Local Anaesthesia Agents Flashcards
List the types of LA agents in terms of them being an ester or amide
· An esters and amides are the structural units of the intermediate chain of local anaesthetics
· Amides: contain an “i” in the name “i” before the “-caine” e.g. mepivacaine
· Esterssuch as procaine, chloroprocaine, and tetracaine do not contain an “i” before the “-caine”
State the differences between amides and esters
· All amide LA’s are vasodilators
· Most ester LAs are metabolized by pseudocholinesterase
· Amide LAs are metabolized in the liver
Describe procaine in terms of:
Onset and duration
Action
Effect on CNS
Composition
Contraindications
Onset and duration
• Slow onset because high pKa
• Short duration/ half life because of rapid metabolism. This enables a higher does (10mg/ kg)
Action
• Vasodilator
Effect on CNS
• Initial excitation then depression
Composition
• Para-aminobenzoate is the main (inactive) metabolite, which is associated with hypersensitivity reactions in many people
Contraindications
• Some people have abnormalities in plasma cholinesterases, leading to the risk of methemoglobinemia (a blood disorder in which too little oxygen is delivered to your cells)
Describe uses of benzocaine, and its implications if doses are high
· Is an ester local anaesthetic used in some topical applications like sore throat lozenges, mouthwash, throat spray
· Can also be used for earache, sunburn etc
· Overuse of high concentrations have led to methaemoglobinaemia
Describe the following for Lignocaine
- Onset
- Duration
- Contraindications
- Metabolism
- Excretion
- Half life
Lignocaine • Onset: rapid • Duration: moderate • Contraindications: few • Metabolism: 90% in liver • Excretion: urine (90% as metabolites, 10% as free drug) • Half life: 1.5/ 1.8 hrs
Describe the following for Prilocaine
- Onset
- Duration
- Contraindications
- Metabolism
- Excretion
- Half life
Prilocaine
• Onset: rapid
• Duration: moderate
• Contraindications: no evidence to support it’s risky during pregnancy
• Metabolism: undergoes biotransformation in liver, kidney and lungs
• Excretion: kidneys
• Half life: 1.5/ 1.8 hrs
Describe the following for Articaine
- Onset/ Duration
- Contraindications
- Metabolism
- Excretion
- Half life
Articaine
• Onset/ duration: Similar onset and duration to lignocaine
• Contraindications: can’t be used during pregnancy and breastfeeding
• Metabolism: cholinesterase’s (an enzyme) in plasma
• Excreted as: 90% excreted as articainic acid
• Half life: 1.8 hrs
Describe the following for Mepivacaine
- Onset
- Duration
- Contraindications
- Half life
Mepivacaine
• Chemically related to bupivacaine but pharmacologically related to lignocaine, has a small vasodilation effect
• Onset: Rapid
• Duration: medium
• Contraindications: need to be 4+ years
• Half life: 2-3 hrs
Describe the following for Bupivacaine
- Onset
- Duration
- Contraindications
- Metabolism
- Excretion
- Half life
Bupivacaine
• Onset: slow because high pKa
• Duration: high (12+ hrs)
• Greater muscle affinity than lignocaine (cardiotoxicity). Also more potent
• Half-life: 1.5-5.5 hours ( longer in young children: 8-12 hours)
Generally describe topical anaesthetics
· Composed of either Benzocaine, Cocaine, Lignocaine or Prilocaine
· Only penetrates mucous membranes, not intact skin
· Only penetrates 2-3 mm deep
List 3 topical anaesthetics
· Eutectic Mixture of Local Anaesthetics (EMLA) creams
· Xylocaine
· Oraqix
(EXO)
Describe xylocaines in terms of:
- Composition
- Application specifications
- Onset
- The spray
• 5% lignocaine
- Need to apply to dry mucosa
- Does not work on intact skin
- Onset: 3-5 minutes
- Xylocaine spray: used for mucosal anaesthesia prior to injection, suture removal, alleviate gagging (but can make gagging worse in some patients)
Describe oraqix in terms of:
- Composition
- Application specifications
• Lignocaine 25mg/g + prilocaine 25mg/g
- Inserted into periodontal pocket prior to scaling/ root planing
- Proprietary dispenser needed
Describe Eutectic Mixture of Local Anaesthetics creams in terms of:
- Composition
- Where it works
- Application specifications
- Duration
• Composed of 1:1mixtureof lidocaine and prilocaine
- Designed to provide surface anesthesia of intact skin
- Used before painful procedures such as needle insertions
- Must be applied 1 hour before the procedure
- Lasts 1-2 hours after removal
Why are vasoconstrictors added to LA’s?
· All amide LA’s are vasodilators
· Vasoconstrictors are added to counter effects of vasodilation and slow local absorption of drug = increase duration of action = reduce toxicity
