Introduction to Medicine for Engineers

Chapter 9: Pharmaceuticals in medicine

By Andrew Luzzi and Martin R. Prince, MD, PhD

Use of chemicals, aka "pharmaceuticals" or "drugs" or "agents" to treat disease is a major backbone of the practice of medicine. For many diseases, options for treatment are commonly categorized into surgical options or medical options where "medical treatment" is generally referring to the clever choice of the right pharmaceutical agents to make the disease go away. However, even for surgical options, treatment of the diseases always needs to be supports of pharmaceuticals. Huge texts compile the vast array of drugs which are FDA approved for use in treating diseases and even more agents can be found "off-the-shelf" at pharmacies or health food stores. One popular book, known as Physicians' Desk Reference is provided free to all doctors and clinics. This ubiquitous text has one index based on the generic names, a second index based on trade names, a third index based upon the drug categories (more on this below) and a fourth index showing the shape and color of each pill so that patients can tell you what they are taking even if they do not speak English or know the name of the drug. It is beyond the scope of an introduction to pharmaceuticals to begin delving into specific pharmaceuticals. However, it is useful to understand the categories of pharmaceutical agents which are available and to know the process of how specific agents are chosen as well as how the dose and duration of treatment are titrated to match the needs of individual patients.

9.1 Antibiotics

These are miracle drugs that can restore a person on their deathbed to normal health in short order. Hundreds of choices reflect the many different organisms which can cause infection and destruction of human tissues. Antibiotics are drugs which are used for bacterial infection. A rigorous approach for reasonably healthy patients with mild infection, not yet life threatening, is the "No bug, No drug" rule. In this approach, the infected area is swabbed or aspirated so that the bacteria can be cultured, e.g. grown on petri dishes with agar. Once the bacteria grow, small discs of various antibiotics are placed on the infested agar to determine which antibiotic is the most effective at treating that patient's infection. This antibiotic is then prescribed for the patient. Oral pills are the most tolerated but intravenous and intramuscular injection are more effective. Surface infection on the skin may be treated with an antibiotic cream.

Unfortunately, many patients/physicians are in a hurry and do not want to wait for the culture/drug sensitivity analysis to be completed. In this case, the antibiotic is chosen empirically based upon knowing the bacteria which most commonly cause that particular infection. With the empiric approach, a broad spectrum antibiotic is used, which kills a broad spectrum of bacteria in case the guess about the type of infecting one is not perfect. However, this has the disadvantage of also killing more of the patients' normal flora. Normal flora are bacteria and other microorganisms that are on the patient and in the intestines which help protect against nastier microbes as well as help with digestion and other processes.

9.2 Anti-inflammatory

Anti-inflammatory drugs, as one would expect, reduce inflammatory processes in the body. Inflammation is a natural bodily response to trauma and other stimuli. Inflammation can be beneficial, as it promotes the flow of blood and immune cells to areas where they are needed for healing or immune defense, such as areas where the body has experienced injury and disruption that allows pathogens to invade into the body. However, inflammation typically also causes pain and too much inflammation may negatively affect disease/injury treatment and healing. When there has been only minor injury with no breach of the protective skin, an anti-inflammatory drug can help prevent the body from over-reacting.

Various kinds of anti-inflammatory drugs reduce the redness, swelling, and pain associated with inflammation. Corticosteroids are produced naturally by humans in the adrenal cortex and, among many other effects, regulate inflammation. Synthetic corticosteroids are used to treat inflammatory processes that are more systemic in nature, such as arthritis, allergies, and inflammatory bowel disease. Non-steroidal anti-inflammatory drugs (NSAIDs), are another main category of anti-inflammatory medication. Over the counter (OTC) NSAIDs, such as aspirin and ibuprofen (Advil, Motrin), are used to treat a wide range of inflammatory processes ranging from arthritis to sore muscles to inflammation resulting from injury.

9.3 Painkillers (analgesics)

While anti-inflammatory drugs reduce pain by reducing inflammatory processes, other drugs, commonly referred to as pain killers, reduce pain by directly affecting the central nervous system. The most powerful prescription painkillers are called opioids, which are opium-like compounds that affect the opioid receptors in our brains and, in so doing, decrease a patient's perception of pain and increase tolerance to pain.

Opioids can be injected into patients intravenously or taken by patients orally. The method of administration of the drug, as well as the dose and specific type of drug, depends on what is causing the patient pain. Opioids may be administered intravenously to patients with severe acute pain, such as pain arising from a sickle cell crisis or abdominal pain stemming from a ruptured appendix or myocardial infarction. Patients are often prescribed opioids to be taken orally in order to manage chronic pain, which can stem from a variety of causes, and post-operative pain.

