Dosing term

The validity of the approach based on (6.2) was proven when the fraction of dose absorbed, Fa, was found to increase with AP for several drugs with a wide variety of physicochemical properties and various degrees of extent of absorption [156]. Additional support for the AP concept was provided by a 3-dimensional plot of Fa as a function of the ionization-solubility/dose term (fun/9) and the octanol/water partition coefficient Pc [157]. In fact, because of the recent interest in the apparent permeability estimates Papp measured in the in vitro Caco-2 monolayer system, it was suggested that Papp can replace the octanol/water partition coefficient Pc in (6.2) [157]. 

The unit risk is defined as the upper bound additional lifetime cancer risk associated with exposure to either 1 pg 1 in water or 1 pg m in air. The dose or exposure concentration associated with a given risk can also be calculated by rearranging terms in the slope factor equation shown above to solve for the dose term. The result is termed the risk specific dose (or concentration). The risk specific dose is often used as the basis for the exposure criteria for carcinogens. 

The first six main definitions are related to dose terms ... 

The dosing term, defined in Eq. (5), is the amount of heat absorbed or released due to addition of reactant at a different temperature from that of the reaction mass ... 

The accumulation term can be neglected as soon as the system is working in a pure isothermal mode. The dosing term can be neglected because of the small quantity of added reactant Another possibility is to set the dosing temperature the same as the reaction temperature. A more simplified equation is obtained when ( cc + Qdos are relatively small compared to Qaow... 

In addition to providing advanced measures of both the lead dose and the toxic response portions of dose—neural response relationships, these prospective approaches helped to resolve interpretive questions not answered in earlier cross-sectional studies. For example, the inherent stability of the exposure measure is more discernible and quantifiable with serial measures of PbB or combined measures of blood and bone than isolated PbB measures done concurrently. One can also employ different statistical expressions of the exposure metric, e.g., average PbB, peak PbB, concurrent PbB, or lifetime integrated expression of exposure to estimate relative robustness of dose—response. Second, the potential confounding of dose—response relationships by any reverse causality is more reliably addressed. Reverse causality would hold that the dose term is elevated because of the higher likelihood of Pb exposures due to existing impairment of neurobehavioral function in other words, PbB levels rise with a higher frequency of abnormal hand-mouth activity because of neurobehaviors unrelated to Pb exposures. 

Approximately 500,000 Americans suffer strokes each year. Many of the 80% that survive suffer paralysis and impaired vision and speech, often needing rehabiUtation and/or long-term care. Hence, whereas treatment using rt-PA is likely to be expensive (costs are 2200/dose for treating heat attacks), the benefits of rt-PA could outweigh costs. In the case of heart attacks, the 10 times less expensive microbiaHy derived streptokinase can be used. There is currentiy no competing pharmaceutical for treatment of strokes (18,19). Consequentiy, the cost of manufacture of rt-PA may not be as dominant an issue as would be the case of other types of bioproducts. 

The lethal dose for 50% of the test animals, expressed ia terms of g of material per kg of body weight. 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

The effect of mechanical treatment on floe behavior is illustrated in Figure 5. In one work (40), identical slurries were treated with varying doses of the same polymer. At each dosage, it can be assumed that the same type of floe formed at the same rate. However, the dosage response was completely different depending on which parameter of the flocculated slurry was measured. Thus the term optimal flocculation caimot be appHed to any flocculant—substrate combination if the soHd—Hquid separation process or process parameter is not specified. 

Lead is toxic to the kidney, cardiovascular system, developiag red blood cells, and the nervous system. The toxicity of lead to the kidney is manifested by chronic nephropathy and appears to result from long-term, relatively high dose exposure to lead. It appears that the toxicity of lead to the kidney results from effects on the cells lining the proximal tubules. Lead inhibits the metaboHc activation of vitamin D in these cells, and induces the formation of dense lead—protein complexes, causing a progressive destmction of the proximal tubules (13). Lead has been impHcated in causing hypertension as a result of a direct action on vascular smooth muscle as well as the toxic effects on the kidneys (12,13). 

Several additional terms related to the absorption of x-radiation require definition energy of a x-ray photon is properly represented in joules but more conveniently reported in eV fluence is the sum of the energy in a unit area intensity or flux is the fluence per unit time and the exposure is a measure of the number of ions produced in a mass of gas. The unit of exposure in medicine is the Rn ntgen, R, defined as the quantity of radiation required to produce 2.58 x C/kg of air. The absorbed dose for a tissue is a measure of energy dissipated per unit mass. The measure of absorbed dose most... 

In hospitals and long-term cate units, unit-dose packages ate used mote and mote. This system aHows better control of the dispensed dmgs in institutional settings and precludes the dispensing of larger numbers of doses than needed. 

Single dose or short-term treatment with aerosolized steroids inhibits both the late asthmatic response and allergen-induced bronchial hyperresponsiveness (45,92). However it does not affect the early asthmatic response nor does it induce bronchodilation (45,92). Long-term treatment with steroids protects against both the early and late asthmatic responses and also reduces bronchial hyperresponsiveness (44,71,86,93). Over time, the airways relax (dilate) and measures of airway function, such as forced expiratory volume in one second (FEV ), gradually return to almost normal levels. 

Although performance varies with the isotopes for which they are intended, and with the balance in the design between resolution and efficiency, the overall sensitivity of a y-camera collimator is on the order of 5000 counts/(MBqmin) (several hundred counts/(/iCi-min)). In terms of photons detected per photon emitted, this is equivalent to about 2 x lO ". In other words, about two photons out of 10,000 emitted arrives at the crystal. This necessitates exposure times that range from several minutes to the better part of an hour. Fortunately, the large number of photons available from a modest injected radioactive dose more than offsets the poor detector sensitivity. The camera s abiUty to resolve small objects, however, is ultimately limited by the collimator inefficiency. 

Chemical Toxicity. Radiopharmaceuticals are subject to the same requirements for safety as are other pharmaceuticals, and are tested for chemical toxicity in much the same manner. It is generally understood, however, that patients are likely to receive relatively few doses of any given radiopharmaceutical so that the effects of long-term chronic exposure to the compound rarely need be assessed. Safety margins, that is, the ratio of the adininistered dose to the lowest dose that produces an observable effect, are usually on the order of 100 or more. 

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