Pharmacology: follow a medicine through the body
Pharmacology is an interdisciplinary field of science which studies how chemicals (drugs) interact with biological systems. Pharmacology is generally divided into two areas of research: what occurs to the drug as it moves through the body and what the drug does. The two question approach to pharmacology provides a better understanding for why the same dose may produce varying effects among different individuals. This guide is for learning and does not provide a dosage plan.
Trace movement into and out of the body
Absorption is the process of a drug entering the circulatory system. Distribution is the process by which drugs move from the bloodstream into tissue. The drug itself undergoes metabolic changes that result in an altered molecular structure. Finally, drugs are removed (excreted) as either the drug or one of its metabolites. Often these steps occur simultaneously. Together these processes are abbreviated ADME. An intravenous dose enters the circulation directly, bypassing absorption.
The route of administration helps explain why the same medicine may reach its target differently in different formulations. Entry into the circulation, movement to tissues and action at a target are separate steps. A medicine applied locally may also have a different intended role from a systemic preparation. Follow the particular product and route instead of treating every formulation as interchangeable.
The ADME framework
- Absorption
- Distribution
- Metabolism
- Excretion
Connect the target with the effect
Pharmacodynamics describes how drugs produce effects through interaction with molecular targets, such as receptors and enzymes. Understanding the mechanisms by which drugs bind to target sites and induce physiological responses will help you understand both the desired clinical effects of medications as well as possible adverse effects. Knowing a mechanism alone cannot predict an individual patient's response. A variety of factors including drug concentration at the site of action; presence of disease; and co-administered medications can influence the effects of the drug.
A desired effect and an unwanted effect can both arise from a medicine's actions. Describing the target helps explain a mechanism, but it does not by itself establish that a treatment is suitable for a particular person. The response also depends on exposure and the clinical setting. Keep a mechanism explanation separate from a decision about prescribing or changing treatment.
A dose does not tell the whole story
Kidney and liver function, age, and other factors may cause drugs to be metabolized differently than expected, or change how a drug works. An interaction can increase or decrease a drug effect, or introduce another risk. When taking non-prescription products such as vitamins, supplements, herbs, etc., include these in your medicine history. There are many examples where multiple different products contain the same active ingredient. The clinician/pharmacist must review all medications/products for potential interactions - this guide is not designed to verify that any combination of products will be safe.
A medicine history is useful only when it reflects what someone actually uses, including occasional products. Non-prescription medicines and supplements can matter as well as regular prescriptions. The word natural does not establish that a product is safe or free of interactions. The relevant ingredients and the complete combination need checking by a clinician or pharmacist when making personal treatment decisions.
Build a useful revision note
Write a revision note on each medicine to cover their mechanisms, primary clinical applications, major contraindications/ warnings and appropriate monitoring. Clearly differentiate adverse reactions from allergic reactions – do not treat them as synonymous terms. Refer to the most recent product literature and local guidelines relating to practice at the time that you apply this learning to your practice. Do not alter, discontinue or initiate a medication based on a generic student resource. Contact the clinician or pharmacist responsible for your care.
A practical revision note separates purpose, mechanism, cautions and monitoring. Those headings answer different questions: why the medicine is used, how it acts, what could make use unsuitable and what needs checking. Product information and local guidance provide context when knowledge is applied. A short educational explanation cannot replace those sources or the assessment needed for an individual patient.
Check your understanding
A short quiz, with an explanation after each answer.
Which term describes drug movement and handling?
Choose one medicine from a teaching case. Write separate notes on its handling and its actions, then identify what information you would need before judging safety for that patient. Finally, use the quiz to confirm that the two main branches of pharmacology remain distinct.