However, opioid use can have adverse effects. Patients using opioids often experience nausea, drowsiness, and constipation. Additionally, opioids are physically addicting. Therefore, healthcare providers must be careful both to administer safe doses of drugs and also recognize and discourage drug seeking behavior.

There are many different pain medicines, and each one has advantages and risks. OTC pain relievers are good for many types of pain. There are two main types of OTC pain medicines: acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs). Aspirin, naproxen (Aleve), and ibuprofen (Advil, Motrin) are examples of OTC NSAIDs.

9.4 Local anesthetics

Local anesthetics are drugs that induce temporary lack of sensation in one part of the body. Various techniques and drugs exist to induce local anesthesia, and the specific method of induction is determined by the desired outcome of the medication.

Topical anesthetics, which are one category of local anesthetics, are applied to a body surface and, by increasing the excitability threshold of the nerves in that area, numb local tissue. Topical anesthetics exist in many forms and have a wide range of applications. Cream can be applied to an arm to numb the skin before the administration of an IV, spray can be used to numb the throat before the insertion of a scope, liquid can be applied via cotton swab to the mouth before the administration of an injectable anesthetic prior to dental work, and other forms of topical anesthetic and methods of administration exist and are used for a wide range of purposes.

Nerve blocks are another broad category of local anesthetic use. Unlike topical anesthetics, which are generally applied to and affect superficial tissue, nerve blocks involve the direct injection of an anesthetic, among several other drugs, onto a nerve. In so doing, entire parts of the body, such as limbs and joints, can be relieved of sensation, resulting in less pain during certain procedures and surgeries.

A third category of local anesthetic use is epidural anesthesia. With epidural anesthesia, an anesthetic is injected into the epidural space around the spinal cord in order to numb different parts of the body. Epidural anesthesia is commonly used to provide pain relief during labor and delivery and is also commonly used to provide pain relief during operations on the lower part of the body.

9.5 General anesthetics

While local anesthetics are used to numb different parts of the body, general anesthetics are drugs that induce unconsciousness in patients. They are commonly used during more intensive and/or uncomfortable operations so that the patient does not feel any pain during the procedure or have any memory of the procedure after its completion. Under general anesthesia, patients also experience skeletal muscle relaxation which can make surgery easier.

General anesthetics are just one part of general anesthesia. Anesthesia refers to the coma-like state into which patients are induced for various reasons. The induction and maintenance of patients into a state of anesthesia is a complicated process that involves the simultaneous administration of several drugs, including sedatives, paralytics, pain killers, general anesthetics, and often others. General anesthetics can be administered through an IV or as vapors using a mask.

Various measures must be taken to ensure the safety of the patient while under general anesthesia. A physician or registered nurse monitors the administration of drugs throughout the procedure, in addition to monitoring the vital signs (heart rate, respiratory rate, temperature and blood pressure) of the patient. Also, because of the depressing effects of the anesthesia medication, patients are unable to breathe for themselves. Various methods of mechanical ventilation exist to assist the breathing of the patient while under general anesthesia.

9.6 Muscle relaxants

Muscle relaxants are drugs that act to decrease muscle contraction and relax muscles. Most muscle relaxants are referred to as "centrally acting". This means that they reduce muscular contraction by increasing the inhibitory signals sent to motor neurons by the central nervous system. These drugs are used to treat various conditions, many having to do with muscle spasms and muscle pain. Muscle relaxants are typically taken orally.

Because of their depressive effects on the central nervous system, muscle relaxants often induce fatigue and lethargy in patients. Nausea, vomiting, and other more rare side effects can also result from the use of muscle relaxants. Additionally, muscle relaxants have the potential to be abused for recreational purposes and patients occasionally become addicted. Both physicians and patients must be aware of this possibility and take measures to prevent dependence.

9.7 Anti-anxiety (anxiolytic)

Benzodiazepines are a class of drugs categorized by a similar fundamental structure that have general anti-anxiety, sleep-inducing, muscle relaxing, and calming effects. The drugs work by enhancing the function of a neurotransmitter in the brain in order to decrease the excitability of neurons. In doing so, benzodiazepines are used to treat panic disorders, anxiety disorders, and some cases of insomnia.

