They are general depressants for all excitable cells, the C.N.S. is most sensitive. Sedative dose given at day time can produce drowsiness, reduction in anxiety & excitability. However, barbitrates do not have selective antianxiety action. Barbiturates can impair learning, short term memory, judgement & produce euphoria in addicts. They have anticonvulsant property & longer acting agents (Phenobarbitone) have specific anti- convulsant action independent of general CNS depression. Respiration is depressed at relatively higher doses. Hypnotic doses produces a slight decrease in BP and heart rate. Toxic doses produce mared fall in BP due to ganglionic blockade, vasomotor centre depression & direct decrease in cardiac contractility. Tone & motility of bowel is decreased & reduce urine flow by decreasing BP & increasing ADH release.
Mania, delirium Intractable insomnia, counteract CNS stimulation. Anti convulsant. Preanaesthetic medication.
Sedative : 15-30 mg daily. Hypnotic : 60-210 mg daily in divided doses.
Concurrent admin. of C.N.S. & alcohol depressants. Renal & hepatic impairment. Acute intermittant porphyria, severe pulmonary insufficiency (emphysema).
Tolerance and physical dependence occurs. Pregnancy, decreased hepatic, renal, cardiac, respiratory functions.
Hangover, mental confusion, impaired performance. Idiosyncrasy, rashes, swelling of eyelids. Overdosage may produce respiratory depression, hypotenion,dizziness, ataxia, coma and death.
Folate, pyridoxin, dicoumarol & phenylbutazone, lower plasma phenobarbitone levels. Additive sedative effect with alcohol and other CNS depressants.
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