Pharmacology is the study of how medicines work in the body and how they are used safely to treat disease. This cheat sheet helps students understand drug actions, dosing, routes of administration, side effects, and safety checks. These basics are important for anyone studying health science, nursing, medicine, pharmacy, or emergency care.
Knowing the language of pharmacology makes medication information easier to read and apply.
Key Facts
- Pharmacokinetics describes what the body does to a drug through absorption, distribution, metabolism, and excretion, often remembered as ADME.
- Pharmacodynamics describes what a drug does to the body, including receptor binding, therapeutic effects, and toxic effects.
- The basic dose formula is dose to give = desired dose / available dose x quantity.
- The oral route is convenient but usually has slower onset because the drug must pass through the digestive system before reaching the bloodstream.
- The intravenous route delivers medicine directly into the bloodstream and usually has the fastest onset.
- A drug's half-life is the time required for the amount of drug in the body to decrease by 50%.
- Therapeutic index compares a drug's effective dose to its toxic dose, and a narrow therapeutic index means careful monitoring is needed.
- The six rights of medication administration are right patient, right medication, right dose, right route, right time, and right documentation.
Vocabulary
- Pharmacology
- Pharmacology is the study of drugs, including how they work, how the body processes them, and how they are used safely.
- Pharmacokinetics
- Pharmacokinetics is the study of how a drug is absorbed, distributed, metabolized, and excreted by the body.
- Pharmacodynamics
- Pharmacodynamics is the study of how a drug affects the body and produces its effects.
- Therapeutic Effect
- A therapeutic effect is the intended helpful effect of a medication, such as lowering fever or reducing pain.
- Adverse Effect
- An adverse effect is an unwanted or harmful reaction caused by a medication.
- Contraindication
- A contraindication is a condition or situation in which a drug should not be used because it may cause harm.
Common Mistakes to Avoid
- Confusing generic and brand names is wrong because one drug can have several brand names but only one generic name, which can lead to duplicate dosing.
- Ignoring units in dosage calculations is wrong because mixing mg, g, mL, and tablets can produce a dose that is too high or too low.
- Assuming all routes work at the same speed is wrong because IV, oral, inhaled, topical, and subcutaneous drugs enter the body at different rates.
- Focusing only on the desired effect is wrong because adverse effects, allergies, interactions, and contraindications are part of safe medication use.
- Skipping the patient safety checks is wrong because even the correct drug can be unsafe if given to the wrong patient, at the wrong dose, or by the wrong route.
Practice Questions
- 1 A medication order says 500 mg, and the available tablets are 250 mg each. How many tablets should be given?
- 2 A patient receives 100 mg of a drug with a half-life of 4 hours. How much drug remains after 8 hours, assuming simple half-life decay?
- 3 A liquid medication contains 125 mg in 5 mL. How many mL are needed to give a 250 mg dose?
- 4 Explain why an intravenous medication usually acts faster than an oral medication, and name one safety concern this creates.
Understanding Pharmacology Basics
Medicines do not behave the same way in every person. Age, body size, pregnancy, kidney function, liver function, genes, hydration, and illness can change the amount of medicine that reaches tissues. A dose that suits one adult may be unsafe for a child or an older person.
Blood flow matters too. A medicine injected into muscle may enter the blood slowly if a person is cold or in shock, because less blood reaches the muscle.
Some medicines taken by mouth are changed by the liver before much of the original medicine reaches the rest of the body. This first pass effect helps explain why a swallowed dose can be very different from an injected dose.
At the target tissue, many medicines act by attaching to proteins called receptors. A drug that activates a receptor is called an agonist. A drug that blocks another substance from activating a receptor is called an antagonist.
For example, some asthma medicines relax airway muscles by activating receptors, while some allergy medicines block receptors involved in symptoms. Receptors are not found in only one place. This is one reason a useful medicine can cause unwanted effects in other organs.
As the dose rises, the effect often rises at first, then levels off. Increasing a dose beyond that point may add more risk without adding much benefit.
Dose calculations require careful attention to units. A prescription may be written in milligrams, while a liquid label gives a concentration in milligrams per milliliter. The student must identify how much medicine is ordered, how much is supplied, and what volume contains that supply.
Weight based doses need an accurate body weight, often in kilograms. One kilogram equals about two point two pounds, so a pounds to kilograms conversion may be needed first. Decimal mistakes can be dangerous.
Writing a leading zero in zero point five helps prevent a dose from being read as five. Avoiding an unnecessary zero after a whole number prevents ten from being mistaken for one point zero.
Safe medication use depends on more than getting the calculation right. Health workers compare the current medicine list with new orders to find duplicate drugs, interactions, and medicines that should have been stopped. Nonprescription pain relievers, cold products, vitamins, herbal products, and alcohol can alter treatment or increase harm.
An allergy is an immune reaction, such as hives or swelling, while a side effect may be a predictable unwanted effect, such as drowsiness. These should not be treated as identical. Monitoring is part of treatment.
A blood pressure medicine may require blood pressure checks. Insulin requires attention to blood glucose and meals. Clear records allow the next caregiver to know what was given, when it was given, and how the person responded.