gistfile1.txt

// It's best to escape the whole url:
// This will also convert the ampersand to an entity.
// esc_url() is for printing to the screen.
// esc_url_raw() is for database saves.

echo '<a href="' . esc_url( 'https://twitter.com/share?url=' . $pxjn_share_url . '&text=' . $pxjn_share_text ) . '"><span class="share tweetthis">Tweet This</span></a>';