Thiopental (TPL) Flashcards
Please note that the drug card information is for Educational Use ONLY, and the source is from Carrie Bowman's glossary of drug cards permitted by use of Georgetown NAP students. No permission is given to use these cards for anything other than as a study resource for our program.
What are the trade names of Thiopental?
Pentothal, Trapanal
What is the formal drug classification of Thiopental
Thiobarbiturate due to the presence of sulfur at position C-2 in its chemical structure
What are the clinical uses of TPL
- as an anesthesia induction agent and is less commonly used to maintain anesthesia
- used for treatment of increased ICP
What is the MOA of TPL?
GABAa channel
- when thiopental binds to the GABAa receptor, it hyperpolarizes the cell membrane and increases the excitability threshold of the postsynaptic neuron by increasing chloride conductance through the ion channel thereby augmenting and imitating the action of GABA.
- TPL’s action on the GABAa receptor is dose-dependent; at low concentrations, TPL slows the rate at which GABA dissociates from its receptor increasing the duration of GABA-activated chloride channel opening that grants TPL its hypnotic and sedative properties
- at higher concentrations, TPL does not bind GABA but rather directly opens the chloride ion channels, which is what may be responsible for barbiturate-anesthesia.
- ***Also inhibits the synaptic transmission of various excitatory neurotransmitters including Ach and glutamate
How is TPL metabolized?
- low heptatic extraction ratio with capacity-dependent elimination
- 10-20% of TPL is metabolized by the liver to hydroxythiopental and carboxylic acid derivatives (which are water soluble) and excreted in the urine
- oxidation, desulfuration, and hydrolysis
What is the redistribution/ how is it redistributed of TPL?
- dependent on CO and Blood volume, thus hypovolemia can lead to less dilution of drug causing increased CNS effect
- once in the blood, the drug rapidly distributes to high-perfusion, low-volume tissue regions like the brain and more slowly to muscle tissue
- redistribution to both these areas is primarily responsible for the termination of the induction dose
What is the distribution half life of TPL?
2-4 minutes
What is the Volume of Distribution of TPL?
- 5 L/kg
- high affinity to fat, large volume of distribution, and slow rate of hepatic clearance allow the drug to accumulate in the body when it is administered in high doses over a protracted length of time
Is TPL protein bound?
72-82% protein bound to albumin
-high protein binding occurs with low plasma concentration, and decreased protein binding occurs with hypoalbuminemia, uremia, cirrhosis, or taking other protein bound drugs
What are the CNS side effects of TPL?
-40% of patients report a garlic/onion taste
What is significant regarding the hypersensitivity reaction of TPL?
anaphylaxis is rare but when it occurs it is associated with high fatality rate
What are the cardiac effects of TPL?
- causes peripheral vasodilation leading to venous pooling
- cardiac depression resulting from decreased contractility caused by reduced calcium availability can also result from administration of this drug
What are the respiratory effects of TPL?
-respiratory depression and “double apnea”
What are the contraindications to use of TPL?
- may lead to respiratory depression, so avoid in pts with obstructions, difficult airways, or with status asthmaticus
- in pts with CV instability or shock
- Contraindicated with pts with Porphyria
Why is TPL contraindicated with Porphyria?
because it may cause an acute life-threatening attack
