ExCPT · Drugs and Drug Therapy · 6 min read
Interactions, Incompatibilities and Vaccines
- Identify major drug-drug, dietary, and herbal interactions and describe the pharmacy technician's responsibility to escalate computer alerts and patient inquiries to the supervising pharmacist.
- Distinguish between types of physical incompatibilities in compounded preparations, including precipitation, emulsion cracking, drug sorption, and container leaching.
- Explain vaccine classifications, storage and cold chain requirements, administration routes, and technician duties under pharmacist supervision.
Fundamentals of Drug-Drug Interactions and the Technician's Role
A drug-drug interaction occurs when one medication alters the therapeutic effect, absorption, metabolism, or excretion of another medication. When processing prescription orders, pharmacy computer systems frequently flag these issues. When a drug interaction alert appears, the pharmacy technician should follow pharmacy procedures to bring it to the supervising pharmacist for review before dispensing. Pharmacists perform the final clinical verification on all prescription fills and compounded preparations. The pharmacist explains the clinical consequences of drug interactions and counsels patients, and pharmacy technicians must always refer clinical questions directly to the pharmacist.
Pharmacodynamic interactions occur when drugs have opposing or additive physiological effects. For example, combining two or more central nervous system depressants, such as opioids and benzodiazepines, significantly increases the risk of severe respiratory depression. Taking the anticoagulant warfarin concurrently with nonsteroidal anti-inflammatory drugs increases the risk of severe gastrointestinal bleeding. Combining angiotensin-converting enzyme inhibitors or angiotensin receptor blockers with potassium-sparing diuretics increases the risk of hyperkalemia. Furthermore, co-administration of phosphodiesterase-5 inhibitors, like sildenafil, with organic nitrates causes profound and life-threatening hypotension. Combining multiple medications that prolong the QT interval increases the risk of fatal cardiac arrhythmias such as Torsades de Pointes. Additionally, serotonin syndrome is a toxic condition that can result from combining multiple serotonergic agents, such as selective serotonin reuptake inhibitors and monoamine oxidase inhibitors.
Pharmacokinetic interactions involve changes in drug absorption, distribution, metabolism, or excretion. Cytochrome P450 enzyme inhibitors decrease the metabolism of substrate drugs, which can lead to elevated serum levels and toxicity. Conversely, cytochrome P450 enzyme inducers increase the metabolism of substrate drugs, which can lead to reduced therapeutic effectiveness. Renal clearance can also be altered; for instance, the concomitant use of nonsteroidal anti-inflammatory drugs and methotrexate decreases methotrexate clearance, increasing the potential for methotrexate toxicity.
Common mistakes
- Overriding or closing a computer drug interaction alert without notifying the supervising pharmacist.
- Assuming live attenuated vaccines like measles, mumps, and rubella or varicella can be given to pregnant or severely immunocompromised patients.
- Confusing the administration angles for vaccines, such as using a 45-degree angle for an intramuscular deltoid injection instead of the required 90-degree angle.
- Failing to maintain or log storage unit temperatures at regular intervals using a calibrated monitoring device, which threatens cold chain integrity.
Key points
- When drug interaction alerts appear, pharmacy technicians follow pharmacy procedures to bring them to the pharmacist, who performs final clinical verification and patient counseling.
- Critical drug interactions include respiratory depression from opioids plus benzodiazepines, hyperkalemia from ACE inhibitors/ARBs with potassium-sparing diuretics, severe hypotension from sildenafil with nitrates, and GI bleeding from warfarin with NSAIDs.
- Dietary and herbal factors significantly alter therapy; examples include intestinal CYP3A4 inhibition by grapefruit juice, calcium chelation of fluoroquinolones and tetracyclines, and enzyme induction by St. John's Wort.
- Physical incompatibilities include calcium-phosphate precipitation in total parenteral nutrition, emulsion cracking, nitroglycerin sorption to PVC, and DEHP leaching into lipid or surfactant-rich drugs.
- Visual inspection of compounded sterile preparations against contrasting backgrounds detects precipitation, cloudiness, or particulates before dispensing.
- Cold chain requirements demand storing refrigerated vaccines between 2°C and 8°C and frozen vaccines (such as varicella) between -50°C and -15°C, monitored with calibrated devices.
- Under pharmacist supervision, technicians assist by collecting screening questionnaires, providing Vaccine Information Statements, preparing doses, and reporting suspected adverse events for pharmacist submission to VAERS.
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