Drug interactions

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  • 薬物相互作用

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The mechanisms of the various drug interactions can be divided into those of pharmacokinetic and pharmacodynamic interactions. Pharmacokinetic interactions are due to an alteration in the absorption, distribution, metabolism and excretion of one drug by another. On the other hand, the pharmacodynamic interactions are due to the pharmacological interactions caused by the concurrent use of drugs.<BR>(1) drug absorption interactions-Most drugs are thought to be absorbed by passive transport in the lipid-soluble form. Drug absorption is governed by the pKa of the drug and gastrointestinal pH. The absorption of tetracycline and new-quinolone are reduced by the formation of insoluble chelates with di-and trivalent metals such as Ca2+, Mg2+ and Al3+.<BR>(2) Drug displacement interactions-The anticoagulant effect of wafarin are markedly enhanced by the concurrent use of phenylbutazone and can lead to serious bleeding. This is because warfarin and phenylbutazone are highly bound to plasma proteins and compete for the same binding sides, the free warfarin serum levels can be increased by the concurrent use of phenylbutazone.<BR>(3) Drug metabolism interactions-The anticoagulant effects of warfarin are thus markedly reduced by the concurrent use of phenobarbital and rifampicin (enzymeinducing agents). On the other hand, the anticoagulant effects are enhanced by the concurrent use of cimetidine and disulfiram (enzyme inhibitory agents).<BR>(4) Tubular excretion interactions-Drugs which use the same active transport system in the kidney tubules can compete with one another for secretion. The cephalosporin serum levels thus markedly increase by the use of probenecid.<BR>(5) The inhibitory interaction on GABA receptor-Non-steroidal anti-inflammatory drugs in the presence of new-quinolone antimicrobials induce convulsions via pharmacological interactions with γ-aminobuturic acid (GABA) receptor.

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