Pharm 100 - Lesson E.2

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Pharm 100 - Lesson E.2
2011-07-25 23:58:16

Lesson E.2
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  1. Over-the-counter (OTC) drugs
    • Over-the-counter (OTC) drugs are sold to the general public without a physician’s prescription based on the premise that the general public are able to diagnose mild symptoms and to select appropriate agents to treat these symptoms. In most cases this is true, but self medication can also have serious consequences. The conditions which should be satisfied when using an OTC are:
    • (1) The illness and/or symptoms are mild. Serious illness or symptoms should be treated by a physician.
    • (2) If the illness or symptoms become worse, consult a physician.
    • (3) Self medication should not exceed two weeks without consulting a physician.
    • (4) If adverse events occur, stop taking the drug immediately.
  2. Definition of OTC Drugs
    Any drug that can be purchased without a physician’s prescription. The general public oftendoes not consider these agents as drugs. A substance that can be purchased in the supermarket is notconsidered a drug by the general public. In reality, OTC products are drugs and can cause toxicities and drug interactions with prescription drugs
  3. Agents included are:
    Internal analgesics, cough and cold remedies, vitamins, laxatives, antacids, antihistamines,topical creams and ointments, sleeping aids, sunscreens, antacids, anti-acne agents, etc. There areseveral thousand preparations available for the treatment of a myriad of symptoms. The Canadianconsumer spends vast sums of money on these products.
  4. Role of Government
    The sale of OTC drugs is controlled by a section of the Food and Drug Act. The Act controls safety, efficacy, advertising and sale of these products. All OTC drugs must undergo rigid safety assessment. A number of recent additions to the market place were available by prescription before being released onto the OTC market. The of OTC products is often questionable. Not all have been subjected to controlled clinical trials, but are available because they have been used for years. The only appropriate manner for assessing the efficacy of any drug are controlled clinical trials.
  5. (a) Acetylsalicylic acid (ASA):
    • This compound has been widely used for well over a century. The compound possesses analgesic (reduces pain), antipyretic (reduces fever), and anti-inflammatory (reduces inflammation)properties. In appropriate doses, the drug is effective for pain, fever and inflammation.
    • The mechanism of action of ASA for all three effects is that it inhibits synthesis of prostaglandins, endogenous substances which enhance the mediation of pain, fever and have a role in inflammation.
    • The major toxicity of ASA is gastric irritation which occurs in 2% of the population. ASA breaks down the mucosal protective barrier in the stomach and leads to irritation and increased bleeding. This is a serious problem when ASA is taken chronically in high doses. Enteric coated ASA tablets will reduce the gastric irritation, but the onset of action is slow and are not useful for relief of pain but are useful in chronic inflammation. An enteric-coated tablet will not dissolve in the acid of the stomach, but will in the more alkali media of the intestine.
    • Other toxicities include tinnitus (ringing in the ears) (high doses). ASA is associated with Reyes syndrome in children when it is given during fever. Acetaminophen is the drug of choice in children with fever; Reyes syndrome is a rare but serious illness affecting the central nervous system.
  6. ASA
    • True allergic reactions to ASA are rare but do occur. These people are also allergic to tartrazine(yellow food colour). They must avoid salicylate-containing products.
    • ASA poisoning in children and adults is common. ASA-containing products, all OTC productsfor that matter, should be stored out of the reach of children. Prevention is much safer than thetreatment.
    • Buffered ASA preparations are no more effective than ASA alone. These products contain ASAand an antacid to neutralize the acid in the stomach and thus reduce gastric irritation. They do notcontain sufficient antacid and are not any better than a conventional ASA tablet.
    • Effervescent analgesics (Alka Seltzer) contain ASA and a high concentration of sodium in theform of the systemic antacid (sodium bicarbonate) and thus should be used infrequently. Theseproducts are considered to be an analgesic as well as an antacid. The high concentration of sodiummay be detrimental to an individual with hypertension or kidney disease. These people should avoidthese products. A healthy individual may use effervescent analgesics, provided the use is infrequent. However, it is preferable to use an analgesic and an antacid as separate entities.
  7. Acetaminophen:
    • Acetaminophen was first introduced into therapeutics in 1877 but did not gain popularity untilthe 1950’s. Acetaminophen is an analgesic and antipyretic, and is equal in efficacy to ASA for thesetwo effects. Unlike ASA, acetaminophen is not anti-inflammatory.
