Routes of drug administration
Definition:A route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body.
Routes of administration can broadly be divided into:
Entral : used for systemic (non-local) effect, substance is given via the digestive tract.
Parenteral: A drug administered parenterally is one injected via a hollow needle into the body at various sites and to varying depth.
But in our daily practice the term parental is reserved for injections; that is why we can add a third category called:
Other routes of administration. (Topical, Inhalation, ..etc.)
1-Entral route of administration: -(Oral) Swallowing (p.o., per os)
- Buccal / Sublingual: placed under the tongue
- Rectum: Absorption through the rectum
Oral route: - It is intended for systemic effects resulting from drug absorption through the various epithelia and mucosa of the
Advantages:
1- Convenient -- can be self- administered, portable, no pain, easy to take.
2- Cheap - no need to sterilize, compact, multi-dose bottles, automated machines produce tablets in large quantities.
3- Variety - fast release tablets, capsules, enteric coated, layered tablets, slow release, suspensions, mixtures.
Disadvantages:
1- Sometimes inefficient: only part of the drug may be absorbed
2- First-pass effect: drugs absorbed orally are initially transported to the liver via the portal vein 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.
The first pass effect is the term used for the hepatic metabolism of a pharmacological agent when it is absorbed from the gut and delivered to the liver via the portal circulation. The greater the first pass effect, the lower the bioavailability of the drug (the rate and extent of the drug reaching systemic circulation).
3- Food - Food and G-I motility can affect drug absorption. Often patient instructions include a direction to take with food or take on an empty stomach. - Absorption is slower with food (milk and milk products) for tetracyclines and penicillins, etc. However, for propranolol bioavailability is higher after food, and for griseofulvin absorption is higher after a fatty meal.
4- Sometimes may have adverse reactions e.g. Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agent may be included with an antibiotic.
5-Not suitable for unconscious patient - Patient must be able to swallow solid dosage forms. Liquids may be given by tube.
6-May cause irritation to gastric mucosa, nausea and vomiting.
7- Destruction of some drugs by gastric acid and digestive juices.8-Unpleasant taste of some drugs.
9- Effect too slow for emergencies.
10- Local effect : Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties.
3- Buccal/Sublingual route:
Some drugs are taken as smaller tablets which are held in the mouth (buccal tablet) or under the tongue (sublingual tablet).
- Buccal tablets are often harder tablets [4 hour disintegration time], designed to dissolve slowly.
- E.g Nitroglycerin, as a softer sublingual tablet [2 min disintegration time], may be used for the rapid relief of angina.
- Nicotine containing chewing gum may be used for cigarette smoking replacement.
Advantages
1- Avoid hepatic first pass - The liver is by-passed thus there is no loss of drug by first pass effect for buccal administration. Bioavailability is higher.
2- Rapid absorption - Because of the good blood supply to the area, absorption is usually quite rapid.
3- Drug stability - pH in mouth relatively neutral (of the stomach - acidic). Thus a drug may be more stable.
Disadvantages
1- 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.
2- Small doses only can be accommodated easily.
4-Rectal route: Most commonly by suppository or enema.
1. Unconscious patients and children
2. If patient is nauseous or vomiting
3. Absorption may be variable
4. Good for drugs affecting the bowel such as laxatives
5. Irritating drugs contraindicated
Eg. Some drugs are commonly given by this route including indomethacin, theophylline, metoclporomide, diclofenac.
Advantages:
1-By-pass liver: Some of the veins draining the rectum lead directly to the general circulation, thus by-passing the liver.
2-This route may be most useful for patients unable to take drugs orally or with younger children.
Disadvantages:
1-Erratic absorption - Absorption is often incomplete and erratic. However for some drugs it is quite useful.
2-Not well accepted by some patients.
