Half-life table

All the SSRIs have similar spectrums of efficacy and similar side-effect profiles. However, they are structurally and in some instances clinically distinct. For example, allergy to one SSRI does not predict allergy to another. Similarly, response or nonresponse to one SSRI does not necessarily predict a similar reaction to another medication in the class. SSRIs also have distinct pharmacokinetic properties, the most important of which are differences in half-life (Table 2-1) and the propensity to inhibit cytochrome P450 (CYP) enzymes (Table 1-1). 

This tricyclic drug is superior to placebo and equivalent to standard HCAs in outpatient populations. It is a more potent agent on a per milligram basis (i.e., average daily dose is 20 to 60 mg), partly because of its low first-pass effect and long half-life ( Table 7-5). Flence, patients develop substantially higher plasma levels per milligram dose of protriptyline versus other TCAs. 

Etodolac is a racemic acetic acid derivative with an intermediate half-life (Table 36-1). Etodolac does not undergo chiral inversion in the body. The dosage of etodolac is 200-400 mg three to four times daily. 

Piroxicam, an oxicam (Figure 36-1), is a nonselective COX inhibitor that at high concentrations also inhibits polymorphonuclear leukocyte migration, decreases oxygen radical production, and inhibits lymphocyte function. Its long half-life (Table 36-1) permits once-daily dosing. 

Similar to the case with fish, we are not aware of field studies with fluorene in plants. Figure 2 shows the very rapid depuration of label from duckweed in culture, resulting in the high K2 (Table III) and the short half-life (Table V). In view of the volatility of fluorene, and its short half-life it would not be expected to persist long in plants after a spray with a solvent containing fluorene. McLeese et al. (27) examined the uptake and depuration of "585 oil by mussels and found a similar result. The steady state bioconcentration factor was 160 but the half-life was only 0.3 days. 

Br lodination of proteins may be replaced by bromation. The Br-label is considered to be more ble than those of the radionuclides of iodine It splits off by positron decay and has a short half-life (Table 1). Protdns are labeled enzymatically either by bromperoxidase from the microorganisms Pecillus capitatus and Bonnermisoma hamifera or by myeloperoxidase... 

Su has an extremely long half-life (Table 21.2). Its decay would be represented by a horizontal straight line as for 3 Cs in Fig. 21.3. 

As one would expect for an element with such a long half-life (Table 13.2), relatively large amounts of uranium-238 can be found in certain rocks and mineral deposits. Uranium-238 decays first to thorium-234, which then itself decays. These first two steps are part of the uranium series, which ends with a stable, nonradioactive isotope of lead, lead-206 (Figure 13.5, page 296). You would not expect to find much of the short-lived isotopes in a sample of rock, and indeed you have to look carefully for them, but they are there. The... 

Radioactivity decays exponentially with time. The time required for a material to lose half of its radioactivity is the half-life. Tables of physical properties of radioactive materials list their half-life values. A material that has some radiation level at one point in time will have one half that radiation level after one half-life. Some materials decay quickly and have half-life values of days or less. Carbon-14 decays slowly and has ahalf-life of 5730 years. Uranium-238 is both radioactive and very toxic. It has a half-hfe of 4.5 bUhon years. 

Table 9.3 Thermo gravimetric analysed PTFE half-life table ...

The rate of decay for radioactive elements is specified by their half-life (Table 8-2). The half-life of a radioactive element Is the time required for half the nuclei in a sample to decay. For example, Th-234, a beta emitter discussed earlier, has a half-life of 24.1 days, meaning that half of all nuclei in a particular sample decay to Pa-234 In 24.1 days. If we start with 1000 Th-234 atoms, there are 500 Th-234 atoms left after 24.1 days the other 500 atoms have decayed to the daughter element Pa-234. After 24.1 more days (48.2 days total), 250 Th-234 atoms are left (Figure 8-3). U-238, In contrast, has a much longer half-life of 4.5 billion years. All the U-238 on the planet Is undergoing radioactive decay however, the slow rate means it will be around for many years. 

Analysis of the data in Table 14.6 showed that the drags could be divided into three groups according to values of one of the most important pharmacokinetic parameters, (elimination half-life) (Table 14.7). 

---