Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
52 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
Deffinition |
Effects of one drug are altered by the co-administration of another drug |
|
|
|
Epidemiology |
In-patients 1-2% Out-patients 2-4% |
|
|
|
Susceptible patients |
1. Patients with polypharmacy 2. Hepatic or renal disease 3. Long-term therapy for chronic diseases 4. Critically-ill and elderly patients (altered homeostatic mechanisms) |
|
|
|
3 Mechanisms of Drug interactions |
1. Pharmaceutical 2. Pharmacodynamic 3. Pharmacokinetic |
|
|
|
Useful interactions (increased effect) MI patients |
Antiplatelets + fibrinolactin (but risk of bleeding) |
|
|
|
Useful interactions (increased effect) Asthma patients |
Beta 2 agonist (bronchodilation) + corticosteroid (anti-inflammatory) |
|
|
|
Useful interactions (increased effect) Antibiotics Penicillinase producing staphylococci |
Amoxicillin + clavulanic acid (inhibits penicillinase) |
|
|
|
Useful interactions (increased effect) Antibiotics Imipenem |
Imipenem (inactivated by renal dipeptidase) + cilastin (inhibits renal dipeptidase) |
|
|
|
Useful interactions (increased effect) Parkinson's |
Levodopa (metabolized in the periphary) + carbidopa (inhibits levodopa metabolism in periphary so increases concentrations in CNS) |
|
|
|
Useful interactions (increased effect) Combination of antimicrobials in Tuberculosis |
1. To prevent the slowly growing micro-organisms frim developing resistance and causing re-infection 2. To attack the micro-organisms in all of 3 forms in body (alveoli, intracellular, and in caseating material) |
|
|
|
Useful interactions (increased effect) Antivirals |
Saquinavir + ritonavir (increases systemic bioavailability of saquinavir by: 1. Inhibiting first-pass effect (by inhibiting CYP3A) 2. Inhibiting fecal elimination (p-glycoprotein) |
|
|
|
Grapefruit |
Also inhibits CYP3A May cause toxicity of certain drugs Can be used with cyclosporin (which is mainly metabolized by CYP3A) for immunosuppression in transplant patients |
|
|
|
Useful interactions (minimize adverse effects) Isoniazid neuropathy |
Caused by pyridoxine (vit B6) deficiency (isonizid binds competitively to the enzyme that activates pyridoxine) Prevented by prophylactic use of this vitamin (B6) |
|
|
|
Useful interactions (minimize adverse effects) Levodopa peripheral side effects |
Peripheral side effects (nausea and vomiting) are reduced by using carbidopa (peripheral dopa decarboxylase inhibitor) |
|
|
|
Useful interactions (acutely block an adverse effect) Neuromuscular blockade |
Cholinesterase inhibitor to reverse neuromuscular blockade |
|
|
|
Useful interactions (acutely block an adverse effect) Opioid overdose |
Use naloxone |
|
|
|
Useful interactions (acutely block an adverse effect) Benzodiazepine overdose |
Flumazenil |
|
|
|
Useful interactions (acutely block an adverse effect) Reverse effect of warfarin |
1. Vitamin K (increases synthesis of clotting factors) 2. Fresh Frozen Plazma (FFP) |
|
|
|
Harmful interactions Dose-response curves Steep vs shallow |
Drugs with steep dose-response curves (low therapeutic index) are more likely to cause harm from drug interactions |
|
|
|
Harmful effects Steep dose-response curves Drugs with narrow therapeutic index |
Verapamil Sulfonylureas Levodopa |
3 drugs |
|
|
Harmful effects Drugs with high risk of interactions Whrn the patient is dependant on therapeutic effect |
Immunosuppressants (cyclosporin, tacrolimus) Glucocorticoids OCPs Anti-epileptics Anti-arrhythmics Anti-psychotics Anti-retrovirals |
7 drugs |
|
|
Harmful effects Concentration-dependant toxicity |
Digoxin Lithium Aminoglycosides Cytotoxic agents Warfarin Thioprine Anti-arrhythmic drugs |
7 drugs |
|
|
Harmful effects Drugs with saturable hepatic metabolism |
Phenytoin Theophylline Aspirin Ethanol |
4 drugs |
|
|
Harmful effects Drugs with high risk of drug interactions |
Monoamine oxidase inhibitors (MAOI) that metabolize catecholamines |
|
|
|
MAOI Drug Interactions |
Tyramine (inert substance that is in fermented cheese and wine) it displaces catecholamines from sympathetic nerve terminals to the systemic circulation, this may cause hypertensive crisis (end organ damage) |
|
|
|
Examples of Severe Drug Interactions |
1. Unwanted pregnancy from failure of contraceptive pills 2. GI or cerebral hemorrhage in warfarin patients 3. Hypertensive crisis in MAOI patients 4. Cardiac arrhythmias, secondary to interactions causing electrolyte imbalance (like diuretics) or prolongation of QT interval 5. Blood dyscrasias, from interactions between allopurinol and azathioprine |
