Drugs have three names. The Chemical Name is the scientific name typically given to a drug when it’s discovered that describes the molecular structure of the drug. The Generic Name is a non-proprietary name or abbreviation of the chemical name such as Acetaminophen. Finally, the Trade Name or Brand Name is the name given to the drug by the pharmaceutical companies that make the drug. In the case of Acetaminophen, the brand name most of us are familiar with is Tylenol.
The Dose is the amount of a drug or chemical entering the body. This is usually given as mg of the chemical per kg of body weight.
Remember the Six Rights of Medication Administration; Right Medication; Right Dose, Right Time, Right Route, Right Patient, and Right Documentation.
Let’s review some terms and key concepts…
The term Affinity is used to describe the attraction between a drug and a receptor. Drugs with a High Affinity bind more easily to receptors. Drugs with a Low Affinity require a higher concentration of the drug to get a response.
The Drug Potency is the amount of the drug that’s required to produce a therapeutic response.
The Effective Dose is the amount of the drug that produces a response in 50% of the people taking it.
The Toxic Dose is the amount of the drug the produces adverse effects in 50% of the people taking it.
LD50 or the Medial Lethal Dose is the dose required to kill half the members of a tested population after a specified test duration.
The Margin of Safety or the ratio between the Toxic Dose and the Effective Dose is called the Therapeutic Index. The higher the Therapeutic Index is, the safer the drug is considered to be. In general, non-prescription drugs have a much higher Therapeutic Index than prescription drugs.
Controlled drugs are rated in the order of their abuse risk and placed in Schedules by the Federal Drug Enforcement Administration (DEA). The drugs with the highest abuse potential are placed in Schedule I, and those with the lowest abuse potential are in Schedule V. These schedules are commonly shown as C-I, C-II, C-III, C-IV, and C-V.
Schedule I drugs are considered by the government to have a high potential for abuse, no established medical use, and a lack of safety for use of the drug even under medical supervision. Examples include Heroin, LSD, Cocaine, and Marijuana.
Schedule II drugs have a High abuse potential and severe dependence liability although they do have accepted medical use but with severe restrictions. These class of drugs are available through signed prescription only and in limited quantities. Examples include Opium, Ritalin, Morphine and Methadone.
Schedule III drugs have less abuse potential than Schedule I and II, and accepted medical use by prescription only. Abuse of the drug or other substance may lead to moderate or low physical dependence or high psychological dependence. Examples include Codeine, short-acting barbiturates, amphetamines, Pentobarbital, as well as Anabolic Steroids.
Schedule IV drugs have a low potential for abuse relative to the drugs or other substances in Schedules III and accepted medical use by prescription. Abuse of these drugs or other substances may lead to limited physical or psychological dependence relative to the drugs or other substances in Schedule III. Examples include Xanax, Valium, Ativan, and Ambien.
At the lower end of the spectrum are Schedule V drugs, which are considered by the government to have a low potential for abuse, a currently accepted medical use in the United States. Abuse of these drugs can lead to a mild physical dependence. Prescriptions may not be necessary, but transactions must be recorded. An example would be cough suppressants with small amounts of codeine such as Robitussin as well as other prescription drugs with small amounts of opiates.
The Cumulative Action of drugs is the increasing effect that multiple doses of the same drug cause due to a buildup of the drug in the bloodstream.
Hypersensitivity is a reaction to a drug that is more profound than expected. This often times leads to an exaggerated immune response.
Idiosyncrasy is a reaction to a drug that is significantly different from what is expected.
Indication refers to the medical condition for which the drug has therapeutic value.
Pharmacodynamics is the study of the biochemical and physiological EFFECTS of drugs in the body. Most drugs work through interactions with receptor sites which are protein coatings found on the outer surface of the cell membrane. These receptor sites receive a signal from the body’s chemicals such as neurotransmitters, hormones and enzymes which cause a molecular event to occur within the cell. Drugs either Enhance (Agonist), Diminish (Partial Agonist), or Block (Antagonist) the generation, transmission or receipt of the signal. Generally, when a drug binds or attaches to a receptor site, a chemical reaction occurs that initiates the desired physiological or therapeutic response. Such drugs are called Agonists. Some drugs work by partially or completely blocking the chemical event through the principle of Antagonism. In such cases, a drug competes with another drug or chemical for position at a receptor site. A classic example of this is Naloxone (or Narcan) which competes with narcotic drugs. In this case Narcan would be an Antagonist.
