pharmacokinetics Flashcards
Define bioavailability
The proportion of the drug that reaches the systemic circulation unchanged
What is the bioavailability of IV medications?
100%
If a drug is lipid soluble, how does it affect it’s ability to be absorbed and it’s duration of action
Lipid soluble drugs are easily absorbed and have a prolonged duration of action because they are stored in fatty tissues
What occurs in phase 1 hepatic metabolism of drugs?
Chemical change (reduction, oxidation, hydrolysis) usually by cytochrome p450 enzyme complex, leading to activation, inactivation or toxic state of the drug
What occurs in phase 2 hepatic metabolism?
Drug metabolites are made water soluble so that they can be excreted in urine
What happens to enalapril in phase 1 metabolism by the liver?
It is metabolised from a pro-drug to it’s active form
What happens to diazepam in phase 1 metabolism by the liver?
Release of it’s active metabolites
What is the maximum drug size for renal excretion?
500 Daltons
What is the effect of an enzyme inducer on the oral contraceptive pill activity?
Increased metabolism and therefore reduced bioavailability and therefore decreased effectiveness
Which drugs are enzyme inducers?
Phenobarbitone ETOH Phenytoin Rifampicin Griseofulvin Carbamazepine
Which drugs are enzyme inhibitors?
Antibiotics: metronidazole, ciprofloxacin, erythromycin Antifungals: fluconazole, ketoconazole Cimetidine ETOH (acute) AMiodarone
How is the cytochrome p450 enzyme complex affected by phenytoin?
Enzyme inducer
How is the cytochrome p450 enzyme complex affected by metronidazole?
Enzyme inhibitor
How is the cytochrome p450 enzyme complex affected by ETOH?
Inducer if chronic
Inhibitor if acute
How is the cytochrome p450 enzyme complex affected by griseofulvin?
Enzyme inducer
