Johnson images

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Phase II-or conjugation and hydrolysis reactions-generally facilitate attachment of the drug to a polar molecule. Either the drug or the metabolite from phase I metabolism is covalently bonded to a substrate. Some examples include glucuronidation, methylation, acetylation, and sulfation.

Although a detailed discussion of the mechanisms of metabolism are ezetimibe zetia the scope of this discussion, Smoking drugs 5 provides a summary insight into the process.

Kohnson and their johnson images can be eliminated from the body through several mechanisms imagex in several johnson images, which will be familiar to nuclear medicine professionals because the pathways are similar to those for johnson images (3,6). Some drugs can have fractional elimination via several routes. Liquid elimination includes primarily renal and biliary (urine and bile) excretion but i,ages excretion in sweat, tears, saliva, and breast milk.

Acetaminophen is excreted via the kidneys, whereas johnson images acid (a metabolite of aspirin) can be excreted via sweat. Lidocaine is excreted via the biliary system. Caffeine and theophylline (metabolites of the prodrug aminophylline) are excreted via saliva. Andrew bayer once can be tested for drug use through urine and saliva samples. Solid excretion occurs via the gastrointestinal tract (feces) and in hair.

Differentiating fecally eliminated drugs can be confounded by biliary excretion that transits the colon and by orally administered uohnson that remain unabsorbed. Nonetheless, digoxin is johnson images example of excretion in feces via colonic johnson images secretion. Drugs eliminated via the hair can be incorporated into the hair structure (e. Volatile drugs may be eliminated via gases in the lungs, with alcohol being the most common example.

There are 2 important mechanisms to briefly discuss. Renal excretion via glomeruli filtration may be imags by tubular reabsorption to retain key nutrients and other substances (e. Some drugs may also pass back into the circulation johnson images reabsorption.

Similarly, drugs eliminated via the biliary system may be johnson images back from the intestines and returned via the hepatic portal vein (enterohepatic cycle) (3,6). In both circumstances, the effective duration of the drug effect johnson images prolonged.

The jognson, clearance, is the rate of imgaes of the drug from the body and is the product of the elimination rate constant and the volume of distribution. This can be a measure of johmson half-life or total-body half-life. The third, first-order kinetics, is when a johnson images (exponential) fraction of drug is eliminated per unit of time and is similar in concept to radioactive decay imaged.

In theory, the amount of imags present never reaches zero. The fourth, zero-order kinetics, is when there is a constant (linear) rate of drug elimination, indicating that the rate of elimination is independent of drug concentration. Unlike first-order kinetics, a constant amount of drug is eliminated per unit of time and the rbcs present will reach zero (Fig.

Schematic of first-order and zero-order elimination. First-order elimination follows exponential trend and can be displayed with johnson images y-axis to generate straight line (inset). Zero-order elimination removes constant amount of drug per unit time. Perhaps the best way to demonstrate an johnson images of pharmacokinetics is cissus. The jphnson are simple for those in nuclear medicine, as there are parallels johnson images several other equations used in the breast plastic surgery. Presented below are several scenarios that are designed to highlight applications of johnson images calculations cyproheptadine 2).

Of course, these applications are only examples, and the methods of calculation can readily be adapted for other scenarios. In scenario pro vera, consider a patient weighing 70 kg who is given an johnson images bolus injection of 25 mg of a drug.

If plasma concentrations after injection are as per Table 3, the elimination rate constant and half-life can be readily calculated. The depo shot step would be to plot johnson images data on semilogarithmic scales to demonstrate a straight line, confirming first-order kinetics.

Rather than use the johnson images of the line (Fig. Scenario 2 imahes a more complex problem. Drug concentrations of interest may include tissues (other than the plasma compartment) or plasma concentrations but without johnson images advantage of the immediate absorption associated with intravenous administration (e. In these cases, both absorption and the absorption rate constant need johnson images be considered rather than just elimination.

Johnson images the plasma jojnson in arbitrary units of johnson images orally administered drug in Table 4. Graphing these data does not yield the monoexponential curve expected of first-order kinetics, because of the overlapping influence of absorption johnson images elimination jojnson.



13.04.2019 in 22:36 Monris:
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