Like muscle relaxants, anxiolytic benzodiazepines also pose significant risk for abuse. Patients using anxiolytic benzodiazepines naturally develop a tolerance, and some patients will increase their drug use in order to receive the same effects from the drugs. It is possible to become dependent on anxiolytic benzodiazepines and go through withdrawal when usage stops

9.8 Chemoterapy

Chemotherapy treatments use cytotoxic drugs - or drugs that are toxic to living cells - to help cancer patients fight their disease. The cytotoxic drugs in chemotherapy are optimized to destroy rapidly multiplying cells occurring in cancer. Chemotherapy is administered in a variety of ways, including orally, topically, with the use of an injection, through an IV, and more. This method can successfully kill cancer cells, which are rapidly multiplying, and subsequently slow or stop cancer growth and alleviate cancer symptoms. However, the drugs also have a cytotoxic effect on healthy cells, which results in a wide range of adverse effects for the patient. Because of this, chemotherapy treatment is often given in cycles, allowing rest time so that the patient's body can recuperate and rebuild healthy cells that were killed during treatment.

Even with incorporated rest time during chemotherapy treatment, patients who are undergoing treatment experience a spectrum of side effects. As stated, chemotherapy drugs target rapidly dividing cells. Hair follicle cells, bone marrow cells, and cells in the digestive tract are all non-cancerous rapidly dividing cells that are typically affected by chemotherapy treatment. As such, patients undergoing chemotherapy typically experience hair loss, a decrease in blood cell production, and inflammation of the mucosal lining. Chemotherapy also typically induces nausea, vomiting, and fatigue in cancer patients, along with a variety of other adverse effects.

9.9 Cardiac drugs

Normal functioning of the cardiovascular system is critical to human life to ensure oxygen delivery to the brain and other organs. When a patient is critically ill and the cardiovascular system is no longer functioning properly, there are a host of pharmaceuticals (referred to as cardiac drugs) that can influence different components of this system to keep the patient alive long enough for recovery. There is a delicate balance between the pumping of the heart and the resistance in the arterioles throughout the body. During sepsis, arterioles relax, decreasing peripheral vascular resistance, causing the blood pressure to drop. To compensate, the heart needs to pump faster and more vigorously. But in many patients, the heart is already maxed out and cannot pump any harder. Epinephrine (also known as adrenaline), can stimulate the heart rate, the heart pumping power, known as inotropy, and can cause peripheral vascular arteriolar constriction to increase peripheral vascular resistance. This has the effect of increasing blood pressure. Epinephrine can also dilate bronchioles which is useful to treat allergic reactions causing bronchoconstriction.

Elements of the cardiovascular system may be controlled by alpha receptors or beta receptors. Alpha receptors mediate vasoconstriction, so drugs stimulating the alpha receptors cause vasoconstriction and raise the blood pressure. Beta receptors cause vasorelaxation and bronchodilation, so compounds that activate beta receptors cause vasodilation and lower blood pressure. Beta blockers will slow the heart rate and decrease the cardiac workload, giving the heart a rest. Beta blockers also prevent dramatic increases in heart rate due to stress, so some people use these prior to important lectures or phobic experiences. Beta 1 receptors also mediate increased cardiac output by increasing heart rate and inotropy. Beta 2 receptors mediate bronchodilation and thus beta 2 agonists are better for treating asthma and allergic reactions.

There are many pharmaceuticals which are very selective, primarily affecting only 1 element of the cardiovascular system. Hydralazine, for example, primarily causes decreased peripheral vascular resistance and can be useful for rapidly treating malignant hypertension.

9.10 Hormone replacement therapy

When an organ fails or needs to be removed, the functioning of that organ may be replaced by taking the compounds produced by that organ in the form of a pill. For example, if the thyroid gland has a suspicious nodule and is surgically removed, the patient will then have low thyroid hormone levels. This can be corrected by taking thyroxine once a day. After many bouts of pancreatitis, the destroyed pancreas will no longer produce digestive enzymes. These can then be taken orally with each meal. The islet cells in the pancreas, which produce insulin, may be destroyed, requiring the patient to take regular doses of insulin. Without insulin, fat, muscle and other cells will not transport sugar in the blood into the cell. The cells are starving and the patient is hyperglycemic. High viscosity, hyperglycemic blood gradually destroys the blood vessels, creating havoc throughout the entire patient. Older women produce less estrogen, especially after menopause. Estrogen replacement therapy preserves bone density, stabilizes menopause symptoms, e.g. hot flashes, and restores a premenopausal status to female reproductive tissues. But a side effect of estrogen replacement therapy is increased breast cancer and endometrial cancer risk, so it must be used cautiously. Other examples of hormone replacements include pituitary, adrenal, and androgens. Patients undergoing gender conversions may use hormones to alter their physical appearance, and athletes may use androgens to boost their athletic performance.