    • The mechanism of action is similar to that of ASA, i.e. it inhibits prostaglandin synthetase, theenzyme responsible for the formation of postaglandins.
    • Acetaminophen is the drug of choice in cases where ASA causes G.I. irritation and in febrileconditions in children and young adults (acetaminophen is not associated with Reyes syndrome). Acetaminophen is available in a liquid preparation and is convenient for use in children.
    • At therapeutic doses, acetaminophen is very well tolerated; it does not cause gastric irritation. Acetaminophen overdose can lead to fatal liver injury. The individual usually consumes at least 5 to10 grams (20 tablets) or more. There is some evidence that liver injury can occur with largetherapeutic doses if taken for a long time. Alcoholics and individuals with liver disease are moresusceptible to the liver toxicity
  8. Ibuprofen:
    • Ibuprofen is a non-steroidal, anti-inflammatory agent which appeared as an OTC product in theearly 1990’s. Ibuprofen is an effective analgesic and antipyretic as well as an anti-inflammatorycompound. Two hundred mg of ibuprofen is more effective than 325 mg of ASA in a number ofconditions, including dental pain and menstrual pain. As an anti-inflammatory, it is probably the mostefficacious OTC anti-inflammatory agent on the market. The mechanism of action of ibuprofen is areversible inhibition of the synthesis of prostaglandins.
    • The adverse effects of ibuprofen include gastric irritation (less than that caused by uncoatedASA), skin rash, dizziness, blurred vision, and fluid retention. Ibuprofen is at least as well tolerated asASA. Special care should be taken by the elderly with all OTC analgesics.
  9. (d) Combination products:
    ASA, acetaminophen and ibuprofen are often used in combination with other ingredients andanalgesics. A popular combination is either ASA or acetaminophen with codeine and caffeine. Therationale for these mixtures is to obtain additional analgesic effects from drugs which act by differentmechanisms. ASA and acetaminophen act peripherally (sensory pain nerves) and codeine acts at thelevel of the central nervous system (brain and spinal cord). Acetaminophen, ASA and codeine incombination is a “rational mixture”, e.g. “222”, but the dose of codeine is small and increased efficacyover ASA alone has not been fully documented. Caffeine can also augment the analgesic response ofASA and acetaminophen. In most cases, a single-ingredient product is preferred; acetaminophen,ASA or ibuprofen are effective in relieving mild to moderate pain, fever, and inflammation (ASA andibuprofen).
  10. (e) Topical analgesics:
    • Most pain is best treated with an internal analgesic, but there are topical products available forthe relief of pain associated with minor sprains and overworked muscles. Examples of these agentsare: Absorbine Jr., Deep Heat Rub, Ben Gay, and capsicum.
    • These preparations contain camphor, menthol, methylsalicylate, capsicum and turpentine oils. These agents are all counter-irritants and cause vasodilation and a feeling of warmth. Local warmthmay act as an analgesic, but a heating pad may be as effective. Camphor and menthol also block thesensory pain receptors and thus diminish the pain at its source. Most of these preparations are lesseffective than internal analgesics, but may be effective for mild conditions. Do not use on brokenskin. Some preparations incorporate ASA into a gum which is chewed for a sore throat, e.g.Aspergum. ASA is released too slowly to reach therapeutic plasma levels. Aspergum has causederosions of the buccal mucosa and has nothing to recommend its use
  11. (f) Generic versus brand name:
    Over-the-counter products, including analgesics, are available as brand name products (Aspirin)or as a generic product, e.g. a house brand. Generics have a reputation of performing poorly. Thisdates back to the 1960’s and early 1970’s when indeed there were problems. All generic productswhich are on the Canadian market in 1998 must meet the same standards as the brand name products. The consumer should have full confidence in generic products.
  12. Drugs for the Treatment of the Common Cold
    • There is no known cure for the common cold. Treatment is directed at relieving the symptoms. The drugs most commonly used are: decongestants, antitussives, antihistamines, expectorants, andanalgesics.
    • Cold preparations are often termed “shotgun” preparations containing a variety of substances. It is prudent to examine each component of a cold preparation and try to distinguish fact from fiction.
    • It is interesting to note that cold preparations are no longer recommended for children under 6years of age. These preparations have led to deaths in some young children. The manufacturers havevoluntarily removed these products from the market. Apparently the multiple ingredient products ledto overdose as either too high a dose was given or multiple products were used.
