Final answer:
Administer N-acetylcysteine immediately to treat acetaminophen overdose and monitor vital signs while providing supportive care.
Step-by-step explanation:
The most appropriate action for a patient who has ingested 20 500mg acetaminophen tablets 6 hours ago is to initiate treatment for acetaminophen overdose immediately. Due to the patient's serum acetaminophen level being 60 uG/ml and the fact that the liver function tests are minimally elevated, it's crucial to start antidotal therapy with N-acetylcysteine (NAC). NAC acts as a glutathione precursor and can help prevent further liver damage if administered within 8 hours of ingestion. The guidelines for acetaminophen toxicity suggest that if the serum level is above the treatment line on the Rumack-Matthew nomogram, then NAC should be administered. The patient's vital signs should continue to be monitored closely, and supportive care should be provided as needed.