PHAR2911 · Pharmaceutics And Professional Practice
Dosage Forms & Routes of Administration
This chapter is PHAR2911's foundational molecule-to-medicine map: how a bare drug substance is turned into a usable product by a formulation, and how the four physical states (solid, liquid, semisolid, aerosol) are matched to a route of administration. It matters because the exam routinely asks you to justify a route against canonical trade-offs (onset, first-pass metabolism, bioavailability) and to name forms precisely — and method plus justification, not the bare label, is what earns the marks.
What this chapter covers
- 01Molecule to medicine: why we never give the bare drug
- 02Formulation two meanings: the form (noun) vs the process (verb) + excipient roles
- 03Route families: GI/enteral, parenteral, respiratory, skin, other
- 04Local vs systemic intent drives the whole design
- 05Four physical states mapped to routes: solid / liquid / semisolid / aerosol
- 06Semisolid definitions: cream (o/w), lotion, ointment, gel, paste
- 07Oral liquids and inhalation devices: syrup, elixir, DPI/MDI/SMI/nebuliser
- 08Route trade-offs: onset, first-pass metabolism, bioavailability, reversibility
Justify a route for a fast-acting, first-pass-sensitive drug
- +1Rule out plain oral: a swallowed tablet is subject to first-pass metabolism, so little active reaches the circulation - reject on bioavailability grounds.
- +1Rule out IV: it is fast and 100% bioavailable, but invasive, needs aseptic technique and is irreversible once injected - and there is no access plus we want self-administration.
- +1Choose sublingual/buccal: the rich oral-mucosa blood supply gives fast onset, and drug absorbed here drains to the systemic circulation, bypassing first-pass metabolism.
- +1Check the disqualifiers: sublingual is unsuitable for bitter or high-molecular-weight drugs; this one is small and non-bitter, so it qualifies.
Key terms
- Formulation
- Both the dosage form a medicine is presented in (a noun: tablet, cream, aerosol) and the process of combining the active drug with excipients to make that form (a verb).
- Excipient
- Any ingredient in a product that is not the active drug - diluents, binders, disintegrants, lubricants, preservatives, vehicles, sweeteners - giving the dose accuracy, stability, palatability and deliverability.
- Route of administration
- The way a drug is delivered to the body; it can act locally (at the site applied) or systemically (absorbed into the bloodstream), and is chosen first because it constrains which dosage form is possible.
- First-pass metabolism
- Loss of drug through the gut wall and liver before it reaches the systemic circulation after oral dosing; sublingual and buccal routes bypass it, while oral and (partly) rectal routes are subject to it.
- Cream vs ointment
- A cream is an oil-in-water (o/w) emulsion that rubs in and washes off; an ointment is an oily, occlusive semisolid that holds drug against the skin - the single most-tested topical distinction.
- Disperse systems (solution / suspension / emulsion)
- A solution has the drug fully dissolved (one phase); a suspension has solid particles dispersed in a liquid (shake before use); an emulsion has liquid droplets dispersed in another immiscible liquid.
Dosage Forms & Routes of Administration FAQ
What is the difference between a cream, a lotion and an ointment?
All are topical semisolids. A cream is an oil-in-water emulsion that rubs in and washes off; a lotion is a runnier o/w system with higher water content; an ointment is an oily, thick, occlusive semisolid that holds drug against the skin. A paste is a stiff semisolid carrying a high solids load (about 20 to 50%), which makes it protective.
What are the four physical states of dosage forms?
Solid (tablets, capsules, powders/granules), liquid (solutions, suspensions, emulsions), semisolid (creams, ointments, gels, pastes) and aerosol (MDI/DPI/SMI inhalers, nasal sprays, nebulisers). Knowing the state tells you the likely manufacturing problems, quality tests and which routes the form can serve.
Why don't we just give patients the pure active drug?
A pure drug substance is usually a tiny mass of powder that is often unstable, bitter, poorly soluble and impossible to dose accurately. Pharmaceutics combines it with excipients into a stable, accurate, patient-acceptable product - the molecule-to-medicine idea that runs through the whole unit.
Which routes avoid first-pass metabolism?
Sublingual and buccal absorption drains to the systemic circulation and bypasses first-pass metabolism, and IV delivery is 100% bioavailable by definition with no first-pass. Plain oral dosing is subject to first-pass, and rectal dosing achieves only a partial bypass.
Is the difference between local and systemic action examinable?
Yes, and it should be the first thing you state. A local route wants the drug to stay put (a non-absorbing cream, an eye drop bathing the cornea); a systemic route wants reliable absorption. The same molecule has opposite design goals depending on intent, so classify intent before picking the form.
Exam move
Drill the chapter as a four-step checklist rather than a list of facts. (1) State the intent - local or systemic - because it flips the design goal. (2) Pick the route from site of action + onset needed + patient ability + drug stability, and always name its trade-off (first-pass? sterility? reversibility? bioavailability?). (3) Pick the matching physical state from the dosage-form family tree (solid/liquid/semisolid/aerosol). (4) Use the exact definitions verbatim: cream = o/w emulsion, ointment = oily, paste = 20 to 50% solids, syrup = high-sucrose, elixir = hydroalcoholic. Examiners reward the justification chain and precise naming, so practise writing the chain out, never just the bare answer.