Pharmacokinetics is the Study of the metabolism and action of drugs. How drugs enter the body, how they move through the body and how they are eliminated from the body. Once a person has been exposed to a drug, the drug must get into the body and to its target site in an active form in order to cause an effect. Naturally, the body has defenses for such events such as Membrane barriers, Biotransformation enzymes, antioxidants, and Elimination mechanisms. The acronym ADME refers to Absorption, Distribution, Metabolism (or Biotransformation) and Excretion.
Absorption is the movement of a drug from its point of entry into the body into systemic circulation. Factors that influence the rate of absorption include: the concentration of the drug, the site of absorption, the pH of the drug, the status of the person’s circulation and the solubility of the drug. Through Inhalation, the drug is readily absorbed by gases and into the blood stream via the alveoli. This is enhanced by the Large surface area of the alveolar surface, high blood flow, and the proximity of blood to alveolar air. When a drug is Ingested, absorption occurs through the GI tract. In the stomach, the drug has to compete with stomach acids. If it makes it to the small intestine, the prolonged contact time with the large surface make this good location for absorption.
Distribution is the manner in which a drug is transported from the site of absorption to the site of action. Blood carries the drug to and from its site of action, storage depots, organs of transformation, and organs of elimination. Distribution is influenced by cardiovascular function such as heart rate and blood pressure as well as physical barriers such as the blood brain barrier and the placenta barrier.
Biotransformation is the process by which drugs are inactivated and transformed into a form that can be eliminated from the body. These inactive forms are called metabolites. The rate of transformation will determine how often a drug needs to be administered to maintain its desired effect. For example, Epinephrine transforms in 3-5 minutes. Key organs in biotransformation include the LIVER (which is the most significant), the lungs, the kidneys and the intestines.
Finally, Excretion is the process of eliminating drugs from the body. This accomplished primarily through the kidneys but may also involve the liver, the lungs, intestines, sweat and mammary glands.
Potentiation is the enhancement of one drug’s effect by another drug such as the way promethazine may enhance the effect of morphine. This should not be confused with Synergism which is defined as the combined action of 2 or more drugs that is greater than the sum of the 2 drugs acting independently
Refractory is the failure of a patient to respond as expected to a certain medication.
The Routes or Sites of Exposure or Administration of a drug include; Ingestion (via the Gastrointestinal Tract), Inhalation (via the Lungs), Dermal or Topical (via the Skin) and Injection either intravenous, intramuscular or intraperitoneal (which is the injection of a substance into the peritoneum or abdomen).
The typical effectiveness of administration from the most effective route to the least effective route are IV, Inhalation, Intraperitoneal, Intramuscularly, Ingestion and finally Topical.
The Therapeutic Action of a drug is its intended action.
Tolerance is described as a decreased sensitivity or response to a drug that occurs after repeated doses. When this occurs, increased doses may be required to achieve the desired effect.
Before we get too far in discussing types of drugs, remember this rule in “general terms”. Alpha typically affects our vessels, Beta 1 typically affects our heart and Beta 2 typically affects our lungs. Think Alpha for Veins, Beta 1 we have one heart and Beta 2, we have two lungs.
MEDICATIONS THAT AFFECT THE NERVOUS SYSTEM
Let’s begin by quickly reviewing the Autonomic Nervous System. It’s separated into two main divisions: the Sympathetic and the Parasympathetic and controls blood pressure, heart and respiratory rates, body temperature, digestion, metabolism, the balance of water and electrolytes, the production of body fluids (saliva, sweat, and tears), urination, defecation, sexual response, and other processes.
In general, the Sympathetic division prepares the body for stressful or emergency situations—fight or flight. In doing so, it increases the heart rate and the force of heart contractions, opens (or dilates) the airways to make breathing easier and stimulates the body to release stored energy for increased muscular strength. The sympathetic division also causes palms to sweat, pupils to dilate, and hair to stand on end while at the same time, slowing body processes that are less important in emergencies, such as digestion and urination.
