PharmacologyCNS Flashcards
Some NT of CNS
Norepinephrine Epinephrine Dopamine Acetylcholine Serotonin Gamma amino butyric acid (GABA) Glutamate
Rank type of drugs from central sedative to central stimulative
- general anesthetics
- hypnotics
- sedatives* ,neuroleptics
- anxiolytics*
- antiepileptics/anticonvulsants
- antidepressives*
- Analeptics*
- psychoactives
What are less common CNS drugs
With medical indication 症状:
- central muscle relaxants, opiates and central α2-agonists
- Drugs against Parkinson
Without med. Indication
e.g. LSD, cannabinoids, (but med. indication CB-antagonists
Drugs with CNS side effect but are non-CNS drugs
antihistaminics, local anesthetics, antiarrhythmics, antihypertensive drugs
Pre-condition for central action
- passage BBB (lipophil, active transport)
- interaction with central structures like
- receptors (pre-, postsynaptic)
- transporter
- enzymes (e.g. delayed degradation of neurotransmitters)
- ion channels (Na+, K+, Ca++)
Type of NT and its % in CNS synapse
gamma amino butyric acid 30-40% (inhibitory)
glutamate 30-40% (excitatory)
acetylcholine ca. 10
dopamine ca. 1%
norepinephrine ca. 1%
serotonin (5-hydroxytryptamine= 5-HT) ca. 1%
CNS drugs are difficult because
- main effects and side effects are hard to differentiate
- BBB limits the drugs to be lipid soluble agents or drugs by specific transport systems
Understanding the effects of drugs on individual neurons
does not predict the effect on the whole organ
Projection of 5HT
everywhere
Projection of DA
mostly frontal lobe
Projection of Ach
everywhere except cerebellum
Projection of NA
everywhere
Benzodiazepines
main CNS drugs
BZD mess with…
GABA!
BDZ receptor linked to GABA-A receptor complex (bound to Cl channels).
GABA: an inhibitory neurotransmitter
BDZ increase the affinity of the receptor for GABA, and thus increase Cl- conductance and hyperpolarizing current
Therefore, BDZ are indirect GABA-agonists
Therapeutic use of BZD
Sedative-hypnotic Anxiolytic Muscle relaxants Anticonvulsants Alcohol withdrawal Premenstrual syndrome Psychoses (only supportive) Adjunct in mania of bipolar disorder
Patterns of use of BZD
45% of Use <30 days 80% of Use <4 months 15% of Use >12 months (7-18% Europe) Women, twice the rate as men <40% of Anxiety Diagnosis Treated >40% of Panic Disorder Treated
Sedative/Hypnotic effect of BZD
- Transient - lowest effective dose- time-limited
- Insignificant decrease in sleep latency-1 hour
- increase in sleep duration
- ? effect on sleep architecture ( REM, stages 3 and 4)
- Rebound insomnia - worsening of sleep - worse than before trying benzos.
- Daytime drowsiness, dizziness, lightheadedness
Anxiety effect of BZD
- benzos good for immediate symptom relief-faster than SSRI’s for panic.
- long-acting, low potency preferred (clonazepam or chlordiazepoxide)
- best used for exacerbations of anxiety-short term vs continuous use
Adverse Effects of BZD
-Sedation, CNS Depression worse if combined with EtOH -Behavioural Disinhibition irritability, excitement, aggression (<1%), rage -Psychomotor & Cognitive Impairment coordination, attention (driving) poor visual-spatial ability (not aware of it) ataxia, confusion -Overdose: Rare fatalities if BZD alone - Severe CNS & Respiratory Depression if combined with: alcohol barbiturates narcotics tricyclic antidepressants
Pharmacokinetics of BZD
Lipid-soluble:
fast cross blood-brain-barrier: rapid onset of action.
