CNS Depressants
Lab # 2
CNS Depressants: Classification
They are classified according to their pharmacological action into:
1- Sedative – hypnotics
2- Tranquillizers
3- Anaesthetics
I- Sedative - hypnotics
Definitions
Sedatives:
Drugs which calm the patient & cause sedation and in large doses
cause sleep
Hypnotics:
Drugs which induce sleep that resembles the natural sleep
Ex. Barbiturates
Sleep
Definition:
Physiological depression of consciousness
Sleep cycle:
Starts with latency period → NREM → REM → cycles of NREM
alternate with REM (about 4 cycles)
NREM
- Non rapid eye movement
- Lasts for 90 min.
- Thinking
REM
- Rapid eye movement
- Lasts for 20 min.
- Dreaming
II- Tranquillizers
Definition:
Tranquillizers are drugs which relief mental anxiety & stress without
affecting the consciousness
Ex. Chlorpromazine (CPZ)
MOA: D2 receptor antagonist
III- Anaesthetics
Definition:
Drugs which cause unconsciousness & generalized loss of pain
sensation, thus allow surgical procedures to be carried out
Ex. thiopental (IV) , halothane (inhalation)
MOA:
Interfering with propagation of nerve impulses by interfering with
electrolytes movement through the cell membrane
Sedative – hypnotics: Classification
Sedative-hypnotics
Barbiturates
1-Long acting (12-24 hr)
Ex. Phenobarbital
2-Intermediate acting (8-12hr)
Ex. Amobarbital
3-Short acting (4-8 hr)
Ex. Pentobarbital
4-Ultrashort acting (0.5-1hr)
Ex. Thiopental
Non-barbiturates
Benzodiazepines
Non- benzodiazepine
1- Barbiturates
MOA:
They have GABA like action → ↑ opening time of chloride
channels → ↑conductance of chloride ions →
hyperpolarization
Classification:
1-Long-acting
2-Intermediate-acting
3-Short acting
4-Ultrashort acting
2- Benzodiazepines
MOA:
Bind non-selectively to BZD receptors omega1 (GABA-dependant) & omega2.
chloride dependant →hyperpolarization
‡ omega1 → ‡ GABA receptors
Gi protein → ↓cAMP → relaxation
Ex.
- Diazepam (sedative)
- Triazolam (hypnotic)
3- Non-barbiturate Non-BZD
1- 5-HT agonist e.g. buspirone (5-HTA1)
2- Chloral hydrate (prodrug) converted to trichloroethanol
3- Antihistamine e.g. diphenhydramine
4- Paraldehyde
5- Promethazine
General signs for CNS depressants
1- ↓ vitality
2- ↓ excitability
3- ↓ HR & RR
Specific signs of sedative-hypnotic
Drugs: thiopental, phenobarbital & chloral hydrate
Sings:
1- Staggering gait
2- Sleeping posture
3- Loss of righting reflex (onset time)
4- ↓ Touch & pain reflexes (lost with thiopental)
Specific signs for CBZ
Signs:
1- No loss of righting reflex
2- Creeping gait
3- Abdomen touches the ground
4- State of catalepsy (loss of muscles control)→ onset time
5- ↓ Touch & pain reflexes