The Parasympathetic division, on the other hand, controls body process during ordinary situations—rest and digest or feed and breed. In generally, its job is to conserves and restore. When the parasympathetic takes over, it slows the heart rate, decreases blood pressure and stimulates the gastrointestinal tract to process food and eliminate waste. The energy obtained from the processed food is used to restore and build tissues during this time of rest and digest.
Parasympathetic and sympathetic divisions are often described as always in opposition to each other. Really their relationship is more complimentary. One analogy is that the parasympathetic division is like the brake while the sympathetic division acts like the accelerator. The sympathetic division functions during actions that require a rapid response and the parasympathetic division functions during actions that don’t require such an immediate reaction.
Naturally occurring Catecholamines (Norepinephrine, Epinephrine and Dopamine) act as hormones or neurotransmitters and are used to communicate primarily with the Sympathetic branch of the Autonomic Nervous System. Acetylcholine also acts as a chemical messenger communicating with the Autonomic Nervous System, but generally speaking, Acetylcholine deals primarily with the Parasympathetic branch. Nerve fibers that secrete norepinephrine are called adrenergic nerve fibers and nerve fibers that secrete acetylcholine are called cholinergic nerve fibers. Don’t get the terms Catecholamine and Cholinergic confused.
Drugs or chemicals that enter our body can act on cholinergic or adrenergic receptors which can have similar effects as Acetylcholine and Norepinephrine.
Let’s look at drugs that affect the Sympathetic Nervous System first.
Sympathetic Nervous Systems Drugs
Adrenergics are a classification of drugs used to mimic the naturally occurring catecholamines (epinephrine, norepinephrine and dopamine) OR stimulate the release of norepinepherine, thus causing a sympathetic response. When you think of Adrenergic, think adrenaline and DRY. In the eyes, pupils will be dilated. Vasoconstricion results in reduced mucous secretion in the those, decreased salivation and dry-mouth, constipation, intestines relax, bronchial dilation in the lungs, coronary artery dilation and an increase in the contractile force and rate of the heart. Therapeutically, these drugs are used to combat life-threatening disorders, which include acute attacks of bronchial asthma, shock, cardiac arrest, and allergic reactions. In addition these types of drugs are often times used in nasal decongestants and appetite suppressants.
Keeping things simple, adrenergic drugs stimulate Alpha, Beta 1 and/or Beta 2 receptor sites. In general terms; Alpha receptor stimulation will constrict vessels. Beta 1 receptor stimulation will Increase the automaticity of the heart and the heart rate, increase conductivity, increase the force of the heart contractions and releases rennin. Beta 2 receptor stimulation relaxes bronchial smooth muscles which results in bronchodilation as well as increases the conversion of stored liver glycogen to glucose for energy. One way to help remember this is to remember that Alpha affects vessels, we have 1 heart and Beta 1 affects the heart and we have 2 lungs and Beta 2 affects the lungs.
Alpha Adrenergic Agonists are used to treat HYPOtension typically in life-threatening situations through Vasoconstriction. An example is Norephinepherine also known as Levophed. Pseudoepinepherine is a sympathomimetic used as a nasal decongestant and is commonly found in Dimetapp, Sudafed, Cenafed and Triaminic.
Beta 1 Adrenergic Agonists are used to treat Bradycardia, Low Cardiac Output, Paroxysmal atrial or nodal tachycardia, Ventricular Fibrillation and Cardiac Output. An example is Dobutamine Hydrochloride also known as Dobutrex
Beta 2 Adrenergic Agonists are used to treat Acute and Chronic Bronchial Asthma, Emphysema, Bronchitis, Acute Hypersensitive or Allergic Reactions to Drugs and aids in delaying delivery in premature labor. Examples include: Albuterol Sulfate (also known as Proventil, Ventolin or Volmax), Metaproterenol Sulfate and Terbutaline.
