TPL and Methohexital Flashcards
1
Q
thiopental
A
- CLASS
- Thiobarbiturate with sulfur @ carbon #2
- USE
- anesthesia induction agent
- Tx of increased ICP
- MOA
- Binds to the GABAA receptor, enhances and mimics the action of GABA by increasing chloride conductance through the ion channel → hyperpolarization of the cell membrane and increases the threshold of excitability of the postsynaptic neuron
- At low concentrations barbs enhance the effects of GABA, decreasing the rate of dissociation of GABA from its receptor and increasing the duration of GABA-activated Cl ion channel openings.
- At larger concentrations, the barbs activate the Cl channels directly, without the binding of GABA, acting as the agonist itself. The GABA-mimetic effect at slightly higher concentrations may be responsible for what is termed barbiturate anesthesia.
- PHARMACOKINETICS
- onset: Rapid
- 10 -30 sec for induction dose
- DOA: 5 - 8 min with rapid redistribution
- E1/2 time: 11.6 hrs
- PB: 70 - 85%
- Vd: 2.5 L/kg
- Metabolism;
- 99% metabolized by liver
- normal doses: first order kinetics
- higher doses: zero order kinetics
- CYP450 INDUCER
- Elimination: <1 % excreted unchanged in urine
- SIDE EFFECTS
- NEURO:
- sedation
- ↓CBF, ICP & CMRO2- isoelectric EEG
- does NOT preclude SSEP monitoring
- confusion in elderly
- hyperactivity in children
- CV:
- ↓ SNS outflow → peripheral vasodilation → ↓BP → compensatory ↑HR
- RESP:
- dose dep resp depression
- dec ventilatory response to hypoxia/hypercapnia
- GI:
- N/V, liver toxicity
- OTHER:
- some muscle relaxation → not surgical depth
- HISTAMINE RELEASE w/ rapid IV administration
- accelerated heme production
- CAUTIONS/CONTRAINDICATIONS
- severe liver disease
- porphyria
- pregnancy → readily crosses placenta
- do not mix with LR (LR too acidic) → precipitates
- MOST POTENT CYP450 INDUCER → ↑ metabolism of oral anticoagulants, phenytoin, TCAs, corticosteroids, and vitamin K, (MAY NEED TO DOSE NMBS MORE FREQUENTLY)
- DOSE
- induction: 3 - 5 mg/kg IV
- peds induction: 5 - 6 mg/kg
- infants induction: 7 - 8 mg/kg
2
Q
methoxital
A
- CLASS
- oxybarbiturate with methyl group @ carbon #3; oxygen @ #2
- USE
- methyl radical imparts convulsant activity
- MOA
- Binds to the GABAA receptor, enhances and mimics the action of GABA by increasing chloride conductance through the ion channel → hyperpolarization of the cell membrane and increases the threshold of excitability of the postsynaptic neuron
- At low concentrations barbs enhance the effects of GABA, decreasing the rate of dissociation of GABA from its receptor and increasing the duration of GABA-activated Cl ion channel openings.
- At larger concentrations, the barbs activate the Cl channels directly, without the binding of GABA, acting as the agonist itself. The GABA-mimetic effect at slightly higher concentrations may be responsible for what is termed barbiturate anesthesia.
- PHARMACOKINETICS
- Onset: Rapid
- DOA: rapid termination of effect: 5 - 8 min (redistribution)
- E1/2 time: 3.9 hrs
- PB: 70 - 85%
- Metabolism:
- 99% hepatic + extrahepatic (extensive)
- CYP450 INDUCER
- Elimination: < 1 % excreted unchanged in urine
- SIDE EFFECTS
- NEURO:
- sedation
- ↓CBF, ICP & CMRO2- isoelectric EEG
- can cause seizures in predisposed patients
- myoclonus
- hiccups
- CV:
- ↓ SNS outflow → peripheral vasodilation → ↓BP → compensatory ↑HR
- RESP:
- dose dep resp depression
- dec ventilatory response to hypoxia/hypercapnia
- GI:
- N/V, liver toxicity
- OTHER:
- some muscle relaxation → not surgical depth
- HISTAMINE RELEASE w/ rapid IV administration
- accelerated heme production
- CAUTIONS/CONTRAINDICATIONS
- severe liver disease
- asthma
- porphyria
- pregnancy → readily crosses placenta
- do not mix with LR (LR too acidic) → precipitates
- do not mix with opioids, catecholamines, NMBs, midazolam (too acidic)
- MOST POTENT CYP450 INDUCER → ↑ metabolism of oral anticoagulants, phenytoin, TCAs, corticosteroids, and vitamin K, (MAY NEED TO DOSE NMBS MORE FREQUENTLY)
- DOSE
- induction: 1-2 mg/kg IV
- peds: 20-30 mg/kg PR