Persist longer in high fat-to-lean body mass (obese and elderly )
Abuse liability (Valium)
Biotransformation & Half-Life:
Hepatic oxidation: long-t1/2, active metabolites
Glucuronidation: short-t1/2, no active metab.
absorbtion distribution, metabolism and excretionof BZD
Well absorbed,
peak plasma concentrations approx. 1 hour
Several pharmacologically active intermediates
IG: Interactions of BZD with other drugs
- CNS Depressants
- p450 2C9 (TCAs, warfarin, phenytoin)
- p450 3A4 (triazolam, midazolam, alprazolam, CBZ, quinidine, terfenadine, erythromycin)
- Disulfiram & Cimetidine increaseBZD levels
Other sedative-hypnotics than BZD
-Barbiturates - pentobarbital,phenobarbital,
secobarbital, butalbital (Fiorinal)
-Barb-like: glutethimide, chloral hydrate, ethhchlorvynol (Placidyl), meprobamate (carisoprodol/Soma)
-Azapirone: buspirone (2-10 mg TID - max 60 mg/d)
-slow onset of action (1-3 wks)
-not abused, no withdrawal
-effective for anxiety disorders-not for acute
-does not block benzo withdrawal
-not sedating, anticonvulsant or mm relaxing
-no resp dep/ cognitive/psychomotor impair
IG: Non-Benzo Hypnotics
- Zolpidem (Ambien) imadozopyridine
- Zaleplon (Sonata) pyrazolopyrimidine
- Bind to specifically to BZ-1 sites
- Both rapid onset (1h-2.5 h) - short action/1/2 life
- Decrease sleep latency, increase REM sleep
- 5-20 mg dose range
- Safe in older adults, metab in liver, no active metabolites
- Potentiate ETOH impairment
- Both reinforcing, potentially abusable, and performance-impairing
Parkinson disease
a degenerative disorder of the CNS caused by death of neurons that produce the brain neurotransmitter dopamine @substantia nigra. It is the most common degenerative disease of the nerves
Parkinson’s disease is a disorder of the extrapyramidal system associated with disruption of neurotransmissions within the striatum; A disruption of neurotransmission within the striatum (proper function requires balance between dopamine and acetylcholine
Dyskinesias of Parkinson’s disease are
Tremor at rest Rigidity Postural instability Bradykinesia (slow movement) Akinesia (complete absence of movement)
Therapeutic goal of PD
- Improve Activity of Daily Living’s
- Restore balance between DA and ACH by activating DA receptors or blocking ACH receptors
- Drug selection and dosages are determined by activities of daily living performance
Classification of Drug Therapy for Parkinson’s Disease
Dopaminergic agents
- Promote activation of dopamine receptors
- Levodopa (Dopar)
Anticholinergic agents
- Prevent activation of cholinergic receptors
- Benztropine (Cogentin)
Mechanism of action for PD drugs
Dopaminergic Agents: Promotion of dopamine synthesis Prevention of dopamine degradation Promotion of dopamine release Direct activation of dopamine receptors (D2)
Anticholinergic Agents:
Blockade of muscarinic cholinergic receptors in the striatum
Drug Therapy for Parkinson’s Disease
May take a while for effect to show Levodopa Carbidopa Amantadine Bromocritine Pergolide Selegiline Benztropine
Epilepsy
Group of disorders characterized by excessive neuron stimulation within the central nervous system
Seizure types/epilepsy
Generalized seizures:
Convulsive (tonic-clonic)/Grand Mal
Nonconvulsive (absence)/Petite Mal
Partial (focal)Seizures:
Simple partial
Complex partial
Antiepilectic Drugs
Suppress neuronal discharge at the seizure’s focus and brain
Mechanism of action
-Suppression of sodium influx
-Suppression of calcium influx
Therapeutic Considerations for epilepsy
Treatment goal Diagnosis Drug Selection Plasma drug levels Compliance 服薬順守 Withdrawal
IG: Phenytoin
-Drug for Partial and tonic-clonic seizures
-Mechanism of action-selective inhibition of sodium channels
-Varied oral absorption
-Half-life 8-60 hours
-Adverse effects:
Nystagmus
Sedation
Ataxia
Diplopia
Cognitive Impairment
-Drug interactions:
Decreases effect of oral contraceptives, warfarin, glucocorticoids
Increases levels of diazepam,isoniazid,cimetidine,alcohol, valproic acid