The catecholamine Dopamine improves blood flow to the kidneys by vasodilating renal and mesenteric arteries and is used primarily in acute renal failure, heart failure and shock. An example of Dopamine is Dopamine Hydrochloride also known as Intropin. However, because dopamine cannot cross the blood-brain barrier, dopamine given as a drug does not directly affect the central nervous system, rather it does so indirectly.
Adrenergic Blocking Agents (or Antagonists) are drugs that selectively interact with Alpha and Beta Receptors to inhibit sympathetic stimulation or block the release of norepinephrine from storage sites. The depression of adrenergic nerves results in a vasodilation effect reducing peripheral vascular resistance which is why drugs in this category are mostly antihypertensive agents.
Now let’s discuss drugs that affect the Parasympathetic Nervous System.
Parasympathetic Nervous System Drugs
As we stated before, Acetylcholine acts as a chemical messenger that communicates primarily with the Parasympathetic branch of the Autonomic Nervous System. Nerve fibers that secrete Acetylcholine are called cholinergic nerve fibers.
Stimulation of cholinergic nerves is achieved either directly or indirectly. Direct acting agents (or cholinergics) activate the cholinergic receptor sites by mimicking the effects of acetylcholine. The effects of cholinergic stimulation includes: vasodilation of blood vessels; slower heart rate by decreasing the firing rate of the SA node; constriction of bronchioles, constriction of the pupils, intestinal cramps, increased secretion of mucus in the respiratory tract and an increased secretion of salvia; sweat and tears. When you think of Cholinergic, think of WET. An acronym often times used to summarize the functions of the parasympathetic nervous system is SLUDD (salivation, lacrimation, urination, digestion and defecation). In general, Cholinergics have limited medical use, although some are used to relieve urinary incontinence and in eye surgeries.
Cholinergic Blocking Agents also known as Anticholinergics are compounds which compete with and prevent acetylcholine from stimulating the receptor site and thus act as antagonists (or against) the Parasympathetic Nervous System and indirectly causing a Sympathetic Nervous System response. By blocking acetylcholine receptors Anticholinergics result in a drying effect. Results include decreased bronchial secretions, decreased salivary secretions, decreased sweating, increased heart rate by increasing conduction through the myocardium and pupil dilation. Like we stated earlier, the Sympathetic and Parasympathetic divisions are always complementing each other. When one is reduced, the other takes over. This relationship is why an Anticholinergic that blocks a Parasympathetic response indirectly results in a Sympathetic response. Common Anticholinergics include Atropine and Atrovent.
Once a cholinergic nerve is stimulated, it requires the enzyme Cholinesterase to return it to its normal resting state. Indirect stimulation of cholinergic nerves occurs by inhibiting the cholinesterase enzyme, thus permitting a build up of acetylcholine on the nerve receptor sites. As a result, acetylcholine increases in quantity with successive nerve impulses so that large amounts of acetylcholine can accumulate and repetitively stimulate receptors. Blocking cholinesterase and the accumulation of acetylcholine will cause an over stimulated parasympathetic response. Cholinesterase inhibitors are commonly found in chemical warfare nerve agents and certain insecticides. Atropine can be used as an antidote for organophosphate poisoning caused by the inhibition of cholinesterase. The atropine blocks the excess acetylcholine but does nothing to reverse the inhibition of the cholinesterase.
Remember, when you think of Cholinergic, think of WET. In the eyes, pupils will be constricted. Vasodilation results in mucous secretion in the nose, increased saliva secretions in the mouth, nausea, vomiting, abdominal cramps, diarrhea, sphincter relaxation, bronchi constriction in the lungs, coronary artery contraction and a decrease in the contractile force and rate of the heart. When you think of Adrenergic, think adrenaline and DRY. In the eyes, pupils will be dilated. Vasoconstricion results in reduced mucous secretion in the those, decreased salivation and dry-mouth, constipation, intestines relax, bronchial dilation in the lungs, coronary artery dilation and an increase in the contractile force and rate of the heart.
Other CNS Medications
Opioids are a class of Analgesics that are used to primarily to relieve moderate to severe pain associated with acute and chronic disorders such as MIs, postoperative pain or terminal cancer as well as pulmonary edema, preoperative sedation, anesthesia, cough suppression and diarrhea. Cautionary side effects include sedation, respiratory depression, and constipation.