  13. (a) Antihistamines:
    • Drugs which block the histamine receptor (H1) and prevent histamine from producingvasodilation and inflammation.
    • These drugs do not alter the course of a cold, but may alleviate some symptoms if there is anallergic component to the cold. The question which remains unanswered is the extent to whichhistamine is released in a cold. There is very limited evidence that they are of major benefit.
    • Most antihistamines have anticholinergic properties (atropine-like) and this may aid in reductionof secretions. Anticholinergics (atropine) decrease nasal and salivary secretions. In terms of efficacy,antihistamines have a very limited role in alleviating the symptoms of a cold.
    • Antihistamines can cause drowsiness, especially the older preparations. The newerantihistamines cause less sedation.
  14. (b) Decongestants:
    • These compounds are all "-adrenergic receptor stimulants (agonists), and when they activate the" receptor, they cause vasoconstriction and a reduction in congestion
    • Phenylephrine, and pseudoephedrine sympathomimetic " receptor agonists are the agents mostcommonly used. Phenylpropanolamine was withdrawn from the market as it caused strokes in youngwomen. Although a rare event, it was deemed a serious event, justifying the removal from the market.
    • Doses which are orally effective as decongestants may also alter blood pressure and redistributeblood flow, a problem in hypertensive subjects. Doses used in cold preparations are usually too low tobe fully effective.
    • These agents are best applied locally (nose drops). 0.5% Phenylephrine is an effectivedecongestant. Long-acting preparations are best. Use should not exceed seven days.
    • Problems with local decongestants include rebound congestion; long-term use leads to chronicrhinitis and local irritation. These agents are effective in that they will reduce symptoms (congestion). Long-term use should be avoided. Occasional use of these agents is acceptable; theyrelieve symptoms and toxicities are rare. The oral preparation of choice is pseudophedrine. It iseffective and does not cause CNS excitation as occurs with phenylpropanolamine and phenylephrine
  15. (c) Cough suppressants:
    • Cough is often due to bronchial and/or throat irritation. Cough is a complex event involvingsignals from the bronchioles which are processed by the cough centre in the medulla (a region of thebrain). Centrally-acting cough suppressants block the processing of the information in the medulla,hence reducing the frequency of the cough. Peripheral cough suppressants block the nerve endings inthe throat and bronchioles.
    • Codeine and dextromethorphan HBr are two widely used, centrally-acting (medulla) coughsuppressants.
    • Codeine – 30 mg of codeine can suppress the cough centre. Most OTC preparations contain 8mg/dose, a dose which is ineffective. This dose is limited as codeine can cause dependence (codeineis a narcotic opiate).
    • Dextromethorphan HBr – 30 mg is an effective cough suppressant. Most preparations contain7.5 mg/5 ml, but there are preparations which contain therapeutic doses of the drug. Dextromethorphan HBr does not cause dependence and is preferred to codeine. The initial questionwhich should be answered: Is it rational to suppress the cough? Productive cough usually should notbe suppressed, but a non-productive cough should be suppressed. A non-productive cough is alsoknown as a dry cough, whereas a productive cough is effective at clearing the airways of mucus andhence is not suppressed.
    • Peripheral antitussives, camphor and menthol are added to vaporizers or rubbed on the throat andchest. The efficacy of these agents are questionable. They may exert a small response to inhibitperipheral nerves in the throat, but the placebo response is likely to be greater. On the other hand,they do no harm
    • All antitussives have a 30 to 40% placebo response. The agent of choice is a full therapeuticdose of dextromethorphan Hbr.
  16. (d) Expectorants:
    • Expectorants are substances that stimulate secretions in the bronchial tree and loosen the phlegmin the upper airway passages. The agent most commonly used is glyceryl guaiacolate – it is ofquestionable value. The dose in OTC preparations is far too low to be effective. There is controversyover whether full therapeutic doses produce any beneficial effect. These agents are claimed to reducethe viscosity of the sputum by increasing secretions.
    • Clinical trials have not demonstrated a good response. Other agents that have been used areammonium chloride and potassium iodide. There is nothing to recommend any of these agents
  17. (e) Analgesics:
    Analgesics are effective in reducing the fever and the achy feeling associated with the cold. Drugs of choice are ASA or acetaminophen; acetaminophen may be a better choice. They are usefulfor fever and as analgesics. They are better taken as single entity products.
  18. (f) Cold therapy:
    • What do the medical experts for Consumers Union suggest?
