Drug Interactions Flashcards
A drug interaction occurs when:
The effects of one drug are altered by the co-administration of another drug, herbal medicine, food, drink, or other environmental agents.
Why is it difficult to obtain an accurate estimate of the incidence of drug interactions?
1) Unawareness
2) Under reporting
Which patients suffer from much greater rejection rates of transplants?
Epileptic patients (due to drug interactions)
Which patients are susceptible to drug interactions?
1) Poly-pharmacy
2) Hepatic or renal disease
3) Long-term therapy for chronic diseases: (epilepsy, diabetes, patients in intensive care, transplant patients, etc.)
4) More than one prescriber
5) Critically ill and elderly patients (altered homeostatic mechanisms)
6) Elderly patients
Drug interactions can be:
1) Useful
2) No consequence
3) Harmful
How can drug interactions be useful?
1) Increased therapeutic effect
2) Minimize adverse effects
3) Block acutely an adverse effect (antidote)
Imipenem deactivation can be countered with which drug?
Cilastatin
Isoniazid neuropathy can be prevented by:
Pyridoxine (B6)
What are some severe adverse drug interactions?
1) Unwanted pregnancy
2) Stroke
3) GI or cerebral hemorrhage
4) Cardiac arrhythmias
5) Blood dyscrasias
Which 2 drugs can cause blood dyscrasias?
Allopurinol and azathioprine
What are the mechanisms of drug interactions?
1) Chemical
2) Pharmacodynamic
3) Pharmacokinetic
Chemical drug interactions happen by:
Mixing drugs together outside of the body
Give some examples of chemical drug interactions:
1) Inactivation of heparin with gentamicin
2) Inactivation of heparin with hydrocortisone
3) Inactivation of gentamicin with hydrocortisone
4) Inactivation of penicillin with hydrocortisone
5) Aminoglycosides and penicillins inactivate each other
6) Diazepam can be precipitated by infusion fluids, and adsorbs to the plastic of IV bags and tubing
7) Phenytoin can be precipitated by infusion fluids
What are some examples of pharmacodynamic drug interactions?
1) Drowsiness caused by an H1-blocking antihistamine and alcohol
2) β-blockers and verapamil may precipitate heart failure, heart block, and asystole in patients with SVT
3) Antihypertensive drugs may be less effective with use of NSAIDs
4) Warfarin and aspirin may cause excessive bleeding
5) Combined diuretics
6) Potassium-sparing diuretics with potassium supplements and/or ACEi.
7) Antagonistic interactions
Why are antihypertensive drugs less effective with use of NSAIDs?
1) Inhibition of biosynthesis of vasodilator prostaglandins in the kidney
2) Sodium and water retention
Warfarin mode of action?
Inhibits the coagulation cascade
Aspirin mode of action?
Inhibits platelet function
Aspirin may predispose to ___ by direct irritation and by inhibition of PGE2 biosynthesis in the gastric mucosa.
Gastric bleeding
Give an example of interruption of physiological control loops.
β-blocking drugs with insulin mask insulin-induced hypoglycemia symptoms
Combined diuretics can cause:
1) Excessive intravascular fluid depletion
2) Electrolyte loss
3) “Pre-renal” renal failure
Thiazide and loop diuretics commonly cause:
Hypokalemia = digoxin toxicity (because of increased binding of digoxin to plasma membrane Na+/K+ -ATPase)
β2-Agonists (salbutamol) may reduce:
The plasma potassium concentration
Potassium-sparing diuretics with potassium supplements and/or ACEi may cause:
Hyperkalemia
___ is one of the most common
causes of fatal adverse drug reactions.
Hyperkalemia
The bronchodilator action of selective β2-agonists will be antagonized by:
β-blockers
The opioid antagonist __blocks actions of opioids.
Naloxone
___ blocks the action of benzodiazepines.
Flumazenil
___ blocks the action of oral anticoagulants (warfarin).
Vitamin K
___ antagonizes the action of antipsychotics.
Levo-Dopa
Neuroleptics and tricyclic antidepressants (TCAs) given with drugs producing electrolyte imbalance (diuretics) may cause:
Ventricular arrhythmias
Drugs that prolong the QT interval can cause:
Fatal polymorphic ventricular tachycardia (torsade de pointes).
Selective serotonin reuptake inhibitors and MAOIs can cause:
Serotonin syndrome
___ is an antibacterial with MAOI activity.
Linezolid
MAOIs can prevent metabolism of __ in the gut.
Tyramine
Tyramine is found in:
Cheese and red wine
What affects absorption of drugs?
1) Changes in gastric pH due to drugs
2) Some drugs within the GIT form chelates that are not absorbed
Which drugs aren’t absorbed when GI pH is changed?
1) Aspirin
2) Itraconazole
___ and ___ can complex with iron and antacids containing calcium, magnesium, and aluminum.
Tetracyclines; Fluoroquinolones
___ are often co-prescribed with calcium supplements for treatment of osteoporosis and they reduce the bioavailability of each other, leading to therapeutic failure.
Bisphosphonates
What are some examples of adsorbents?
1) Charcoal
2) Kaolin (Clay)
What are some examples of anion-exchange resins?
1) Cholestyramine
2) Colestipol
Drugs that affect the rate of gastric emptying can affect absorption of other drugs absorbed in:
The upper part of the small intestine
Drugs with anticholinergic effects decrease:
Gut motility and gastric emptying
What are some drugs with anticholinergic effects?
1) TCAs
2) Phenothiazines
3) Antihistamines
Opioids inhibit gastric emptying and reduce the absorption rate of __, without affecting
the extent of absorption.
Paracetamol
Anticholinergics reduce the bioavailability of __, as a result of increased metabolism in
the intestinal mucosa.
Levodopa
Metoclopramide increases gastric emptying and increases the absorption rate of:
1) Paracetamol
2) Propranolol
3) Mefloquine
4) Lithium
5) Cyclosporine
Drugs that inhibit P glycoprotein such
as ___ may increase bioavailability of
___, and thus its toxicity.
Verapamil; Digoxin
___ may cause a malabsorption syndrome causing reduced absorption of drugs
Neomycin
___ reduces absorption of co-administered fat soluble drugs and vitamins.
Orlistat