saturday, september 12, 2015 1 routes of drug administration

Friday, April 21, 2023

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Routes of drug administration


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Objectives: To discuss the peculiar features of

the various routes of drug administration

• To apply the advantages and disadvantages of the various routes of drug administration to optimize patient therapeutic benefit


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Buccal/Sublingual

Buccal or sublingual dosage form enable drugs to be taken as smaller tablets held in the mouth or under the tongue.

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 while nicotine-containing chewing gum may be used for cigarette smoking replacement.


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Advantages of buccal sublingual administration:

First pass - The liver is by-passed thus there is no loss of drug by first pass effect for buccal administration. Bioavailability thus is higher.

Rapid absorption - Because of the good blood supply to the area absorption is usually quite rapid.

Drug stability - pH in mouth relatively neutral (cf.

stomach - acidic). Thus a drug may be more stable.


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Disadvantages Holding the dose in the mouth may be

inconvenient.

If any is swallowed that portion must be treated as an oral dose and subject to first pass metabolism.

Only small doses can be accommodated easily.


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Rectal

Most commonly used for suppository or enema.

Some drugs given by this route include aspirin, dipyrone, paracetamol, theophylline, chlorpromazine and some barbiturates


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Advantages of Rectal route

By-pass liver - Some of the veins draining the rectum lead directly to general circulation, thus by-passing the liver. There is therefore reduced first-pass effect.

Useful - This route may be most useful for patients unable to take drugs orally or with younger children.


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Disadvantages of rectal route

Erratic absorption - Absorption is often incomplete and erratic.

However for some drugs it is quite useful.

Researches are being conducted to look at methods of improving the extent and variability of rectal administration.

Not well accepted.


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Some Parenteral Routes of Administration


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Intravenous

Drugs may be given into a peripheral vein over 1 to 2 minutes or longer by infusion.

Rapid injections are used to treat epileptic seizures, acute asthma, or cardiac arrhythmias


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Advantages of IV Rapid - A quick response is possible

Total dose - The whole dose is delivered to the blood stream. Large doses can be given by extending the time of infusion.

Veins relatively insensitive to irritation by irritant drugs.


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Disadvantages of IV Suitable vein may be difficult to locate.

May be toxic - Because of the rapid response, toxicity can be a problem with rapid drug administrations (could then be given as an infusion while monitoring for toxicity).

Requires trained personnel

Expensive - Sterility, pyrogen testing and larger volume of solvent means greater cost for preparation, transport and storage.


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Subcutaneous

This involves administration of the drug dose just under the skin.

Advantages: Can be given by patient, e.g. in the case of

insulin

Absorption slow but usually complete.

Absorption rate can be improved by massage or heat.

Vasoconstrictor may be added to reduce the absorption of a local anesthetic agent, thereby prolonging its effect at the site of interest.


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Disadvantages subcutaneous administration

Can be painful

Irritant drugs can cause local tissue damage

Maximum of 2 ml injection thus often small doses limit use.


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Intramuscular Injection administered into the

deltoid muscle of the upper arm or the gluteal muscle of the buttock.

Advantages: Larger volume, than sc, can be given by IM

A depot or sustained release effect is possible with IM injections, e.g. procaine penicillin


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Disadvantages of intramuscular injection

Trained personnel required for injections.

The site of injection will influence the absorption, generally the gluteal muscle of the buttock is the best site

Absorption is sometimes erratic, especially for poorly soluble drugs, e.g. diazepam, phenytoin.

The solvent maybe absorbed faster than the drug causing precipitation of the drug at the site of injection.


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Inhalation

Drugs administered as fine particles of liquids or solids or as aerosols or spray.

The drug may be required for local or systemic effects.• Local effect - bronchodilators

Systemic effect - general anesthesia


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Advantages of inhalation (Nasal) administration

Rapid absorption, by-passing the liver

Absorption of gases is relatively efficient, solids and liquids are excluded if larger

than 20 micron

only 10 % of the dose may be absorbed.


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Example of Drugs administered by inhalation into the lungs

Drugs Comments

Corticosteroids Beclomethasone dipropionate, betamethasone valerate & triamcinolone acetonide used for relief of brochial asthma

Ergotamine tartrate

Available as a pressurized aerosol preparation & provides relief from migraine much faster than from oral preparations

Sympathomimetics

Fenoterol, rimiterol, salbutamol, salmeterol, & terbutaline are well absorbed from the lungs giving early relief from asthmatic attack.

Sodium cromoglycate

Well absorbed from the lungs when administered as a fine powder or spray but poorly absorbed from the gastro-intestinal tract. Inhalation of the powder may cause bronchospasm; isoprenaline may be administered concurrently to minimize this effect.


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Topical Local effect - eye drops, antiseptic,

sunscreen, callous removal, etc.

Systemic effect - e.g., nitroglycerin ointment.

Absorption through the skin, especially via cuts and abrasions but also intact skin, can be quite marked.


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Other Routes of Administration

Intra-nasal - some systemic absorption has been demonstrated for propranolol and some low dose hormones

Intra-arterial for cancer chemotherapy to maximize drug concentrations at the tumor site

Intrathecal directly into the cerebrospinal fluid.

saturday, september 12, 2015 1 routes of drug administration

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