Drugs solution

Some drug solutions are expressed in ratios, for example 1 100 or 1 500. These ratios mean that there is 1 part of a drug in 100 parts of solution or 1 part of the drug in 500 parts of solution. 

Processes based on fluidized bed coating have been developed (49). In this process, the bioactive agent is dissolved in an organic solvent along with the polymer. This solution is then processed through a Wurster air suspension coater apparatus to form the final microcapsule product. A solvent partition technique based on continuous injection of a polymer-drug solution into flowing mineral oil has been reported (50). 

FIG. 20 22 Schematic of supercritical antisolvent with enhanced mass-transfer process to produce nanoparticles of controllable size. R, precipitation chamber SCF pump, supply of supercritical COg I, inline filter H, ultrasonic horn P, pump for drug solution G, pressure gauge. 

In a typical experimental situation a membrane is used between two compartments, one containing a drug solution ( donor compartment) and the other sink conditions (i.e., zero concentration receiver compartment). For a homogeneous barrier membrane of thickness h, Pick s First Law may be written as... 

Water-soluble polymers can also be used as aqueous solutions for drug delivery. Although the polymer is already dissolved, its increase in viscosity of the drug solution causes the drug to be retained somewhat longer in the desired application. This technique is common with ocular, nasal, and oral applications of drug solutions. 

The pH of a drug solution may have a very dramatic effect on its stability. Depending on the reaction mechanism, a change of more than 10-fold in rate... 

In many drug solutions, it is necessary to use buffer salts in order to maintain the formulation at the optimum pH. These buffer salts can affect the rate of drug degradation in a number of ways. First, a primary salt effect results because of the effect salts have on the activity coefficient of the reactants. At relatively low ionic strengths, the rate constant, k, is related to the ionic strength, p, according to... 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

Sterile filtration, with subsequent aseptic filling, is common because of the heat sensitivity of many drugs. Those drug solutions that can withstand heat should be terminally autoclave sterilized after filling, since this best assures product sterility. 

When drug solutions and containers can withstand autoclaving conditions, this method is preferred to other sterilization methods because moist heat sterilizes quickly and inexpensively. However, judgment must be exercised and experiments run to ensure that the solution and container are permeable to steam. Oils and tightly closed containers, for example, are not normally sterilizable by steam. 

Fig. 8 Comparison of time-release profiles from three different preparations of betaxolol (—) drug solution representing marketed product (--------) supension formulation (-----------) gel formulation.

Performance of nebulizers is not measured in the same manner as pMDIs and DPIs. Since the drug solution is not supplied with the device, the time scale of compatibility is much smaller. Droplet size and distribution and dose delivery are, however, very important. 

Fig. 9 Diagrammatic representation of two types of osmotically controlled systems. Type A contains an osmotic core with drug. Type B contains the drug solution in a flexible bag, with the osmotic core surrounding.

The eye is unique in its therapeutic challenges. An efficient mechanism, that of tears and tear drainage, which quickly eliminates drug solution, makes topical delivery to the eye somewhat different from most other areas of the body [137]. Usually less than 10% of a topically applied dose is absorbed into the eye, leaving the rest of the dose to potentially absorb into the bloodstream [138], resulting in unwanted side effects. The goal of most controlled-delivery systems is to... 

If initial solute uptake rate is determined from intestinal tissue incubated in drug solution, uptake must be normalized for intestinal tissue weight. Alternative capacity normalizations are required for vesicular or cellular uptake of solute (see Section VII). Cellular transport parameters can be defined either in terms of kinetic rate-time constants or in terms of concentration normalized flux [Eq. (5)]. Relationships between kinetic and transport descriptions can be made on the basis of information on solute transport distances. Note that division of Eq. (11) or (12) by transport distance defines a transport resistance of reciprocal permeability (conductance). 

The steady-state flux of drug solute across the cell monolayer-filter support system (Fig. 5) is... 

Where hydrogels are concerned, the subscript 3 denotes a drug solute for which diffusional transport is of interest. 

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