Skip to Main Content

++

LEARNING OBJECTIVES

++

After completing this chapter, the reader should be able to:

++

  • ► Define and understand the terms and concepts of solubility and miscibility.

  • ► Identify the descriptive terms for solubility, their meaning, and their percent value.

  • ► Recognize factors that affect solubility.

  • ► Calculate the solubility of poorly soluble strong electrolytes by using Ksp values.

  • ► Calculate the solubility of weak electrolytes as a function of pH and understand what the answer means.

  • ► Calculate the pH of precipitation for weak electrolytes in aqueous and mixed solvent systems.

  • ► Describe the role of drug dissolution from dosage forms in drug bioavailability.

  • ► Relate the parameters of the Noyes-Whitney equation to the variables that affect the dissolution rate of drug particles.

  • ► Recognize and appreciate the United States Pharmacopeia (USP) requirements for dissolution studies.

  • ► Discuss how various physicochemical, formulation, and physiological factors can influence dissolution behavior.

  • ► Define and understand the partitioning law, partition coefficients, and apparent partition coefficients.

  • ► Calculate the partition coefficients for different types of solutes in aqueous/organic solvent systems.

  • ► Determine the effect of pH on the partition coefficient of weak electrolytes and on their excretion in different body fluids.

++

SOLUBILITY

++

General Solubility Concepts

++

Solubility is the concentration of a solute when the solvent has dissolved all the solute that it can at a given temperature. A useful definition of solubility is the concentration of solute in a saturated solution at equilibrium. Saturated solution concentration is the solubility of the solute at that temperature. Solubility is a physical property, and values for the solubility of pure substances are found in the literature. It is possible for some substances to dissolve in a higher concentration than could be attained at equilibrium, have increased solubility, and form supersaturated solutions. One compound that readily forms supersaturated solutions is caffeine. The term miscible is used to refer to the solute when it is a liquid and will form a solution with a solvent over any concentration range.

++

The solubility of most substances varies with temperature, having a nearly exponential relationship, as seen in one of the solubility curves for two inorganic potassium salts shown in Figure 5-1.

++
++

Solubility Expressions

++

The solubility of solid solutes in liquid solvents, particularly in water, is an important consideration in the preparation, storage, and use of liquid pharmaceutical formulations and products.

++

Descriptive terms for solubility are found in the United States Pharmacopeia/National Formularly (USP/NF) and in Remington's Pharmaceutical Sciences. An interpretation of these terms is given in Table 5-1 The descriptive terms are general solubilities and cover a range of values. For example, a substance described as “soluble” requires between 10 and 30 parts (mL) ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPharmacy Full Site: One-Year Subscription

Connect to the full suite of AccessPharmacy content and resources including 30+ textbooks such as Pharmacotherapy: A Pathophysiologic Approach and Goodman & Gilman's The Pharmacological Basis of Therapeutics, high-quality videos, images, and animations, interactive board review, drug and herb/supplements databases, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPharmacy

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.