Say the development of a drug costs $1 Billion on average and that only every tenth drug gets approval. So you are looking at a $10 Billion cost for every successful drug development. But you can then sell this drug exclusively under current patent laws for about 20 years, worldwide. By that calculation, you'd need to sell 1.000.000 doses of the drug for a price of $500 each every year to break even.

That sounds trivial to achieve given that there are 7 billion people alive and innovative drugs will go for vastly more than that even in strictly regulated markets like many European countries (my son gets a pretty advanced drug that costs about $12.000 (EDIT: yearly) to procure but which is covered by our (national) insurance scheme).

Additionally, a lot of the cost of basic drug research is actually covered by government-financed research, not private investment.

If you are still worried, you could use a prize model, similar to what was done during covid: Identify certain qualities that a new drug should have (i.e. be an effective vaccine against malaria) and guarantee a big enough market (i.e. promise to buy at least 1 Billion doses at $10 each) and you can bet that there'll be plenty of companies trying to get at that money.