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Glossary

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# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
paediatric

Of or relating to children.

palliative

To do with relieving rather than curing symptoms.

pancreas

A glandular organ situated behind the stomach that secretes insulin and pancreatic digestive enzymes.

pancreatitis

A condition of the pancreas causing severe abdominal pain, shock and collapse, which can be fatal.

pancytopenia

Low numbers of all blood cells.

PAP smear

A specimen of cells from the cervix, usually obtained in scrapings from the opening, which may be examined by microscope to look for abnormalities.

paraesthesia

Abnormal sensations of touch on the skin.

partial early virological response (pEVR)

Hepatitis C RNA viral load has dropped by at least 2 log10 (99%) by week 12 of treatment, but is still detectable. See also ‘complete early virological response (cEVR)’.

partial response (PR)

After starting treatment, some decline in RNA (more than a 2 log10 drop). However viral load remains detectable at week 24. Also known as ‘non response’.

pathogen

Any micro-organism which can cause disease. There are four main types: bacteria, fungi, protozoa, viruses.

pathogenesis

The origin and step-by-step development of disease.

pc

Abbreviation of a Latin term meaning after food.

PCR

Polymerase chain reaction, a method of amplifying fragments of genetic material so that they can be detected. Some viral load tests use this method.

pegylated interferon

A drug taken by injection and used to treat hepatitis C in combination with other drugs. Pegylation slows the release of interferon in the body; injections are required once a week. See also ‘interferon alfa’.

perianal

Around the anus.

perinatal

Around the time of birth.

peripheral neuropathy

Damage to the nerves of the hands and/or feet, causing symptoms ranging from numbness to excruciating pain.

person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.

pharmacokinetic

The study of how a drug is absorbed and distributed throughout the body.

phase I

The earliest stage of a clinical trial in humans, designed to see if a drug, or vaccine is safe and what the maximum safe dose is.

phase I/II

Stage of a clinical trial to see what the most effective dose of a drug is.

phase II

Stage of a clinical trial to see if a drug is effective in the short-term.

phase III

Stage of a clinical trial when the experimental drug is given to large numbers of people, at the dose determined in phase I or phase II. Often the trial drug is compared with a treatment already in use or with an inactive placebo.

phenotype

Trait or behaviour which results from a particular genotype.

phosphate

Phosphorus combined with oxygen in the blood forms a variety of phosphates, vital for energy production, muscle and nerve function, and bone growth. Raised levels can be a sign of conditions such as kidney disease and diabetes.

PI

See protease inhibitor.

pilot study

Small-scale, preliminary study.

placebo

A pill or liquid which looks and tastes exactly like a real drug, but contains no active substance.

placebo effect

A commonly observed phenomenon, in which patients given a placebo have better clinical results than patients given no treatment at all (even though there is no active drug in a placebo). This may be because patients expect to get better.

plasma

The fluid portion of the blood.

positive predictive value

When using a diagnostic test, the percentage of those testing positive who are correctly diagnosed. This will vary according the prevalence in the local population.

powered

A study has adequate statistical power if it can reliably detect a clinically important difference (i.e. between two treatments) if a difference actually exists. If a study is under-powered, there are not enough people taking part and the study may not tell us whether one treatment is better than the other. 

preclinical

Of in vitro research or research involving animals, undertaken prior to research in humans.

prevalence

The proportion of people who currently have an infection or a condition. This will include people who acquired the infection or condition several years ago and still have it. See also ‘incidence’. 

primary endpoint

A single endpoint in an RCT which most accurately reflects the beneficial effects of treatment.

pro-drug

A drug that is broken down into another active form inside the body.

prognosis

Likely outcome, such as the risk of disease progression.

proliferation

Multiplication (e.g. of immune system cells) to control an infection.

prolonged release

Medication where the active ingredient is released at a controlled rate over a period of time, usually up to 24 hours.

prophylaxis

Taking a drug to prevent an illness. Primary prophylaxis is the use of drugs to prevent a first occurrence of illness. Secondary prophylaxis is the use of drugs to prevent re-occurrence of illness.

prospective study

A type of longitudinal study in which people join the study and information is then collected on them for several weeks, months or years. See also ‘retrospective study’. ). 

protease inhibitor

Drugs containing active ingredients which inhibit an enzyme of the hepatitis C virus and directly impede reproduction of the virus. Used to treat hepatitis C in combination with other drugs. Includes boceprevir (Victrelis) and telaprevir (Incivo).

protein

A substance which forms the structure of most cells and enzymes.

prothrombin time (PT)

A test of the time it takes for blood to clot. When the liver is damaged clotting is slower.

protocol

A detailed research plan that describes the aims and objectives of a clinical trial and how it will be conducted.

protozoa

A group of single-celled animals, a few of which cause human disease.

psoriasis

A disease in which the skin develops raised, rough, reddened areas.

psychiatry

A branch of medicine that treats people, using drugs and other physical methods, to change the way they act and feel.

psychology

A branch of medicine that tries to explain why people act, think and feel the way they do.

psychosis

Mental health problems that stop someone from thinking clearly and telling the difference between reality and their imagination.

pulmonary

Affecting the lungs.

p-value

The result of a statistical test which tells us whether the results of a study are likely to be due to chance and would not be confirmed if the study was repeated. All p-values are between 0 and 1; the most reliable studies have p-values very close to 0. A p-value of 0.001 means that there is a 1 in 1000 probability that the results are due to chance and do not reflect a real difference. A p-value of 0.05 means there is a 1 in 20 probability that the results are due to chance. When a p-value is 0.05 or below, the result is considered to be ‘statistically significant’. Confidence intervals give similar information to p-values but are easier to interpret. See ‘confidence interval’.