Calcium, absorption plasma concentration

Some idea of the rate of absorption can be obtained from examination of the plasma concentration-time profile. It should be remembered, however, that the time to maximum plasma concentration Y ) is not when absorption is complete but when the rates of drug absorption and elimination are equal. Thus two drugs with the same absorption rate will differ in /max if elimination rates differ. Assessment of the rate of absorption can also be confounded by complex or slow drug distribution. For example, the calcium-channel blocker amlodipine has a much later /max than other similar drugs. This is not due to slow absorption but to partitioning in the liver membrane with slow redistribution. A quantitative assessment of the rate of absorption can be obtained by deconvolution of plasma profiles following IV and oral administration. 

There are occasional anomalies to the rule that food reduces and delays peak plasma concentration. The anti-fungal drug, griseofulvin, has enhanced absorption if taken with a meal - possibly because it becomes emulsified by bile salts and passes more readily into the lymphatic drainage of the gut which bypasses the liver, entering the venous system directly. The immuno-suppressant cyclosporin, and calcium salts in general, show a similar increase in absorption when taken with a fatty meal. 

PTH is secreted from the parathyroid glands in response to a low plasma concentration of ionized (free) calcium. PTH immediately causes the transfer of labile calcium stores from bone into the bloodstream. PTH increases rates of dietary calcium absorption by the intestine indirectly via the vitamin D3 system activation of enterocyte activity. Within the kidney, PTH directly stimulates calcium reabsorption and a phosphate diuresis. 

CALCIUM CHANNEL BLOCKERS TCAs t plasma concentrations of TCAs when co administered with diltiazem and verapamil. Reports of cardiotoxicity (first- and second-degree block) when imipramine is given with diltiazem or verapamil Uncertain, but may be due to a combination of i clearance of TCAs (both diltiazem and verapamil are known to inhibit CYP1A2, which has a role in the metabolism of amitriptyline, clomipramine and imipramine) and t intestinal absorption (diltiazem and verapamil inhibit intestinal P-gp, which may t amitriptyline bioavailability) Monitor ECG when commencing or altering treatment... 

ESTRAMUSTINE CALCIUM AND DAIRY PRODUCTS i plasma concentrations of estramustine and risk of poor therapeutic response Due to l absorption of estramustine owing to the formation of a calcium-phosphate complex Administer estramustine 1 hour before or 2 hours after dairy products or calcium supplements... 

PREDNISONE, CORTISONE ZINC, CALCIUM, CHROMIUM, MAGNESIUM, SELENIUM 1 plasma/body concentrations of these minerals Attributed to t loss and/or 1 absorption Be aware and monitor plasma concentrations of these minerals provide supplements... 

The principal physiological role of vitamin D is in the maintenance of the plasma concentration of calcium. Calcitriol acts to increase intestinal absorption of calcium, to reduce its excretion by increasing reabsorption in the distal renal tubule, and to mobilize the mineral from bone - of the 25 mol of calcium in the adult body, 99% is in bone. The daily intake of calcium is around 25 mmol, and intestinal secretions add an additional 7 mmol to the intestinal contents 10 to 14 mmol of this is normally absorbed, with 18 to 22 mmol excreted in feces. Bone turnover accounts for exchange of 10 mmol of calcium between bone and plasma daily. The kidneys filter some 240 mmol of calcium daily, almost all of which is reabsorbed urinary excretion of calcium is about 3 to 7 mmol per day. 

The presence of food in the stomach, especially if it is fatty, delays gastric emptying and the absorption of certain dmgs the plasma concentration of ampicillin and rifampicin may be much reduced if they are taken on a full stomach. More specifically, calcium, e.g. in milk, interferes with absorption of tetracyclines and iron (by chelation). 

In patients with renal failure, the occurrence of conditioned zinc deficiency may be the result of a mixture of factors, which at present are ill defined. If 1,25-dihydroxycholecalciferol plays a role in the intestinal absorption of zinc, an impairment in its formation by the diseased kidney would be expected to result in malabsorption of zinc. It seems likely that plasma and soft tissue concentrations of zinc may be "protected in some individuals with renal failure by the dissolution of bone which occurs as a result of increased parathyroid activity in response to low serum calcium. In experimental animals, calcium deficiency has been shown to cause release of zinc from bone. In some patients who are successfully treated for hyperphosphatemia and hypocalcemia, the plama zinc concentration may be expected to decline because of the deposition of zinc along with calcium in bone. Thus, in the latter group in particular, a diet low in protein and high in refined cereal products and fat would be expected to contribute to a conditioned deficiency of zinc. Such a diet would be low in zinc. The patients reported by Mansouri et al. (37), who were treated with a diet containing 20-30 g of protein daily and who had low plasma concentrations of zinc, appear to represent such a clinical instance. Presumably the patients of Halsted and Smith (38) were similarly restricted in dietary protein. In other patients with renal failure whose dietary protein was not restricted, plasma zinc concentration were not decreased. Patients on dialysis had even higher levels, particularly... 

Oxalate is an end product of metabolism, predominantly derived from breakdown of glyoxylate and glycine. Plasma concentration of oxalate is 1,0 to 2.4mg/L (11 to 27fxmol/L) and it is excreted in the urine at a rate of 17.5 to 35.1 mg/24 hours (200 to 400pmol/24 hours). Only 10% to 15% of urinary oxalate is derived directly from dietary sources. Intestinal oxalate absorption is increased when the availability of calcium in the intestine is reduced. Hyperoxaluria is... 

Effects on Kidney In the kidney, PTH enhances the efficiency of Ca reabsorption, inhibits tubular reabsorption of phosphate, and stimulates conversion of 25-OHD to calcitriol (Figure 61-3, see below). As a result, filtered Ca + is avidly retained and its plasma concentration increases, whereas phosphate is excreted and its plasma concentration falls. Newly synthesized calcitriol interacts with specific high-affinity vitamin D receptors (VDRs) in the intestine to increase the efficiency of calcium absorption, thereby also increasing the plasma Ca concentration. 

Although the lipid solubility of sotalol is relatively low compared with other jS-blocking adrenoceptor drugs (28), oral bioavailability is deemed to be 1(X)%. Sotalol is absorbed somewhat slower than most other j8-blockers, with peak concentrations occuring within 2-3 hours (29). Although food may impair the absorption of sotalol (28), administration of either calcium carbonate or aluminum hydroxide antacids has little effect on absorption (30). After administration of a single 160 mg oral dose of sotalol, both enantiomers reached maximal plasma concentrations in approximately 3 hours (31) and, hence, did not exhibit stereoselective absorption. 

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