Opiod Agonists are narcotic analgesics which include morphine or morphine like drugs such as codeine, Darvon, Demerol, fentanyl, hydrocodone and methadone.
Non Opioid Agonists are non-narcotic analgesics that some times also have anti-inflammatory and fever reducing properties. Such drugs include asprin and Non-Steroidal Anti-Inflamatory (or NSAIDS) such as ibuprophen and acetaminophen (or Tylenol).
Opioid Antagonists are receptor antagonists that act on opioid receptors by blocking the receiving signals from opioids. Naloxone (or Narcan) is a commonly used opioid antagonist that binds to opioid receptors with higher affinity than agonists but do not activate the receptors. This effectively blocks the receptor, preventing the body from responding to opiates and endorphins.
Anestetics are drugs that cause anesthesia or reversible loss of sensation. They are different than analgesics which relieve pain without eliminating sensation. Examples range from low level anestetics like Nitrous Oxide (or Nitronox) to higher level benzodiazepines such as diazepam (or valium) and midazolam (or Versed).
Sedative and Antianxiety Medications are commonly used to decrease anxiety and assist sleep by depressing the CNS system. The two main categories are Benzodiazepines and Barbiturates. As mentioned a moment ago, examples of Benzodiazepines include diazepam and midazolam. Examples of Barbiturates include Phenobarbital and Seconal. Barbiturates are typically less frequently used due to their more intense effect.
Psychiatric Medications work by increasing the amounts of the CNS neurotransmitters Norepinephrine, Dopamine and Serotonin in patients with psychiatric disorders. Such drugs are broken down into Antipsychotics, Antidepressants and Antimanics.
Antipsychotics are also known as neuroleptics because they affect the nerves. Examples include; Phenothazines (or Thorazine), Seroquel, Risperdal, and Haldol.
Depressive illness is caused by a decrease of the chemicals or neurotransmitters norepinephrine, dopamine and serotonin in the brain that are responsible for mood. Antidepressants work by stimulating chemical changes that increase the levels of these neurotransmitters. Different antidepressant medications affect one or more of these neurotransmitters. The three main categories of antidepressants are Selective Serotonin Reuptake Inhibitors, Tricyclic antidepressants and monoamine oxidase Inhibitors (or MAOIs).
Selective Serotonin Reuptake Inhibitors block the reuptake of serotonin which increases the level of serotonin in the brain. Common Selective Serotonin Reuptake Inhibitors are Celexa, Lexapro, Prozac and Zoloft.
Similar to Selective Serotonin Reuptake Inhibitors, Tricyclic Antidepressants (or TCAs) also block the reuptake of serotonin but are less specific and also block the reuptake of norepiniphrine resulting in an increase of both neurotransmitters in the brain. Examples of common Tricyclic Antidepressants include; Elavil, Adapin and Tofranil.
MAOIs increase the availability of neurotransmitters by preventing the breakdown of neurotransmitter molecules by inhibiting the activity of monoamine oxidase, which thus preventing the breakdown of monoamine neurotransmitters. Examples of MAOIs include Tranylcypromine and Phenelzine (also known as Nardil).
Antimanic drugs are used to treat bipolar disorders. Examples include lithium as well as Tegretol and Depakote which are also used to treat seizure disorders.
Anticonvulsants and Antiseizure
The goal of an anticonvulsant (often times referred to as Antiseizure) is to suppress the rapid and excessive firing of neurons that initiate a seizure. Medications used to treat seizures include, Barbiturates such as Phenobarbital, Benzodiazapines such diazepam and others such as Tegretol and Depakote.
Stimulants is a name given to several groups of drugs that tend to increase alertness and physical activity often times used in treating ADHD. Examples include Methylphenidate also known Ritalin and Metadate.
MEDICATIONS THAT AFFECT THE CARDIOVASCULAR SYSTEM
Beta-Blockers are used to decrease the workload of the heart by blocking sympathetic stimulation of the beta receptors on the SA node and myocardial cells, thus decreasing the force of the contractions and causing a reduction in heart rate. Examples include; Metoprolol , Labetalol, Sotalol and Propranolol.