    • – Rest
    • – get plenty of rest
    • .– Fluids
    • – the patient should drink plenty of fluids.
    • – Analgesics and antipyretics
    • – acetaminophen would be a good choice for fever and as ananalgesic.
    • – Chicken soup? There have been claims that chicken soup may have a beneficial effect on thecold. The efficacy has not been tested in a clinical trial, but would one dare to argue with theefficacy of Mom’s chicken soup?
    • The recommendation would include, fluids, rest and acetaminophen. If congestion is a problem,short-term use of pseudophedrine or a similar agent would be useful. Dextromethorphen would beuseful if the cough is troublesome and non-productive. All drugs should be taken as single-entityproducts.
  19. Antitussives
    • The comments made earlier under cold preparations apply to antitussives when used as a single-entityagent. These preparations are intended to suppress cough. They may contain a large number ofingredients, including alcohol, sugar, codeine or dextromethorphan, and an expectorant, usuallyglyceryl guaiacolate or ammonium chloride.
    • OTC antitussives usually do not contain sufficient quantities of the active ingredients to be effective.
    • The preparation of choice is one with a therapeutic dose of dextromethorphan HBr and no otheringredient. Some OTC antitussives contain a large amount of alcohol and individuals may ingest themixture for the alcohol content.
  20. Mouth Washes and Lozenges
    • Mouth washes and lozenges are used to control bad breath and treat sore throats. Mouth washescontain an antiseptic, e.g. phenols, benzoic acid or cetylpryridinium chloride.
    • The contact time with organisms in the mouth is too short for these agents to kill germs “by themillions” and their efficacy as an antibacterial agent is questionable. They are best considered as acosmetic. Good oral hygiene may prevent bad breath and the need for a mouth wash. Some of themouth washes and rinses are advertised as preventing plaque. They may indeed have a small effect,but should not take the place of good oral hygiene and visits to the dentist.
    • Lozenges contain an antiseptic and a local anesthetic and are intended to relieve the pain of a sorethroat. The local anesthetic may provide some relief, but the major therapeutic benefit obtained is dueto the increase in salivary secretions produced by these agents (keeps throat moist). However, anyhard candy is just as effective. The antiseptic is not considered effective. On the other hand, they donot produce any toxicities.
  21. Sleeping Preparations
    • Sleep aid preparations are extended to help an individual fall asleep or to relieve sleeplessness. Themain ingredients are an antihistamine which has sedative properties (e.g. doxylamine ordiphenhydramine) and an analgesic (usually acetaminophen).
    • There is general agreement in the literature that these “sleep aids” are of little value in treatinginsomnia. The drug placebo differences in most studies are small. Non-pharmacological methodsshould be tried first, e.g. limiting caffeine, relaxing before bedtime, a hot milk drink, and reading.
  22. Hay Fever Preparations
    • About 15% of Canadians suffer from hay fever or more properly named, allergic rhinitis. Hay feveris an antibody-mediated inflammatory disease of the nasal mucous membranes. If a geneticallysusceptible individual is exposed to an allergen (e.g. pollen), they develop antibodies to the allergen. Subsequent exposure to the allergen allows the allergen to bind to the antibody on cell surfaces andthis reaction will cause the cell to liberate histamine and other substances that cause local dilation ofthe small blood vessels. This leads to congestion and a runny nose. As one of the main substancesreleased is histamine, the antihistamines are drugs of choice in treating hay fever. They are effectivebut will not alleviate all the symptoms. If congestion is severe, a decongestant may be used for a shortperiod of time. The first-generation antihistamines all cause sedation and drowsiness. Most also haveanticholinergic properties (atropine-like) and produce a dry mouth, etc. The second-generationantihistamines (e.g. cetirizine and loratidine) do not produce sedation and are the preferred agents.
    • Preparations such as Dristan, which contain antihistamines, decongestants and analgesics should notbe used. Individuals who suffer from hay fever would be well advised to try to avoid exposure to theallergen, e.g. ragweed pollen.
    • Decongestants should be used with caution in treating symptoms of hay fever. Long-term use ofdecongestants, especially sprays, will produce chronic rhinitis. Occasional use is acceptable, butrebound congestion will occur (see cold preparations).
  23. Poison Ivy
    • Poison ivy, poison oak and poison sumac are responsible for many cases of contact allergic dermatitiseach year. The allergenic component is a resin found mainly in the leaves of the plants. Contact withthe resin in a sensitized individual leads to a red, itchy eruption (inflammatory response).
