BMS 113 · Common Core (Tronc commun)Section 3.1 · Pharmaceutical dosage forms
Section 11 of 31
Why dosage forms exist
Explain why pure active ingredients are not given as such and what a pharmaceutical dosage form contains.
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Why this matters
If you think the pure active ingredient is the medicine, you will misread every label and every dose instruction that follows. This section gives you the vocabulary of crude, pure and pharmaceutical preparation that Unit 3.2 and later units assume you already know. Get it wrong here and the difference between a safe tablet and a dangerous one will look like a manufacturing detail.
What you need to know first
No pharmacology is needed. Start from everyday knowledge: you have swallowed tablets and seen syrups in bottles, so you already know what a finished medicine looks like. Unit 3.1 explains what a dosage form is.
Words to know (5)
Dosage form
The finished form in which a drug is given to a patient, such as a tablet, syrup, cream or injection. A morphine injection in a sealed ampoule is a dosage form.
Active ingredient
The substance in a medicine that produces the pharmacological or biological effect. Paracetamol is the active ingredient of a paracetamol tablet.
Excipient
An added ingredient with no pharmacological effect of its own that makes the product usable, stable and acceptable. A disintegrant lets a tablet break up in the gut.
Crude drug preparation
A medicine from a natural source that is unprocessed or only minimally processed, so its strength varies. Dried poppy juice is a crude preparation.
Pure drug preparation
The isolated or synthesised active ingredient alone, which is measurable but hardly ever given as such. Purified morphine extracted from opium is a pure preparation.
One idea at a timeIdea 1 / 6
In one sentence A medicine reaches you as a crude, a pure or a pharmaceutical preparation, and only the last one is the finished product that you take.
Drugs are prepared in three ways
The three preparations describe a path from source material to the product a patient can use. Crude drug preparations come from natural sources with no processing or only minimal processing. Pure drug preparations contain the active ingredient isolated or synthesised, and are hardly ever given as such. Pharmaceutical preparations, also called pharmaceutical dosage forms (PDF), are the finished products actually dispensed — tablets, syrups, creams, injections. A dosage form is the means by which drug molecules are administered to the body.
For example
Dried poppy juice is a crude preparation; morphine extracted from it is a pure preparation; a morphine injection in a sealed ampoule is a pharmaceutical dosage form.
Pause and check yourself
Which of the three preparations is the finished product actually dispensed to the patient?
Show the answer
The pharmaceutical preparation, also called the dosage form: it is the tablet, syrup, cream or injection that is dispensed to the patient.
Read detailed explanations
Why a milligram, or a microgram, needs a dosage form
The smaller the dose, the more the formulation matters. A drug whose whole therapeutic dose weighs a few milligrams or micrograms cannot be handed out as a powder: a household spoon delivers hundreds of milligrams, and even a pharmacy balance may not resolve the difference between a therapeutic and a toxic amount. Formulation solves this by dilution and division. A diluent or filler is mixed with the active ingredient so that the mixture is large enough to handle, and then the mixture is divided into units of equal weight — tablets, capsules or sachets. The technical term for the result is content uniformity: every unit must contain the same amount of active ingredient within narrow limits. The vocabulary here is worth fixing. A diluent or filler increases bulk; a binder holds powder particles together; a disintegrant makes the tablet break up in the digestive tract; a glidant improves powder flow; a lubricant stops the powder sticking to the tablet press. A beginner’s misconception is that all this is manufacturing trivia. It is not: an uneven mix produces tablets that differ from one another, so one patient under-doses and the next over-doses while both believe they took the same medicine.
