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SOE Pharmacology > 16. Induction Agents > Flashcards

16. Induction Agents Flashcards

1
Q

Ideal induction agent

A

Physical

> Cheap and easy to make
> Long shelf life at room temperature
> Water soluble and so easy to store
> Painless on injection
> Safe if injected intra-arterially
> Rapid onset time
> Rapid offset time
> No excitation or emergence phenomena
> No accumulation following infusion
> No interaction with other drugs

Biological properties:
> Analgesic
> No effects on patient’s physiology, other than rendering them unconscious
> No toxic effects

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2
Q

Ketamine

Uses

A

1 Induction agent - especially in hypotensive patient group / HD unstable
2 Procedural sedation - burns / dressing changes
3 Bronchodilator
4 Analgesic

  1. Induction and maintenance of anaesthesia
    especially in refractory asthma
    because of its profound bronchodilator effects

2
• Sedation on ICU/for short procedures,
e.g. dressing change in burns

3.
• Analgesia especially in the military field

  1. • In neuroaxial blockade to prolong its effect

5
• Drug of abuse

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3
Q

Ketamine
Effects

CVS x5

RS x4

CNS x7

GI

A

EFFECTS

CVS Increases 
•  noradrenaline and
adrenaline release
•  HR
•  CO
•  BP
•  Cardiac O2 consumption
RS
• Inc RR
• No loss laryngeal reflex
• Airway maintained
• Profound bronchodilation

CNS
• Dissociative anaesthesia
(i.e. strong analgesic and light ‘sleep’)

  • Increase CBF/ ICP/ CMRO2
  • Inc IOP
  • Amnesia

• Traditionally avoided in head injury as it was thought
to Inc ICP. In fact it does this no more than opioios do.

• Emergence phenomena, delirium, hallucinations.
Reduced by co-administration of benzodiazepine

• Inc Muscle tone

GI
• Nauea and vomiting
• Salivation

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4
Q

Ketamine

absorption / distribtuion

A

ABSORPTION/ DISTRIBUTION

  • Well absorbed orally and IM
  • Oral bioavailability 20%
  • Protein binding 20–50%
  • VD 3 L/kg
  • t½ 2.5 hours
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5
Q

Ketamine

metabolism

excretion

A

• Metabolised in liver by
P450
to norketamine (30% potency)

• Norketamine metabolised by conjugation
to inactive compound

• Excreted in urine

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6
Q

Ketamine

MOA

A

MOA

• Non-competitive antagonist at NMDA receptor

Weak agonist at MOP KOP and DOP receptors

• Inhibits reuptake of serotonin, dopamine and
noradrenaline

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7
Q

Ketamine -

What is it

Whats the preparation

Whats the dose

for induction
analgesia

A

Phencyclidine derivative

• Colourless solution in
glass vial:
10/50/100 mg/mL

• Available as racemic mix
or as S (+) enantiome (less delirium)

• IV/IM/PO/PR/intrathecal/
epidural administration

• Induction dose:
1–2 mg/kg IV
5–10 mg/kg IM

• Analgesic dose:
0.2–0.5 mg/kg

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8
Q

Ketamine

CHEMICAL PROPERTIES

A

• Chiral compound most
preparations are racemic,
but S-Ketamine is available
as single enantiomer

• Inhibits dopamine transporters
8x more than R-Ketamine

• S-Ketamine is twice as potent
as racemic mixture

  • 3-4x affinity for NMDA receptor than R-Ketamine
  • Recover mental function more quickly

Patients report more pleasant experience at doses causing same effect

• Water soluble forming
acidic solution pH 3.5–5.5

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9
Q

Propofol

Name

Composition

Vials

Dose

A

(2,6-diisopropylphenol) Phenolic derivative

• 1%/2% white lipid-water
emulsion in soya bean oil
and purified egg phosphatide

• 20/50/100 mL vials and
50 mL pre-filled syringe

DOSE
• 1.5–2.5 mg/kg (adult)
• 2–7 mg/kg (child)
• 4–12 mcg/kg/hr
maintenance
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10
Q

