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Main organ of drug elimination.
Kidney is the main organ of drug elimination. If a drug is too hydrophobic, it will simply enter the nephron and not stay within the tubule to be eliminated. To be eliminated, drugs need to be sufficiently hydrophilic. This is achieved through metabolism within the liver.
How many phases of drug metabolism are there? Describe the phases.
Two Phases: Phase I and Phase II. During phase I, the liver makes lipophilic molecules into more polar molecules. This may increase, decrease, or not change the drug's activity. This phase may be enough to eliminate the drug via the kidney. Phase II: Conjugation of the drug by adding a molecule to it that makes the drug much more polar and hydrophilic, allowing for elimination by the kidneys. Most often, these drugs are inactive after conjugation. Usually Phase I comes before Phase II, but sometimes it's in reverse order.
describe the system that metabolizes most drugs in phase I.
Cytochrome P450 system (CYP): this system is involved in metabolizing endogenous compounds and exogenous toxins. There are different families of CYP. CYP is followed by a designation denoting the specific enzyme. Specific families of CYP act on specific substrates and not others. Some drugs may also induce CYP and cause drugs to be metabolized more quickly.
Elimination of drugs
Primarily by the kidney. Other routes include: lung, lactation, intestines, biles
What is the half life of a drug (T1/2)
the time it takes to decrease the concentration of a drug by half.
What is clearance (CL)
the removal of the drug from the blood, can be derived from adding up all the rates of elimination of a drug thru every route of elimination.
A stable steady state can only be achieved thru continuous IV infusion of a drug. when the dosing of a drug and elimination of a drug interact to maintain a relatively stable amount of drug in the body. 90% of steady state concentration will be achieved in 3.3. (4 is 100% steady state) half lives. The wash-out, or clearance of the drug from the body, is at the same rate as drug infusion (for example, drug concentration declines to 50% of steady state level in half life)
Fixed dose, fixed time interval regimens (for oral drugs)
continuous infusion of drugs can only be effectively accomplished in the hospital or under medical supervision. this makes it inconvenient for most uses. Therefore drugs are commonly given in boluses either via oral admin or injection. Via these routes, the drug concentration will fluctuate around a steady state. The more frequently the boluses are given, the less fluctuation around steady state there is.
Difference between injections and oral dosings
Injections deliver the entire drug immediately, while oral dosing takes time for the drug to be absorbed.
what is pharmacodynamics?
It describes how drugs act on the body. It examines drug receptors and what sort of effects drug receptor complexes create.
Describe drug-receptor interactions.
Most drugs act by interacting with receptors, which are protein complexes on the cell surface or within the cell that cause changes to the cell or its functions. This creates a biochemical change in the body. Anything that binds to a receptor is called a ligand.
drug can be released from the receptor and the receptor's biological function returns to its normal physiological state.
For the remaining life of that receptor it will be bound to the drug and will act accordingly.
Compete for a particular receptor. This type of drug is one where the drug competes with endogenous substances for being able to bind the receptor and exert an action. Drugs and endogenous molecules have different affinities for binding the receptor. Another factor is the concentration involved ~if the drug is given at quantities that arrive at the target site much larger than endogenous competing substances, then there is going to be more binding of the drug.
Agonists vs antagonists
agonists are drugs that promote or increase the physiological functions of the receptors. antagonists inhibit or slow down the physiological function of the receptor.
when a drug may have antagonistic effects while actually agonizing a different receptor (ex: epinephrine which appears to antagonize histamine receptors, but actually agonizes B2 adrenoceptors which have the opposite effects from the histamine receptors
does not have the effects of a full agonist in that they may partially but not fully activate a receptor
Ligand gated ion channels
Regulate the flow of chemical ions into and out of the cell. Common ion channels control Sodium, potassium, calcium and chlorine. Ligand gated channels allow the flow of ions in response to binding with a ligand. Ligands can activate or inhibit the flow of ions depending on whether they are agonists or antagonists.
remains completely within the cell, so a drug needs to be lipophilic enough to pass thru the cell membrane in order to bind w/receptor. once bound, the drug-receptor complex moves into the nucleus and promotes dna transcription to mRNA and ultimately increased protein synthesis. steroid hormones are common ligands.
when repeated drug use results in a smaller effect. receptors make sure that your body isn't harmed by "too strong" responses in the long term so if you are constantly using drugs that cause strong responses the receptors inactivate. a)receptor becomes desensitized, resulting in smaller effect of drug. b)down-regulation, or less synthesis of the receptor because the dna is not being transcribed as frequently, c)endocytosis of the membrane receptor
the higher the concentration of a drug at the active site, the higher the pharmacological effect
the measurement of the amount of drug necessary to achieve a certain magnitude of effect, i.e. the concentration of the drug when it has achieved 50% of the maximum effect (EC 50). one of the largest contributing factors to potency is the affinity of the drug for the receptor.
the measurement of how efficient the drug produces its effects and is dependent on the number of drug-receptor complexes formed and how efficient these complexes create cellular responses. "E-max" or the maximal effect of the drug. Not predicated on concentration at all.
therapeutic index (TI), i.e. therapeutic margin or window
measurement of how safe a drug is. ratio between toxic dose and therapeutic dose. the larger the number the safer the drug (TD50/ED50). example of small therapeutic index is warfarin which reduces ability for blood to coagulate.
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