From Quora: If bacteriophages are cheap, effective and don't lead to resistance, why isn't the healthcare industry replacing antibiotics with them?

Why isn't there an aggressive push being made by the healthcare industry to replace antibiotics with bacteriophages when they are cheap, effective and don't cause antibiotic resistance?

As you might suspect, there are a number of issues.

First and foremost, antibiotics have been a terrible investment for pharmaceutical development for the last few decades.  Brad Spellberg has estimated that the Net Present Value of a new antibiotic is negative $50M USD.  That is, discovering a new antibiotic and bringing it to market is likely to be a money loser.  We have come to expect antibiotics to be cheap, so margins are low.  Antibiotics are typically taken for a few days, so there is no long-running revenue stream.  Low margin + short-term use = no profits to be made.

Brad's calculation was made for tradtional antibiotic entities - small molecules whose development and manufacture the pharma industry has perfected to a high degree.  Bacteriophage are much messier - fragile and finicky biological entities whose purity and integrity are much harder to assess, particularly at large scale.  Thus R&D costs are likely to be higher and riskier, making the NPV numbers even worse for bacteriophage.

Bacteriophage are also much harder to protect as intellectual property.  The concept of using phage as antibiotics is a century old, and cannot be patented.  Individual phage certainly can - but because phage are so diverse and abundant, there is a good chance that a competitor could find an unrelated phage that is functionally equivalent to a patented phage.  Thus it is much harder to keep competitors at bay once you have shown the feasibility and profitability of a given phage formulation.

And not least - phage science has been a backwater for decades, and a lot of the people who work in this field produce weak science.  There are any number of examples of publications showing some small effect in a contrived clinical model which claim a breakthrough.  This has been going on for a couple of decades now.  The only sign of actual progress has been from AmpliPhi Bio (formerly BioControl), who have gotten as far as Phase II clinical trials with a phage treatment for Pseudomonas ear infections.

The bottom line is that there is not enough money in antibiotic development in general, and bacteriophage development in particular, to fund a serious and sustained effort to bring the technology to maturity.  It absolutely is technically feasible, and there absolutely is a clinical need.  But until society assigns the same sort of value to antibiotics as it does to (for instance) cancer therapeutics, progress will be very slow.