Excipients are inert, not inactive
Excipients carry no pharmacological effect, which is exactly why they are called inert, but they are far from inactive in the product. They decide how the dosage form behaves from the moment it is swallowed. A disintegrant governs how quickly the tablet breaks apart; a binder resists that break-up and can slow release; a coating decides whether the tablet dissolves in the stomach or only in the small intestine; a sweetener or flavour decides whether the patient will accept the medicine at all. The same active ingredient in the same amount can therefore produce different blood levels when the excipients change. This explains a practical rule of dispensing: a patient who reacts badly to one brand of a medicine may be reacting to a colourant or a preservative rather than to the active ingredient, and a change of excipients can change how a patient tolerates a product even when the active ingredient is identical. The misconception to discard is that a generic product is automatically interchangeable in every respect because it contains the same molecule. The molecule identifies the drug; the excipients and the manufacturing process shape the dosage form, and the dosage form shapes the dose that reaches the body. When in doubt, check the label, which lists both the active ingredients and the excipients of the preparation.
Explore the diagram
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From crude drug to dosage form
Drugs reach the patient in three successive states: the crude preparation, the pure active ingredient, and the finished dosage form that combines that active ingredient with excipients.
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01 / 6Crude drug preparation
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Crude drug preparation
Material from a plant, animal or mineral source that has had no processing, or only drying, pulverising or partial extraction. It keeps most or all of the active and inactive compounds of the source, and also any toxic substances naturally present, so the dose of active substance cannot be guaranteed.
Schematic; not to scale. The three states are successive stages, not competing products: most modern medicines begin from a crude source or from synthesis and end as a dosage form.
Key points to remember
✓Medicines reach patients as crude, pure or pharmaceutical preparations.
✓A pure active ingredient is measurable, but it is hardly ever given as such.
✓Dosing, instability, destruction at the site, local irritation and practicality are the five reasons formulation is needed.
✓A dosage form equals active ingredient plus excipients.
✓Dosage forms protect the drug and the patient, and they make the dose accurate and repeatable.
Go deeper
Worked example
From pure powder to a usable medicine. A small clinic receives pure paracetamol powder. The prescriber wants to treat fever in an adult with the familiar 500 mg dose, using the tablet described in the lecture notes. You are asked to explain why the powder cannot simply be handed over and what the dosage form must add.
Measure the dose: 500 mg of pure powder must be weighed accurately for every single dose. Without a calibrated balance at the point of care this is slow and error-prone, and the error is invisible to the patient.
Make it administrable: pure paracetamol powder is bulky, dusty and bitter. It is unpleasant on the tongue and impossible to swallow comfortably in that state.
Add excipients with jobs: a diluent or filler gives the tablet a workable bulk, a disintegrant lets it break up in the digestive tract, a binder holds it together, and a glidant and lubricant let the tablet press work efficiently.
Protect and inform: the tablet is coated if the taste or the environment threatens the drug, and the label states the active ingredient, the excipients, the strength, the dosage form and the storage instructions.
The pure substance is not the medicine. The dosage form turns a measurable chemical into a safe, accurate, acceptable and stable product — which is why formulation is a clinical decision, not a manufacturing detail.
Common misconception
Many beginners believe that the pure active ingredient is the strongest and best form of a medicine and that excipients are pointless filler that could be removed. In reality the pure substance is often impossible to dose or take safely, and excipients are what make the dose accurate, the tablet swallowable and the drug stable.
Check your reasoning
The same active ingredient can be harmless in one dosage form and dangerous in another. Explain how the dosage form, rather than the active ingredient, can change the risk.
Reveal an answer
The dosage form controls how much drug is released, where and how fast. An enteric coating keeps an irritant away from the stomach; a sustained-release tablet spreads one large dose over many hours; a solution is absorbed at once. Destroy the design — by chewing a sustained-release tablet or by injecting an oral solution — and the same quantity of the same molecule can arrive at once or in the wrong place.
Where this comes from
BMS 113 General Pharmacology I lecture notes · Unit 5, pp. 21–24 and Unit 3, pp. 20–23
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About this course and its sources
Bilingual lessons organised from the supplied BMS 113 General Pharmacology I lecture notes. Diagrams are original educational schematics; pharmacology, nursing and French-language review are pending.