Friday, November 15, 2013

In Praise of Lasix: A Utility Approach to Pharmacotherapeutics

In a prior post, I focused on reducing polypharmacy to oligopharmacy or nopharmacy because of an underlying belief that most medications are useless at best, harmful or wasteful or distracting at worst.  But I'm not a complete nihilist.  I've also done a good deal of thinking about some medications that I think we should use more of.  On the basis of Bayesian and therapeutic threshold approaches to decision making, it stands to reason that one should have a lower threshold for using high utility/efficacy agents.  The utility of a given agent is the product of the probability that a disease it treats is present and the utility of the agent for that disease (which is itself the probability of an effect in any case and the magnitude of that effect.)  Thus, if the utility of the agent is high (furosemide/Lasix), it could be useful even if the probability of disease is low (CHF in a patient with normal BNP and ECHO); indeed it could have more net utility than a low utility agent (Digoxin) in a high probability disease (EF 30%, BNP 1000). Note also that if the agent is effective at treating a common disease (as opposed to a rare one), it's general utility will be higher. It follows that the threshold for the use of these high utility agents (when I say high utility I mean net utility, thus the benefits greatly outweigh any side effects) should be low - and we should actively look for opportunities to use them.  Here are the drug utility equations (where Drug X treats Disease X):

General Utility (drug X) ~ Prevalence of Disease X * (Probability of effect in Disease X * Magnitude of Effect)

Specific Utility (drug X) == Probability of Disease X * (Probability of effect in Disease X * Magnitude of Effect)

So, in sum, drugs have higher utility when they treat common diseases, and when their effects on disease are both likely and of high magnitude.  Lasix fits this bill because fluid overload states are common, Lasix makes almost everybody pee (if given in adequate doses) and it makes them pee a lot (if given in adequate doses.)