    • Poison ivy, as well as other offending plants, are best avoided. If contact does occur, washing thearea with Tide detergent, as soon as possible, will bind and remove the resin.
    • Calamine lotion gives temporary relief if exposure is mild. Calamine lotion is an astringent andprevents the itching, but does not modify the inflammatory response. 0.5% hydrocortisone ointment isa topical anti-inflammatory agent that is effective. This compound is more effective than calaminelotion as it can prevent some of the inflammation produced by the poison ivy resin. It is the preferredOTC agent for any inflammatory condition that is to be treated topically.
  24. Insect Bites
    Insect bites (e.g. bees) contain a venom which produces a local inflammatory response similar to thatdescribed for poison ivy. Treatment of mild insect bites in the non-allergic person is identical to thatfor poison ivy. Calamine lotion and 0.5% hydrocortisone cream are agents most widely used. Coldcompresses may be beneficial to prevent the spread of venom from bee stings. A word of caution –there are individuals who are very sensitive to bee stings. One or two bee stings may lead to a lifethreatening reaction. These individuals should carry epinephrine, which is usually prescribed by aphysician.
  25. Sunscreens
    • Solar energy emits UVA, UVB and UVC radiation. UVC (200-290 nm) is screened by the ozonelayer. UVB (290-320 nm) is responsible for sunburn and tanning, and is also implicated in cancer. UVA (320-400 nm) is responsible for drug photosensitivity, immediate pigment darkening reaction,and also contributes to sunburn. It has been estimated that about 75% of some forms of skin cancerare caused by UV radiation.
    • Sunscreens contain compounds that are absorbed into the stratum corneum (outer layer of the skin)and absorb or scatter UV energy and prevent if from reaching the dermis (lower layer of skin).
    • The agents used are: para-aminobenzoic acid derivatives, benzophenone and cinamic acids.
    • Sun protection factor (SPF):
    • SPF = minimum erythema dose (UV) of sunscreen-protected skin /// minimum erythema dose (UV) of unprotected skin
    • Minimum erythema dose is the time of exposure to UV radiation that will cause a burn or reddeningof the skin.
  26. Choice of sunscreen will depend on:
    • – Skin type. If the skin is very fair, it will burn quickly and will need a product with goodprotection (SPF 15). If the person has dark skin, they will require less protection.
    • – Type of activity will determine choice of the product. Swimming and water skiing require awater-insoluble product. Mountain climbers and skiers need a higher SPF product as the UV isgreater at higher elevations
    • .– Site of application (lips and nose versus arms). The lips and nose have a thin stratum corneumas compared to the arms and require a sunscreen with a higher SPF.
    • – Condition of the skin. If the skin is dry, a cream is a good choice. If the skin is oily and theindividual is prone to acne, a gel or alcoholic solution would be a good choice.
  27. Antacids Systemic and non-systemic.
    • Systemic antacid, e.g. sodium bicarbonate, is absorbed by the G.I. tract and can cause systemicalkalosis. Calcium carbonate is also absorbed (about 10%) and can increase Ca2+ load and is used as asource of calcium.
    • Non-systemic antacid is not absorbed and does not cause systemic alkalosis. Aluminum hydroxide –very little absorbed. Magnesium from magnesium hydroxide is absorbed to the extent of 5%.
    • Conclusion: Antacids are useful for epigastric distress (heartburn) or excess acid. Use should belimited to a few days or a week, and if symptoms persist, a physician should be consulted.
  28. (a) Sodium bicarbonate:
    • Sodium bicarbonate is very widely used by the public in home remedies. It very rapidly neutralizesacid in the stomach.
    • Disadvantages: (i) it causes systemic alkalosis; (ii) it liberates CO2 which can cause gastric distentionand may cause perforation of the ulcer; and (iii) sodium may be retained and hypertension may beaggravated.
  29. (b) Aluminum hydroxide:
    • Aluminum Hydroxide is a non-systemic antacid that is in the form of insoluble complexes and thushas a slow onset of action.
    • It acts as a demulcent, i.e. it coats the mucosal lining of the stomach, protecting it from the acid. Oneof the more popular antacids.
