Flashcards in Lesson E2 - Over-the-Counter (OTC) Drugs Deck (37):
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.
Any drug that can be purchased without a physician’s prescription. The general public often
does not consider these agents as drugs.
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.
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
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
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
ASA is associated with Reyes
syndrome in children when it is given during
An additional use for ASA is in the prevention of strokes and myocardial infarcts. Low dose
ASA has been shown to reduce the risk of these serious diseases. The mechanism is to inhibit
platelet aggregation and hence
Acetaminophen was first introduced into therapeutics in 1877 but did not gain popularity until
the 1950’s. Acetaminophen is an analgesic and antipyretic, and is equal in efficacy to ASA for
these two effects. Unlike ASA, acetaminophen is not
The mechanism of action is similar to that of ASA, i.e. it inhibits prostaglandin synthetase, the enzyme responsible for the
formation of postaglandins.
At therapeutic doses, acetaminophen is very well tolerated; it does not cause
Ibuprofen is a non-steroidal, anti-inflammatory agent which appeared as an OTC product in the
early 1990’s. Ibuprofen is an effective analgesic and antipyretic as well as an
The mechanism of
action of ibuprofen is a reversible
inhibition of the synthesis of prostaglandins.
This recent addition to the OTC group of analgesics, is an effective analgesic, antipyretic and
anti-inflammatory agent. It may well emerge as the most effective OTC anti-inflammatory agent
available. It is an inhibitor of
ASA, acetaminophen and ibuprofen are often used in combination with other ingredients and
analgesics. A popular combination is either ASA or acetaminophen with codeine and caffeine.
The rationale for these mixtures is to obtain additional analgesic effects from drugs which act by
different mechanisms. ASA and acetaminophen act peripherally (sensory pain nerves) and
codeine acts at the level of the central nervous system (brain and spinal cord). Acetaminophen,
ASA and codeine in combination is a “rational mixture”, e.g. “222”, but the dose of codeine is
small and increased efficacy over ASA alone has not been fully documented.
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,
Drugs which block the histamine receptor (H1) and prevent histamine from producing
vasodilation and inflammation
Most antihistamines have anticholinergic properties (atropine-like) and this may aid in reduction
of 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
These compounds are all α-adrenergic receptor stimulants (agonists), and when they activate the
α receptor, they cause vasoconstriction and a reduction in
congestion. Phenylephrine, and pseudoephedrine sympathomimetic α receptor agonists are the agents most
Problems with local decongestants include rebound congestion; long-term use leads to
rhinitis and local irritation.
Codeine and dextromethorphan HBr are two widely used, centrally-acting (medulla) cough
Expectorants are substances that
stimulate secretions in the bronchial tree and loosen the phlegm in the upper airway passages. The agent most commonly used is glyceryl guaiacolate – it is of
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
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
reddening of the skin
Systemic antacid, e.g. sodium bicarbonate, is absorbed by the G.I. tract and can cause systemic
alkalosis. Calcium carbonate is also absorbed (about 10%) and can increase Ca2+
load and is
used as a source of calcium.
Non-systemic antacid is not absorbed and does not cause
Sodium bicarbonate is very widely used by the public in home remedies. It very rapidly
neutralizes acid in the stomach.
Aluminum Hydroxide is a non-systemic antacid that is in the form of insoluble complexes and
thus has a
slow onset of action.
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 of
action that aluminum hydroxide. It has
good neutralizing capacity.
Histamine is involved in the release of gastric acid. The histamine receptors in the acid secreting
cells of the stomach are distinct from those which cause allergies. The receptor in the stomach
has been designated H2. Famotidine and ranitidine are relatively new drugs which block the H2
receptors and reduce the amount of acid secreted. These agents are more effective than
in reducing acid and are more convenient to take
Excretion of a soft formed stool, may have increased peristalsis or increased
hydration of the stool.
Implies a more fluid evacuation. The effect always involves increased motor
activity of the G.I. tact.
Adsorbents – Kaolin and pectin (Kaopectate and related products). Add bulk to the G.I. tract
and may absorb toxins. The absorbents are useful to control the acute
symptoms of self-limiting
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
monoamine oxidase inhibitors. Monoamine oxidase inhibitors will prevent the metabolism
of the decongestant 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
from plasma 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 to the tetracyline preventing absorption.
5. Mineral oil used as a laxative will retard the absorption of a number of drugs. Mineral oil
is not absorbed and any drug that is dissolved in the mineral oil will not be absorbed
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 over
6. Select the appropriate dosage form, e.g. liquid for children. Palatability must be