Drug Interactions Flashcards
Drug interaction
One drug/vehicle alters effect of another; not an adverse reaction (unexpected), not toxic effect (overdose), not side effect (expected)
What are the major types of drug interactions?
Pharmacological, Pharmacodynamic, Pharmacokinetic
Pharmacologic interaction
- Physical/chemical interaction between drugs, drug solutions, dosing equipment
- Ex: Doxy and temp. (becomes less active w/ improper storage) - detrimental
- Enrofloxacin + LRS (LRS chelates abx and makes inactive) - detrimental
- Often caused by MIXING - cloudy, precipitation, catheter flushing
- Consequences: difficult to predict, precipitates can be toxic/irritants, drugs can be inactivated or NOT biologically available - treatment failure
Pharmacodynamic interactions
- Additive, synergistic, or antagonistic interaction of the effect of combining two drugs and effect on patient
- Ex: synergistic activity of two antibiotics - helpful
- Either act on same receptors or those that regulate common process - direct vs. physiological interaction or elicit effects that are not receptor-mediated but have final common pathways - systemic interaction
Pharmacokinetic interactions
- Interactions b/t drugs which impact the absorption, distribution, metabolism or excretion of the drug
- most common and most difficult to keep track of
- Ex: herbal supplements in combination with prescription drugs (not FDA regulated, can have toxic SE, can affect metabolism of other drugs) - can be detrimental
What are some detrimental drug interactions?
Toxicity and Treatment failure
What are helpful drug interactions?
Using known interaction to increase the efficacy of some treatments or decrease the incidence of adverse drug effects
How to prevent pharmacologic interactions
- Don’t mix drugs prior to injection
- sequential rather than simultaneous drug addition to IV
- Flush catheter!!!
- Use immediately after preparation
Additive pharmacodynamic interaction
- Sedation - e.g barbiturates and benzodiazepines
- Analgesia - combo of opioids and NSAIDs (Physiological interactions)
Synergistic Pharmacodynamic Interactions
Greater than expected increase in drug activity from drug combo; e.g. Penicillins + aminoglycosides
Antagonistic interactions
Pharmacodynamic effects are the basis of the use of reversal agents which often have same drug target or biological pathway Ex: metdetomidine (analgesic) and atipamezole (reversal)
Complex physiological interactions
- Diuretics (furosemide)
- Interact w/ many drugs due to effects on renal function
- Ex: Digitalis
Absorption Pharmacokinetic Interactions
Can affect uptake of drug by the body
- Oral absorption - drug binding:
- pH effect on uptake
- Gut drug transporters - either bringing in or out of gut lumen/portal circulation
Oral Drug Physical Interactions
- Cations interaction with drugs is common mechanism- decrease uptake/bioavailability
- Ex: oral antacids, gastric protectants (sucralfate), cation rich feed/oral supplements, Milk diets in nursing animals are high in Ca, Can be used for drug overdose tx
Pharmacokinetic interaction alterations in Gastric pH
- Can impact dissolution/uptake
- For non-transport (passive) mediated uptake
- Antacids (incr pH) decr absorption of weak acids
- Infections (decr pH) incr absorption of weak acids Ex: antifungals - absorption pH sensitive