    • Disadvantages: (i) aluminum hydroxide forms phosphates in the intestine and thus can decreasephosphate absorption (may lead to osteomalacia, which is loss of bone calcium); (ii) aluminumhydroxide decreases absorption of the tetracyclines and anticholinergic agents; and (iii) causesconstipation
  30. (c) Magnesium hydroxide (Milk of Magnesia):
    • Magnesium hydroxide is widely used as an antacid and cathartic. It is a non-systemic antacid. Magnesium hydroxide reacts with acid in the stomach very rapidly and has a more rapid onset ofaction that aluminum hydroxide. It has good neutralizing capacity.
    • Disadvantages: (i) cathartic action; and (ii) some of the magnesium ions can be absorbed andnormally this is quickly excreted by the kidney. However, in cases of poor kidney function,magnesium ion can be retained and magnesium toxicity may result (neurological and cardiovascularimpairment).
  31. (d) Magnesium trisilicate:
    • Non-systemic. Slow onset of action. The gelatinous consistency of the silicons in the stomach isthought to provide a physical barrier against the acid.
    • Disadvantages: (i) large doses are required to raise gastric pH above 2.5 and at these doses will oftencause diarrhea; and (ii) magnesium ion can be absorbed and lead to toxic effects.
  32. (e) Antacid mixtures:
    To overcome the constipating effects of aluminum hydroxide and the cathartic action of themagnesium antacids, these two types of antacids are often combined in a single preparation.
  33. (f) Antacid therapy:
    The objective of antacid therapy should be to hold the pH of gastric contents at about 4. This meansproper dosing of antacids. The dose should be based on the rate of acid secretion as required forsymptoms. Avoid systemic antacids containing sodium bicarbonate. The aqueous suspensions aremore affective than tablets.
  34. H2 Antagonists
    • Histamine is involved in the release of gastric acid. The histamine receptors in the acid secretingcells of the stomach are distinct from those which cause allergies. The receptor in the stomach hasbeen designated H2. Famotidine and ranitidine are relatively new drugs which block the H2 receptorsand reduces the amount of acid secreted. These agents are more effective than antacid in reducingacid and are more convenient to take. Antacids are usually taken every three hours and Famotidineonce a day.
    • Famotidine and ranitidine are free of major adverse effects. Skin rashes, headache and confusionhave been reported but are infrequent.
  35. Cathartics and Laxatives
    • Laxative effect: Excretion of a soft formed stool, may have increased peristalsis or increasedhydration of the stool.
    • Cathartic effect: Implies a more fluid evacuation. The effect always involves increased motoractivity of the G.I. tact.
  36. (a) Stimulant cathartics (also called contact cathartics)
    • They all increase motor activity of the intestine and can cause intestinal cramps. They increasemucus secretion and increase secretion of water and electrolytes into lumen of G.I. tract.
    • Examples of stimulant cathartics:
    • i. Castor oil.
    • ii. Phenolphthalein – major site of action is the colon.About 15% of an oral dose is absorbed and can cause serious toxicities, e.g. severe enteritis,rash, and jaundice. Not recommended.
    • iii. Bisacodyl – acts on the colon.Very effective.About 5% of an oral dose is absorbed; however, the major undesirable effect observed has beenexcessive cathartic action resulting in fluid and electrolyte deficits.
    • iv. Anthroquinone cathartics – cascara sagrada and senna are available but are not recommended.
  37. (b) Saline cathartics:
    • Examples are magnesium sulfate (epson salt).
    • Mechanism of action: These salts are slowly and incompletely absorbed from the digestive tract andretain water by osmotic forces. Intestinal transit is increased indirectly. They may enhance secretionof cholecystokinin, a substance which may enhance intestinal motility.
    • Undesirable effects: (i) dehydration, and (ii) magnesium ion may be absorbed leading to toxicity
  38. (c) Bulk-forming laxatives:
    • Polysaccharides, e.g. methylcellulose. Dietary fibre and bran are included in this category.
    • Mechanism of action: These polysaccharides swell in water to form an emollient gel or viscoussolution and thus serve to maintain soft stools. Intestinal microflora may metabolize thepolysaccharides and these products may contribute to the osmotic effect in the gut.
    • These indigestible bulk substances may indirectly stimulate peristalsis.
    • The effect is seen in 12-24 hours but full effect is seen in 2 or 3 days after therapy has begun. Theseare the preferred laxatives for most indications.
  39. (d) Emollient laxatives:
    • These agents soften stools without stimulation of peristalsis.
    • 1. Surface active agents (e.g. dioctyl sodium sulfosuccinate):
    • Mechanism of action: These compounds are believed to act by lowering surface tension and allowingwater to penetrate the fecal mass.
