A solution which is isotonic with blood has a freezing-point Note that, although the freezing depression, ΔTf, of 0. Drug absorbed by the conjuctiva enters the systemic circulation. The interaction of the surfactant and fatty alcohol components of emulsifying mixtures which leads to high viscosity body is timedependent, giving the name 'self-bodying' to these emulsions. Hydrophobic drugs may bind to muscle protein, leading to a reduction in free drug and perhaps to prolongation of action: Dicloxacillin is 95% bound to protein; ampicillin is bound to the extent of 20%, and as a consequence dicloxacillin is absorbed more slowly from muscle than is ampicillin. The conjugate when referring to both weak bases formed in this way are subject to acids and bases.
It is therefore not surprising that there will be a reduction in solubility, often leading to precipitation. Replace negative numbers with a bar above the number. In a second-order reaction: The rate of reaction depends on the concentration of two reacting species. The higher the pKa of a weak acid, the stronger is the acid. The general rules for applying this system are: Determine the intercepts of the plane on the a, b, and c axes in terms of unit cell lengths.
The sum of pKa and pKb is greater than 14. There are several different types of copolymer Figure 6. In relation to rectal absorption of drugs, which of the following statements are correct? Book Description A revision guide for students giving bullet points of basic information on physical pharmacy. Ion pair formation: occurs between ions of similar charge is a consequence of electrostatic interaction between ions decreases the absorption of quaternary ammonium salts results in the formation of a neutral species 4. The continuous phase is the phase in which the disperse phase is distributed.
Drugs such as diazepam may be adsorbed onto solid substrates to minimise taste problems, but care should be taken to ensure that desorption does not become a rate-limiting step in the absorption process. Osmotic pressure is a colligative property, which means that its value depends on the number of ions in solution. The right of David Attwood and Alexander T. Biological membranes are composed of bilayers of phospholipids and cholesterol or related structures. For a more complete picture of the dissociation it is necessary to take into account all possible ways in which the molecule may be ionised and all the possible species present in solution. To achieve the very low interfacial tension required for their formation it is usually necessary to include a second amphiphile the cosurfactant such as a short-chain alcohol in the formulation. This text is derived from the textbook Physicochemical Principles of Pharmacy and is designed to be used alongside it for those revision periods when time is short.
Log P is less than 5. Essential information concerning the formulation of these dosage forms is included helping to remove the complexities of the various topics. Protein binding decreases the free drug concentration. If, in addition, the blood supply to the region is limited there will be an additional restriction to rapid removal. In general, the extent of adsorption of a solute is inversely proportional to its solubility in the solvent from which adsorption occurs.
The bulk pH is not the actual pH at the membrane. The oxidative degradation of some drugs, for example, prednisolone and morphine, in solution may be pH-dependent because of the effect of pH on the oxidation-reduction potential, E0, of the drug. The distribution of the solute between the two phases is represented by the partition coefficient or distribution coefficient, P, defined as the ratio of the solubility in the nonaqueous oily phase, Co, to that in the aqueous phase, Cw, i. The exceptions to this are proteins and natural polypeptides. These drugs should also be kept out of contact with heavy metals and should be stabilised with antioxidants. The rate of drainage of drops decreases as their viscosity increases and this can contribute to an increased concentration of the drug in the precorneal film and aqueous humour: Hydrophilic polymeric vehicles, such as poly vinyl alcohol and hydroxypropylmethylcellulose are used to adjust viscosity. Water-soluble active substances will be insoluble in fatty bases, while the less water-soluble material will tend to be soluble in the base, and will thus diffuse from the base more slowly.
Water-soluble drugs are better absorbed from a fatty excipient than from a water-soluble one. The zeta potential of the suspension particles: — Most suspension particles dispersed in water have a charge acquired by specific adsorption of ions or by ionisation of ionisable surface groups. Suitable for all years of the pharmacy degree plus anyone else who wants to brush up on their knowledge. A suspension acceptable pharmaceutical formulation. Aerosols are dispersions of a liquid or solid in air. The Integrated Foundations of Pharmacy series supports those who are at the beginning of their journey to become a pharmacist.
Repulsion between particles is decreased. Because of their potential instability in solution, therapeutic proteins are often formulated as lyophilised powders. Preservatives such as the methyl and propyl parabens present in formulations can be sorbed into rubber and plastic membranes and closures, thus leading to decreased levels of preservative and, in the extreme, loss of preservative activity. The Alza Ocusert device releases controlled amounts of pilocarpine over a period of 7 days. Note also that moisture contains dissolved oxygen and hence the preparations should be stored in dry conditions. For this second edition there is a new chapter added on pharmaceutical nanotechnology, and clinical notes are incorporated, in line with. Nematic liquid crystals: — Groups of molecules orientate spontaneously with their long axes parallel, but they are not ordered into layers.
Indicate which of the following general statements are true: A weakly acidic drug is unionised when the pH of the solution is at least 2 pH units below its pKa. The Gouy—Chapman layer of an ionic micelle is compressed in the presence of electrolyte. When these are left on the skin they prevent water loss from skin with a disrupted epidermal layer the skin surface and therefore will allow up to 80% of hydrocortisone to increase the hydration of the pass into the dermis but only 1% through stratum corneum. Antioxidants should be included in the formulation. Monolayers of polymers and proteins are often of this type. Indicate which of the following general statements are true: Acidic drugs are less soluble in acidic solutions than in alkaline solutions. Microemulsions are formulated so that the disperse phase is in the nanometre size range.