Final answer:
The highest priority for a patient who has ingested an unknown quantity of pills is to ensure their airway, breathing, and circulation are stable, and seek immediate medical assistance.
Step-by-step explanation:
When dealing with a 24-year-old female patient who has swallowed an unknown quantity of pills, the highest priority is to maintain airway, breathing, and circulation (ABCs). Her initial alertness changing to slurred speech and lethargy indicates a progression towards more severe symptoms of a possible overdose, such as those seen with barbiturates like Phenobarbital. The symptoms of overdose may include sluggishness, incoordination, difficulty thinking, and, in severe cases, coma or death. It is crucial to seek immediate medical assistance, as she may need emergency interventions like gastric lavage (stomach pumping), activated charcoal, or specific antidotes. Measurement of her vital signs and close monitoring is also paramount to manage her condition effectively.