IV drug delivery administers medications directly into the bloodstream for rapid effect. This method relies on a continuous system of fluid, container, and tubing to transport the drug to the patient. A potential problem is the unintended loss of the drug as it travels through the plastic administration set. This interaction between the medication and the tubing material can compromise the intended therapeutic dosage, making the selection of proper equipment a serious safety consideration.
Understanding Drug Adsorption and Absorption
The loss of medication during intravenous infusion occurs through sorption, a collective term for two distinct mechanisms: adsorption and absorption. Adsorption is the phenomenon where drug molecules stick to the surface of the plastic tubing material. This is typically a rapid, surface-level interaction influenced by the tubing’s surface area and chemical properties.
Absorption, in contrast, involves the drug molecules penetrating and diffusing into the plastic matrix of the tubing itself. This process is generally slower than adsorption, resulting in the drug becoming dissolved within the polymer material. Both processes reduce the concentration of the active pharmaceutical ingredient that ultimately reaches the patient, potentially leading to sub-therapeutic dosing.
The susceptibility of a drug to sorption is determined by its physicochemical properties, particularly its lipophilicity, or lipid solubility. Highly lipophilic drugs are attracted to fatty substances and tend to interact strongly with the plastic components of standard intravenous tubing. These drugs are prone to partitioning out of the aqueous solution and into the plastic. Additionally, drugs with low molecular weight can more easily diffuse into the tubing matrix, exacerbating the absorption effect.
Identifying High-Risk Drug Categories
Medications requiring low-sorbing tubing are overwhelmingly those with high lipophilicity, causing them to be drawn to the plastic. Cardiovascular medications are a major category of concern, with nitroglycerin being a prominent example. A significant percentage of nitroglycerin can be lost to standard tubing in the initial phase of infusion, which is unacceptable for a drug used in emergency situations.
Another class includes certain sedatives and anticonvulsants, specifically benzodiazepines like diazepam. Diazepam is highly sorbed to plastic materials, with losses sometimes reaching up to 50% in initial infusion through standard polyvinyl chloride (PVC) lines. This loss can severely impair the intended therapeutic effect, such as treating status epilepticus.
Immunosuppressants, such as tacrolimus and cyclosporin A, also exhibit high sorption levels due to their complex, lipid-soluble structures. These drugs are administered in precise, low concentrations, making any loss a significant threat to maintaining therapeutic blood levels for organ transplant patients. Other high-risk examples include certain chemotherapy agents, lipid-soluble vitamins, and some hormones.
Materials Used in Low-Sorption Systems
Standard intravenous administration sets are frequently constructed from polyvinyl chloride (PVC) due to its flexibility, strength, and low cost. PVC is inherently rigid and requires the addition of plasticizers, such as diethylhexyl phthalate (DEHP), to make it pliable. The presence of these plasticizers makes the PVC matrix more attractive to lipophilic drugs, enhancing the absorption process and resulting in drug loss.
Low-sorbing systems use materials that are chemically more inert and do not rely on plasticizers for flexibility. These alternatives are often polyolefin (PO)-based materials, including polymers like polyethylene (PE) and polypropylene (PP). These non-PVC materials minimize physical and chemical interaction with lipophilic drug molecules. For instance, polyolefin-based tubes deliver over 90% of highly sorptive drugs like diazepam, compared to higher losses with PVC tubing.
Other non-PVC materials used in specialized tubing include polybutadiene (PBD) and thermoplastic elastomers (TPEs). These materials are designed to reduce both surface adsorption and matrix absorption, providing a safer fluid path for sensitive medications. By eliminating plasticizers and using polymers with low lipophilicity, these alternatives prevent the drug from partitioning out of the solution and into the tubing wall.
Clinical Impact and Safety Protocols
The impact of drug sorption is a reduction in the delivered dose, which can lead to treatment failure, especially with drugs that have a narrow therapeutic window. For instance, a significant initial loss of a cardiovascular drug like nitroglycerin may result in an inadequate therapeutic response. This is particularly dangerous during the early phase of infusion when the loss to the tubing surface is at its maximum.
To mitigate these risks, healthcare facilities must implement strict safety protocols focused on proper tubing selection. Pharmacy verification is a primary safeguard, ensuring the correct low-sorbing line is dispensed alongside the high-risk medication. Distinct visual labeling on specialized tubing and packaging helps to clearly differentiate it from standard PVC sets.
Nursing staff must be trained in mandatory double-checks to confirm the use of the appropriate administration set. Clear communication between pharmacists and prescribers regarding specific tubing requirements is essential to prevent medication errors. Adhering to these protocols ensures that the patient receives the intended and accurate dose of the medication.