Isotonicity solution tonicity

Fluids can be classified further according to their tonicity. Isotonic solutions (i.e., normal saline or 0.9% sodium chloride [NaCl]) have a tonicity equal to that of the ICF (approximately 310 mEq/L or 310 mmol/L) and do not shift the distribution of water between the ECF and the ICF. Because hypertonic solutions (i.e., hypertonic saline or 3% NaCl) have greater tonicity than the ICF (greater than 376 mEq/L or 376 mmol/L), they draw water from the ICF into the ECF. In contrast, hypotonic solutions (i.e., 0.45% NaCl) have less tonicity than the ICF (less than 250 mEq/L or 250 mmol/L) leading to an osmotic pressure gradient that pulls water from the ECF into the ICF. The tonicity, electrolyte content, and glucose content of selected fluids are shown in Table 24—3. 

It has been also observed that hypertonic and hypotonic salt solutions tend to irritate sensitive tissue and cause pain when applied to mucous membranes of the eye, ear, and nose, etc., whereas isotonic solution causes no tissue irritation when it comes in contact with the tissue. Obviously, the tonicity of formulations that come in to direct contact with blood, muscle, eye, nose, and delicate tissues is critical. Therefore, the issue of tonicity is important in small- and large-volume injectables, ophthalmic products, and products intended for tissue irrigation. The degree of tissue irritation or hemolysis or crenation observed depends on the degree of deviation from isotonicity, the volume injected, the speed of injection, the concentration of the solutes in the injection, and the nature of the membrane. The parenteral and ophthalmic formulations are therefore adjusted to isotonicity if possible. 

Use only isotonic solutions such as normal saline to reconstitute the ATP-vesicles. Using hyper- or hypo-tonic solutions for this purpose may cause membrane leak of the vesicles. The reconstituted ATP-vesicles should be used within 2 h to avoid self-fusion of the vesicles. 

Solutes that cannot freely cross cell membranes, such as sodium, are referred to as effective osmoles. The concentration of effective os-moles in the ECF determines the tonicity of the ECF, which directly affects the distribution of water between the extra- and intracellular compartments. Addition of an isotonic solution to the ECF will result in no change in intracellular volume because there will be no change in the effective osmolality of the ECF. Addition of a hypertonic solution to the ECF, however, will result in a decrease in cell volume, whereas addition of a hypotonic solution to the ECF will result in an increase in cell volume. Table 49-1 summarizes the composition of commonly used intravenous solutions and their respective distribution into extracellular and intracellular compartments following infusion. 

Ophthalmic Dosage Forms. Ophthalmic preparations can be solutions, eg, eye drops, eyewashes, ointments, or aqueous suspensions (30). They must be sterile and any suspended dmg particles must be of a very fine particle size. Solutions must be particle free and isotonic with tears. Thus, the osmotic pressure must equal that of normal saline (0.9% sodium chloride) solution. Hypotonic solutions are adjusted to be isotonic by addition of calculated amounts of tonicity adjusters, eg, sodium chloride, boric acid, or sodium nitrate. 

The tension or osmotic pressure of a solution also, ionic strength, usually measured as weight percentage. Often the tonicity of a solution is presented as relative to some physiological solution (e.g., blood plasma). See Hypertonic Hypotonic Isotonic Isotonic Buffers... 

Tonicity agent/stabilizer Provides isotonicity to the formulation such that it is suitable for injection Examples include polyols, salts, and amino acids Help maintain the protein in a more compact state (polyols) Minimize electrostatic, solution protein-protein interactions (salts) Stabilizers include cryo and lyoprotectants Examples include polyols, sugars, and polymers Cryoprotectants protect proteins from freezing stresses Lyoprotectants stabilize proteins in the freeze-dried state... 

As you doubtlessly learned in physiology, osmosis is diffusion of water through a semipermeable membrane. The semipermeable membrane allows water to move through it, but most solute particles are either too big or too polar to make it across the membrane. The relative concentration of solutes in osmotic systems is called the tonicity. Two solutions are isotonic if they contain equal concentrations of particles. If the concentrations are not equal, the one with the greater concentration is the hypertonic solution, and the one with the lower concentration is the hypotonic solution. It is critically important to notice that tonicity is a comparative concept, and it makes no sense to call a solution hypertonic without indicating to which solution you are comparing it. For example, is a 5% NaCl solution hypotonic or hypertonic You are probably tempted to say hypertonic, because you are mentally comparing this solution to normal saline, which is 0.89% (w/w) NaCl. So, 5% NaCl is hypertonic to normal saline. However, 5% NaCl is hypotonic to 10% NaCl and isotonic with another solution of 5% NaCl. 

