What is pharmacokinetics?
the study of how drugs move in the body
What are the 4 components pharmacokinetics?
- Absorption
- distribution
- metabolism
- excretion
What is passive transport?
moving form high to low concentration -> drugs are small, non-ionized and lipid soluble
What is active transport?
moving from against concentration gradient, required energy ATP -> drugs are larger ionized and non-lipid soluble
What is fast onset (IV) in absorption?
fast absorption
What is slow onset (IM) in absorption?
slow absorption
What are the three routes of administration in absorption?
- Enteral route = delievered to GI tract throught -> PO. cheek, SL, NG, rectal
- Topical route = delivered to mucous membranes = slower absorption
- Parental route = anything other than enteral/topical -> IV, IM, SC, IP, bone, spinal cord
What does drug ionization in absorption mean?
- ionized = positive/negative charge
- non-ionized = no charge
What are two types of drug interactions in absorption?
- drug-drug interaction = tetracycline capsule + carbonate (CaCO3) > delays absorption
- drug-food interaction = high fat meal + carbamazepine > higher rate of absorption
What does bioavailabilty mean in absorption?
The fraction of an administered dose of an unchanged drug that reaches the site of action (F)
What is drug distribution?
describes how are transported throughout the body
What is drug solubility in distribution?
drug solubility is the ability for a drug to cross the plasma membrane.
- lipid soluble = easier to cross plasma membrane
- water soluble = has more barriers
What are blood brain barriers in distribution?
protect the brain from toxic substances/pathogens, levodopa used in place of dopamine = pro drug.
What is the fecal placental barrier in distribution?
protects the baby from harmful substances/pathogens but not as efficient as the blood brain barrier.
What is metabolism?
the process of changing the activity of a drug and make it more likely to be excreted
What is a prodrug in metabolism?
it is a metabolite that is more active than the original molecule
What is a hepatic enzyme in metabolism?
cytochrome P450 system (CYP450) -> responsible for most metabolism of drugsm nutrients and endogenous susbtances. Changes in enzyme activity after drug actions. the result of the change depends on whether the drug is a substrate, an inducer or an inhibitor of the CYP450 system.
6 parts of the CYP450 system in metabolism?
- Substrate = substance on which an enzyme acts when a drug is metabolized by CYP450 enzyme
- Enzyme inducer = drug speeds up the metabolic activity
- Enzyme inhibitor = drug that has the ability to decrease metabolic activity. End result = less active property and more inactive property
- Drug = metabolized by enzymes = inactive metabolite
- Prodrug = metabolized by enzymes = active metabolite
- First-past effect = important mechanism of metabolism
What is patient variation in metabolism?
- Patients with liver disease have lower hepatic enzyme
- smoking and chronic alcohol consumption can induce hepatic enzyme = may require higher doses
- Genetic variations cause “slow metabolizers” and “fast metabolizers”
- Pharmacogenomics = customize therapy to DNA
What is excretion?
The process of removing drugs from the body through; renal, pulmonary or glandular excretion.
What are time-response relationships in excretion?
the therapeutic response most drugs depend on their concentration in the plasma
What is plasma half-life (t 1/2) in excretion?
- the length of time required for a drugs concentration to decrease by 1/2 (1-2 minutes to months). Drugs with longer half-lives are better for chronic conditions
- it takes approximately 4/-5 t1/2 before the drug is considered eliminated (94% gone)
What is maintaining therapeutic range in excretion?
- most conditions required repeated dosing in order to keep drug plasma within the therapeutic range
- we reach plateau in approximately 4 t1/2 of the drug if we give equal dose
What are loading and maintenance doses in excretion?
- loading dose = allows us to reach plateau levels faster with larger dose
- maintenance dose = allows us to maintain a certain level of dose
