Pharmacology, Set II
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- General depressants which decrease CNS activity at low doses
- Barbiturates
- Decrease neural and skeletal muscle activity at higher doses
- Barbiturates
- Block activity in reticular activating system thereby producing sedation and inducing sleep
- Barbiturates
- Barbiturates block activity in the __ thereby producing sedation and inducing sleep
- reticular activating system
- Barbiturate with the longest half-life
- Phenobarbital
- Barbiturate with an intermediate half-life
- Butabarbital
- Barbiturates enhance __ receptor activity
- GABAa
- Barbiturates increase Cl- conductance as with benzodiazepines, however
- through a separate site
- inhibits GABA transaminase
- Thiopental
- Enzyme responsible for inactivation of GABA
- GABA transaminase
- At low doses, barbiturates block __ excitation
- glutamate receptor-mediated
- At high doses, barbiturates
- Block K+ and Na+ channels
- Net effect of a barbiturate is enhancement of __ and blockade of
-
inhibitory neurotransmission;
excitatory neurotransmission - Barbiturates are anxiolytic, but with substantial
- drowsiness and ataxia
- Barbiturates depress higher cortical centers, resulting in
-
euphoria
impaired judgment
giddiness
excitement - barbiturates have this effect on body temp
- decrease it
- barbiturates have this effect on monosynaptic reflexes
- none
- why don't barbiturates have an effect on monosynaptic reflexes
- not centrally active muscle relaxants
- do barbiturates have analgesic activity
- no
- Barbiturates depress respiration increasingly with
- increasing doses
- Very high doses of barbuiturates result in collapse of
- vasomotor center
- Barbiturates depress sympathetic ganglia activity which has this effect on bp
- decrease blood pressure
- barbiturates induce liver microsomal enzymes which
- alters drug metabolism
- Metabolism of barbiturates is achieved this way
- in the liver by oxidation
- barbiturates are generally well absorbed from
- GI tract and muscle
- Oxybarbiturate (e.g., phenobarbital) onset parallels
- rate of absorption
- Oxybarbiturate duration of action parallels
- rate of elimination
- Thiobarbiturate (e.g., thiopental) onset and duration of action related to
- distribution
- Rapid distribution to brain due to high lipid solubility thus rapid onset of action
- thiobarbiturates
- thiobarbiturates have rapid distribution to brain, but slower distribution to
- muscle and fat tissues
- Usefulness of barbiturates for anxiolysis is limited by
- low selectivity
- use of barbiturates as anxiolytics
- Pre-anesthetic to reduce anxiety
- barbiturates are effective hypnotics; however...
- other medications are more selective
- problem assoc with use of barbiturates for anticonvulsant activity
- Respiratory depression
- barbiturates decrease __ associated with surgery or head injury
- cerebral edema
- barbiturates are useful in treating __ arising from disease or poisoning
- acute seizures
- Idiosyncratic effects of barbiturates are seen mainly in these patients
- geriatric and debilitated
- Common ADRs of barbiturates are just extended __ effects
- CNS depressant
- Uticaria
- hives
- swelling in deep layers of skin
- Angioneurotic edema
- scaly skin disorder
- Exfoliative dermatitis
- lesion resulting from death of liver parenchymal cells, resulting in jaundice
- Parenchymatous hepatitis
- in a few cases, barbiturates result in __; a blood disorder involving loss of white blood cells
- Agranulocytosis
- dose of barbiturate which results in poisoning
- 5 – 10x therapeutic dose
- dose of barbiturate which results in death
- 15 x therapeutic dose
-
Stupor or coma
Respiratory depression
Circulatory collapse
are all sx of - barbiturate toxicity
- can be used as a supportive measure in treatment of barbiturate toxicity
- Dopamine
- Altered porphyrin synthesis
- Porphyria
- with barbiturates, tolerance develops to CNS depressant effects in this amount of time
- within a few weeks
- Chronic use of barbiturates has this effect on GABAa receptor
- down-regulation
- are barbiturates habit-forming?
- yes!
- dependance of an individual to barbiturates are both
- psychological and physical
- Withdrawal from barbiturates is more dangerous than withdrawal from
- opiates
- GABAA receptor down-regulation leads to __, which persists following drug withdrawal
- elevated central cholinergic activity
- The net effect of abstinence from barbiturates
- CNS excitation
- treatment for abstinence syndrome with barbiturates
- Hospitalization and stabilization on lowest dose that prevents abstinence syndrome
- Gradual withdrawal from barbiturates happens over this period of time
- 2 – 3 weeks
- Substitution with __ to treat abstinence sydrome is not recommended
- non-barbiturates
- benzodiazepines and barbiturates are generally
- sedative hypnotics
- Chloral hydrate
- Noctec
- Methyprylon
- Noludar
- Glutethimide
- Doriden
- Ethinamate
- Valmid
- Methaqualone
- Sopor® Parest® Quaalude
- Ethchorvynol
- Placidyl
- Chloral hydrate is metabolized by
- alcohol dehydrogenase
- active metabolite of chloral hydrate
- trichlorethanol
- trichloroethanol is further oxidized to
- trichloroacetic acid
- Trichloroethanol half life is
- 8 hrs
- Superior to barbiturates with respect to modifying sleep patterns, REM rebound
- Chloral hydrate
- When combined with ethanol, chloral hydrate rapidly and effectively
- promotes sleep
- chloral hydrate slows ethanol metabolism, thereby
- enhancing effects of ethanol