Which route of medication has the fastest rate of absorption?

Continuing Education Activity

A medication administration route is often classified by the location at which the drug is applied, such as oral or intravenous. The choice of routes in which the medications are applied depends not only on the convenience but also on the drug’s properties and pharmacokinetics. This activity describes medication administration routes and explains the interprofessional team's role in improving care for patients who undergo medication administration.

Objectives:

• Outline the routes of medication administration.

• Identify the most common adverse events associated with routes of medication administration.

• Describe the importance of routes of medication administration.

• Review how interprofessional strategies between healthcare team members can improve factors related to medication route selection to improve pharmaceutical outcomes in patients.

Access free multiple choice questions on this topic.

Introduction

A medication administration route is often classified by the location at which the drug is administered, such as oral or intravenous. The choice of routes in which the medication is given depends not only on the convenience and compliance but also on the drug’s pharmacokinetics and pharmacodynamic profile. Therefore it is crucial to understand the characteristics of the various routes and techniques associated with them. Many interprofessional healthcare team members are involved in the administration of medications to patients.

Anatomy and Physiology

Enteral Route of Medication

1. Oral administration of medication is a convenient, cost-effective, and most commonly used medication administration route. The primary site of drug absorption is usually the small intestine, and the bioavailability of the medication is influenced by the amount of drug absorbed across the intestinal epithelium. The first-pass effect is an important consideration for orally administered medications. It refers to the drug metabolism whereby the drug concentration is significantly diminished before it reaches the systemic circulation, often due to the metabolism at the liver.   

2. A sublingual or buccal route is another form of the enteral route of medication administration that offers the benefit of bypassing the first-pass effect. By applying the drug directly under the tongue (sublingual) or on the cheek (buccal), the medication undergoes a passive diffusion through the venous blood in the oral cavity, which bypasses the hepatic portal vein and flows into the superior vena cava. Compared to sublingual tissue, which has a highly permeable mucosa with rapid access to the underlying capillaries, buccal tissue is less permeable and has a slower drug absorption.[1]  

3. A rectal route is another enteral route of medication administration, and it allows for rapid and effective absorption of medications via the highly vascularized rectal mucosa. Similar to sublingual and buccal routes, rectally administered medications undergo passive diffusion and partially bypass the first-pass metabolism. Only about half of the drug absorbed in the rectum directly goes to the liver.[2]  

Parenteral Route of Medication 

1. Intravenous injection is the most common parental route of medication administration and has the benefit of bypassing the first-pass metabolism by the liver. Given their superficial location on the skin, peripheral veins provide easy access to the circulatory system and are often utilized in the parenteral administration of medications. The upper extremity is usually the preferred site for intravenous medication as it has a lower incidence of thrombophlebitis and thrombosis than the lower limbs. The median basilic or cephalic veins of the arm or the metacarpal veins on the hand's dorsum are commonly used. In the lower extremity, the dorsal venous plexus of the foot can be used.

2. An intramuscular medication route can be administered in different body muscles, including deltoid, dorsogluteal, ventrogluteal, rectus femoris, or vastus lateralis muscles. Although the dorsogluteal site, or the buttock's upper outer quadrant, is a common site chosen traditionally for intramuscular injections by healthcare professionals, it poses a potential risk of injury to the superior gluteal artery and sciatic nerve.[3] On the other hand, the ventrogluteal site, or the anterior gluteal site, targets the gluteus medius muscle and avoids these potential complications; thus, it is recommended.

3. Subcutaneous injections are another form of the parental route of medication and are administered to the layer of skin referred to as cutis, just below the dermis and epidermis layers. Subcutaneous tissue has few blood vessels; therefore, the medications injected undergo absorption at a slow, sustained rate. Subcutaneous medication can be administered to various sites, including the upper arm's outer area, abdomen avoiding a 2-inch circle around the navel, the front of the thigh, upper back, or the upper area of the buttock behind the hip bone.  

