Interaction medicamenteuse 1

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DRUG –DRUG INTERACTIONS
Dr.Abdul latif Mahesar
King Saud University
May 2010

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DRUG –DRUG INTERACTION
•When one drug is administered, a response occurs, if a
second drug is given and response to other drug is
altered , a drug interactions is said to have occurred
•This effect may be
•Desired or beneficial (efficacy ↑es with out ↑in
toxicity)
e.g. Multi drug treatment of T.B
Amoxicillin + clavulanic acid
L-Dopa + Carbidopa
Naloxone to treat Morphine overdose

•Undesired or harmful (toxicity is ↑ed with ↓in
efficacy)
•Aspirin and Warfarin
•Propranolol + Salbutamol
•Paracetamol + Alcohol
•Gentamycin + loop diruetics
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•Clinically important drug interactions
•1. Drugs that have steep dose response curve and small
therapeutic index, small change in concentration at site will
lead to substantial increase in effect.
e.g. Digoxin , Lithium
2. Drugs that are known enzyme inducers/inhibitors

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3. Drugs that exibit saturable metabolism
e.g. Phenytoin , Theophylline
4. Drugs used for prolong period and precise plasma
concentration are required
e.g. oral contraceptive , antiepileptic drugs , lithium
5. Different drugs used to treat same disease
e.g. Theophylline, Salbutamol
6. In patients with impaired kidney and liver functions
7. In elderly who receive several drugs at the same time