parenteral

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A route of administration in pharmacology and toxicology is the path by which a drug, fluid, poison, or other substance is brought into contact with the body.^[1]

A substance must be transported from the site of entry to the part of the body where its action is desired to take place (even if this only means penetration through the stratum corneum into the skin). Using the body's transport mechanisms for this purpose, however, is not trivial. The pharmacokinetic properties of a drug (that is, those related to processes of uptake, distribution, and elimination) are critically influenced by the route of administration.

Classification

Routes of administration can broadly be divided into:

• topical: local effect, substance is applied directly where its action is desired.
• enteral: desired effect is systemic (non-local), substance is given via the digestive tract.
• parenteral: desired effect is systemic, substance is given by routes other than the digestive tract.

The U.S. Food and Drug Administration recognizes 111 distinct routes of administration. The following is a brief list of some routes of administration.

Topical

• epicutaneous (application onto the skin), e.g. allergy testing, typical local anesthesia
• inhalational, e.g. asthma medications
• enema, e.g. contrast media for imaging of the bowel
• eye drops (onto the conjunctiva), e.g. antibiotics for conjunctivitis
• ear drops - such as antibiotics and corticosteroids for otitis externa
• intranasal route (into the nose), e.g. decongestant nasal sprays. Nasal administration can also be used for systemic effect. This is related to the transmucosal route through a mucous membrane via insufflation.
• vaginal, e.g. topical estrogens, antibacterials

Enteral

Enteral is any form of administration that involves any part of the gastrointestinal tract:

• by mouth (orally), many drugs as tablets, capsules, or drops
• by gastric feeding tube, duodenal feeding tube, or gastrostomy, many drugs and enteral nutrition
• rectally, various drugs in suppository or enema form

Parenteral by injection or infusion

• intravenous (into a vein), e.g. many drugs, total parenteral nutrition
• intraarterial (into an artery), e.g. vasodilator drugs in the treatment of vasospasm and thrombolytic drugs for treatment of embolism
• intramuscular (into a muscle), e.g. many vaccines, antibiotics, and long-term psychoactive agents. Recreationally the colloquial term 'muscling' is used.^[2]
• intracerebral (into the cerebrum) direct injection into the brain. Used in experimental research of chemicals^[3] and as a treatment for malignancies of the brain.^[4] The intracerebral route can also interrupt the blood brain barrier from holding up against subsequent routes.^[5]
• intracerebroventricular (into the cerebral ventricles) administration into the ventricular system of the brain. One use is as a last line of opioid treatment for terminal cancer patients with intractable cancer pain.^[6]
• intracardiac (into the heart), e.g. adrenaline during cardiopulmonary resuscitation (no longer commonly performed)
• subcutaneous (under the skin), e.g. insulin, a slang term for this method of administration is skin popping (usually done with recreational drugs)
• intraosseous infusion (into the bone marrow) is, in effect, an indirect intravenous access because the bone marrow drains directly into the venous system. This route is occasionally used for drugs and fluids in emergency medicine and paediatrics when intravenous access is difficult.
• intradermal, (into the skin itself) is used for skin testing some allergens, and also for mantoux test for Tuberculosis
• intrathecal (into the spinal canal) is most commonly used for spinal anesthesia and chemotherapy
• intraperitoneal, (infusion or injection into the peritoneum) e.g. peritoneal dialysis
• Intravesical infusion is into the urinary bladder.
• Intracavernosal injection is into the base of the penis.

Other parenteral

• transdermal (diffusion through the intact skin), e.g. transdermal fentanyl patches in pain therapy, nicotine patches for treatment of addiction
• transmucosal (diffusion through a mucous membrane), e.g. insufflation (snorting) of cocaine, sublingual, i.e. under the tongue, nitroglycerine, buccal (absorbed through cheek near gumline), vaginal suppositories
• inhalational, e.g. inhalational anesthetics
• intracisternal: given between the first and second cervical vertebrae – used to withdraw cerebrospinal fluid for dignostic purposes.

