The POTENCY of local anesthetics is related to
A. Blood supply at the site of injection
B. Extent of protein binding
C. Total dose of LA
D. Lipid solubility
E. Addition of vasoconstrictors to the solution
The answer is D. Potency is related to lipid solubility. Vascular supply at the injection site, total dose of LA and any addition of vasoconstrictors all determine the blood levels of the particular anesthetic. The amount of LA that is protein bound also determines duration of action. In general, local anesthetic agents with greater protein binding have a greater affinity for receptor sites and remain within sodium channels for a longer period of time. This means that agents with higher protein binding capacity are associated with a longer duration of action.
This phenomenom is confirmed by both in vitro as well as clinical practice. Poorly protein bound agents, such as procaine, are readily washed out in vitro experiments, and duration of local anesthetic blockade can be extremely short whereas those which are highly protein bound, such as bupivacaine, are less easily washed out in vitro experiments and blockade is interrupted for a longer period of time. The clinical activity of the agents which are more protein bound such as bupivacaine, are associated with a longer duration of clinical anesthesia. The less well protein bound agents such as procaine and chloroprocaine, are associated with short duration of clinical activity.
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