Source? Haven't read that particular book but the vast majority of studies I've seen conclude that cocaethylene and/or the combination of cocaine+alcohol is at the very least as cardiotoxic as cocaine, if not much more. That particular combination is thought to have like 10-20x the risk of sudden death compared to cocaine alone (in humans).
I've only seen one paper where the conclusion is that cocaethylene is as toxic as cocaine, but less toxic than cocaine+alcohol. That wasn't a human study for though, they used 18 dogs as test subjects (doesn't seem very significant yet it still agrees on the idea that cocaine+ethanol carries an increased risk).