PNS

Question 1

Succinylcholine

Answer 1

1. Is a quaternary ammonium compound.
2. Structure resembles two molecules Ach linked together.
3. Acts as partial agonist at Nm receptors. Prolonged depolarisation, phase 1 block.
4. Causes fasiculations, later flaccid paralysis.
5. With continued exposure it leads to phase 2 block due to desensitisation of membrane.
   Partially reversed by anti cholinesterases.

Question 2

Pharmacokinetics

Succinylcholine

Answer 2

1. Is rapidly hydrolysed by pseudocholinesterases. Hence have short duration of action 3-8 min.
2. Transient apnoea is seen at peak
3. Succinylcholine apnoea - in people with liver disease, genetic defect.

Question 3

Adverse effect

Succinylcholine

Answer 3

1. Muscle pain due to initial fasiculations.
2. Increased IOP due to contraction of external ocular muscles.
3. Aspiration of gastric contents due to increased intragastric pressure.
4. Hyperkalaemia
5. Sinus bradycardia
6. Succinylcholine apnoea.
7. Malignant hyperthermia.

Question 4

D-tubocurarine

Answer 4

1. Alkaloid which has Nm blocking activity.
2. Prototype drug of competitive blockers.

Moa - dTc is antagonist of AcH at Nm receptors.
Anticholinesterases are used to reverse effects.

Question 5

D-tubocurarine

Actions

Answer 5

1. Cause histamine release - hypotension, bradycardia.
2. Flaccid paralysis.
3. Used as adjuvant to general anaesthesia.

Question 6

Pharmacokinetics

Answer 6

1. Poorly absorbed from GI tract.
2. Administered intravenously.
3. Do not cross bbb, placenta.
4. Metabolized in liver, excreted in urine.

Question 7

Drug interactions

Answer 7

1. D-tubocurarine + antibiotics = amino glycosides inhibits release of ACh from motor never and potentiates d-tc.
2. Thiazides+ d-Tc = hypokalaemia from thiazides potentiates dTc.
3. Succinylcholine + thiopentone = are chemically incompatible and form precipitate in syringes.
4. General anaesthetics + d-tc : enhances and potentiates dTc.

Question 8

Factors affecting Nm blockers

Answer 8

1. pH changes : metabolic and respiratory acidosis may increase duration of block.
2. Hypothermia: potentiates Nm block by delaying metabolism.
3. Myasthenia gravis : patients are highly sensitive to Nm blockers .
4. Antibiotics: potentiates effect
5. Inhalation anaesthesics : enchances effect

Question 9

Uses

Answer 9

1. As adjuvant to general anaesthesia for skeletal muscle relaxation during surgery.
2. Succinylcholine is used for electroconvulsive therapy to prevent trauma.
3. Tetanus and status epilepticus.
4. For ventilatory support in critically ill patients.