Barbiturates
Barbiturates exhibit the following properties:
1) These are non-selective CNS depressants, producing sedation and reducing anxiety which leads to unconsciousness. However, their overdose is fatal as they may cause respiratory and cardiovascular failure.
2) They act partly by enhancing the action of GABA but used in anaesthesia, and epilepsy; they are no longer used as sedatives or hypnotics.
3) They are potent inducers of hepatic drug-metabolising enzymes (cytochrome P450 system in particular), thus may cause drug interactions. 4) They are also involved in attacks of acute porphyria in liable individuals.
5) They may give rise to tolerance and dependence.
1) These are non-selective CNS depressants, producing sedation and reducing anxiety which leads to unconsciousness. However, their overdose is fatal as they may cause respiratory and cardiovascular failure.
2) They act partly by enhancing the action of GABA but used in anaesthesia, and epilepsy; they are no longer used as sedatives or hypnotics.
3) They are potent inducers of hepatic drug-metabolising enzymes (cytochrome P450 system in particular), thus may cause drug interactions. 4) They are also involved in attacks of acute porphyria in liable individuals.
5) They may give rise to tolerance and dependence.
Classification
1) Long Acting (8 hours or more): Phenobarbitone.
2) Intermediate Acting (4-8 hours): Amylobarbitone, Butobarbital and Pentobarbitone.
3) Short Acting (less than 4 hours): Secobarbital and Hexobarbitone.
4) Ultra Short Acting: Thiopentone and Methohexitone.
1) Long Acting (8 hours or more): Phenobarbitone.
2) Intermediate Acting (4-8 hours): Amylobarbitone, Butobarbital and Pentobarbitone.
3) Short Acting (less than 4 hours): Secobarbital and Hexobarbitone.
4) Ultra Short Acting: Thiopentone and Methohexitone.
Pharmacological Actions
1) CNS Depression:
Barbiturates cause CNS depression ranging from mild sedation to profound central depression. Death occurs when the vital medullary centres, including the respiratory and vasomotor centres are depressed. The amnesic action of barbiturates causes drug automatism and unintended poisoning. Respiratory depression can occur with hypnotic dose in patients having chronic lung disease.
Barbiturates are the only CNS depressants which reduce the effect of narcotic analgesics, may be due to lowered pain threshold.
Barbiturates are the only CNS depressants which reduce the effect of narcotic analgesics, may be due to lowered pain threshold.
2)Cardiovascular System
lood pressure is lowered by hypnotic doses of barbiturates which reduce the cardiac output and induce vasodilatation and peripheral pooling of biood. In higher doses, they cause depression of the vasomotor centre and induction of hypotension with depression of compensatory vascular sympathetic refiexes.
3) Enzyme Induction:
This may give rise to drug interactions and barbiturate tolerance.
This may give rise to drug interactions and barbiturate tolerance.
Uses
Use of barbiturates as sedatives or hypnotics has declined. Phenobarbitone is used as an anticonvulsant and antiepileptic; and thiopentone is used as an IV anaesthetic agent. The enzyme-inducing effect of phenobarbitone is used in the treatment of hyperbilirubinaemia and resultant kernicterus in neonates.
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