Ok, I used htmlspecialchars()
to get this right. The code will be like:
echo '<td><input type=text style=width:100px name=itembrand value="' . htmlspecialchars($itembrand) . ' " </td>';
echo '<td><input type=text style=width:150px name=itemname value="' . htmlspecialchars($itemname) . '" </td>';
echo '<td><input type=text style=width:150 name=serialnr value="' . htmlspecialchars($serialnr) . '" </td>';
echo '<td><input type=text style=width:150px name=addinfo value="' . htmlspecialchars($addinfo) . '" </td><td>';