This chapter describes the key concepts of acids and bases in correlation with appropriate dosage forms. An understanding of acidic and basic behaviour is significant for understanding how active pharmaceutical ingredients (APIs) will behave before, and following, administration to a patient. Moreover, the strength of acids and bases is determined by their structure and the solvent environment. Meanwhile, an ideal dosage form ensures that the API remains stable in storage for as long as reasonably practicable. The chapter also considers the significance of buffers in physiological systems and in chemical applications. These are used to maintain pH levels at the required value.
Chapter
Acids and bases
Judith Madden
Chapter
Colligative properties
Philip Denton
This chapter details the colligative properties of a solution. It explains that some properties are found to be independent of the nature of the solute, being dependent only on the number of solute particles present and the nature of the solvent. Several colligative properties include osmotic pressure, vapour pressure, and tonicity. The chapter also cites that colligative properties are measurable in systems where there is a solution phase in equilibrium with a second phase that is made up of the same solvent as the solution. All colligative properties arise due to the reduction in the chemical potential of solvent molecules following the addition of solute.
Chapter
Disperse systems
Jayne Lawrence
This chapter looks at disperse systems. It explains that dispersions are formed from dispersed and continuous phases, each being formed from solid, liquid, or gas. Dosage forms that consist of two or more gases are always single-phase systems, so two-phase systems consisting of a liquid phase and suspended solid particles are examples of a disperse system. An understanding of disperse systems can help control the physical properties of a substance so that it is appropriate to specific formulations. The chapter also notes that DLVO theory can help with the understanding that the dispersed particles flocculate will depend on the forces between the dispersed particles.
Chapter
Drug discovery, development, and delivery
Craig A. Russell and Afzal R. Mohammed
This chapter provides an overview of drug discovery, development. It looks at delivery as an important area of the pharmaceutical industry. In rational drug design, candidate compounds are identified by studying the biological and physical properties of the therapeutic target. The chapter then discusses the optimization of lead compounds, which is the candidate compound considered to be the best prospect. Quantitative structure-activity relationships (QSAR) refer to mathematical models based on chemical compounds' biological activity and physicochemical descriptors. The chapter also looks into the correlation between routes of administration and associated dosage forms before the four phases involved in clinical trials of new medications.
Chapter
Gases
Ben Forbes
This chapter highlights the significance of the chemical and physical properties of gases when developing medicines, such as whether the gas is a volatile agent or whether a substance has a gaseous phase. The chapter examines, more generally, the properties of gases. It takes a look at transitions from solid or liquid into gaseous states. Gases have a variety of roles in pharmaceutical operations, including surface area measurement, distillation, lyophilization, and sterilization. The chapter also highlights examples of practical applications of gases and gas-based pharmaceutical dosage forms in pharmacy. It provides an overview of several gas-based dosage forms, such as pharmaceutical aerosols for respiratory drug delivery, nebulizers, foams, non-inhalation aerosols, and aerosol powder devices.
Chapter
Hydrophobicity and partitioning
William McAuley
This chapter looks at the importance of hydrophobicity and partitioning. It notes that the hydrophobicity of a drug molecule is important for a wide range of situations in relation to pharmaceutical products. The hydrophobicity of active pharmaceutical ingredients (APIs) has an influence on various pharmaceutically relevant phenomena, including solubility and interactions with packaging. Partitioning is an example of a phase transition and it occurs when an API distributes itself between two immiscible liquids. The chapter also looks into the differences between the distribution coefficient and the partition coefficient, which has a wide application in pharmaceutical sciences, such as drug delivery, formulation, and packaging.
Chapter
Introduction to pharmaceutics
Philip Denton
This chapter introduces the key concepts surrounding pharmaceutics. It explains that medicine come in a range of forms, but all are composed of an active pharmaceutical ingredient (API). All pharmaceutical products begin as a chemical compound which interacts with a target in the body. This compound acts like a drug when it exhibits a desirable pharmacology. The chapter highlights that all pharmacists have good knowledge of medicine, the formulation of drugs, and dosage. It considers the understanding of the physicochemical properties of compounds, such as the behavior of dosage forms before their administration and in vitro and the fate of dosage forms in vivo as they make their way to the biological target.