Other Routes of Medication 

1. An intranasal drug route facilitates drug absorption by passive diffusion across the single-layered, well-vascularized respiratory epithelium directly into the systemic circulation.

2. An inhaled medication is delivered rapidly across the large surface area of the respiratory tract epithelium. Drugs absorbed into the pulmonary circulation enter directly into the systemic circulation via the pulmonary vein, bypassing the first-pass metabolism. The particle size of the inhaled medication is usually 1 to 10 µm for effective delivery. The efficacy of drug delivery to the lungs depends not only on the drug particle size and morphology but also on the patient’s respiratory physiology, such as tidal volume and tracheal inspiration velocity.[4]

3. A vaginal route is an underexplored drug delivery route that is not commonly used but has the advantages of bypassing the first-pass effect and can serve as an effective method for local and systemic therapy. The venous plexuses from the vagina communicate with the vesical, uterine, and rectal venous plexuses and drain into the internal iliac veins. The veins from the middle and upper vagina drain directly into the inferior vena cava and bypass the hepatoportal system.

Indications

Enteral Route of Medication

1. Oral medications are convenient and are indicated for patients who can ingest and tolerate an oral form of medications. Some medications with short half-lives are administered orally as timed-release or sustained-release forms that get absorbed over several hours.

2. Sublingual and buccal routes are indicated for medications with high first-pass metabolism that need to avoid clearance by the liver. For instance, nitroglycerin is cleared more than 90% during a single pass through the liver; therefore, it is given as a sublingual form. The sublingual and buccal routes also have advantages of rapid absorption, convenience, and low infection incidence.

3. A rectal route is useful for patients with gastrointestinal motility problems such as dysphagia or ileus that can interfere with delivering the drug in the intestinal tract. The rectal route is also often utilized in patients near the end-of-life undergoing hospice care.[5]

Parenteral Route of Medication

1. An intravenous route directly administers the medications to the systemic circulation. It is indicated when a rapid drug effect is desired, a precise serum drug level is needed, or when drugs are unstable or poorly absorbed in the gastrointestinal tract. It is also the route utilized in patients with altered mental status or severe nausea or vomiting, unable to tolerate oral medications.  

2. An intramuscular route can be utilized when oral drug absorption occurs in an erratic or incomplete pattern; the drug has high first-pass metabolism or when the patient is not compliant. A depot preparation of the drug can be given intramuscularly, and the medication dissolves slowly into the circulation to provide a sustained dose over a more extended time. An example includes haloperidol decanoate. Vaccines are also administered via the intramuscular route.[6]   

3. A subcutaneous route is used when the drug's molecular size is too large to be effectively absorbed in the intestinal tract or when better bioavailability or a faster absorption rate is needed than the oral route. It is easy to administer and requires minimal skills, so patients can often self-administer the medication themselves. Common medications administered subcutaneously include insulin, heparin, and monoclonal antibodies. 

Other Routes of Medication

1. An intranasal route of medication can be utilized in administering nasal decongestants for cold or allergy treatment. Other uses include desmopressin for the treatment of diabetes insipidus or intranasal calcitonin for the treatment of osteoporosis. An inhaled medication route can be utilized to administer albuterol or corticosteroids such as fluticasone and to deliver inhaled anesthetics to patients.

2. A vaginal route is not commonly used but can deliver low, continuous dosing of medications which can help achieve stable drug levels. A variety of formulations can be given vaginally, including tablets, creams, gels, ointments, and pessaries. Common medications given via vaginal route include vaginal estrogen therapy for urogenital atrophy, contraceptive rings, antibiotics, or antifungals.[7]

Contraindications

Each medication administration route has unique contraindications, and the healthcare team members need to recognize them. An oral medication route is contraindicated for patients who cannot tolerate oral drugs, such as those who have altered mental status or have nausea or vomiting that hinder them from safely ingesting the drug orally. A rectal route is contraindicated in patients with active rectal bleeding or diarrhea or after a recent rectal or bowel surgery. An intramuscular route is contraindicated in an active infection or inflammation at the site of drug administration, myopathies, muscular atrophy, thrombocytopenia, or coagulopathy.

