in the use of drugs of which the dosing involves a loading dose then a For a dose ratio of 2, dosing interval equals the drug biological half life (T1/2). Half-life is the time interval in which half of the drug in a system is lost . Such a dosing interval provides a ratio, the maximum steady-state. At steady state with a dosing interval equal to the half-life: . The relationship between oral and intravenous dose rates to achieve the same.
- Glossary of Terms and Symbols Used in Pharmacology
The following section will go over different type of reaction, as well as how its half-life reaction are derived. The last section will talk about the application of half-life in the elimination phase of pharmcokinetics. In other words, saturating the amount of substrate does not speed up the rate of the reaction.
Below is a graph of time t vs. We can also easily see that the length of half-life will be constant, independent of concentration. For example, it takes the same amount of time for the concentration to decrease from one point to another point.
In order to solve the half life of first order reactions, we recall that the rate law of a first order reaction was: We can visually see this on the graph for first order reactions when we note that the amount of time between one half life and the next are the same. Another way to see it is that the half life of a first order reaction is independent of its initial concentration.
However, second order reactions decrease at a much faster rate as the graph shows.
We can also note that the length of half-life increase while the concentration of substrate constantly decreases, unlike zero and first order reaction. In order to solve for half life of second order reactions we need to remember that the rate law of a second order reaction is: These drugs follow nonlinear pharmacokinetics.
Pharmacokinetic models are useful to describe data sets, to predict serum concentrations after several doses or different routes of administration, and to calculate pharmacokinetic constants such as clearance, volume of distribution, and half-life. The simplest case uses a single compartment to represent the entire body. Factors to be taken into consideration when deciding on the best drug dose for a patient include age, gender, weight, ethnic background, other concurrent disease states, and other drug therapy.
Half-lives - Chemistry LibreTexts
Cytochrome P is a generic name for the group of enzymes that are responsible for most drug metabolism oxidation reactions.
The importance of transport proteins in drug bioavailability and elimination is now better understood. The principal transport protein involved in the movement of drugs across biologic membranes is P-glycoprotein. P-glycoprotein is present in many organs, including the GI tract, liver, and kidney.
Biological half-life - Wikipedia
When deciding on initial doses for drugs that are renally eliminated, the patient's renal function should be assessed. A common, useful way to do this is to measure the patient's serum creatinine concentration and convert this value into an estimated creatinine clearance CrClest.
Comparability The ability of a system to deliver data that can be compared in standard units of measurement and by standard statistical techniques with the data delivered by other systems. While not a critical component of accuracy, comparability of data generated by a system is critical to evaluating its accuracy and usefulness.
Diagnostic and Statistical Manual of Mental Disorders, 4th ed. DependenceDrug DependenceHabituationTolerance. The equilibrium constant of the reversible reaction of a drug with a receptor to form a drug-receptor complex; the reciprocal of the dissociation constant of a drug-receptor complex. Under the most general conditions, where there is a 1: Obviously, affinity depends on the chemical natures of both the drug and the receptor. A ligand that binds to a receptor and alters the receptor state resulting in a biological response.
A partial agonist is an agonist that produces a maximal response that is less than the maximal response produced by another agonist acting at the same receptors on the same tissue, as a result of lower intrinsic activity.
See also Agonist, Full. A full agonist is an agonist that produces the largest maximal response of any known agonist that acts on the same receptor.
An inverse agonist is a ligand that by binding to a receptor reduces the fraction of receptors in an active conformation, thereby reducing basal activity. This can occur if some of the receptors are in the active form in the absence of a conventional agonist.
Some drugs may act as haptens or allergens in susceptible individuals; re-administration of the hapten to such an individual results in an allergic response that may be sufficiently intense to call itself to the attention of the patient or the physician.
Hence, allergic responses to different haptens are fundamentally alike and qualitatively different from the pharmacologic effects the hapten-drugs manifest in normal subjects, i.