Routes of Administration &

Dosage Forms

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The oral routeThe most frequently used route for local and systemic treatments…Why? Advantages: Convenient , simple ,safe, cheap, variety of forms.Disadvantages: Slow onset of action.Variable gastric emptying (factors).Possibility of irregular or poor absorption ( low bioavailability).Drug solubility may be altered by some substances in the GIT (e.g. Ca+2).Destruction of certain drugs in the GIT (due to enzymes or secretions).First pass effect (i.e. presystemic metabolism). Not suitable for unconscious or vomiting patients and for pre- or post-operative use.

Examples: Tablets, suspensions, solutions, emulsions, powders, granules, capsules, gels, elixirs.

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The buccal/sublingual route

Two sites are used for absorption from the buccal cavity:

1.For sublingual absorption, the area under the tongue is used: Very fast onset of action but with short duration.

2. For buccal absorption, the buccal sulcus is used. This is the area between the upper lip and the gum: Fast onset of action and longer duration than the sublingual routes.

Buccal tablets are often harder tablets [4 hour disintegration time], designed to dissolve slowly. Nitroglycerin, as a softer sublingual tablet [2 min disintegration time], may be used for the rapid relief of angina. This ROA is also used for some steroids such as testosterone and oxytocin.

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The buccal/sublingual routeAdvantages: • Quick onset of action.• Rapid absorption - Because of the good blood supply to the area

absorption is usually quite rapid. • Avoiding the first pass metabolism: As the liver is by-passed, there is no

loss of drug leading to higher bioavailability. • Drug stability: pH in mouth relatively neutral (stomach - acidic). Thus a

drug may be more stable. • Can be administered to unconscious and vomiting patients (e.g.

antiemetic drugs).

Disadvantages: • Holding the dose in the mouth is inconvenient. If any is swallowed that

portion must be treated as an oral dose and subject to first pass metabolism.

• Small doses only can be accommodated easily.

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The parenteral routeThis route describes drug administration by injection such as •Intravenous route (i.v.): Very fast onset of action.•Subcutaneous route (s.c.): The easiest and least painful type of injection to administer.•Intramuscular route (i.m.): The drug can be formulated in an aqueous solution (fast onset), a suspension or in an oily vehicle (slower onset and more prolonged action).

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The parenteral route Advantages: • Rapid - Total dose - Large doses can be given by

extending the time of infusion. • GI stability

Disadvantages: • Requires trained personnel . • Suitable vein – Safety issue. • Expensive - Sterility, pyrogen testing or preparation,

transport and storage.

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The rectal route• More local than systemic.• Examples: suppositories, ointment, creams, powders, enemas and tablets. Advantages: • Can be used when the oral route is unsuitable (vomiting, unconscious and

uncooperative patients). Can also be used when the drug causes GIT irritation.

• Only some of the drug absorbed from the rectum will be subject to the first pass effect (much less than the oral route).

Disadvantages: • Erratic or irregular absorption : Absorption is often incomplete and may

give rise to a variable effect. • Inconvenient.

P.S. Similar properties to the vaginal route.

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The topical route• Applied to the skin: Mainly to local effect such as antifungals. But may also be systemic ( nitroglycerine cream): Avoids first pass

effect and provides close to zero-order kinetics over prolonged time intervals.

• Also applied to other topical surfaces such as Eye (ophthalmic preparations), Ear (otic or aural preparations) Nose (nasal dosage forms).

• Examples: Ointments, creams, pastes, lotions, gels, solutions, topical aerosols.

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The inhalation (respiratory) route

• Drugs are administered usually by inhalation through the nose or mouth.

• Mainly for local effect such as bronchodilators (treatment of asthma) • And can be used to produce a systemic effect (such as general

anesthesia). The lungs provide an excellent surface for absorption (in the alveolar region)

when the drug is delivered in gaseous or aerosol. Rapid absorption, by-passing the liver.

• Absorption of gases is relatively efficient, however solids and liquids are excluded if larger than 20 micron and even then only 10 % of the dose may be absorbed.

• Examples: Aerosols (solution, suspension, emulsion, powder forms), inhalations, sprays, gases.

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Dosage Forms

• Drug substances (i.e. active pharmaceutical ingredients) are seldom administered alone, but rather as a part of a formulation in combination with one or more non-medical agents (i.e. excipients) that serve varied and specialized pharmaceutical functions.

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Pharmaceutical Ingredients can serve several functions

• solubilize• suspend• thicken• dilute• flavor

• color• emulsify• stabilize• preserve

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Types of Dosage Forms

• Solutions• Syrups• Elixirs• Suspensions• Emulsions• Creams• Ointment• Lotions

• Capsules• Tablets• Suppositories• Pessaries• Powders• Granules• Parenteral• Aerosols

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Why use dosage forms?

•Protection of a drug substance from destructive influences of atmospheric oxygen or humidity•Protection from influence of gastric acid after oral administration•To mask taste of offensive drugs.•To provide liquid preparations of substances that are either insoluble or unstable•To provide clear liquid dosage forms

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Why use dosage forms?

• To provide time-controlled release of drugs• To provide optimal topical administration• To provide for the insertion of a drug into

one of the body’s orifices• Provide for placement of drugs into the

blood stream• Provide for lung inhalation of drugs

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Key points

*The route can be chosen to give local or systemic effects, fast or slow

*The oral route is the most commonly used route

*Gastric emptying, stability and other materials present in the GIT may limit availability of drug from the oral route

*Sublingual absorption gives a short, fast-onset activity

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Key points

*Buccal absorption takes place between the gum and lip. This route can be used with unconscious patients and to avoid first pass metabolism

*Rectal absorption partially avoids first pass metabolism. It is useful for nil-by-mouth patients and in cases of gastric irritation.

*Inhalation requires a much lower dose than the oral route, with a rapid onset

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Key points*Administration to the skin maybe used for both

local and systemic effects*Injections can give the fastest onset of action but

prolonged action is also possible using oily intramuscular injections.

*A wide range of different dosage forms have been devised which have different properties and uses.

*The same drug may usefully be used in different formulations to assist different types of patients.

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