Pharmacology for Midwifery PDF

Pharmacology for Midwifery Dr. Shereen Arabiyat CHAPTER 1: Dosage Forms Fundamentals of Pharmacology: An Applied Approach for Nursing and Health 2nd Edition by Alan Galbraith (Author), Shane Bullock (Author), Elizabeth Manias (Author), Barry Hunt (Auth...

Pharmacology for Midwifery Dr. Shereen Arabiyat CHAPTER 1: Dosage Forms Fundamentals of Pharmacology: An Applied Approach for Nursing and Health 2nd Edition by Alan Galbraith (Author), Shane Bullock (Author), Elizabeth Manias (Author), Barry Hunt (Author), Ann Richards (Author) Tablets Solids are usually administered in tablet form, sometimes described erroneously as pills. Note that the word ‘pill’ means a round or ovoid body, usually coated with sugar or even silver or gold paint. A tablet is a disc containing one or more medications, prepared by compressing a granulated powder in the die of a suitable machine. As most drugs are administered in very small quantities, sometimes less than a milligram, other materials must be added to make them easy to handle and, in extreme cases, allow them to be seen. This problem is overcome by incorporating the appropriate amount of an inert filler. Tablets have to disintegrate in the gastrointestinal tract; to make this easier, a substance such as starch, which swells when in contact with fluids, is incorporated. These substances are termed excipients. The other two substances incorporated in tablets are a binding agent to help keep the tablet whole in the container and a lubricating material to help prevent the ingredients from sticking to the manufacturing machinery.  Tablets may be sugar-coated or film-coated to disguise bad-tasting drugs. Some drugs that are unstable in solution can be administered as chewable tablets to patients who have difficulty in swallowing, and various flavorings can be added to disguise the taste of the drug. When chewable tablets are sugar-coated, they are called dragees – a name used for the colored balls used as cake decorations. Nicotine is even available in a chewing-gum formulation Enteric coated preparations Sometimes tablets are formulated so that disintegration takes place in the intestines rather than in the stomach. Capsules Capsules come in two main forms, hard and soft gelatin types. Hard gelatin capsules contain the drug as a solid. In soft gelatin capsules, the drug is in a non-aqueous solution. If the drug is a liquid, such as the oily form of vitamin E, it may be dissolved in another oil, usually soybean oil. Soft gelatin capsules are completely sealed and contain a drug in liquid or semiliquid form. They are useful not only for liquid drugs but also for drugs that are not dissolved easily in water. In the latter case, the drug can be dissolved in a relatively non-toxic solvent such as propylene glycol, thus enabling the drug to be absorbed more rapidly from the gastrointestinal tract Caplets The name ‘caplet’ has been coined to describe a capsule-shaped tablet coated with a gelatine-like material. Sustained release preparations With drugs that have a short half-life in the body, it is sometimes convenient to formulate the drug in such a way that it is released slowly into the gastrointestinal tract. These preparations are termed sustained- release, slow-release or retard forms. Many drugs are formulated in this way as it increases patient compliance – it is easier to remember to take a drug once or twice a day rather than three or four times a day. There are various ways in which slow release can be brought about. The active drug can be embedded in a matrix of relatively inert material, which disintegrates gradually in the gut, thus releasing the drug slowly. The drug can be prepared in a layered tablet, with layers of drug enclosed in successive layers of inert coating. As one layer of coating disintegrates, some drug is released and no further amount is released Oral liquid preparations Many patients, especially children, find the swallowing of tablets difficult; for these people, pharmacists have formulated many drugs in liquid form. These preparations are usually made according to the characteristics of the drug concerned. Flavorings, varying from raspberry to the more exotic tastes of coconut and passionfruit, are usually added to such preparations to make them more palatable. It is better not to make the taste too attractive in order not to encourage children to treat medicines pleasant. Sugar can be added to liquid preparations to form syrups, which enhance palatability, but it is common today to use sugar alcohols, such as sorbitol, as sweetening agents. Sorbitol has a lower calorific value than sucrose and is therefore more suitable for diabetics, while also helping to prevent dental caries. Another advantage of sorbitol use in syrups is that, taken in excess, it can act as an osmotic laxative and will discourage drug abuse of potentially addictive preparations, such as codeine syrups. Saccharin or cyclamates can be used to make liquids completely free of calories. A linctus is a syrup formulated specifically for coughs. In cases where the drug is insufficiently soluble in water, alcoholic solutions may be prepared. Such preparations are termed elixirs. Tinctures, like elixirs, contain alcohol but are more concentrated. Most tinctures, such as tincture of iodine, are used mainly for topical treatment Suspensions and Emulsions In cases where relatively insoluble drugs are used without alcohol and the drug is a solid, the resulting preparation is termed a suspension; if the drug is a liquid, the term emulsion is used. Even with the addition of stabilizers, these preparations have the tendency to separate into two or more layers. Therefore, thorough mixing before administration of such preparations is essential Some drugs, such as penicillin, are relatively unstable in solution and are prepared as desiccated powders, water being added to the powder before use. Even after reconstitution, the resulting suspensions usually need refrigeration until the course is finished Topical preparations The application of a drug to an area of the body for direct treatment is termed topical application. This type of application is not restricted to the skin and hair: the mouth and the entire gastrointestinal tract can have medications applied for topical treatment. Even body cavities can have