|
|
|
Pharmaceutical Interactions definition |
Interactions of drugs outside the body Drugs may also interact in the lumen of the gut (tetracyclin + iron, colestyramine + digoxin) |
|
|
|
Examples of pharmaceutical drug interactions by percipitation |
1. Thiopentone and suxamethazone 2. Diazepam and infusion fluids 3. Phenytoin and infusion fluids |
|
|
|
Examples of pharmaceutical drug interactions by inactivation |
1. Heparin (p) and hydrocortisone 2. Gentamicin (p) and hydrocortisone 3. Penicillin (p) and hydrocortisone |
|
|
|
Phatmaceutical drug interactions in the gut by bile acid binding resins |
Mechanism: ion exchange, inhibit absorption of drugs that are ionized at normal pH Examples: digoxin, thyroxine, and diuretics |
|
|
|
Phatmaceutical drug interactions in the gut by chalating agents |
Iron with tannic acid Tannic acid chalates iron and prevents its absorption |
|
|
|
Pharmacodynamic interactions H1-blocking antihistamine and Alcohol |
Drowsiness Additive or synergistic interactions can be produced by anti-depressants, hypnotics, and some anti-epileptics |
|
|
|
Pharmacodynamic Interactions Anti-hypertensive drugs |
Anti-hypertensive drugs may be less effective by concurrent NSAIDs due to inhibition if biosynthesis of vasodilator prostaglandins in kidneys, and sodium water retention |
|
|
|
Pharmacodynamic Interactions Beta-blockers and verapamil |
Both have negative inotropic effects so they may percipitate HF in SV tach. patients They may also cause heart block and asystole |
|
|
|
Pharmacodynamic interactions Warfarin and Aspirin |
Warfarin (anticoagulant) and Aspirin (antiplatelet) Aspirin may percipitate gastric bleeding by: 1. Direcr irritation 2. Inhibition of PGE2 biosynthesis |
|
|
|
Pharmacodynamic Interactions Interruption of physiological control loops |
Beta-blockers in insulin-dependant diabetics may mask warning signs of insulin-induced hypoglycemia |
|
|
|
Pharmacodynamic Interactions Electrolyte imbalance Metolazone + Furosemide |
Cause excessive intavascular fluid depletion, electrolyte imbalance, and 'pre-renal' renal failure |
|
|
|
Pharmacodynamic Interactions Electrolyte imbalance Thiazide + Loop Diuretics |
They commonly cause hypokalemia This increases binding of Digoxin to Na/K-ATPase, thus higher Digoxin toxicity Beta-2-agonists (salbutamol) may also cause hypokalemia |
|
|
|
Pharmacodynamic Interactions Electrolyte imbalance Lidocaine |
Lidocaine with concurrent Diuretic-induced hypokalemia (by thiazide or loop diuretics) may cause antagonism od anti-dysrhythmic effect |
|
|
|
Pharmacodynamic Interactions Electrolyte imbalance Lithium |
Lithium with Diuretics-induced reduction in lithium clearance causes increase in plasma lithium conc. |
|
|
|
Pharmacodynamic Interactions Electrolyte imbalance ACEI |
ACEI with Potassium chloride and/or Potassium-retaining diuretics may cause hyperkalemia |
|
|
|
One of the most common causes of Fatal adverse drug interactions |
Hyperkalemia |
|
|
|
Pharmacodynamic Interactions Antagonistic interactions Beta-2-agonists |
Bronchodilator action is antagonized by Beta-blockers |
|
|
|
Pharmacodynamic Interactions Antagonistic interactions Anti-psychotics |
Action is antagonized by Levodopa |
|
|
|
Pharmacodynamic Interactions Neurolyptics/TCAs |
May lead to ventricular arrhythmias if used with drugs that cause electrolyte imbalance (diuretics) |
|
|
|
Pharmacodynamic Interactions Drugs that prolong QT interval |
If multiple drugs that prolong QT interval are used concurrently, can cause fatal polymorphic ventriculat tachycardia (Torsade de Pointes) |
|
|
|
Pharmacodynamic Interactions Drugs affecting serotonin |
Combinations can lead to Serotonin Syndrome Example: SSRIs + MAOI *Linezolid is an antibiotic that has some MAOI activity |
|
|
|
Pharmacodynamic Interactions Additive or synergistic effect Risk of bleeding |
Warfarin + clopidogerel + NSAIDs |
|
|
|
Pharmacodynamic InteractionsAdditive or synergistic effect Increased Neuromuscular Blockade |
Neuromuscular blockers + Aminoglycosides |
|
|
|
Pharmacodynamic InteractionsAdditive or synergistic effect Increased Sedation |
Alcohols + Benzodiazepines |
|
|
|
Pharmacodynamic Interactions Additive or synergistic effect Increases risk of QT interval prolongation |
Pimozide + Sotalol |
|
|
|
Pharmacodynamic InteractionsAdditive or synergistic effect Risk of bone marrow suppression |
Clozapine + Co-trimoxazole |
|