Other

• epidural (synonym: peridural) (injection or infusion into the epidural space), e.g. epidural anesthesia
• intravitreal

Advantages and disadvantages

There are advantages and disadvantages to each route of administration

Inhalation

Advantages

• Fastest method, 7-10 seconds for the drug to reach the brain
• User can titrate (regulate the amount of drug they are receiving)

Disadvantages

• Most addictive route of administration because it enters the brain so quickly
• Difficulties in regulating the exact amount of dosage
• Patient having difficulties in giving themselves a drug by inhaler

Injection

Injection incompasses intravenous (IV), intramuscular (IM), and subcutaneous (subcut) (sub-Q no longer a safe abbreviation)

Advantages

• Fast: 15-30 seconds for IV, 3-5 minutes for IM and subcutaneous
• 100% bioavailability
• suitable for drugs not absorbed by the gut or those that are too irritant (anti-cancer)
• One injection can be formulated to last days or even months, e.g., Depo-Provera, a birth control shot that works for three months
• IV can deliver continuous medication, e.g., morphine for patients in continuous pain, or saline drip for people needing fluids

Disadvantages

• Onset of action is quick, hence more risk of addiction when it comes to injecting drugs of abuse
• Patient's can't self-administer
• Belonephobia, the fear of needles.
• If needles are shared, there is risk of HIV and other infectious diseases
• It is the most dangerous route of administration because it bypasses most of the body's natural defenses, exposing the user to health problems such as hepatitis, abscesses, infections, and undissolved particles or additives/contaminants
• If not done properly, air boluses (bubbles) can occur, and be fatal
• Need for strict asepsis

Uses

Some routes can be used for topical as well as systemic purposes, depending on the circumstances. For example, inhalation of asthma drugs is targeted at the airways (topical effect), whereas inhalation of volatile anesthetics is targeted at the brain (systemic effect).

On the other hand, identical drugs can produce different results depending on the route of administration. For example, some drugs are not significantly absorbed into the bloodstream from the gastrointestinal tract and their action after enteral administration is therefore different from that after parenteral administration. This can be illustrated by the action of naloxone (Narcan), an antagonist of opiates such as morphine. Naloxone counteracts opiate action in the central nervous system when given intravenously and is therefore used in the treatment of opiate overdose. The same drug, when swallowed, acts exclusively on the bowels; it is here used to treat constipation under opiate pain therapy and does not affect the pain-reducing effect of the opiate.

Enteral routes are generally the most convenient for the patient, as no punctures or sterile procedures are necessary. Enteral medications are therefore often preferred in the treatment of chronic disease. However, some drugs can not be used enterally because their absorption in the digestive tract is low or unpredictable. Transdermal administration is a comfortable alternative; there are, however, only a few drug preparations are suitable for transdermal administration.

In acute situations, in emergency medicine and intensive care medicine, drugs are most often given intravenously. This is the most reliable route, as in acutely ill patients the absorption of substances from the tissues and from the digestive tract can often be unpredictable due to altered blood flow or bowel motility.

Notes

1. ^ "Exposition" may be a more appropriate term in toxicology. "Administration", however, can be used for deliberate substance use.
2. ^ Fenway Community Health
3. ^ MDMA (ecstasy) metabolites and neurotoxicity: No occurrence of MDMA neurotoxicity from metabolites when injected directly into brain, study shows.
4. ^ A potential application for the intracerebral injection of drugs entrapped within liposomes in the treatment of human cerebral gliomas.
5. ^ Blood-brain barrier changes following intracerebral injection of human recombinant tumor necrosis factor-α in the rat
6. ^ Acute Decreases in Cerebrospinal Fluid Glutathione Levels after Intracerebroventricular Morphine for Cancer Pain

References

Inaba, Darryl and Cohen, William. 2007. Uppers, Downers, All Arounders. Medford, Oregon: CNS Productions, Inc.

See also

• Dosage form
• Medical injection
• Catheter
• Hypodermic needle
• Drug injection
• ADME
• List of medical inhalants

External links

• The 10th US-Japan Symposium on Drug Delivery Systems
• FDA Center for Drug Evaluation and Research Data Standards Manual: Route of Administration.
• FDA Center for Drug Evaluation and Research Data Standards Manual: Dosage Form.
• MeSH Drug+Administration+Routes

[1][A.S.P.E.N.]

v • d • e Route of administration / Dosage forms Oral Enteral/digestive tract Pill · Tablet · Capsule · Orally disintegrating tablet · Elixir Respiratory tract Inhaler (Metered-dose, Dry powder) · Nebulizer Circulatory system Sublingual administration ENT Eye drop · Ear drop · Intranasal Transdermal Ointment · Cream · Transdermal implant · Transdermal patch · Lotion · Liniment · Gel · Shampoo · Paste Injection/parenteral Subcutaneous · Intravenous · Intramuscular · Intrathecal · Intracavernosal Vaginal Pessary (vaginal suppository) · Vaginal ring · Douche · Intrauterine device Rectal Suppository · Enema