Isomerism of the anaesthetic drugs
Norhan AbdelAlim Ali;
Abstract
Isomers are two or more different substances with the same molecular formula (i.e. the same number of different types of atoms).
There are two main types of isomerism: I). Structural isomerism, and
' 2). Stereoisomerism.
Structural isomers (e.g. enflurane and isoflurane) have different molecular structures, and usually behave like different drugs.
Occasionally, structural isomers are interconvertible (they are tautomers or dynamic isomers); this occurs with the barbiturates and midazolam.
Stereoisomers have identical structures, but a different configuration or spatial arrangement.
Stereoisomerism in drugs is often due to chirality or "handedness";
i.e. the presence of right-handed (R)-and left-handed (S)-forms of the drug, which are nonsuperimposable mirror images (enantiomers).
Approximately 60% of the anaesthetic agents are chiral drugs; some of these are administered as single enantiomers. For example, etomidate is used as the (R) (+)-isomer; its (S) (-)-enantiomer has only slight sedative and hypnotic activity. However, many synthetic chiml drugs are equal mixtures of (R)-and (S)-isomers, and there are often important differences in their activity and pharmacokinetics.
Halothane, enflurane, and isoflurane are chiral drugs with different anaesthetic potencies.
Similar differences occur with intravenous anaesthetics; thus, the
(S)(+)-kctamine causes fewer psychotic emergence reactions, less agitated behaviour, and better intraoperative amnesia and analgesia than its enantiomer.
At present, atracurium consists of I 0 stereoisomers, which have different activities and pharmacokinetic properties; however, studies of the related compound norcoraydine suggest that the single isomer with the (R)-cis (R )-cis configuration may produce the best neuromuscular blockade.
There are two main types of isomerism: I). Structural isomerism, and
' 2). Stereoisomerism.
Structural isomers (e.g. enflurane and isoflurane) have different molecular structures, and usually behave like different drugs.
Occasionally, structural isomers are interconvertible (they are tautomers or dynamic isomers); this occurs with the barbiturates and midazolam.
Stereoisomers have identical structures, but a different configuration or spatial arrangement.
Stereoisomerism in drugs is often due to chirality or "handedness";
i.e. the presence of right-handed (R)-and left-handed (S)-forms of the drug, which are nonsuperimposable mirror images (enantiomers).
Approximately 60% of the anaesthetic agents are chiral drugs; some of these are administered as single enantiomers. For example, etomidate is used as the (R) (+)-isomer; its (S) (-)-enantiomer has only slight sedative and hypnotic activity. However, many synthetic chiml drugs are equal mixtures of (R)-and (S)-isomers, and there are often important differences in their activity and pharmacokinetics.
Halothane, enflurane, and isoflurane are chiral drugs with different anaesthetic potencies.
Similar differences occur with intravenous anaesthetics; thus, the
(S)(+)-kctamine causes fewer psychotic emergence reactions, less agitated behaviour, and better intraoperative amnesia and analgesia than its enantiomer.
At present, atracurium consists of I 0 stereoisomers, which have different activities and pharmacokinetic properties; however, studies of the related compound norcoraydine suggest that the single isomer with the (R)-cis (R )-cis configuration may produce the best neuromuscular blockade.
Other data
| Title | Isomerism of the anaesthetic drugs | Other Titles | المتشابهات الكيميائية في أدوية التخدير | Authors | Norhan AbdelAlim Ali | Issue Date | 2001 |
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