local anaesthetics premviyasa NB Flashcards
definition
Loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.
esters
procaine
cocaine
tetracaine
amides
bupivicaine
mepivicaine
prilociane
lidocaine
articaine
ideal properties
❖I = should not be irritating to tissue
❖N = should not cause any permanent alteration of
nerve structure
❖S = systemic toxicity should be low
❖T = time of onset of anaesthesia should be short
❖E = should be effective regardless of it being injected or applied topically
❖D = Duration of action should be long enough to complete procedure
❖Have the potency to give complete anaesthesia without the use of harmful concentration solutions
❖Should not produce an allergic reaction ❖Should be free in solution and undergo
biotransformation in the body
❖Should be sterile or capable of being sterilized by heat without deterioration
chemical structure of la
lipophilic aromatic ring
tertiary amide end
intermediate hydrocarbon linkage
mechanism of action and nerve impulses
Nerve impulses begin in a dendrite, move toward the cell body, and then move down the axon.
depolarization → hyperpolarization → repolarization → resting potential
Local anesthetics prevent nerve impulse transmission by blocking voltage gated sodium channels without causing central nervous system depression or altered mental status
calculation of dosage
- Pt’sweight(70Kg)
- Drugconcentrationas%,e.g.0.5%,2%,etc. 3. AmountofLAinacartridge(1.8,ml)
- Maximumdoseofanaestheticbasedupon milligrams per Kg (Lignocaine= 7mg/Kg)
pharmacokinetics esters
metabolised by plasma esterase
PABA metabolite - causes hypersensitivity reaction
pharmacokinetics amides
metabolised by hepatic cytochrome P450
long half-life
no PABA in amides
pharmacokinetics factors (failure)
(1) increased local blood flow leading to accelerated removal of drug from perineural injection compartments;
(2) local tissue acidosis leading to a greater proportion of the drug in the hydrochloride form, which diffuses more poorly across biologic membranes; and
(3) local tissue oedema, which increases diffusion distances for drug into nerves and promotes further dilution.
pharmacodynamic factors failure
o the effects of inflammation on both peripheral
sensitization of nerves and central sensitization.
o Infected mandibular tooth, inferior alveolar nerve block (performed proximally at a site presumably remote from the infected area) also has an unexpectedly frequent failure rate. (DS Moodley)
lidocaine
- Most widely used anaesthetic
- Cheap, autoclavable
*Available in sol.1,5%,2%,4%and10% - Topical and parenteral use
- T1/21,5hrs
- Metabolised in the liver
- Excreted in urine
*antiarrhythmic and local anaesthetic - blockade affects all nerve fibres sequence
autonomic, sensory and motor - Loss of nerve function clinically is as follows: pain, temperature, touch, proprioception, skeletal muscle
articaine
- newest local anaesthetic arsenal
- approved by (FDA) in April 2000.
- Amide class of local anaesthetics,
- available in 4% strength with 1:100,000 or 1:200,000 epinephrine.
- Unique among the amide local anaesthetics
- The thiophene ring
– increases its liposolubility
– Additional ester group- biotransformation in the plasma as well as in the liver - potency 1.5 times that of lidocaine
- faster onset
- increased success rate
la + adrenaline
reduces the blood flow
long anaesthetic time
reduces chances of toxicity
unwanted effects
caused by la agent
intravenous injection
overdose
CNS - cerebral stimulation
depression the medulla (rest and vasomotor centres)
CVS - direct action on heart and action on the vascular bed
allergic reaction
esters - para-aminobenzoic acid-component (PABA)