    • Toxicity: Large doses may cause nausea and vomiting.
    • 2. Mineral oil:
    • Mechanism of action: Mineral oil softens stools by retarding the absorption of water.
    • Toxicity: (i) mineral oil will decrease absorption of fat soluble vitamins (A, D, E and K); (ii) duringoral administration, mineral oil can gain access to the lungs and cause “lipoid pneumonia”; and (c)mineral oil may inhibit gastrointestinal reflex mechanisms and prevent complete evacuation of thebowel. For these reasons mineral oil should not be used.
  40. (e) Uses of cathartics and laxatives:
    • 1. Constipation.
    • 2. In conjunction with anthelmintics to remove helminths.
    • 3. Prior to radiological examination.
    • 4. Prior to bowel surgery.
    • 5. They may be used to soften stools in patients suffering from C.V. disease or hemorrhoids.
    • Abuses: These compounds are readily available as over-the-counter preparations and one finds that alarge number of people abuse these drugs.
    • Dangers of Abuse: (i) spastic colitis and other functional disturbances can result from long-term use,and (b) water and electrolyte disturbances are often observed.
  41. Antidiarrheal Agents
    Diarrhea, unlike constipation, can be a serious problem, especially in young children and in theelderly. The major problem is dehydration. Mild self-limiting diarrhea can be treated with agents thatabsorb water such as kaolin and pectin. Severe or diarrhea which is not self-limiting should be treatedby a physician. Specific therapy might include antibiotics and intravenous fluids to replace fluids andelectrolytes.
  42. Antidiarrheal Agent classes
    • Adsorbents – Kaolin and pectin (Kaopectate and related products). Add bulk to the G.I. tract andmay absorb toxins. The absorbents are useful to control the acute symptoms of self-limiting diarrhea.
    • The other agent which is effective is Loperamide. This compound is a synthetic opioid that does notpenetrate into the central nervous system. It inhibits peristaltic activity by acting on the muscles of theG.I. tract, thus reduces cramps. It is effective for traveller’s diarrhea as it inhibits cramps, and shouldbe carried by travellers. It is the drug of choice. It should be used cautiously in infectious diarrhea asthe organism is not expelled and may injure the mucosa.
    • Preparations containing antibiotics, atropine, etc., should not be used.
  43. Drug Interactions with OTC Preparations
    • OTC preparations can produce a number of drug interactions with other drugs.
    • 1. Antihistamines are CNS depressants and will cause additive CNS depression with alcohol,narcotic analgesics and other CNS depressants.
    • 2. Decongestants – sympathomimetics are contraindicated (should not be used) with monoamineoxidase inhibitors. Monoamine oxidase inhibitors will prevent the metabolism of thedecongestant and hence increase its concentration in the body and the response is exaggerated.
    • 3. ASA given with oral anticoagulants may produce bleeding. ASA displaces some drugs fromplasma protein binding sites. In addition, ASA prevents platelets from adhering to each other. Platelets adhering to each other is necessary to stop a cut from bleeding.
    • 4. Antacids will interfere with absorption of some drugs, e.g. tetracyclines. Antacids will bind tothe tetracyline preventing absorption.
    • 5. Mineral oil used as a laxative will retard the absorption of a number of drugs. Mineral oil is notabsorbed and any drug that is dissolved in the mineral oil will not be absorbed.
  44. Selection of an OTC Product
    • 1. Select the product that has the simplest formulation (single ingredient).
    • 2. Select a product with a therapeutically effective dose.
    • 3. Select a product that lists all the ingredients and their amounts.
    • 4. Select a good generic, if available.
    • 5. Be wary of gimmicks. Fancy preparations such as Bufferin have no added benefits overconventional products
    • 6. Select the appropriate dosage form, e.g. liquid for children. Palatability must be acceptable.
  45. What over-the-counter drugs should be readily available?
    • 1. Ibuprofen as an anti inflammatory.
    • 2. Acetaminophen as an analgesic and antipyretic.
    • 3. 0.5% hydrocortisone cream.
    • 4. A second generation antihistamine.
    • 5. Famotidine or an antacid.
    • 6. Kaolin and pectin.
    • 7. Pseudoephedrine.
    • 8. Rubbing alcohol to cleanse wounds.
    • 9. Dextromethorphan HBr
    • 10. Loperamide.
    • The list would vary depending on the needs of the individual. The ten products listed would besufficient for most occasions.