Local Anesthetics: Systemic Effects, Absorption & Metabolism

• Systemic effects of local anesthetics (LA) are being outlined

Absorption and Metabolism of LA Agents

• LA agents aren't easily absorbed through intact skin
• LA agents are absorbed into the bloodstream when applied to mucous membranes or injected into tissues
• Distribution occurs throughout the body
• Metabolism and elimination also occur

Systemic Actions of LA Agents

• LA agents cause reversible blockage of conduction in nerve endings and nerve trunks
• They promote direct relaxation of smooth muscle
• They induce myocardial depression, decreasing conduction rate, force of contraction, and electrical excitability
• LA agents depress the central nervous system, and initial signs are excitatory

Absorption into The Circulation

• The action of LA wears off
• Toxicity may occur
• The rate of systemic absorption depends on factors such as the agent, its concentration/dose, the tissues' vascularity, the presence/absence of a vasoconstrictor, and accidental intravascular injection

Metabolism and Elimination

• The process is dependent on patient physiology
• Most commonly used LA agents are metabolized in the liver to create inactive metabolites
• Articaine is also metabolized in plasma
• LA agents are then excreted via urine
• Reduced liver and kidney function may indicate requirement of lower and safer doses

Signs of Systemic Toxicity

• Systemic toxicity signs are rare in dentistry, they may include:
• Perioral signs: tingling and numbness of lips
• Visual and hearing disturbances like tinnitus
• Mood changes: irritability, agitation, anxiety, restlessness
• Light-headedness/dizziness
• Increased depth and rate of respiration
• Drowsiness, coma, and convulsions
• Respiratory and cardiac arrest

Reducing Systemic Toxicity Can be Achieved Through

• Avoiding intravascular injection through aspiration
• Injecting slowly
• Using safe doses
• Choosing less-toxic drugs like 3% prilocaine with felypressin
• Using vasoconstrictors

Maximum Safe Dose

• Maximum safe doses of various agents are as follows, and are affected by patient age:
• Lidocaine 2%: 4.4mg/kg. The max number of 2.2ml cartridges is 6.8 for adults (70kg) and 2.0 for a 5 year old.
• Prilocaine 3%: 5.0mg/kg. The max number of 2.2ml cartridges is 6.0 for adults (70kg) and 1.8 for a 5 year old.
• Mepivacaine 3%: 4.4mg/kg. The max number of 2.2ml cartridges is 4.5 for adults (70kg) and 1.3 for a 5 year old.
• Articaine 4%: 7.0mg/kg. The max number of 2.2ml cartridges is 5.0 for adults (70kg) and 1.5 for a 5 year old.

LA Agents - Contraindications and Cautions

• Lidocaine
• Contraindications include hypersensitivity, which is very rare
• Exercise caution when using betablockers like propanolol
• Prilocaine:
• Contraindications include hypersensitivity, which is very rare
• Exercise caution when using sulphonamides and betablockers
• Mepivacaine:
  • Contraindications include hypersensitivity, which is very rare, and children under 4
  • Exercise caution during pregnancy, breastfeeding, and when using betablockers
• Articaine:
  • Contraindications include hypersensitivity, individuals under 4, and deficiency in plasma cholinesterase
  • Exercise caution during pregnancy only if benefits outweigh risks, avoid breastfeeding for 48 hours after administration, in individuals taking betablockers and in ID blocks due to the risk of post-op paraesthesia
• Epinephrine/Adrenaline:
  • Contraindications include cocaine use within the last 24 hours
  • Exercise caution when using tricyclic antidepressants, mono-amine oxidase inhibitors, betablockers, calcium-channel blockers, diuretics, or for individuals with cardiac conditions, hypertension, or circulatory problems
• Felypressin
  • Use with caution in late stages of pregnancy due to the theoretical risk of inducing labour, the substance is similar to oxytocin

Additional Cautions

• Limit LA to 2 x 2.2ml cartridges per day for individuals with any of the above conditions
• Limit to 1 cartridge per day with renal failure/dialysis or liver failure, and liaise with a patient's physician regarding safe dosage

LA equipment

• LA equipment consists of cartridges, plungers and safety plus needles.
• Safety plus needle sizes include:
• Extra short needles: 30G 10mm
• Short needles: 30G 25mm
• Long needles: 27G 35mm

Safe LA delivery

• Safe LA delivery involves using different LA agents and understanding how they work
• It includes knowing the systemic effects of LA agents
• Being aware of contraindications and cautions on LA delivery
• Demonstrating how LA equipment is safely used

Future Learning

• Next sessions will include oral anatomy and nerve supplies
• How to deliver infiltrations and inferior dental blocks, and the legal aspects and complications of LA delivery