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1 introduction to dosage form design learning objectives uponcompletion of this chapter you should be able to denedosage form stability excipient pharmaceutical necessity chemical stability physical stability microbiological stability rst ...

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            1
            Introduction to dosage form
            design
             Learning objectives
             Uponcompletion of this chapter, you should be able to:
              Definedosage form, stability, excipient, pharmaceutical necessity, chemical
               stability, physical stability, microbiological stability, first pass effect, elimination
               and excretion.         copyright 
              List the drug properties that must be considered in dosage form design.
              Describe the qualities that are built into an ideal dosage form/drug delivery
               system, and identify from a list of ingredients and an ingredient table, how the
               ingredient contributes to the manageable size of the dosage form, its
                                           Press
               palatability or comfort, its stability (chemical, microbial, or physical), the
               convenience of its use or the release of drug from the dosage form.
              List the properties of the routes of administration that must be considered in
               the design of dosage forms.
              Briefly outline the movement of an orally administered drug from its site of
               administration through its elimination from the body:
               – administration
                      content 
               – liberation from the dosage form by (a) dissolution; (b) diffusion
               – absorption
               – distribution
               – metabolism
               – elimination.
              Distinguish betweenthefollowing patterns of drug release from dosage forms:
               – immediate release
               – delayed release
               – sustained release
               – controlled release.
     Sample 
              Rankthedifferent routes in terms of speed of onset of action.
           Pharmaceutical 
            Introduction
            What is pharmaceutics and why do pharmacists study this subject?
            Historically pharmacists provided two services in the healthcare system: they
            extracted drugs from their natural sources and prepared or ‘compounded’ the
            drug into a convenient form for patient use, the dosage form.
              Extracted from Remington Education: Pharmaceutics by Shelley Chambers Fox
                     2 | Pharmaceutics
                        Currently little dosage form compounding is required of most
                     pharmacists, but the pharmacist in a compounding specialty practice has
                     the need to design dosage forms that are both safe and effective. The
                     pharmacist in charge of an admixture service must develop policies and
                     procedures to ensure the products prepared remain sterile as well as
                     physically and chemically stable. And our most pressing pharmaceutical task
                     is to ensure that patients and caregivers are properly educated in the
                     appropriateuseofeyedropsandinhalers,injectionsandtransdermalpatches
                     suchthatthedrugscontainedinthesedosageformswillprovidetheintended
                     benefit. The products of biotechnology for rheumatoid arthritis and multiple
                     sclerosis are injectable dosage forms used primarily by the patient in the
                     home setting. New technologies to deliver drugs through the skin utilize
                     handheld devices for iontophoresis and thermal ablation. Pharmacists serve
                     as the dosage form experts both to other medical personnel and to our
                     patients. The study of pharmaceutics provides the scientific foundation for
                     the design and appropriate use of dosage forms and drug delivery systems.
                                                                       copyright 
                        Definitions                                               Press
                        Adosageformistheformthatwetakeourdrugin–inotherwords,a
                        tablet, a syrup, an ointment, an injection. The concept of a drug
                        delivery system includes products that are designed to provide
                        optimal control over the release of a drug to achieve enhanced safety
                        or efficacy.      content 
                        Thistextisaboutthephysicochemicalprinciplesofdosageformanddrug
                     delivery system design, and the biological environment in which these
                     systems are designed to perform to deliver a drug to its receptors.
                     Properties of the drug
                     Key Point
                      To design a dosage form for a drug, the following properties must be considered: water
                      solubility; log P, a measure of lipophilicity; molecular weight; stability in solution;
                      enzymatic degradation; and location of drug receptors.
          Sample 
                     Pharmaceutics is a science that applies both drug chemistry and drug biology
                     to the problem of delivering drugs to their target tissues. During the
                    Pharmaceutical 
                     preformulation process, key chemical and physical properties of the drug are
                     studied in order to rationally design a delivery system and predict the fate of
                     the drug in vivo after administration. Some aspects of drug chemistry that
                     must be considered in the development of a dosage form include:
                           Extracted from Remington Education: Pharmaceutics by Shelley Chambers Fox
                                                                    Introduction to dosage form design   |  3
                         Water solubility: The drug must be dissolved in aqueous body fluids
                            before it can cross membranes.
                         LogP:Thedrugmusthave sufficient lipophilicity to cross membranes.
                         Molecular weight: Large molecular weight drugs have difficulty moving
                            across membranes.
