Osmotic-diuretics

The functional capacity and reabsorption capability of the renal tubule towards various electrolytes and nonelectrolytes are restricted to a limited extent only, and this vary with respect to each ionic species. A large intake of any of these substances by an individual, may enhance its concentration in the body fluids and will ultimately affect the glomerular filtration rate and the reabsorption capacity of the tubule. The substance will finally appear in the urine with an increased volume of water. Such a substance which increases the output of urine in this fashion is called osmotic diuretics. 

It is used quite often as a urinary acidifter, for instance, during therapy with methenamine. Dose 500 mg to 1 g to 6 times daily usual, 600 mg 4 times per day. 

It is an osmotic diuretic with a low renal threshold. It is also administered to maintain the output of urine during surgical procedures. It is also recommended to decrease intra-ocular pressure in acute glaucoma. 

Dose Oral, up to 20 g from 2 to 5 times per day as a 40% solution in water or carbonated beverages, has been given as maintencmce therapy after i. v. application for the reliefofcerebral oedema. D. Mannitol BAN, USAN, 

On commercial scale it is produced by the catalytic or electrolytic reduction of certain monosaccharides, for instance, glucose and mannose. 

Indications prophylaxis of renal hypovolemic failure, mobiUzation of brain edema, and acute glaucoma. 

All rights reserved. Usage subject to terms and conditions of iicense. 

NaCI reabsorption in proximal tubule and effect of mannitol 

These drugs contain the sulfonamide group -SO2NH2. They are suitable for oral administratioa In addition to being filtered at the glomerulus, they are subject to tubular secretioa Their concentration in urine is higher than in blood. 

---

Manufacture of vitamin C starts with the conversion of sorbitol to L-sorbose. Sorbitol and xyHtol have been used for parenteral nutrition following severe injury, bums, or surgery (246). An iron—sorbitol—citric acid complex is an intramuscular bematinic (247). Mannitol administered intravenously (248) and isosorbide administered orally (249) are osmotic diuretics. Mannitol hexanitrate and isosorbide dinitrate are antianginal dmgs (see Cardiovascular agents). 

Osmotic diuretics increase the density of the filtrate in the glomerulus. This prevents selective reabsorption of water, which allows the water to be excreted. Sodium and chloride excretion is also increased. 

The osmotic diuretics urea and mannitol are administered intravenously (IV), whereas glycerin and isosorbide are administered orally Administration by the IV route may result in a rapid fluid and electrolyte imbalance, especially when these drugs are administered before surgery with the patient in a fasting state ... 

The osmotic diuretics are contraindicated in patients with known hypersensitivity to the drags, electrolyte imbalances, severe dehydration, or anuria and those who experience progressive renal damage after instituting therapy (mannitol). Mannitol is contraindicated in patients with active intracranial bleeding (except during craniotomy). 

If the patient is to receive an osmotic diuretic, the focus of the assessment is on the patient s disease or disorder and the symptoms being treated. For example, if the patient has a low urinary output and the osmotic diuretic is given to increase urinary output, the nurse reviews the intake and output ratio and symptoms the patient is experiencing. In addition, the nurse weighs the patient and takes the vital signs as part of the physical assessment before starting drug therapy. 

Mannitol is an agent that may be used in patients with I impending cerebral herniation. Mannitol is an osmotic diuretic that shifts brain osmolarity from the brain to the blood. Doses of 100 g (1-2 g/kg) as an intravenous bolus should be used. Repeated doses typically are not recommended because mannitol may diffuse into damaged brain tissue, leading to rebound increased ICP.21... 

Diuretics are drugs that cause an increase in urine output. It is important to note that, except for the osmotic diuretics, these drugs typically enhance the excretion of solute and water. Therefore, the net effect of most diuretics is to decrease plasma volume, but cause little change in plasma osmolarity. Five classes of diuretics and their major sites of action are ... 

Osmotic diuretics proximal tubule and descending limb of the Loop... 

Osmotic diuretics such as mannitol act on the proximal tubule and, in particular, the descending limb of the Loop of Henle — portions of the tubule permeable to water. These drugs are freely filtered at the glomerulus, but not reabsorbed therefore, the drug remains in the tubular filtrate, increasing the osmolarity of this fluid. This increase in osmolarity keeps the water within the tubule, causing water diuresis. Because they primarily affect water and not sodium, the net effect is a reduction in total body water content more than cation content. Osmotic diuretics are poorly absorbed and must be administered intravenously. These drugs may be used to treat patients in acute renal failure and with dialysis disequilibrium syndrome. The latter disorder is caused by the excessively rapid removal of solutes from the extracellular fluid by hemodialysis. 