A subcutaneous route of medication is contraindicated in an actively infectious or inflamed site. Doses that require to be injected more than 1.5 mL at once should be avoided. Subcutaneous injection volumes larger than 2 mL are associated with adverse effects, including pain and leakage at the injection site.[8] An intranasal medication is contraindicated in patients with nasal trauma, anatomic obstruction, presence of a foreign body, or copious mucous or bleeding. Similarly, an inhaled medication is contraindicated in patients with airflow obstruction.

Equipment

The equipment required depends on the route chosen for medication administration. In general, equipment needed for the parenteral route may include gauze, dry cotton swab, nitrile gloves, chlorhexidine or alcohol-based antiseptic agent, tourniquet, appropriately gauged intravenous catheter, syringe, normal saline flush, and a bandage. A local anesthetic agent may be used for larger cannulas or to minimize discomfort in some patients, such as pediatric patients. A lubricant can be utilized in rectal or vaginal administration of medication to reduce friction and discomfort.

Personnel

One personnel is usually sufficient for all routes of medication administration. Still, additional assistance may be helpful if the patient is unable to stay in an optimal position or when administering to children.

Preparation

The “five rights” are emphasized for the preparation of medication administration: right patient, right drug, right dose, right site, and right timing.[9] It is essential to explain to patients how the medication will be administered, obtain consent for procedures when indicated (e.g., central venous catheter), and help prepare patients before they receive their medication. The site of application of the medication should be chosen based on its adequacy and indications. The label on the medication should be checked for its name, dose, and approved usage route.

Technique

Techniques involved in each route of medication administration are different, and some of the important points are summarized as follows:

Intravenous Route

A tourniquet may be used over the site intended for the intravenous medication to make the vein more visible and easier to access. However, when used, the tourniquet must be removed before injecting the medication to prevent extravasation. In central lines or peripherally inserted central catheter (PICC) lines for the medication administration, ultrasound guidance is often used.[10]  

Intramuscular Route

Intramuscular injection should be done at a perpendicular angle as it has been shown to be the most effective method for patient comfort, safety, and medication efficacy.[11] Skin traction and deep pressure to the muscle can help decrease patients' pain and discomfort.[12] When injecting to the dorsogluteal site, aspirating for a few seconds is recommended, given its proximity to the gluteal artery.[13]

Subcutaneous Route

A subcutaneous route requires minimal skills and training, and patients can often quickly learn to inject medications to themselves. It is recommended that instead of using the same site, patients rotate the sites of injection to avoid complications such as lipohypertrophy that can cause incomplete medication absorption.[14] The injection is usually at an angle if using a needle/syringe or at a perpendicular angle if using an injector pen.

Rectal Route

It is recommended to have the patient lie onto the left side with the right knee bent towards the chest as this position enables the medication to flow into the rectum and subsequently to the sigmoid colon by gravity. Separate the buttocks with the non-dominant gloved hand and gently insert the medicine 2 to 4 cm into the rectum using a dominant hand's gloved index finger. A lubricant may be used for the patient’s comfort. If administering a laxative suppository, the patient will need a bedpan or commode or be placed close to the toilet. It is recommended that the patient remains on the side for 5 to 10 minutes unless otherwise specified by the medication’s directions.[15]    

Vaginal Route

Position the patient onto their back with legs bent and feet resting flat on the bed. A lubricant can be used to reduce friction against the vaginal mucosa as the medication is administered. Gently separate labial folds with the non-dominant gloved hand while with the dominant gloved index finger, insert the lubricated suppository to about 8-10 cm along the posterior vaginal wall.

