Final answer:
The intraosseous route is the preferred method of parenteral administration in emergency situations for infants and toddlers when other sites are not available.
Step-by-step explanation:
Among the types of parenteral administration of medication, one route is utilized in emergency cases for infants and toddlers when no other sites are accessible. That route is the intraosseous route. This method involves the injection of medication directly into the bone marrow where it is quickly absorbed into the blood. It is considered a reliable method in emergency situations when intravenous access cannot be established, especially in young children. In comparison to other routes, such as intrathecal (into the spinal canal), intrapleural (into the pleural cavity), and intraarterial (into an artery), the intraosseous route is preferred because it can be accessed quickly and provides a non-collapsible entry point into the systemic circulation.
To answer the specific question, the intraosseous route (option 4) is used in emergency cases for infants and toddlers when no other sites are available.