Propofol

USES

A 
USES
• Induction and
maintenance of
anaesthesia
• Sedation
• Refractory nausea
and vomiting
• Status epilepticus
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11
Q

Propofol

EFFECTS

CVS
x4

RS
4

CNS
3

GI
1

A 
CVS
•  ↓ BP and SV (15%−25%)
•  ↓ CO (25%)
• Vasodilatation secondary to NO production
• Bradycardia/ asystole
RS
• Depression
• ↓ Laryngeal reflex
• ↓ RR ↓ VT
• ↓ Response to ^pCO2 and \/pO2
• Bronchodilation
CNS
• Hypnotic,
 smooth and 
rapid induction
↓ CPP ↓ ICP ↓ CMRO2
• Myoclonic movements

GI
• Antiemetic
(antagonist at D2 receptor)

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12
Q

Propofol

SIDE-EFFECTS

A

• Pain on injection (improved with newer
‘Propfol-Lipura®’

which has /\ medium chain triglycerides
rendering drug more lipid-soluble)

• Epileptiform movements
(however it is not epileptogenic and is used
for treatment of status epileptious)

• Unlicensed in < 16 yr olds after 
complications of long-term use in ICU 
(fat overload syndrome, 
fatty deposits in liver, lung, heart and kidneys/metabolic
acidosis/refractory bradycardia)

• Lipaemia with long-term use

• Green urine and hair, secondary to
quinol
metabolites

  • Increased energy needed for DCCV
  • Physically incompatible with atracurium
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13
Q

Propofol

MOA

A

MOA

  • Uncertain
  • May potentiate GABAA receptor
  • May have action at cannabinoid receptor
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14
Q

Propofol

ABSORPTION/
DISTRIBUTION

A

ABSORPTION/
DISTRIBUTION

  • Protein binding 98%
  • VD 4 L/kg
  • Rapid distribution to tissues

• Rapid elimination
(t½ 1–5 hours, context sensitive)

which may be increased following slower release from adipose tissue

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15
Q

Propofol

METABOLISM
AND EXCRETION

A

• Hepatic metabolism,
mainly conjugated to
inactive glucuronide

  • Renal excretion
  • Liver/renal dysfunction has little effect on metabolism

• Clearance exceeds hepatic blood flow,
suggestive of extra hepatic metabolism

• No active metabolites

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16
Q

Propofol

CHEMICAL PROPERTIES

A

CHEMICAL PROPERTIES

  • Poorly water soluble
  • Weak organic acid

• pKa = 11 therefore almost totally un-ionised at
pH 7.4

• pH 7.0

• Free radical
scavenger

• Physically
incompatible with
atracurium

17
Q

THIOPENTONE

Type of medication

Dose
Prep

A

Barbiturate

• Yellow powder, 500 mg/vial

DOSE

  • 3–7 mg/kg IV
  • 1 g/22 kg weight PR
18
Q

THIOPENTONE

USES

A

USES

• Induction of anaesthesia
(bolus lasts 5–10 min)

• Status epilepticus

• To achieve ‘burst
suppression’ in raised ICP

19
Q

THIOPENTONE

MOA

A

MOA

• ^ Duration of opening of GABA Cl–
channels in CNS causes hyperpolarisation
and neuronal inhibition

20
Q

THIOPENTONE

EFFECTS

CVS x4

RS X 3

CNS
4

Renal
Urine

Other

A

EFFECTS

CVS

  • ↓ CO
  • ↓SV
  • ↓SVR
  • May cause ^ HR

RS

  • Depression
  • Laryngospasm
  • Bronchospasm

CNS
• Anaesthesia

  • ↓CMRO2
  • ↓Blood flow and volume
  • ↓CSF pressure
  • At low dose is antalgesic

RENAL
• ↓Urine OP
(^ADH and ↓CO)

OTHER
• Severe anaphylaxis
(1/20 000)

• Precipitates porphyria

• Intra-arterial injection ->severe pain and
spasm
and perivascular necrosis

21
Q

THIOPENTONE

CHEMICAL PROPERTIES

A

CHEMICAL PROPERTIES

• Displays tautomerism
or
dynamic isomerism,

the
proportions of the two forms
governed by ambient pH

• Weak acid –
forms alkaline solution when
dissolved in H2O, pH 10.8.

