Clinical Pharmacology

Clinical pharmacology encompasses all aspects of the relationship between drugs and humans. For healthcare professionals, clinical pharmacology is important because it is the scientific discipline that underpins the rational prescribing of medicines to alleviate symptoms, treat illness and prevent future disease.

Pharmacodynamics is the study of how drugs have effects on the body. The most common mechanism is by the interaction of the drug with tissue receptors located either in cell membranes or in the intracellular fluid.

Pharmacokinetics can be simply described as the study of 'what the body does to the drug' and includes:

Prescribers have numerous sources of guidance about how to use drugs appropriately (e.g. dose, route, frequency, duration) for many conditions. However, this advice is based on average dose–response data derived from observations in many individuals.

Patients make important contributions to rational prescribing decisions. Their beliefs and expectations affect the goals of therapy and help in judging the acceptable benefit/harm balance when selecting treatments.

Prescribers choose treatment regimens on the basis that the benefits that accrue will outweigh the adverse effects. However, that outcome is never certain for individual patients even if the best evidence suggests that it is likely.

There are several terms commonly used to describe adverse effects of drug therapy:

A drug interaction has occurred when the administration of one drug alters the clinical effects of another. The result may be an increase or decrease in either the beneficial or harmful effects of the second agent. Although the number of potential interacting drug combinations is very large only a small number are relevant in clinical practice.

A medication error is any preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the health care professional or patient. A prescribing error is a medication error related to an error in prescribing.

When a new drug has been discovered it goes through a development process that aims to deliver sufficient evidence for it to be granted a marketing authorisation (‘license’) by the relevant regulatory authority. This process takes over 10 years and may cost up to $1bn. The development pathway has traditionally included a preclinical phase followed by four clinical phases, shown diagramatically below.

A clinical trial involves the testing of a new medicine (or other therapy) to evaluate whether it is effective and safe. Clinical trials of drugs can be divided into those assessing the treatment of a disease (e.g. asthma) or those assessing treatments to prevent the occurrence of significant healthcare events in the future (e.g. stroke).

The process of testing, developing and marketing of medicines has to regulated to protect the interests of the public. Major regulatory bodies include the Food & Drug Administration (FDA) in the US and the European Medicines Agency (EMA) in Europe. These bodies have various functions.

Many medicines meet the three key regulatory requirements of quality, safety and efficacy. National formularies usually list several thousand licensed medicines and although prescribers are legally entitled to prescribe any of them it is desirable to limit the choice because:

Evidence-based prescribing can be defined as making prescribing decisions on the basis of a systematic review and critical appraisal of clinical research findings in order to provide the optimum standard of care for individual patients.

Prescribing medicines is the intervention that most doctors make to restore or preserve the health of their patients and is the major tool used by modern healthcare systems to improve public health. Prescribing also carries significant risks related to adverse drug reactions and interactions, often caused by injudicious prescribing decisions, as well as prescribing errors. Prescribing is a complex and challenging task involving several sub-components.

Complementary medicine is a therapeutic approach that is used together with conventional medicine. An example might be a patient seeking help from aromatherapy to help with pain control after undergoing surgery.

Drug abuse is the misuse of recreational or therapeutic drugs that may lead to addiction or dependence, serious physiological injury (such as damage to kidneys, liver, heart), psychological harm (abnormal behaviour patterns, hallucinations, memory loss), or death.