adp.Fill(ds);
            dataGridView1.DataSource = ds;

            dataGridView1.Columns[1].DataPropertyName = "quantity";
            dataGridView1.Columns[2].DataPropertyName = "unitprice";
            dataGridView1.Columns[3].DataPropertyName = "totalprice";
            con.Close();

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