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Drug Administration Routes
Muhammad Bilal Mirza 4th Year PMC
doctorbilalmirza@yahoo.com
Oral
Only some advantages and disadvantages of oral administration will be presented in this Chapter. Oral administration will be
covered in more detail in subsequent Chapters.
Advantages:
Convenient - portable, no pain, easy to take.
Cheap - no need to sterilize (but must be hygienic of course), compact, multi-dose bottles, automated machines produce tablets
in large quantities.
Variety - fast release tablets, capsules, enteric coated, layered tablets, slow release, suspensions, mixtures
Disadvantages:
Sometimes inefficient - high dose or low solubility drugs may suffer poor availability, only part of the dose may be absorbed.
Griseofulvin was reformulated about 1970 to include the drug as a micronized powder. The recommended dose at that time
was decreased by a factor of two because of the improved bio availability.
First-pass effect - drugs absorbed orally are transported to the general circulation via the liver. Thus drugs which are
extensively metabolized will be metabolized in the liver during absorption.
e.g. the propranolol oral dose is somewhat higher than the IV, the same is true for morphine. Both these drugs and many others
are extensively metabolized in the liver.
Food - Food and G-I motility can effect drug absorption. Often patient instructions include a direction to take with food or take
on an empty stomach. Absorption is slower with food for tetracyclines and penicillins, etc. However, for propranolol
bioavailability is higher after food, and for griseofulvin absorption is higher after a fatty meal.
Local effect - Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agent may be
included with an antibiotic.
Unconscious patient - Patient must be able to swallow solid dosage forms. Liquids may be given by tube.
Buccal/Sublingual
Some drugs are taken as smaller tablets which are held in the mouth or under the tongue. These are buccal or sublingual dosage
forms. 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. Nicotine containing chewing gum may be used for cigarette smoking replacement.
Advantages:
First pass - The liver is by-passed thus there is no loss of drug by first pass effect for buccal administration. Bioavailability 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.
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.
Rectal
Most commonly by suppository or enema. Some drugs given by this route include aspirin, theophylline, chlorpromazine and
some barbiturates
Advantages:
By-pass liver - Some of the veins draining the rectum lead directly to the general circulation, thus by-passing the liver. Reduced
first-pass effect.
Useful - This route may be most useful for patients unable to take drugs orally or with younger children.
Disadvantages:
Erratic absorption - Absorption is often incomplete and erratic. However for some drugs it is quite useful. There is research
being conducted to look at methods of improving the extent and variability of rectal administration.
Not well accepted.
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
Advantages:
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 at higher concentration in dosage forms.
Disadvantages:
Suitable vein - It may be difficult to find a suitable vein.
Maybe toxic - Because of the rapid response, toxicity can be a problem with rapid drug administrations, could then give as an
infusion, monitoring for toxicity.
Requires trained personnel - Trained personnel are required to give intravenous injections.
Expensive - Sterility, pyrogen testing and larger volume of solvent means greater cost for preparation, transport and storage.
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. 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.
Disadvantages:
Can be painful
Irritant drugs can cause local tissue damage
Maximum of 2 ml injection thus often small doses limit use.
Intramuscular
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
Disadvantages:
Trained personnel required for injections. The site of injection will influence the absorption, generally the deltoid muscle 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.
Inhalation
Local effect - bronchodilators
Systemic effect - general anesthesia
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. Cromolyn is taken as a powder with 50 % of the particles within the range of 2 to 6
micron. Larger than 20 micron and the particles impact in the mouth and throat. Smaller than 0.5 micron and they aren't
retained.
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, can be quite marked. This can be a real problem
in handling toxic materials in the laboratory or pharmacy.
Other ROA's
Other routes of administration include: 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; and intrathecal
directly into the cerebrospinal fluid.
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