Basics and Drug Absorption Flashcards
Chirality affects duration of drug action
Enzymes are stereoselective, will prefer one enantiomer over the other, the form without the best fit will have a longer duration of action
Two effects of drug binding to a receptor
Agonist- drug binds to receptor and stimulates cellular activity
Antagonist- drug binds to receptor and inhibits action of agonists
Actions of drugs not working through receptors
Include chemical antagonists, physiologic antagonists, osmotic agents, and DNA drugs
Pharmacodynamics
Actions of a drug on the body
Pharmacokinetics
Actions of the body on the drug
Selectivity of enzymes/receptors for racemic states
Drugs are chiral, enzymes are usually stereoselective, drugs are racemic mixtures, one form may be inactive or potentially harmful
Warfarin
Given as a racemic mixture, S enantiomer is more potent than R
Fast vs. slow acetylators
Affects rate at which isoniazid is metabolized, slow acetylators have 4-6x blood concentrations of given dose than fast acetylators, drug stays active and unmetabolized longer, duration of action is longer
Advantages of prolonged-release drugs
Less frequent administration, therapeutic effect overnight, fever/less severe side effects, easier patient compliance
Mechanism of action
How a drug works, includes site where it acts and mechanism by which it produces effects
Side effect vs. contraindication
Side effects- undesired effects of the drugs
Contraindications- conditions that prevent the safe use of a drug, co-administering with other drugs may produce undesirable effects
Enteral drug administration
Drug given into the GI tract, limited by absorption from GI tract, inactivation by digestive enzymes, clinical conditions (vomiting, unconsciousness), blood flow, surface area
Parenteral drug administration
Administration by means other than GI tract, usually injection
Target concentration
Target drug concentration in the plasma, desired concentration the physician wants to produce therapeutic effects
Steady state concentration
Drug in equals drug out
Oral drug administration (PO)
Most common enteral and usually convenient, absorption from GI tract, limited by first pass effect, lack of absorption, inactivation by digestive enzymes, vomiting, unconsciousness, blood flow, surface area
Sublingual drug administration (SL)
Enteral, oral mucosa provides good absorption into systemic circulation
Buccal drug administration
Enteral, between tongue and cheek, absorbs into systemic circulation
Rectal drug administration (PR)
Enteral, suppositories, fairly good absorption, good for vomiting or unconscious patient, 50% of drug absorbed with bypass the liver, disadvantages include irregular absorption and rectal irritation
Intravenous (IV)
Parenteral, directly into vein, no absorption, rapid high levels, dose titration (anesthesia)
Intraarterial (IA)
Parenteral, uncommon, some diagnostic and anticancer agents, requires skilled personnel
Intramuscular (IM)
Parenteral, injection into skeletal muscle provides good absorption, rate is dependent on drug form and solubility
Epidural (EPI)
Parenteral, injection into epidural space, used in procedures requiring spinal analgesia
Intraperitoneal (IP)
Parenteral, into IP cavity, not often used due to risk of infection and adhesions, very painful
Topical
Parenteral, percutaneous absorption, localized action absorbed through intact skin
Inhalation
Parenteral, drug can be delivered to target organ in respiratory diseases, lungs have large surface area, good absorption, rapid onset, short duration
Bioavailability
Fraction or % of administered drug that reaches the systemic circulation via a given route, F=1 for IV administration
Amount of drug reaching circulation
Equal to bioavailability (F) x dose given
Dose of new form of drug
Equal to (dose x F of the current form) / F of new form
Minimal effective concentration (MEC)
Threshold plasma concentration, enough drug is present to enter tissues, interact with receptors, produce an effect, measure of drug activity
