The correct answer is Lidocaine.

- Local anesthetics work by blocking sodium channels, thereby preventing nerve impulse conduction.
- The duration of action of these drugs can be influenced by their absorption into the systemic circulation.
- When a vasoconstrictor such as epinephrine is added, it causes local blood vessel constriction, which reduces the systemic absorption of the anesthetic at the injection site.
- This leads to a higher local concentration, prolonging the anesthetic effect and decreasing systemic toxicity.

Among the options:
- Lidocaine, a commonly used intermediate-duration local anesthetic, has its duration of action significantly extended by the addition of epinephrine due to its moderate vasodilatory properties.

- Mepivacaine is less affected because it produces minimal vasodilation, so epinephrine does not greatly extend its duration.

- Bupivacaine already has a long duration of action primarily due to its high lipid solubility and protein binding. Although epinephrine can be added, its effect on prolonging bupivacaine’s duration is less pronounced compared to lidocaine.

- Prilocaine has a similar profile to lidocaine but generally causes less vasodilation, so the addition of epinephrine affects it less.

In summary: Adding epinephrine to lidocaine decreases its systemic absorption by vasoconstriction, thereby increasing the duration of anesthesia and reducing systemic toxicity. This is a key reason why lidocaine is frequently combined with epinephrine in clinical practice.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th Edition, Volume 1, Chapter 21, Page 550