Sechenov School
Home › Pharmacology › Parenteral Routes of Administration (Intravenous, Intra-arterial)

Parenteral Routes of Administration (Intravenous, Intra-arterial)

Injectio intravenosa, Injectio intraarterialis

For medical students3 min readUpdated 2026-10-10

Parenteral routes of administration combine a group of methods for delivering medications into the body that completely bypass the gastrointestinal tract. Intravenous and intra-arterial access ensure a rapid pharmacological effect and require strict adherence to the rules for selecting appropriate dosage forms.

Systemic circulationWith intravenous administration, the drug immediately enters the bloodstream, bypassing gastrointestinal absorption.
Strict contraindicationAdministering oil solutions and suspensions intravenously is strictly prohibited due to the risk of embolism.
Infusion rateDrip infusion is typically performed at a rate of 20–60 drops (1–3 mL) per minute.
Fallback accessIntrasternal administration (into the sternum) is used when venous access is impossible.

Intravenous Administration: General Characteristics and Risks

Intravenous administration (Injectio intravenosa) is a critical parenteral route in which a drug is delivered directly into the systemic circulation. A key feature of this method is the virtually complete absence of a latent period. The pharmacological effect occurs instantly, which in clinical practice is described as a "needle-action" effect.

Due to its speed, the intravenous route is a primary tool in emergency medical care. In addition, it is widely used for scheduled course treatments in both inpatient and outpatient settings.

However, the direct entry of a drug into the systemic circulation carries specific risks and disadvantages:

Requirements for Dosage Forms

Far from all dosage forms are suitable for intravenous administration. A core pharmacological rule establishes that primarily aqueous solutions (solutiones aquosae) are injected into veins. Hypertonic solutions are also clinically acceptable. The only exception where lipid media are permitted is factory-produced specialized lipid nano/microemulsions.

It is strictly prohibited to inject into the vascular bed:

  1. Oil solutions (solutiones oleosae).
  2. Any suspensions (particle dispersions).
  3. Solutions containing visible gas bubbles.

The reason for this strict prohibition lies in the extremely high risk of embolism—the occlusion of blood vessels by insoluble oil droplets, solid particles, or air bubbles, which can lead to fatal consequences.

Technique and Administration Regimens

Depending on treatment goals and drug characteristics, intravenous administration is carried out in two main regimens:

1. Bolus (Slow Push) Administration Performed using a syringe, with the drug administered gradually over approximately one minute. In most cases, preliminary dilution of the drug substance is required (e.g., in isotonic 0.9% sodium chloride solution). The main goal of slow bolus administration is to avoid creating a dangerous peak concentration of the active substance in vital organs such as the heart, lungs, and major arteries.

2. Infusion (Drip) Administration This regimen is used to administer large fluid volumes. It requires specialized infusion sets that allow precise regulation of the solution delivery rate. The rate is typically set within 20–60 drops per minute, equivalent to 1–3 milliliters per minute. Infusion is indicated, in particular, for drugs with a short half-life (e.g., lidocaine) when it is necessary to maintain a stable blood concentration over an extended period.

Intra-arterial and Intrasternal Administration

In addition to the venous bed, other specific routes are used in medical practice.

Intra-arterial Administration (Injectio intraarterialis) The rationale behind this method is injecting the drug directly into the artery supplying a specific organ. The pharmacokinetic goal is to achieve the highest possible local concentration of the drug in the target organ tissues while minimizing systemic effects. Strictly designated groups of drugs are administered intra-arterially:

Intrasternal Administration (Injectio intrasternalis) With this access, the drug is injected directly into the spongy bone of the sternum. The main indication for an intrasternal injection is the acute impossibility of establishing standard venous access. Most frequently, this backup method is used in specific target groups: children and elderly patients in whom catheterization of peripheral or central veins may be difficult.

Mnemonic

The "OGS" rule for IV injections: Oils, Gases, and Suspensions must be strictly avoided due to the risk of embolism.