Calcium Channel Blockers work by relaxing smooth muscles to provide vasodilation as well as reduce heart rate and stroke volume of the heart. Examples include; Diltiazem (or Cardizem), Verapamil and Nicardipine.
Sodium Channel Blockers work by impairing conduction of sodium ions through sodium channels used in the treatment of cardiac dysrhythmias. An example of this would be Lidocaine.
Diuretics control high blood pressure by increasing the rate of urination. Loop diuretics, such as furosemide (also known as Lasix), do this by inhibiting the body’s ability to reabsorb sodium at the ascending loop in the kidney resulting in a retention and excretion of water in the urine. Other diuretics include Thiazides such as hydrochlorothiazide as well as Potassium-sparing diuretics such as Aldactone.
Alpha-Adrenergic Blockers are used to lower blood pressure by dilating peripheral blood vessels causes a decrease in peripheral vascular resistance. Common examples include; Cardura, Minipress and Flowmax.
ANGIOTENSIN-CONVERTING ENZYME INHIBITORS (also known as ACE inhibitors)
ACE inhibitors or angiotensin-converting enzyme inhibitors, are a group of pharmaceuticals that are used primarily in treatment of hypertension and congestive heart failure. Examples include; Benazepril Hydrochloride also known as Lotensin, Captopril also known as Capoten, and Lisinopril also known as Prinvil or Zestril.
ANGIOTENSIN II RECEPTOR ANTAGONISTS
Angiotensin II receptor antagonists, also known as angiotensin receptor blockers (or ARBs), vasodilate arterioles by blocking the effects of angiotensin II, enhancing renal clearance of sodium and water. Their main use is in hypertension (high blood pressure), kidney damage due as a result of diabetes and congestive heart failure. Examples include; Losartan also known as Cozaar and Valsartan also known as Diovan.
Antiplatelet and Anticoagulant Drugs are used to prevent clot formation in patients with a-fib, pulmonary embolism, provide anticoagulation during hemodialysis, prevent clot formation post-surgery, decrease the risk of MIs in patients with atherosclerosis as well as decrease the risk of strokes. Examples include Heparin and Lovenox as well as Thrombolytics such as Retaplase, Alteplase and Streptokinase.
Nitrates are used to prevent and relieve chest pain associated with angina as well as ease the symptoms of congestive heart failure. Nitrates vasodilate blood vessels and improves blood flow which allows more oxygen-rich blood to reach the heart muscle. This also reduces the workload on the heart by reducing preload. An common example of this is Nitroglycerine.
Corticosteroids are a class of steroid hormones which are produced within the adrenal cortex. Corticosteroids are involved in a range of physiologic systems such as immune response, stress response as well as carbohydrate metabolism, regulation of inflammation, blood electrolyte levels, protein catabolism and behavior.
Glucocorticoids such as cortisol control carbohydrate, fat and protein metabolism and are anti-inflammatory by preventing phospholipid release, decreasing eosinophil action and a number of other mechanisms. Synthetic glucocorticoids are commonly used in the treatment of joint pain or inflammation such as arthritis, dermatitis, allergic reactions and asthma.
Mineralocorticoids such as aldosterone control electrolyte and water levels, mainly by promoting sodium retention in the kidney.
There are two types of Adrenocorticoids, Glucocorticoids and Mineralocorticoids.
Glucocorticoids such as Hydrocortisone and Prednisone regulate carbohydrate, fat and protein metabolism, block inflammation by preventing phospholipid release, and regulate the body’s immune response.
Synthetic glucocorticoids are commonly used in the treatment of joint pain or inflammation such as arthritis, dermatitis, allergic reactions and asthma.
Mineralocorticoids such as aldosterone control electrolyte and water levels, mainly by promoting sodium retention in the kidney.
Vitamin K antagonists (VKA) are a class of anticoagulants. They reduce blood clotting by inhibiting the action of vitamin K. The most commonly used Vitamin K antagonists is warfarin also known as Coumadin.