Inhaled Route

Each inhaler has its instructions from the manufacturer. For metered-dose inhalers, some of the essential techniques include: shake the inhaler vigorously for a few seconds before each puff; inhale through the mouth, not the nose when breathing in the medication; keep the tongue under the mouthpiece to avoid blocking the mouthpiece; take a slow deep breath as the medication canister is pressed and hold the breath for 5 to 10 seconds and then exhale. Cleaning the inhaler regularly is recommended to prevent a buildup of medications. Spacers or chambers can help patients inhale the aerosol and help decrease the deposition of the medication in the mouth or throat.

Complications

The medical personnel should recognize the potential complications of each route of medication administration. The parenteral route can cause pain or discomfort in the area of application, bleeding, bruising, infection, or inflammation. Infiltration is a common complication of the intravenous route whereby the intravenous fluid or medication enters the surrounding tissue and not the vein. It is not deemed severe unless the infiltrated medication is a compound that may damage the surrounding tissue, such as a chemotherapeutic agent or a vesicant, in which case the complication is termed extravasation, and this may lead to tissue necrosis. Although the intravenous route has the benefit of rapidly delivering drugs to patients, this may cause nonspecific severe cardiopulmonary effects, and the healthcare personnel should closely monitor the patients.

For intramuscular injections, there are site-specific complications to be aware of. In deltoid muscle injection, an unintentional injury to radial and axillary nerves with resultant paralysis or neuropathy may not always resolve.[16] As discussed previously, the dorsogluteal site injection carries an increased risk of sciatic nerve injury, and therefore the ventrogluteal site is more recommended.[3] Complications associated with the subcutaneous route are more medication-specific. For instance, in subcutaneous insulin, lipohypertrophy or lipoatrophy can develop, leading to slower or incomplete insulin absorption at the injection site.[17] Therefore, using different injection sites is recommended to patients.

In the intranasal route, interseptal nasal perforation had been reported in some patients, particularly those using intranasal steroids for a prolonged period.[18] Rebound congestion in patients on chronic nasal decongestants is seen as the sinusoid vasculatures do not respond as well to the adrenergic drug with prolonged use and result in a hyperemic, congested mucosa. Complications associated with inhaled medications are also often medication-specific. For instance, inhaled corticosteroids can cause local deposition that leads to thrush or dysphonia, and sometimes cough, throat irritation, and contact hypersensitivity also have been reported.[19]

Clinical Significance

Administering medication is the hallmark of treating patients in different healthcare settings. The interprofessional healthcare team members need to understand the unique properties of each route of medication administration. Knowing contraindications and potential complications can help avoid unnecessary risks in patients, while understanding indications can help choose the best medication delivery route.

Enhancing Healthcare Team Outcomes

Each route of medication administration has its unique characteristics that need to be considered by the healthcare team when caring for patients. Specific techniques, such as central venous catheter placement and PICC lines, require more advanced skills and training, and it is important to communicate and plan on how the process will proceed. The healthcare members involved in patient care should also be aware of and actively monitor for potential immediate and delayed medication administration complications. Informing patients well about the process and involving them in the decision-making process whenever appropriate can improve the overall healthcare outcome. For instance, in the rectal or vaginal route, patients may prefer to self-administer the drugs. Healthcare personnel should be aware of potential personal or cultural barriers to these medication routes.[7]

Nursing, Allied Health, and Interprofessional Team Interventions

Minimizing pain or discomfort associated with medication administration can help improve patient experience and health outcomes. Utilizing local anesthetics when appropriate for the parenteral route or using lubricants in the rectovaginal medication route can be helpful.

Nursing, Allied Health, and Interprofessional Team Monitoring

Being aware of and monitoring for potential immediate and delayed complications upon medication administration is essential. For example, in the central venous catheter, adverse effects such as bleeding, hematoma, thrombosis, or infection should be monitored closely.[20] Also, nursing staff should help maintain the area of the venous catheter sterile, check for its functionality regularly, and communicate with other healthcare team members when there are issues.

Review Questions

References

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