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Pharmacology -. Dentalelle Tutoring. Chapter 9. WHY IS EPI USED IN LOCAL ANESTHETICS?. PROLONG DURATION. Meaning..the local anesthetic lasts longer to ensure proper freezing of the tooth and tissues. WAS COCAINE USED AS AN ANESTHETIC?. YES.
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Pharmacology- Dentalelle Tutoring
PROLONG DURATION Meaning..the local anesthetic lasts longer to ensure proper freezing of the tooth and tissues
YES.. ..but not anymore! It was quickly recognized for its addicting properties.
HISTORY • The amide lidocaine (Xylocaine) was released in 1952 • mepivacaine(Carbocaine) was released in 1960 • More recently, bupivacaine (Marcaine) has been made available for dental use
TRUE OR FALSE… No local anesthetic in use today meets all THE NECESSARY requirements
TRUE But…many acceptable agents are available
IDEAL LOCAL ANESTHETIC PROPERTIES OF THE IDEAL LOCAL ANESTHETIC • potent local anaesthesia • reversible local anaesthesia • should be followed by complete recovery without evidence of structural or functional nerve damage • absence of adverse systemic effects & allergic reactions • rapid onset & good duration • should have moderate lipid solubility which allows an anesthetic agent to diffuse across lipid membranes of all peripheral nerves (motor, sensory, autonomic) • adequate tissue penetration • low cost • long shelf life (stability in solution) • ease of metabolism & excretion
AMIDES AND ESTERS Cross-hypersensitivity between amides and esters is unlikely
MECHANISM OF ACTION ACTION OF NERVE FIBERS • A resting nerve fiber has a large number of positive ions on the outside and a large number of negative ions on the inside • The nerve action potential results in the opening of sodium channels and an inward flux of sodium (Na+) • This results in a change in potential • The outward flow of potassium (K+) ions repolarizes the membrane and closes the sodium channels
HOW DO LOCAL ANESTHETICS WORK? IN RELATION TO NERVE IMPULSES?
DECREASING PERMEABILITY TO SODIUM IONS… After combining with the receptor, local anesthetics block conduction of nerve impulses by decreasing the permeability of the nerve cell membrane to sodium ions
MECHANISM OF ACTION ACTION OF NERVE FIBERS SUMMARIZED • Local anesthetics slows or blocks depolarization by reducing Na+ permeability into the nerve cytoplasm, thus inhibiting the flow of K+ out of the cell. ↓ • interferes with the function of the neurons ↓ • prevents the propagation of action potential (the reproduction of nerve transmission) ↓ • prevents the onset of nerve conduction & blocks nerve impulse formation
MECHANISM OF ACTION ACTION OF NERVE FIBERS The mechanism of local anesthetics involves action on Axons and Sodium channels Local anesthetics bind to sodium channels found in the axons of nerves. They stop the propagation of the electrical impulse along the axon.
WEAK BASES When the acidity of the tissue ↑, (as in instances of infection), the effect of a local anesthetic ↓ Therefore, the local anesthetic is a weak bases.
Absorption & L.A. local anaesthetic (L.A.) L.A. tooth L.A. EG: Lidocaine’spKa =7.9(Weak base drug) • ↓ pH • ↑ ionization • ↑ [H+] • *Weak bases are better absorbed when the pH is greater than the pKa L.A. infection In the presence of infection, there may be a reduced clinical effect of L.A. due to the ↓’d pH level. The infection site is more acidic and more ionized and less likely to absorb the L.A drug (weak base).
IF INFECTION IS PRESENT, HOW DOES THE LOCAL ANESTHETIC REACT?
IT IS HARDER TO FREEZE –LIKELY INFECTION MUST BE CLEARED BEFORE FREEZING IS DONE. In the presence of an acidic environment, such as infection or inflammation, the amount of free base is reduced
VERY IMPORTANT! Absorption Distribution Metabolism Excretion
ROUTE Absorption depends on its route When injected into tissues the rate depends on the vascularity of the tissues
PHARMACOKINETICS ABSORPTION Reducing the rate of systemic absorption of a local anesthetic is important when it is used in dentistry because the chance of systemic toxicity is reduced. • A vasoconstrictor is often added to the local anesthetic to reduce the rate of absorption.
PHARMACOKINETICS ABSORPTION • Addition of vasoconstrictor to local anesthetic: • Reduces the blood supply to the area • so as to ↓ rate of diffusion of anaesthetic into the blood vessels • this also prolongs the duration & effectiveness of the desired action • decreases bleeding in the area • Limits systemic absorption • Reduces systemic toxicity
LOCAL ANESTHETIC DISTRUBUTED THROUGHOUT Local anesthetics cross the placenta and blood-brain barrier
PHARMACOKINETICS METABOLISM LA agents are metabolized differently, depending on whether they are amides or esters. • AMIDES: are metabolized primarily by the liver • In severe liver disease or with alcoholism, amides may accumulate and produce systemic toxicity • ESTERS: are hydrolyzed by plasma pseudocholinesterases and liver esterases
EXCRETED BY KIDNEYS Metabolites and some unchanged drug of both esters and amides are excreted by the kidneys
PERIPHERAL NERVE CONDUCTION The main clinical effect of local anesthetic is reversible blockage of peripheral nerve conduction
PHARMACOLOGIC EFFECTS PERIPHERAL NERVE CONDUCTION (BLOCKER) COMMON ORDER OF NERVE FUNCTION LOSS • Autonomic *is the most sensitive to inhibition by local anesthetic agents • Cold • Warmth • Pain • Touch • Pressure • Vibration • Proprioception • Motor The order of loss of nerve function The order of nerve impulse return: opposite (reverse)
WHY ARE LOCAL ANESTHETICS SUCCESSFUL IN TREATING ARRHYTMIAS?
ADVERSE REACTIONS • Although toxicity to local anesthetics is rare in the doses normally used in dentistry, patients can still suffer from a classic toxic reaction.
ADVERSE REACTIONS LOCAL ANESTHETIC TOXICITY causes stimulation of the CNS including: • restlessness, • tremors • seizures • followed by CNS depression and coma.
