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Barbiturates - Coggle Diagram
Barbiturates
Pharmacokinetics
Metabolism
Liver
Excretion
Kidneys
Kidney failure may lead to accumulation
Absorption
Well absorbed via oral or rectal
Injectable= highly irritating= no IM
Distribution
From site of action in the CNS to muscles & then adipose
Drug examples
Short-acting
Pentobarbital
Secobarbital
Intermediate acting
Amobarbital
Butabarbital
Ultra-short acting- IV only
Methohexital
Thiopental sodium
Long acting
Phenobarbital
Adverse Effects
Anesthetic doses
Higher concentrations used for very short procedures like intubation
Coughing & laryngospasm reported w/IV
High doses may reversibly depress liver and kidney function, reduce GI motility, and lower body temp.
Acute poisioning
Ingestion of 10x hypnotic dose= resp. failure/death.
Sedative or hypnotic doses
CNS depression may be exaggerated in elderly & debilitated patients or in those w/kidney or live impairment.
Some, notably elderly, patients can have idiosyncratic effect, causing stimulation instead of sedation
Pharmacologic Effects
Analgesia
None. Patients in pain may become agitated and delirious if barbs are given w/o analgesics
Anticonvulsant effect
Long-lasting agents used to treat epilepsy
CNS depression
Normal doses= relaxation
Larger doses= Inhibitory fibers of CNS are depressed. Leads to disinhibition and euphoria.
Higher doses= hypnosis
Even higher doses= anesthesia
Drug interactions
Barbs effects enhanced by:
Disulfiram, propoxyphene, phenytoin
Drugs w/enhanced or additive CNS depressant effect when used w/barbs
Alcohol, CNS depressants, Opioids, monoamine oxidase inhibitors
Barbs reduce effectiveness of:
Acetaminophen, b-blocker, birth control pills, chlorpromazine, doxycycline, estrogens, griseofulvin, phenytoin, quinidine, steroids, tricyclic antidepressents, warfarin
Medical uses
Ultra-short acting
IV to induce general anes.
Short/intermediate acting
Little use. Benzos have since replaced for insomnia/anxiety. Short-acting barbs used to be popular to abuse due to fast onset.
Long-acting
Tx of eplilepsy
Phenobarbital
Mechanism of Action
Enhances GABA receptor binding ability
Prolong opening of chloride channels
!!!Absolute contraindication= Intermittent porphyria / family history of porphyria!!!