Final answer:
Naloxone (Narcan) should be administered to a client with heroin toxicity as it is an opiate antagonist that reverses opioid-induced respiratory depression.
Step-by-step explanation:
The medication that should be administered to a client presenting with heroin toxicity characterized by unresponsiveness, pinpoint pupils, and a respiratory rate (RR) of 6/min is Naloxone (Narcan). Naloxone is an opiate antagonist that can reverse the effects of opioids like heroin, thereby restoring normal respiratory function. It works by competitively binding to the opioid receptors in the brain, which prevents the opioids from exerting their effects. The use of naloxone in opioid toxicity is critical as it has a rapid onset of action and is effective at reversing potentially life-threatening respiratory depression induced by opioid overdose.