                         Stability in solution: Drugs may hydrolyze, oxidize, photolyze or
                            otherwise degrade in solution.
                         Enzymatic degradation: Some drugs may be substantially degraded by
                            enzymes before they reach their target.
                         Location of receptors: Intracellular drug receptors or receptors in the
                            brain or posterior eye are challenging to target.
                         Selectivity:Somedrugscauseserioustoxicityasaresultofpoorselectivity
                            for their target.
                        Anticancer drugs are notoriously nonselective in their cytotoxic effects;
                        however, drug delivery systems may be designed to selectively target tumor
                                                                              copyright 
                        cells with known biological features. Drug delivery systems can be developed
                        to address the challenges that drugs present: poor solubility, large molecular
                        weight, inaccessible targets and lack of selectivity. Appendix Table A.1
                        provides an overview of the preferred drug properties for different routes of
                        administration.                                                 Press
                           Pharmaceutical example
                           If we consider the opiate pain reliever, oxycodone, its advantages and disadvantages
                           as a drug for administration to the gastrointestinal tract are presented in Table 1.1.
                                             content 
                        Qualities of the ideal dosage form
                        Key Point
                         Pharmaceutical excipients and manufacturing processes are used to prepare dosage
                         forms with the following qualities:
                          onedoseinamanageable size unit
                          palatable or comfortable
           Sample 
                          stable chemically, microbiologically and physically
                          convenient/easy to use
                          releasethedrugtothereceptorsinatimelyfashionwithminimalsideeffectsandfor
                      Pharmaceutical 
                             the optimal duration.
                             Extracted from Remington Education: Pharmaceutics by Shelley Chambers Fox
                            4 | Pharmaceutics
                              Table1.1 Analysisofoxycodone’sphysicochemicalpropertiesforusebytheoral
                              route
                              Design issue                       Drug property                      Analysis
                              Must be dissolved before drug      Water solubility of 100 mg/mL,     Drugis soluble in the contents of
                              can cross membranes                maximum dose 80 mg                 the gastrointestinal tract, even
                                                                                                    better if the patient takes 250 mL
                                                                                                    water with the tablet
                              Must have sufficient lipophilicity  Log P of 0.3 = log ½concoil       This drug will favor partitioning
                              to cross membranes                                   ½concwater      into lipid membranes over water
                                                                 Antilog(0.3) = 1.995
                                                                                                    by a 2:1 ratio
                              Large molecular weight drugs       Formula weight of 315.37           Based on molecular weight,
                              have difficulty moving across                                          oxycodone should move easily
                              membranes                                                             through membranes
                              Drugs may hydrolyze, oxidize,      Stability, solid dosage form,      Stability in the dosage form
                              photolyze, or otherwise degrade    stable to acid                     should not be an issue for this
                              in solution                                                           drug because it is in a solid
                                                                                                copyright 
                                                                                                    dosageform.Stability in stomach
                                                                                                    acid is not an issue
                              Some drugs cannot be used by       Metabolized in the liver, 60–80%   Some drug is lost to enzyme
                              mouth because of substantial       of the dose is delivered to the             Press
                                                                                                    deactivation but most of the
                              losses to enzyme degradation       systemic circulation               drug makes it to the blood
                              Intracellular drug receptors or    Receptors are in the brain         Oxycodone's lipophilicity is low
                              receptors in the brain or                                             for reaching the brain though still
                              posterior eye are challenging to                                      within the range. Its size
                              target                                                                (molecular weight) is within the
                                                       content  optimalrange
                              Some drugs cause serious           Not applicable
                              toxicity as a result of poor
                              selectivity of action
                            Drugs and their delivery systems manufactured by the pharmaceutical
                            industry or compounded by the pharmacist are prepared according to
                            industry and compendial standards and have been carefully designed with
                            each of the following qualities:
                            1.   Onedose in a manageable size unit
                                 Dosage forms should be formulated such that the dose is contained in a
             Sample 
                                 unit that can be counted or measured by the patient with reasonable
                                 accuracy. For example, vehicles such as syrups or water for injection can
                                 be used to prepare solution dosage forms in measureable units.
                           Pharmaceutical 
                            2.   Palatable or comfortable
                                 Manydrugsare bitter or salty, so we add sweeteners and flavors to mask
                                 their taste. Parenteral drugs (injections) and drugs for application to
                                 mucousmembranesmustbecomfortableenoughtopreventtissuedamage
                                    Extracted from Remington Education: Pharmaceutics by Shelley Chambers Fox
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