This solution stable for many days and is
bacteriostatic because of high pH.

• Undissociated acid insoluble and
so, when packaged:

a) Sodium carbonate (6% by weight)
added to powder.

So, when dissolved, it releases –OH–,
therefore preventing accumulation of H+
and
formation of undissociated acid

b) Stored under N2 gas –
prevents acidification of
powder by CO2 in air

• pKa 7.6
therefore 60% un-ionised at pH 7.4

• Highly lipid soluble

22
Q

THIOPENTONE

METABOLISM
AND EXCRETION

A

METABOLISM AND EXCRETION

• Hepatic oxidation by P450 ->
mainly inactive metabolites
(though pentobarbitone is active)

  • Induces P450 after single dose
  • Zero order kinetics with infusion
23
Q

THIOPENTONE

ABSORPTION/
DISTRIBUTION

A

ABSORPTION/ DISTRIBUTION

• Protein binding 80%

• Of the unbound 20%,
only 12% un-ionised

and available
(as 60% ionised at pH 7.4)

• VD 2 L/kg

• Rapid emergence secondary to
rapid redistribution to tissues

• Critically ill patients
are acidotic with ↓ protein binding

therefore less thiopentone needed

• NSAIDs may ↓ protein binding and = ^^ free drug fraction

24
Q

Etomidate

Type

Dose

A

ETOMIDATE
Imidazole hypnotic

• Clear colourless solution:

2 mg/mL in 10 mL vial

DOSE
• 0.3 mg/kg

25
Q

Etomidate

MOA

A 
MOA
• ^ Duration of
opening of GABA C l –
channels in CNS
causes
hyperpolarisation and neuronal
inhibition

• Only the D isomer causes hypnosis

26
Q

Etomidate

USES

A

USES

  • Induction of anaesthesia
  • Treatment of Cushing’s syndrome before surgery
27
Q

Etomidate

EFFECTS

CVS
4-5

RS
2

CNS X8

GI X1

A

EFFECTS
CVS

  • Most stable induction agent
  • Slight ↓ SVR
  • Myocardial O2 consumption not affected
  • Contractility not affected
  • BP not affected

RS

  • Depression
  • No inhibition of hypoxic pulmonary vasoconstriction

CNS

  • Hypnosis
  • Tremor
• Involuntary movements
• ↓ Tone
• Epileptiform activity on EEG in 25%
• ↓ ICP
• ↓ CPP an
↓ CMRO2
• ↓ IOP

GI
• Nausea and vomiting
(especially in conjunction with opioid

28
Q

Etomidate

OTHER effects

A

• Inhibits steroid synthesis,
by inhibition of 11b and 17a hydroxylase,
for 24 hourly after only 1 dose.

Was associated with deaths on ICU
following infusion for sedation.

Use has declined because of this and the
increasing popularity of ketamine

  • Pain on injection in 25%
  • Contraindicated in porphyria
  • Antiplatelet activity
  • Hypersensitivity and histamine release (rare)
29
Q

Etomidate

CHEMICAL
PROPERTIES

A

CHEMICAL
PROPERTIES

• pH of solution 8.1

Pka 4.1

30
Q

Etomidate

METABOLISM
AND EXCRETION

A

METABOLISM
AND EXCRETION
• Rapid metabolism by hepatic and plasma esterases

  • May inhibit plasma cholinesterase
  • Excreted in urine (90%) and bile (10%)
31
Q

Etomidate

ABSORPTION/
DISTRIBUTION

A

ABSORPTION/ DISTRIBUTION

  • Protein binding 75%
  • Rapid distribution
  • VD 3 L/kg

SOE Pharmacology (38 decks)

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