Chapter
Kinetics and drug stability
Gary Moss
This chapter examines the significance of kinetics and drug stability. Kinetic studies can provide information on the mechanism of reactions, and allow the degree of change during a process to be measured against time. Moreover, kinetics is a field that applies to the process of drug absorption, distribution, and elimination by the body. The chapter looks at reaction rates and reaction orders before considering the factors affecting the rate of reaction of dosage forms. The Arrhenius equation may be used to model the relationship between rate constants and temperature, which allows for the estimation of the expected shelf life of a drug at its normal storage temperature.
Chapter
Liquids
Matthew Roberts
The chapter explains that liquids are used in a range of different dosage forms for the delivery of therapeutic agents and they use several routes. Liquid medicines offer a number of advantages over solid medicines such as ease of administration, dose uniformity, and dose flexibility.Physical appearance and properties greatly vary, and liquid dosage forms can range from mouthwashes, oral syrups, and suspensions, to injectable solutions, topical lotions, and shampoos. The chapter then shows that the typical liquid dosage form is composed of the active pharmaceutical ingredient (API) contained within a liquid vehicle, the solvent, and other excipients. Liquid dosage forms can be classified according to the route of delivery, the most common ones being oral and parenteral.
Book
Edited by Philip Denton and Chris Rostron
Pharmasceutics explores the different forms that medicines can take and demonstrates how being able to select the best form — be it a tablet, injectable liquid, or an inhaled gas — requires an understanding of how chemicals behave in different physical states. Taking medication is a common occurrence for many people, whether it be to deal with minor ailments such as a headache or life-threatening conditions such as HIV or cancer. In the UK alone, over 900 million prescriptions are dispensed every year. Overseeing all of this are pharmacists: experts in medicines and their use. This book is part of a series that supports those who are training to become pharmacists.
Chapter
Phase equilibria and transitions
Steve Enoch
This chapter introduces the notions of phase, phase equilibria, and phase transitions. Phase transitions occur at a specific temperature and pressure and, in certain conditions, the phases involved are at equilibrium. Phase diagrams for two-component systems illustrate the preferred phase/phases at a given temperature, pressure being kept constant. The composition of the solid, liquid, and vapour phases can be determined on an appropriate phase diagram from the intersection of an isotherm with the solidus, liquidus, or vaporus. The chapter also shows that three-component phase diagrams are used to illustrate the preferred phase/phases of a system containing three substances at constant temperature and pressure.
Chapter
Solids
Barbara Conway
This chapter discusses the property of solids as they relate to drugs and the physicochemical characteristics of the active pharmaceutical ingredient (API). At normal temperatures, most drugs are solids and maintain their original shape unless they are compressed, as happens during tablet formation. The chapter then looks at the process of polymorphism and the differences between crystalline and amorphous solids. It explores the factors affecting solubility. Solid dosage forms are mostly administered through oral administration, but other routes such as inhalation and suppositories work just as well. To achieve and maintain effective drug levels in the body, it is often necessary to administer immediate release formulations several times daily.
Chapter
Surface phenomena
Imran Saleem and Ali Al-Khattawi
This chapter looks at surface phenomena, particularly the behaviour of molecules at interfaces. All physical entities possess a boundary with their surroundings, so the phenomena occurs at the boundaries and this quality can be utilized in the development of drug delivery systems. Surface free energy is the term used to describe how the molecules at the boundary layer have a higher Gibbs free energy than molecules in the bulk liquid. The chapter considers several techniques dedicated to the measurement of surface and interfacial tension. It also notes the role of surfactants in the formulation of different dosage forms and the development of drug delivery applications.
Chapter
Thermodynamics
Linda Seton
This chapter explains that thermodynamics is the study of the transfer of energy during chemical and physical processes. It provides an overview of the First Law and Second Law of Thermodynamics. All chemical reactions bring about a conversion of energy. The chapter notes that enthalpy is a state function defined as the heat energy absorbed by a system at fixed pressure. It also introduces Hess's Law, which is used to calculate enthalpy changes. It looks at Gibbs energy and shows how this relates to the notions of enthalpy and entropy, before highlighting that the equilibrium constant for a reaction depends on temperature.
