Final answer:
The blood for a trough level of Vancocin (vancomycin) should be collected prior to the fourth infusion. Key factors in drug dosage include half-life and whether the drug is dose or time-dependent. Parenteral administration is used when drugs are not well absorbed orally.
Step-by-step explanation:
The laboratory should collect the blood for a trough level prior to the fourth infusion of Vancocin (vancomycin). This ensures that the minimum plasma concentration of the drug is measured just before the next dose is administered, which is crucial for maintaining effective therapeutic levels without reaching toxicity.
Certain factors must be considered when determining the dosage of a drug, such as the half-life of the drug, whether the drug is dose-dependent or time-dependent, and the route of administration (intravenous, oral, or intramuscular as shown in Figure 14.7).
When the chosen drug is not adequately absorbed in the gastrointestinal tract, parenteral administration is preferred, typically in healthcare settings. This offers a substantially higher plasma level than oral or intramuscular administration.