If the price elasticity of demand for a life-saving drug is perfectly inelastic (equal to zero), a 50% increase in the drug's price will result in a 50% decrease in the quantity demanded by patients.

Perfectly inelastic demand (Ed = 0) means that consumers will purchase the exact same quantity of the good regardless of any price change, typically because the good is an absolute necessity with no substitutes (like insulin for a diabetic). Therefore, a 50% price hike will result in a 0% change in the quantity demanded, allowing the monopolistic pharmaceutical company to extract massive revenues at the expense of consumers.