Frequently asked questions

What disadvantages and risks are associated with the intravenous route?

The primary disadvantage of intravenous administration is the inability to rapidly reverse the drug's action once it enters the systemic circulation. Major risks and disadvantages include:

  • Venous thrombosis — occurs at the injection site.
  • Tissue infection — risk associated with sterility breaches.
  • Hematomas — extensive subcutaneous hemorrhages during a failed puncture.
  • Pain — unpleasant sensations during the procedure.
  • Organizational complexity — the need for sterility and qualified medical personnel.

This is critical in cases of overdose or developing anaphylaxis.

Which anatomical veins are most commonly used for puncture and intravenous administration?

The veins of the cubital fossa are predominantly used for puncture and intravenous access:

  • Median cubital vein (v. mediana cubiti).
  • Median cephalic vein (v. mediana cephalica) — in an M-shaped configuration.
  • Median basilic vein (v. mediana basilica) — in an M-shaped configuration.

These veins are chosen due to their fixation to the deep fascia and the absence of adjacent superficial nerves. Cutaneous nerves run in close proximity to the main trunks of the v. cephalica and v. basilica, increasing the risk of nerve injury.

What diluents are used to prepare drugs for intravenous administration?

Aqueous diluents are used to prepare drugs for intravenous administration:

  • Water for injections.
  • Isotonic sodium chloride solution, such as 0.9% NaCl solution.
  • 5% dextrose solution.

For intravenous bolus injections, preliminary dilution (e.g., in 0.9% NaCl solution) is used to prevent peak concentrations of the substance in vital organs.

What are the primary indications for continuous intravenous infusion?

The primary indication for intravenous infusion is the need to administer large volumes of fluid and drugs with short half-lives. Specific indications include:

  • Detoxification — performing infusion therapy in the presence of intoxication symptoms.
  • Parenteral nutrition — administering nutrient formulas during unconsciousness or swallowing difficulties.
  • Supportive therapy — used in oncohematological patients during inpatient care.

This method requires specialized systems to regulate the infusion rate, which typically ranges from 20 to 60 drops per minute.

What specific complication arises from the accidental intravenous administration of an oil solution?

Accidental intravenous administration of an oil solution leads to a specific complication: embolism.

  • Embolism — dangerous occlusion of blood vessels by oil droplets entering the systemic circulation.

Because of this risk, intravenous administration of oil solutions (solutiones oleosae), as well as suspensions and liquids containing gas bubbles, is strictly prohibited. Intravenous injections must rely primarily on aqueous solutions (solutiones aquosae).

Why are oil solutions contraindicated for intravenous administration?

The administration of oil solutions (solutiones oleosae) is strictly prohibited due to the risk of embolism—the blockage of blood vessels by insoluble oil droplets.

What is the purpose of diluting drugs prior to intravenous bolus injection?

Diluting the drug (typically in 0.9% NaCl solution) and administering it slowly (over about 1 minute) are necessary to prevent dangerous peak concentrations of the substance in the heart, lungs, and major arteries.

In which situations is intrasternal administration used?

Drug administration into the sternum is a backup method. It is used when intravenous access is impossible, which is particularly relevant in the treatment of children and elderly patients.

For which drugs is intra-arterial administration indicated?

Radiocontrast agents, antineoplastic drugs (cytostatics), and, in certain cases, antibiotics are administered intra-arterially to achieve a high concentration in a specific organ.

Go deeper

More topics in Pharmacology

Inhaled CorticosteroidsXylometazolineTopical Synthetic Antifungal AgentsSodium OxybateHIV Entry InhibitorsImmunostimulantsFactors Affecting Drug ActionAstringent AgentsDisease-Modifying Antirheumatic Drugs (DMARDs)Muscarinic Antagonists: Pharmacodynamics and Clinical UseAliphatic Hypnotics (Chloral Hydrate, Clomethiazole)Antiepileptic Drugs SelectionPharmacology →