Which of your test solutions was (a) isotonic with red blood cells (tonicity = 0.30 osmolar) (b) hypotonic (c) hypertonic ... 

The most direct method for measurement of tonicity obviously would be to observe changes in erythrocytes on mixing solution with blood. If hemolysis or crenation or a marked change in the appearance of erythrocytes occurs, the solution is not isotonic. If the cells retain their normal size and shape, the solution is isotonic. Grosicki and Husa used this method early on ... 

Parenteral solutions should be of approximately the same tonicity as blood semm the amount of adjusting substance which must be added to a formulation to achieve isotonicity can be calculated using the... 

Ophthalmic products instilled into the eye may be tolerated over a fairly wide range of tonicity (0.5-1.5 percent NaCl equivalents Hind and Goyan 1950). However, to minimise irritation and discomfort, ophthalmic solutions should ideally be isotonic with the tears, equivalent to 0.9 percent w/v solution of sodium chloride. 

Hypotonic ophthalmic solutions or suspensions can be rendered isotonic by the addition of tonicity agents such as sodium chloride, potassium chloride, dextrose, glycerol and buffering salts. As with other adjuvants, the formulator should give due consideration to possible interactions between the tonicity agent and other components of the formulation, including the drug itself. 

Blood plasma has an osmolarity equivalent to a 0.30 M glucose solution or a 0.15 M NaCl solution. This latter is true because in solution NaCl dissociates into Na+ and Cl and thus contributes twice the number of solute particles as a molecule that does not ionize. If red blood cells, which have an osmolarity equal to blood plasma, are placed in a 0.30 M glucose solution, no net osmosis will occur because the osmolarity and water concentration inside the red blood cell are equal to those of the 0.30 M glucose solution. The solutions inside and outside the red blood cell are said to be isotonic iso means "same," and tonic means "strength") solutions. Because the osmolarity is the same inside and outside, the red blood cell will remain the same size (Figure 18.20b). 

Buffers must maintain the tonicity or osmotic balance of the vehicle (Fig. 3.7). The plasma membrane lets water pass across and flow down its concentration gradient. If the solution outside the cell has the same concentration of particles as inside the cell, then the solution is isotonic, and the movement of water into and out of the cell is equal and there is no net change in the size of the cell (Fig. 3.7, top row). If the solution outside the cell is more concentrated (has less water) than that inside... 

Fig. 3.7 Effects of tonicity on cells. For best fixation, the correct tonicity of the fixative solution is important. Tonicity is a measure of the concentration of particles in a solution. As a result of differences in tonicity across a membrane, water will move across the membrane to make the tonicity equal on both sides. Isotonic means that the concentration of particles is equal inside and outside the cell here the size of the ceU does not change. Hypertonic means that the concentration of particles outside the cell is higher and there is net movement of water out of a cell the cell shrinks. Hypotonic means that the concentration of particles outside the cell is less than inside the cell and there is a net movement of water into the cell the cell swells...

Isotonicity of eye drops is obtained by adding boric acid, borax or a combination thereof. If their use is not possible due to chemical incompatibilities, sodium chloride solution can be employed. Other tonicity substances are mentioned in Table 10.9. 

As a measure of the tonicity of blood one can calculate with the osmotic value because active substances and additives cannot pass the membrane of the erythrocyte (see Sect. 18.5.2). The osmotic value of blood is around 290 mOsm/kg. Some parenteral fluids however contain substances that can pass the membrane fast ethanol, glycerol, urea. Hyperosmotic solutions of these substances may cause haemolysis so they are hypotonic. The iso-osmotic concentration of ethanol is for example 1.39 % m/m. Ethanol 5 % v/v infusion fluid is therefore hyperosmotic but appears to be practically isotonic. 

In biology and biochemistry, the term tonicity is used for substances that cannot cross cell membranes and it is a measure of the osmotic pressure that a substance can exert across a cell membrane, compared with blood plasma. In practice, plasma has an osmolarity of about 3 X 10 osmol.m therefore a 1.5 x 10" mol.m NaCl solution may be said to be isotonic with plasma, assuming that neither Na nor Cl" can cross cell membranes, which is nearly true. If a substance can cross a plasma membrane, then it cannot exert an osmotic pressure across that membrane. The solute will equilibrate across the membrane instead of forcing water to move. Urea exhibits such behavior so a 3 x 10 mol.m Wea solution maybe said to be iso-osmotic with plasma but it is not isotonic. 

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