Pain Lecture

Question 0

How do local anesthetics, the ‘-caine’ drugs, stop pain?

Answer 0

They block sodium channels at the level of the peripheral nerve.

Question 1

How do peripherally acting analgesics, such as aspirin, ibuprofen or Cox-2 inhibitors, lessen pain?

Answer 1

By stopping the production of Prosthaglandins.

Question 2

How do the centrally acting, opioid drugs, stop pain?

Answer 2

They limit the release of substance P in the dorsal horn of the spinal cord.

• May also limit release of other excitatory amino acids in the spinal cord
• Bind to opioid receptors that activate descending analgesic pathways that diminish pain perception (mood altering affect).

Question 3

Why should you never give a local anesthetic with vasoconstrictors to a patient you suspect of recent cocaine use?

Answer 3

B/c cocaine simultaneously activates alpha-1 and beta-1 receptors. Alpha-1 causes vasocontriction, while Beta-1 causes increased HR and contractive force, this combination will lead to hypertension. If vasoconstriction is increased further by epinephrine in a local anesthetic the patient may suffer from a heart attack or stroke and die due to hypertension (high BP).

Question 4

Benzocaine is an ester analgesic that must be dissolved in alcohol & is therefore frequently used as a topical pain reliever. What is the major side-affect of a benzocaine overdose?

Answer 4

Methemoglobinemia. Benzocaine oxidizes the Fe++ into Fe+++ making it incapable of carrying O2 in the blood, leading to suffocation.

Question 5

What are the two major analgesics used in dentistry that are capable of causing methemoglobinemia upon overdose?

Answer 5

1. Benzocaine

2. Prilocaine (Injectable local anesthetic)

Question 6

What is the major class of water soluble, local anesthetics used in dentistry today?

Answer 6

Amides (Includes Lidocaine)

Question 7

Mandibular block injections with Articaine and Prilocaine have resulted in what rare side affect?

Answer 7

Parasthesias = extended paralysis of tongue, lips & cheecks

Note: Prilocaine is also associated with methemoglobinemia!

Question 8

How much epinephrine is in two carpules of a 1:100,000 mix?

Answer 8

1: 100,000 = 1g : 100,000ml = 1,000mg : 100,000ml = 0.01gm/ml
0. 01 mg/ml * 1.7 ml/carpule = 0.017 mg/carp * 2 = 0.034 mg epinephrine in 2 carpules of local anesthetic