The answer is b. (Hardman, pp 695-697.) A significant increase in the amount of any osmotically active solute in voided urine is usually accompanied by an increase in urine volume Osmotic diuretics affect diuresis through this principle. The osmotic diuretics (such as mannitol) are nonelectrolytes that are freely filtered at the glomerulus, undergo limited re absorption by the renal tubules, retain water in the renal tubule, and promote an osmotic diuresis, generally without significant Na excretion. Ln addition, these diuretics resist alteration by metabolic processes. 

Most of the lithium is eliminated in the urine, the first phase of the elimination being 6-8 hours after administration, followed by a slower phase which may last for 2 weeks. Sodium-depleting diuretics such as frusemide, ethacrynic acid and the thiazides increase lithium retention and therefore toxicity, while osmotic diuretics as exemplified by mannitol and urea enhance lithium excretion. The principal side effects of lithium are summarized in Table 8.1. 

Intravenous administration of mannitol (osmotic diuretic) may be considered at a dose of 0.25-2 g/kg over 30-60 minutes. 

The cerebral edema produced by sublethal doses of bromethalin can be ameliorated by treatment with an osmotic diuretic and corticosteroids. Pathology from sublethal doses, even without treatment have been shown to be reversible. 

Mobilization of edemas (A) In edema there is swelling of tissues due to accumulation of fluid, chiefly in the extracellular (interstitial) space. When a diuretic is given, increased renal excretion of Na and H2O causes a reduction in plasma volume with hemoconcentra-tion. As a result, plasma protein concentration rises along with oncotic pressure. As the latter operates to attract water, fluid will shift from interstitium into the capillary bed. The fluid content of tissues thus falls and the edemas recede. The decrease in plasma volume and interstitial volume means a diminution of the extracellular fluid volume (EFV). Depending on the condition, use is made of thiazides, loop diuretics, aldosterone antagonists, and osmotic diuretics. 

For excretion processes, the same reasoning may be used as for absorption. Cases of interaction are only to be expected when active processes are involved. Increased excretion of a chemical following administration of an osmotic diuretic or alteration of the pH of the urine are well known examples of dispositional interaction. 

Osmotic diuretics are the only group of compounds whose action is not associated with a reaction to corresponding receptors, or with direct blocking of any renal transport mechanism. Pharmacological activity of this group depends solely on the osmotic pressure... 

Drugs that may affect lithium include acetazolamide, carbamazepine, fluoxetine, haloperidol, loop diuretics, methyidopa, NSAIDs, osmotic diuretics, theophyllines. 

Forced diuresis is occasionally useful. It may cause volume overload or electrolyte disturbances. Forced diuresis is useful for phenobarbital, bromides, lithium, salicylate, or amphetamines overdoses. Do not use for tricyclic antidepressants, sedative-hypnotics, or highly protein-bound medications. The most common agents employed are furosemide and osmotic diuretics with mannitol. 

Mannitol (OsmitroL others) [Osmotic Diuretic] Uses Cerebral edema, T lOP/ICP, renal impair, poisonings Action Osmotic diuretic Dose Test dose 0.2 g/kg/dose IV over 3-5 min if no diuresis w/in 2 h, D/C Oliguria 50-100 g IV over 90 min T lOP 0.5-2 g/kg IV over 30 min Cerebral edema 0.25-1.5 g/kg/dose IV >30 min Caution [C, ] w/ CHF or volume overload Contra Anuria, dehydration, HE, PE Disp Inj SE May exacerbate CHF, N/V/D Interactions t Effects OF cardiac glycosides X effects OF barbiturates, imipramine, Li, salicylates EMS Monitor ECG for hypo-/hyperkalemia (T wave changes) OD May cause dehydration, t urine frequency/amount hypotension and CV collapse symptomatic and supportive... 

Modern diuretics (natriuretics, saluretics), as used in the treatment of hypertension and heart failure, are administered with the aim to enhance the renal excretion of sodium ions and water. Older diuretics, such as the osmotic diuretic agents, are of little interest in the treatment of the aforementioned cardiovascular disorders, but may be used to lower intracranial pressure associated with brain edema. 

Osmotic diuretics such as mannitol are readily filtered in the glomeruli, but they are hardly subject to tubular reabsorption. For this reason the osmotic... 

An important functional characteristic of the proximal tubule is that fluid reabsorption is isosmotic that is, proximal reabsorbed tubular fluid has the same osmotic concentration as plasma. Solute and water are transported in the same proportions as in the plasma because of the high water permeability of the proximal tubule. Thus, the total solute concentration of the fluid in the proximal convoluted tubule does not change as the fluid moves toward the descending loop of Henle. The corollary of this high water permeability is that unabsorbable or poorly permeable solutes in the luminal fluid retard fluid absorption by proximal tubules. This is an important consideration for understanding the actions of osmotic diuretics. 

Osmotic diuretics owe their effects to the physical retention of fluid within the nephron rather than to direct action on cellular sodium transport. These compounds... 

---