Apparent absorption rate

The drawbacks of SC and IM injections include potentially decreased bioavailability that is secondary to variables such as local blood flow, injection trauma, protein degradation at the site of injection, and limitations of uptake into the systemic circulation related to effective capillary pore size and diffusion. The bioavailability of numerous peptides and proteins is, for example, markedly reduced after SC or IM administration compared to their IV administration. The pharmacokine-tically derived apparent absorption rate constant is thus the combination of absorption into the systemic circulation and presystemic degradation at the absorption site. The true absorption rate constant ka can then be calculated as ... 

The excretion of macro elements occurs via the feces, urine, and stveat, though the first two routes represent the main pathways. Typically, fecal excretion accounts for only 2-7% of the sodium intake. The apparent absorption rate of sodium has been found to vary between 93 and 98%. On average, the apparent absorption rate of macro elements by ovolactovegetarians is lower... 

Tab. 4.5 Fecal excretion and apparent absorption rates of ash and macro elements by ad ults ...

Element (w) n(m) Excretion by feces % Apparent absorption rate, % ... 

Fecal excretion of the macro elements was, on average, 3% for sodium, 19% for potassium, 28% for ash, 36% for phosphorus, 69% for magnesium, and 84% for calcium. The apparent absorption rate is negatively correlated with fecal excretion of the macro elements. The real absorption rate of all these elements is higher than the apparent absorption rate, mainly due to the salivary, biliary and pancreatic excretion of absorbed macro elements into the intestine. 

Tab. 4.12 Fecal excretion and apparent absorption rate of trace elements by adults ...

The majority of ultratrace elements are metals, and their fecal excretion rate is greater than 50% (Table 4.19). Fecal excretion of lead by people with a mixed diet is astonishingly low (50%), while the apparent absorption rate is very high (40% on average). The daily lead intake of test popula-... 

The phytin-rich nutrition of ovolactovegetar-ians lowers the availability of strontium and increases fecal excretion of this alkali metal. The apparent absorption rate of strontium in vegetarians, like that of calcium, is significantly lower than in people with a mixed diet. 

The apparent absorption rate of the macro elements in humans with a mixed diet varied between 98% for sodium, 83% for potassium, 61% for phosphorus, 35% for magnesium, and 13% for calcium. Ovolacto-vegetarians have a significantly decreased apparent absorption rate for magnesium and calcium, and apparent absorption rates for trace elements varied between 81% for iodine, 62% for selenium, 42% for nickel, 37% for molybdenum, 2.5% for zinc, and 2.0% for manganese. 

Fecal excretion of sodium is limited to 1 -2%, which is extremely low in comparison to other elements. The apparent absorption rate of sodium is 98%, and this compares... 

Tab. 1.2-8 Sodium intake, excretion, apparent absorption rate and balance of sodium in people with mixed and ovo-lacto-vegetarian diets...

Metabolism, Excretion, Apparent Absorption Rate, and Balance... 

Thus, the different absorption rates, the effects of other dietary components on the forms of vanadium in the stomach, and the rate of transformation into V appear markedly to affect the proportion of ingested vanadium that is absorbed (Patterson et al. 1986, Chasteen et al. 1986, Wiegman et al. 1982, Hansard etal. 1982b). Studies with humans and an intake of 11 to 39 pg V per day showed renal and lactational excretions of vanadium of approximately 5% and 16%, respectively. The apparent absorption rate varied between 10 and 25% (Table 27.5) (Anke et al. 1998d). Besides the form of vanadium, it is also the quantity of vanadium present that influences the absorption rate of this ultratrace element. 

Kreilgaard, 2001). The anesthetic effect of the two formulations indicated similar cutaneous absorption profiles of lidocaine from both formulations. Howcvct, a threefold increase in apparent absorption rate and a significant decrease in lag time of lidocaine applied in microemulsion vehicle compared to 5% xylocaine were demonstrated with cutaneous microdialysis. This study illustrated that, compared to the pharmacodynamic model, the microdialysis technique has higher sensitivity and less variability to access bioeqmvalence of topically applied chemicals. 

---