Final answer:
Naloxone (A) is the correct antidote for hydrocodone toxicity due to its ability to antagonize the effects of opioids and rapidly reverse life-threatening symptoms such as respiratory depression.
Step-by-step explanation:
If a patient who has been taking hydrocodone to relieve moderate pain has overdosed and experiences toxicity, the appropriate antidote to administer would be Naloxone (A). This medication is an opioid antagonist that can rapidly reverse the effects of opioid toxicity, including respiratory depression that can follow opioid overdose. Hydrocodone, an opiate (narcotic) analgesic, is normally prescribed for pain management, but when taken in excess can lead to life-threatening conditions. Naloxone's action involves antagonizing the effects of hydrocodone at opioid receptors within the body, which can quickly ameliorate symptoms of overdose. However, it is important to note that the duration of Naloxone is short and it must be given via a parenteral route, usually an injection.