topical applications applied, such as antibiotics during surgery Drops Eye and nose drops must be made isotonic in order to avoid pain or discomfort on application. Eye drops are aqueous or oily solutions or suspensions for instillation into the eye. Nose drops are liquid preparations used in the nasal passages. Ear drops are formulated as oily solutions to efficiently coat and adhere to the aural cavity Creams and Ointments Creams have an aqueous base, the water evaporating fairly quickly and leaving the drug on only the superficial layers of the skin. Very little of the drug is absorbed through the skin, where it could have a systemic action. Ointments are lipid-based and accordingly have a greasy appearance and feel. The presence of water-repellent (hydrophobic) substances on the skin, such as petroleum jelly, acts like an occlusive dressing. An occlusive dressing completely shuts out the skin from the air but sweating still occurs. Pastes Pastes have a high powder content and are useful in protecting areas of skin from moisture, as they are water-repellent. Clothes must be protected from pastes (although some dry quickly) and ointments, as they can be messy. Nappy rash and other conditions of the perineal area in babies respond well to pastes. Gels and Lotions For hairy areas of the body, alcoholic gels or lotions are less messy than conventional ointments or creams; however, as evaporation of the carrier is rapid, there is little penetration of the drug. Gels are semisolid in consistency, whereas lotions are more liquid in character. Lotions as calamine lotion for chickenpox should be applied without rubbing. Lotions are special type of suspensions; require shaking well before use. Sublingual (SL) and Buccal administration Administration of drugs by this route avoids the mixing of the drug with food and/or gastric juices, which may impede absorption or destroy the drug. For some drugs, notably glyceryl trinitrate, sublingual administration gives rapid absorption and avoids the hepatic first-pass effect. Transdermal route Rectal route- Suppositories ADVANTAGES If the patient is unconscious, oral administration is relatively difficult unless an enteral tube has been passed. The same goes for children and difficult or uncooperative patients. Nauseous or vomiting patients may find oral administration less than effective. Thus, many antinauseants and antiemetics are available as suppositories. Patients who have difficulty in swallowing due to esophageal strictures or other oral and esophageal pathologies can be given suppositories. Drugs that are destroyed by gastric acid can be given this way. In cases where a vein is difficult to find for intravenous injection, rectal administration of lipid-soluble drugs can result in rapid action. Rectal route- Suppositories DISADVANTAGES Insertion of suppositories can cause anal or rectal irritation. This can be a problem with hemorrhoidal preparations containing local anesthetics, which mask the irritation. Aesthetic considerations from both administrator and patient should always be observed when rectal administration is performed. Patient education is required for suppository use. If not self-administered, suppositories should be inserted with the patient in the left lateral position, which lessens the risk of perforation of the rectum. Suppositories are made to melt at body heat and are best kept refrigerated to maintain their shape. A drop of a lubricant jelly may help Enemas Enemas are liquid preparations for rectal administration. Enemas can be used for topical or systemic treatment or to cause a bowel motion. When used for topical or systemic treatment, they are termed retention enemas and are hypotonic solutions so that the fluid will be taken up by the body and the active ingredient left in contact with both the rectal and colonic mucosa. Pessaries Suppository-shaped medications for vaginal administration are usually termed ‘pessaries’. As vaginal administration of drugs is always for topical treatment, it is important that the drug coats all the vaginal mucosa. To enable this to happen, the medication should be inserted as high in the vagina as possible. Parenteral administration Any method of drug administration that avoids the gastrointestinal tract is termed parenteral administration. Transdermal, lung and intranasal administration are thus parenteral methods Injections, being invasive, require the use of aseptic procedures In intradermal administration, a drug or substance is injected into the dermis using a fine needle or needles (as is the case with an intradermal punch used in some vaccination procedures) The blood supply to the subcutaneous tissue is poor, and so absorption of an injected drug will be relatively slow. This is often an advantage with drugs that cannot be given by mouth. An example is the protein insulin, which is digested if given orally; when injected intravenously, the resultant fast action is not always desirable. Intramuscular injections are not always given for quick action; if the drug is mixed with an oil such as peanut oil, the oil is not absorbed rapidly from the injection site. The drug thus diffuses slowly from the oily solution into the muscle’s capillaries. This can take a few weeks to occur; this type of injection is known as a depot injection. The administration of drugs intravenously avoids the process of absorption, resulting in most cases in very fast action. The action of a drug given by this route may take only seconds, as is the case with the injectable general anesthetics. Nebulizers and inhalers Nebulizers and inhalers are used to administer medications to the lower respiratory passages of the body Metered-dose inhalers deliver medications in an inert propellant gas and require good hand–breath coordination. They are, therefore, not suitable for children under 5 years. Storage of drugs Nurses must be extremely aware of the storage conditions of drugs. Generally, medicines should not be exposed to sunlight, bright light, moisture or extremes in temperature. Some drugs are particularly sensitive and will rapidly deteriorate or become ineffective if subjected to these conditions. The standard storage instructions for labelling pharmacotherapeutical agents are as follows: Store below −18 °C. Store below −5 °C. Store at 2–8 °C. Store below 8 °C. Store below 25 °C.