2. Drug names, drug compendia. Prescription writing

Last updated on January 4, 2019 at 16:17

Drug names

Every drug has many names. They have:

  • 1 generic name
  • 1 chemical name
  • many trade names

All drugs are molecules. However the chemical names of molecules quickly become very long and hard to remember, like N-(4-hydroxyphenyl)ethanamide. Because chemical names are cumbersome we give all drug molecules a generic, international name that is the same anywhere in the world. The generic name that was given to the drug above was paracetamol, which is much easier to remember than N-(4-hydroxyphenyl)ethanamide. In some cases where the chemical name is simple will the generic name be the same as the chemical name, as in acetyl-salicylic acid, also known as Aspirin.

One type of drug may be manufactured by many different pharmaceutical companies, and one company can produce the same active ingredient but in different forms. For example does paracetamol exists in tablet, capsule, suppository, intravenous, intramuscular and liquid suspension formulations. In some cases paracetamol is given together with another drug in the same formulation, like caffeine or codeine. Each of the different pharmaceutical companies can give each formulation a unique name.

Paracetamol tablets produced by the pharmaceutical company Johnson & Johnson is called Tylenol, Panadol by GlaxoSmithKline or Paracet (in Norway) by Weifa. All of these are trade names. Each of the trade names are registered trademarks by the respective companies, so no other company can use their trade names.

The generic name of a drug is often given so that drugs with similar properties or effects have similar names, often similar endings. Here are a few examples:

Ending Property
-antel Antihelminthics
-ase Enzymes
-azepam or -azolam Diazepam derivatives
-caine Local anaesthetics
-cillin Penicillin-based antibiotics
-dil Vasodilators
-ium Quaternary ammonium compounds
-mab Monoclonal antibodies
-olol Beta blockers
-pril ACE inhibitors
-profen Ibuprofen derivatives
-stat Enzyme inhibitors
-stigmine Acetylcholinesterase inhibitors
-trop- Atropine derivatives

It’s not necessary to know this table, however it can be good to see that generic names aren’t always totally random and confusing. A comprehensive list of the conventions of generic names can be found here.

Drug compendia

Drug compendia are large collections of the drugs that are revised by physicians, pharmacists and medical scientists. In these compendia can you find information about drug dosage, usage, mechanism of action, counterindications, risks, side effects and more.

Each country has their own drug compendia. Norway’s drug compendium is called Felleskatalogen. In most countries the drug compendia can be found online.

Prescription writing

Prescription writing routines differ from country to country; however they should always contain at least these 8 points:

  1. Date
    • Prescriptions usually expire after some time
  2. Name, address, age of the patient
  3. R, Rp or Recipe written somewhere at the beginning
    • Recipe means “take” in Latin. As in, take this and this.
    • The right leg of the R is often crossed, so that it looks like Rx (see picture below)
  4. Name and strength of the drug
  5. Directions to the pharmacist
    • If the pharmacist should make “home-made” formulations
  6. Directions to the patient
    • Also called the label
    • Should be accurate and simple
    • “Take 10mg every fourth hour for five days”
  7. Refill information
    • Some countries allow physicians to prescribe prescriptions that can be re-used by the patients. In that case the physician can write so here
    • However, it often says “Do not refill” so that the patient can’t get more drugs than they need
  8. Signature, name, address of the doctor, stamp
Example of what a prescription should look like. Note the R

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1. Definition of pharmacology and the related subjects. Drug development

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3. Drug formulations

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