Intravenous Bolus and Infusion

SEBASTIÁN SCIOLI MONTOTO; MARÍA ESPERANZA RUIZ

The ADME Encyclopedia. A Comprehensive Guide on Biopharmacy and Pharmacokinetics

Springer

Lugar: Basel; Año: 2021; p. 1 - 10

Intravenous bolus and intravenous infusion are the two ways in which a parenteral drug solution can be administered directly into a patient?s vein. A bolus is a rapid injection, typically within seconds or a few minutes, of a solution into a vein. An IV infusion, on the contrary, involves administering the drug solution for longer periods of time. While a short infusion can last 10?20 minutes, long infusions can take several hours, even days.After an IV bolus, also called an IV injection, the complete dose of the drug reaches systemic circulation almost immediately, and that is why it is the first-choice administration route when a rapid onset of action is desired, like in emergency settings. Examples of fast IV injections or bolus administration are adrenaline in cases of cardiac arrest, phenytoin for seizures, or hydrocortisone for anaphylactic shock, among many others [1, 2].During an IV infusion, on the other hand, the solution with the drug is given slowly (typically at a constant/zero-order rate) to the patient. It is the more precise way of administering a drug, and hence it is the route of choice to administer highly toxic drugs or drugs with a narrow therapeutic index (i.e., those showing a narrow difference between the effective and toxic concentrations), such as many immunosuppressors, anticoagulants, or antineoplastic drugs. IV infusions are also the best way to perform an administration when aimed to characterize the drug pharmacokinetic behavior.As both administration modes differ in the kinetics with which the drug?s dose is available to exert its effect, we must resort to pharmacokinetics (PK) for their study. PK is the branch of pharmacology that quantitatively describes the time course of drug concentrations in the body, from absorption to excretion. It is a common expression that PK studies what the body does to the drug, conversely to pharmacodynamics, which studies what the drug does to the body (i. e., clinical or therapeutic effect).The time course of a drug?s concentration is usually divided into stages to facilitate its study: absorption, distribution, metabolism, and excretion, collectively called ADME processes, each of them characterized by particular pharmacokinetic parameters or constants (see Fig. 1). There are two main approaches within classical PK analysis: compartmental and non-compartmental analysis. About the latter, we will only say that it is based on the calculation of statistical moments derived from the drug?s concentration vs. time profile. To illustrate the most important concepts in this section, we will instead use compartmental analysis, based on equations that are obtained or derived from mass balances.In its simplest form, compartment modeling assumes the body as a single compartment and is called a one-compartment model. That is, the body is described as a single and uniform compartment, from which drugs enter and leave. This is the one we will apply here to compare both modes of IV administration, bolus, and infusion. However, the reader should keep in mind that many drugs require more complex modeling for the correct interpretation of its concentration versus time profiles required (e.g., pharmacokinetic models with two or more compartments).