Drug Interactions Flashcards
What is the definition of drug interactions?
The modification of a drug’s effect by prior or concomitant administration of another drug, herb, drink or food.
What is the drug whose activity is affected called? What is the drug that causes such an interaction called?
Object drug
Precipitant
With what drugs in Parkinsonism are drug interactions useful?
Carbidopa is a dopa decarboxylase inhibitor and prevents the systemic side effects of levadopa in the treatment of Parkinsonism.
What are some risk factors that increase the chances of drug to drug interactions?
Advanced age Genetic polymorphisms Concomitant disease Polypharmacy Narrow therapeutic range drugs Dose Multiple prescribing physicians Self prescription Prolonged hospital stays
What chronic illnesses increase the chances of drug interactions?
Liver disease Renal impairment Diabetes mellitus Asthma Epilepsy
What two drugs bind to ions ions in the GI tract?
Tetracycline and erythromycin form complexes with iron, calcium and magnesium.
How do antibiotics lead to failure of oral contraceptive pill?
They destroy the bacterial flora in the large bowel.
Why is a mix of codeine and paracetamol overdose dangerous in relation to stomach emptying?
Codeine delays the stomach emptying so patients can at first present with what seems like non dangerous levels of paracetamol in the blood but once the stomach empties it can rocket up and be dangerous if not treated.
Name two drugs that delay gastric emptying and two that accelerate it
Anticholinergics and opiates
Domperidone and Metoclopramide
Name two drugs that inhibit and two drugs that induce the cytochrome P450 system of metabolism
Clarithromycin and erythromycin
Barbiturates and phenytoin and tobacco smoke
Name two drugs that increase metabolism of cyclosporin by inducing CYP 3A4
Rifampicin and St Johns wort.
What are pharmacodynamic interactions?
Actions of a drug change due to a presence of another drug either acting directly on the same receptor or indirectly on different receptors.
Give an example of direct antagonism
Beta blockers such as atenolol will block the action of agonists such as salbutamol.
What is a synergistic reaction?
One that means two drugs have the same effect on the same receptor.
Give an example of indirect agonism
Warfarin and alcohol
