Final answer:
Fentanyl and Heroin typically have the fastest onset of action, followed by Morphine and Oxycodone, with Vicodin, Methadone, and Opium showing slower onsets due to their pharmacokinetics and typical route of administration.
Step-by-step explanation:
Opioids vary in their onset of action following a single bolus, largely dependent on their pharmacokinetic properties and the route of administration. According to Figure 14.7, which details drug plasma concentration over time post-administration, intravenous administration results in the fastest onset of action. Considering various opioids and their typical routes of administration, we can deduce a general ranking in onset of action.
Drugs like Fentanyl often have the fastest onset when given intravenously, due not only to the route but also to its high lipid solubility and potency. Heroin also has a rapid onset due to its high lipid solubility which allows it to cross the blood-brain barrier quickly, though it's less commonly used in medical settings. Drugs like Morphine, and Oxycodone typically follow, with slightly slower onsets.