Problems also arise from the adsorption of medicaments onto the container walls. Again, the reason for this decrease is that the micellar size per ethylene oxide equivalent decreases with increasing length of the ethylene oxide chain. This book provides the student with all the main tools necessary to understand the broad scope of the pharmacy and pharmaceutical sciences. With a solution of a drug, it is not of course possible to alter the drug concentration in this manner, and an adjusting substance must be added to achieve isotonicity. A hydrophobic aromatic ring can have substituents which make the molecule water soluble.
The authors argued that if a particular concept had never been used in a published pharmacy or pharmaceutical science paper, then it perhaps could be ignored. The sorption of local anaesthetics by polyamide and polyethylene depends on the kind of plastic, the reaction conditions and the chemical structure of the drugs. The increase in entropy and decrease in free energy which accompany the loss of structuring make the formation of the hydrophobic bond an energetically favourable process. Taste masking The intentional adsorption of drugs such as diazepam onto solid substrates should be mentioned, the object being to minimise taste problems. A second example is illustrated in Fig.
The outer compartment contains Freon chlorofluorocarbon propellant ; the inner compartment contains the infusate and connects via a catheter to a vein or artery through a series of filters and flowregulating resistant elements. Addition of electrolytes Addition of electrolytes to ionic surfactants decreases the cmc and increases the micellar size. For instance, there is a limit on the inactive polymorph of chloramphenicol palmitate. Incompatibilities might arise from electrostatic interactions between oppositely charged drugs, or from complexation between drugs and ions or drugs and polymers; these and a variety of other interactions are discussed in the book. The pH of urine may be adjusted for example by administration of ammonium chloride or sodium bicarbonate in cases of overdosing with amfetamines, barbiturates, narcotics and salicylates, to ensure that these drugs are completely ionised and hence readily excreted.
In this review, the process of drug loading is described in detail based on the differences in the driving force for drug incorporation, including hydrophobic interaction, electrostatic interaction, hydrogen bonding, Pi-Pi stacking and van der Waals force. An understanding of the relationship between pH and drug ionisation is of use in the prediction of the causes of precipitation in admixtures, in the calculation of the solubility of drugs and in the attainment of optimum bioavailability by maintaining a certain ratio of ionised to unionised drug. If the surface layer has a higher energy than the bulk, as is the case with these small particles, they will interact more readily with solvent to produce higher degrees of solubility. Surface free energy is an important physicochemical property of a solid that can be assessed indirectly from wettability measurements. It will readily attach itself by hydrogen bonds to four neighbouring molecules, two at the negatively charged sites and two at the positively charged sites. In view of this relationship we can now consider changes in free energy which occur during a spontaneous process. It goes beyond the introductory aspects of the subject to show how basic physicochemical principles are essential to an understanding of every aspect of drug action, from the dosage form to the site of action in the body.
Enthalpy changes accompany such processes as the dissolution of a solute, the formation of micelles, chemical reaction, adsorption onto solids, vaporisation of a solvent, hydration of a solute, neutralisation of acids and bases, and the melting or freezing of solutes. The activity of a particular component is then the ratio of its value in a given solution to that in the reference state. The Miller indices for this plane are then written as 101. From United Kingdom to U. The basic structure of the skin 6 illustrates the routes of penetration of the drug through this barrier layer into the systemic circulation via the capillary blood supply 7.
Todd Professor of Pharmaceutics at the University of Strathclyde. Monolayers of the butyrate and stearate esters were virtually unaffected by changes of pH of the substrate from 3 to 6. The correlation between anaesthetic potency and lipid solubility shown in Fig. A practical illustration of the decreased solubility of gases with increase of temperature is the appearance of gas bubbles on the sides of a vessel containing water when the vessel is heated; the water is saturated with air at lower temperatures and the amount of air that it can contain decreases with increase of temperature, resulting in bubble formation. Reproduced from reference 5 with permission. We may ship the books from Asian regions for inventory purpose. The control exercised over the particle size of cortisone acetate and griseofulvin is due to their very low solubility; the experience is that if the solubility of a drug substance is about 0.
May not contain Access Codes or Supplements. Particle size of drugs and its relationship to absorption and activity. Reduce the numbers to the lowest terms. The effect is therefore as if a high concentration of glucose were administered, but because osmotic pressure is a colligative property dependent on the number of molecules rather than the mass of substance , there is no associated problem of a high osmolarity when starches are used. In this case we infer that the temperature of the surroundings is infinitesimally higher than that of the system, so that the heat changes are occurring at an infinitely slow rate, so that the heat transfer is smooth and uniform. Frequently both physical and chemical adsorption may be involved in a particular adsorption process.
This sixth edition continues to boast a broad chemical and physicochemical base and covers every aspect of drug properties from the design of dosage forms to their delivery by all routes to sites of action in the body. The most common type of cubic phase is the micellar cubic phase formed by the close packing of spherical micelles; a more complex cubic phase, the bicontinuous cubic phase, occurs with some amphiphilic lipids such as glyceryl monooleate see section 6. Below the eutectic temperature, no liquid phase exists. As a consequence of the larger size, the nonionic micelles are frequently asymmetric. All chapters are well illustrated and tables are clearly set out. Both solutions are at 25°C.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the copyright holder. Fortunately, the difference in the bioavailability of different polymorphic forms of a drug is usually insignificant. Many of the powders are slightly hydrophobic for example, indometacin and stearic acid , or even strongly hydrophobic for example, magnesium stearate, phenylbutazone and chloramphenicol palmitate. Such regions, as we have seen, contain open structures into which the nonpolar molecules may fit without breaking hydrogen bonds or otherwise disturbing the surrounding ice-like material. Similarly, plane-polarised light is rotated when travelling along any axis except the long axis in the middle phase and a direction perpendicular to the layers in the neat phase. Deliberate seeding is often carried out in industrial processes; seed crystals do not necessarily have to be of the substance concerned but may be isomorphous substances i.