Induction barbiturates

The polycyclic hydrocarbon type of inducer does not have such major effects, only causing slight liver enlargement and having no effect on liver blood or bile flow. The increase in cytochromes P-450 is not confined to the centrilobular area of the liver, protein synthesis is only slightly increased and there is no increase in phospholipid synthesis. Other enzymes than cytochromes P-450 are also induced by polycyclic hydrocarbons, although generally to a lesser extent than with barbiturate induction. NADPH cytochrome P-450 reductase is not induced by polycyclic hydrocarbons however. 

Barbiturates. The ultrashort-acting barbiturates (see Table 1) methohexital (4), thiopental (5), and thiamylal (6) are used for induction and... 

The other method used is infusion of intravenous anaesthetics such as propofol, etomidate (for induction) and the barbiturates such as thiopental and pentobarbital. Investigations into the mechanism of anaesthesia have made use of all these compounds in order to identify a common mode of action linked to likely mechanisms within the CNS. 

Induction is a part of stage I anesthesia. It begins with the administration of an anestheticdrug and lasts until consciousness is lost. With some induction drugs, such as the short-acting barbiturates, this stage may last only 5 to 10 seconds. 

CYP450 enzyme induction from phenytoin, fosphenytoin, or barbiturates may decrease effect... 

The answer is c. (Hardman, p 323.) Induction of anesthesia by parenteral administration of thiopental sodium and other barbiturates is... 

Urinary D-glucaric acid levels have been shown to be a sensitive indicator of microsomal enzyme induction in workers exposed to chlordecone (Guzelian 1985). However, other substances such as barbiturates, phenytoin, chlorbutanol, aminopyrine, phenylbutazone, and contraceptive steroids as well as other organochlorinated pesticides also cause microsomal enzyme induction and cause changes in urinary D-glucaric acid (Morgan and Roan 1974). 

Thiopental and methohexital belong to the barbiturates which, depending on dose, produce sedation, sleepiness, or anesthesia. Barbiturates lower the pain threshold and thereby facilitate defensive reflex movements they also depress the respiratory center. Barbiturates are frequently used for induction of anesthesia. 

Hypnotic Short-term treatment of insomnia, because barbiturates appear to lose their effectiveness in sleep induction and maintenance after 2 weeks. If insomnia persists, seek alternative therapy (including nondrug) for chronic insomnia. Preanesthetic Used as preanesthetic sedatives. 

Effects on vitamin D Barbiturates may increase vitamin D requirements, possibly by increasing the metabolism of vitamin D via enzyme induction. 

Various barbiturates such as the short acting agent pentobarbital and the ultra-short acting agents thiopental and methohexital are used for anesthesia induction. They produce loss of consciousness without analgesia and with little effects on the cardiovascular system. Unconsciousness is combined with respiratory depression as the barbiturates produce non-selective CNS depression. 

Obstetrics. While an adequate dose of thiopentone is required to ensure adequate anaesthesia, the barbiturate rapidly crosses the placenta. Cardiorespiratory depression in the fetus may occur if the induction-delivery interval is short. 

Taken with alcohol they potentiate the sedative effects and impairment of psychomotor performance. Hepatic enzyme induction by barbiturates or nicotine may reduce plasma levels. Cimetidine may increase levels by enzyme inhi bition. Some antipsychotic drugs may compete for similar metabolic pathways. 

Recovery is sufficiently rapid with most intravenous drugs to permit their use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with sevoflurane and desflurane. Although most intravenous anesthetics lack antinociceptive (analgesic) properties, their potency is adequate for short superficial surgical procedures when combined with nitrous oxide or local anesthetics, or both. Adjunctive use of potent opioids (eg, fentanyl, sufentanil or remifentanil see Chapter 31) contributes to improved cardiovascular stability, enhanced sedation, and perioperative analgesia. However, opioid compounds also enhance the ventilatory depressant effects of the intravenous agents and increase postoperative emesis. Benzodiazepines (eg, midazolam, diazepam) have a slower onset and slower recovery than the barbiturates or propofol and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines (eg, midazolam) can be used to provide anxiolysis, sedation, and amnesia when used as part of an inhalational, intravenous, or balanced anesthetic technique. 

The general pharmacology of the barbiturates is discussed in Chapter 22. Thiopental is a barbiturate commonly used for induction of anesthesia. Thiamylal is structurally almost identical to thiopental and has the same pharmacokinetic and pharmacodynamic profile. 

Barbiturates reduce hepatic blood flow and glomerular filtration rate, but these drugs produce no adverse effects on hepatic or renal function. Barbiturates can exacerbate acute intermittent porphyria by inducing the production of hepatic ct -aminolevulinic acid (ALA) synthase (see Chapter 22). On rare occasions, thiopental has precipitated porphyric crisis when used as an induction agent in susceptible patients. 

Barbiturates and rifampin cause a marked decrease of the anticoagulant effect by induction of the hepatic enzymes that transform racemic warfarin. Cholestyramine binds warfarin in the intestine and reduces its absorption and bioavailability. 

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