4-Parentral route of administration (IV. IM. SC.)
a-Intravascular (IV, IA) placing a drug directly into the blood stream
b-Intramuscular (IM) - drug injected into skeletal muscle
c- Subcutaneous (SC) - Absorption of drugs from the subcutaneous tissues
Diagram Showing IV, IM, and SC Injection
a-Intravascular (IV, IA): - placing a drug directly into blood stream. -May be - Intravenous (into a vein) or - intraarterial (into an artery) -Drugs may be given into a peripheral vein over 2 to5 minutes or longer by infusion.
-Intravenous injections are often used in emergencies e.g. epileptic seizures, acute asthma, or cardiac arrhythmias. -Absorption phase is bypassed, so (100% bioavailability)
Advantages
1- precise, accurate and immediate onset of action: A quick response is possible ,and high concentration attained rapidly
2-Total dose : The whole dose is delivered to the blood stream. Large doses can be given by extending the time of infusion.
3-Fairly pain free.
Disadvantages:
1-It may be difficult to find a suitable vein.
2-Greater risk of adverse effects: May be toxic because of the rapid response, toxicity can be a problem with rapid drug administrations
3-Requires trained personnel to give intravenous injections.
4-Expensive: Sterility, pyrogen testing and larger volume of solvent means greater cost for preparation, transport and storage.
5-Risk of embolism.
B-Intramuscular :(into the skeletal muscle).
Advantages
1-Very rapid absorption of drugs in aqueous solution.
2-Larger volume, than sc, can be given by IM injections.
3-A depot or sustained release effect is possible with IM injections, e.g. procaine penicillin
Disadvantages:
1-Trained personnel required for IM injections. The site of injection will influence the absorption, generally the deltoid muscle is the best site
2-Absorption is sometimes erratic, especially for poorly soluble drugs, e.g. diazepam, The solvent maybe absorbed faster than the drug causing precipitation of the drug at the site of injection.
3-Pain at injection sites for certain drugs
Subcutaneous (SC):
This involves administration of the drug dose just under the skin. Slow and constant absorption .
Advantages:
1-Can be given by patient, e.g. in the case of insulin.
2-Absorption is slow but usually complete, and is limited by blood flow, and affected if circulatory problems exist. Improved by massage or heat.
3-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.
5-Topical route:
1-Skin :A-Dermal cream, ointment (local action)
B--Intradermal, (into the skin itself) is used for skin testing some allergens.
C- Transdermal- absorption of drug through skin (i.e systemic action)
I. stable blood levels(controlled drug delivery system)
II. No first pass metabolism
III. Drug must be potent or patch becomes too large - e.g.,nitroglycerin transdermal patch.
II Mucosal membranes:
1-eye drops (onto the conjunctiva)
2-ear drops
3-intranasal route (into the nose)
6-Inhalation route
Used for gaseous and volatile agents and aerosols.
Advantages
A- Large surface area
B- thin membranes separate alveoli from circulation
C- high blood flow
As result of that a rapid onset of action due to rapid access to circulation.
This route of administration can be used for :
1- Local effect - bronchodilators
Systemic effect - general anesthesia
Disadvantages
1- Most addictive route of administration because it hits the brain so quickly.
Difficulties in regulating the exact amount of dosage.
Sometimes patient having difficulties in giving themselves a drug by inhaler.
Other routes of administration:
- Intrathecal (into the spinal canal) - This means injecting the drug into the cerebrospinal fluid (CSF), through a special CSF needle by making a puncture through L3-L4, or L4-L5, intervertebral space. This method is commonly used in the setting of chemotherapy regimen in CNS prophylaxis or treatment. and for spinal anesthesia .
Intraplueral Means injecting the drug directly into the pleural space to induce pluerodesis (obliteration of the pleural space), or to give chemotherapy directly to the pleural or peritoneal space.
- Intraperitoneal, (infusion or injection into the peritoneum) e.g. peritoneal dialysis in case of renal insuffeciency.
- Intra articular injection: This means injecting the drug into the synovial fluid to get a direct local action of the drug into the joint space, e.g. local steroid hormone injections.
- Epidural injection: This technique is somewhat similar to the intrathecal injection, except that the injection is given in the epidural space. It is commonly used to give local analgesia during labor.
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عملي (7) 24/11/2016