Final answer:
High doses or prolonged use of ibuprofen can lead to renal failure, a life-threatening complication, especially in at-risk populations.
Step-by-step explanation:
One life-threatening complication that may occur in clients taking high doses or long-term ibuprofen is renal failure. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen have the potential to cause kidney damage. This risk may increase in certain populations, including those over 60 years of age, individuals taking diuretics, and those with high blood pressure, heart disease, or pre-existing kidney disease. It is important to recognize that while ibuprofen is useful for treating pain and inflammation, it must be used with caution to prevent serious side effects such as stomach bleeding and kidney damage.