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Local Anaesthetics (view source)

Revision as of 20:30, 26 February 2009

22 bytes added , 20:30, 26 February 2009

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** Metabolism is by hepatic amidases, and excretion occurs via the kidney.

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Local anaesthetics are weak bases and so at body pH of 7.4, more molecules are ionised than unionised. This makes it more difficult for drugs to cross the plasma membrane. Infected tissue has a lower pH than healthy tissue, causing the ratio of ionised:unionised molecules to increase. Because of this, there is poorly cellular uptake of local anaethetics in infected tisse, as they cannot cross the cell membrane. For more about the effect of pH on drugs, see the [[Pharmacokinetics#Physiological Variables|pharmacokinetics]] page.

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===Protein Binding===

The degree of plasma protein binding of individual drugs affects their distribution within the body and the duration of their action. Drugs which have a higher degree of binding have effects for a longer period of time, and in hypoproteinaemic animals, local anaesthetics have a shorter duration of action. For example, [[#Bupivicaine|bupivicaine]] is 95% protein bound, compared to 65% for [[#Lidocaine|lidocaine]], and so its effects will persist longer.

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===Ionisation===

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Local anaesthetics are weak bases and so more molecules are ionised than unionised. This makes it more difficult for drugs to cross the plasma membrane. Infected tissue has a lower pH than healthy tissue, causing the ratio of ionised:unionised molecules to increase. Because of this, there is poorly cellular uptake of local anaethetics in infected tisse, as they cannot cross the cell membrane. For more about the effect of pH on drugs, see the [[Pharmacokinetics#Physiological Variables|pharmacokinetics]] page.

==Side Effects and Contraindications==

==Drugs in this Group==

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