How do local anesthetics, the ‘-caine’ drugs, stop pain?
They block sodium channels at the level of the peripheral nerve.
How do peripherally acting analgesics, such as aspirin, ibuprofen or Cox-2 inhibitors, lessen pain?
By stopping the production of Prosthaglandins.
How do the centrally acting, opioid drugs, stop pain?
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).
Why should you never give a local anesthetic with vasoconstrictors to a patient you suspect of recent cocaine use?
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).
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?
Methemoglobinemia. Benzocaine oxidizes the Fe++ into Fe+++ making it incapable of carrying O2 in the blood, leading to suffocation.
What are the two major analgesics used in dentistry that are capable of causing methemoglobinemia upon overdose?
- Benzocaine
2. Prilocaine (Injectable local anesthetic)
What is the major class of water soluble, local anesthetics used in dentistry today?
Amides (Includes Lidocaine)
Mandibular block injections with Articaine and Prilocaine have resulted in what rare side affect?
Parasthesias = extended paralysis of tongue, lips & cheecks
Note: Prilocaine is also associated with methemoglobinemia!
How much epinephrine is in two carpules of a 1:100,000 mix?
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
