Common Drug Interactions Medicine Notes

Drug Interaction Statins: (Atorvastatin, Simvastatin, Lovastatin) and Grapefruit juice Antiplatelet drugs: (Clopidogrel) NSAIDs: (Aspirin, Celecoxib,Ibuprofen) Anticoagulant drugs:(Warfarin, Heparin) Multivalent ions and Levothyroxine Fluoroquinolones: (Ciprofloxacin Moxifloxacin) Bisphosphonates: (Alendronic acid, Pamidronate) Tetracyclines: (Tetracycline, Minocycline) Nitrates and PDE5 inhibitors ACE inhibitors: (Ramipril,Lisinopril) and Potassium-elevating drugs Ritonavir and Protease inhibitors: (Lopinavir) Beta-blockers and Calcium channel blockers Negative Effect Grapefruit juice contains furanocoumarins which interact with enzymes that reduce statin metabolism – increasing the risk of side effects such as muscle pain and aches Antiplatelet drugs, NSAIDs, and anticoagulant drugs individually increase the risk of bleeding. Therefore, the risk of bleeding is even greater if any of these drugs are taken in combination with one another. Furthermore, other drugs – such as SSRI antidepressants – also increase the risk of bleeding with these medicines. Multivalent ions interact with many medicines, reducing the ability of drugs to carry out their therapeutic goals. Multivalent ions include calcium, magnesium, iron – and are also found in milk and antacids. Multivalent ions reduce the effectiveness of drugs such as levothyroxine, the antibacterial drugs tetracyclines and fluoroquinolones, and the osteoporosis drug class, bisphosphonates. Nitrates cause hypotension and PDE5 inhibitors – such as sildenafil and tadalafil – also cause hypotension. Therefore, there is a significant risk of severe hypotension if both drugs are taken together ACE inhibitors increase potassium levels, raising the risk of hyperkalemia. Taking ACE inhibitors with other K-elevating drugs then – such as trimethoprim or potassium supplements – should be avoided. Ritonavir inhibits CYP enzymes that otherwise metabolize protease inhibitors. This means less dose of protease inhibitors can be used to achieve the same clinical effect without causing excess side effects. Beta-blockers – such as metoprolol – should be avoided with calcium channel blockers (verapamil/diltiazem) as the combination increases the risk of heart failure and a slow heart rate (bradycardia). Broad-spectrum antibiotics and Warfarin Digoxin and Loop or thiazide diuretics Aminoglycosides and Loop diuretics Antihistamines and Benzodiazepines, SSRIs, Antipsychotic drugs Macrolides, Amiodarone, SSRIs, Fluoroquinolones, Quinine, Antipsychotic drugs Corticosteroids: (Prednisolone, Hydrocortisone) and NSAIDs MAO inhibitors: (Isocarboxazid, Tranylcypromine, Phenelzine) and Tyramine Omeprazole and Clopidogrel Macrolides and Statins Broad-spectrum antibiotics – such as penicillins and cephalosporins – kill gut flora which otherwise produces vitamin K. This means that these antibiotics increase the risk of bleeding with warfarin. Loop diuretics (furosemide) and thiazide diuretics (hydrochlorothiazide) increase the risk of digoxin toxicity by causing low potassium levels. Aminoglycosides (gentamicin, amikacin) cause ototoxicity and kidney damage. Taking aminoglycosides with loop diuretics (furosemide) increases the risk of these adverse effects. First-generation antihistamines cause sedation. Taking antihistamines with other drugs that cause sedation – such as those listed – increases the risk of sedation. Some drug classes prolong the QT interval – meaning that they increase the risk of heart rhythm problems, arrhythmias. Taking any combination of drugs in those listed increases the risk of QT prolongation as each of these drugs/drug classes individually carries this risk. Corticosteroids increase the risk of peptic ulceration and GI bleeding when taken with NSAIDs. Tyramine is found in foods such as fermented products, aged meats and cheese, alcohol, soy sauce, and many others. Taking foods with tyramine increases the risk of hypertensive crisis when taken with MAO inhibitors. Omeprazole – a proton-pump inhibitor – reduces the antiplatelet effects of clopidogrel. Macrolides – such as clarithromycin – inhibit CYP enzymes that metabolize statins. Therefore, the risk of adverse effects of statins increases when taken with macrolides. Sulfonylureas, Metformin, Thiazolidinediones Phenytoin and Warfarin, Estrogens, Progestogens Corticosteroids and Beta-2 agonists: (Albuterol, Terbutaline) Alpha-blockers and Antihypertensive drugs Each of these drugs can individually cause hypoglycemia. Taken together, in any combination, this increases the risk of hypoglycemia further (or any other drug class that lowers blood glucose levels). Phenytoin induces CYP enzymes and so reduces plasma concentrations of drugs such as warfarin, estrogens, and progestogens – reducing their clinical effects. Corticosteroids increase the risk of hypokalemia (low blood potassium levels) when taken with beta-2 agonists such as albuterol and terbutaline. Alpha-blockers include drugs such as terazosin, prazosin, and tamsulosin – all of which can lower blood pressure. Taking alpha-blockers with other drugs that lower blood pressure can produce an additive effect that results in dangerously low blood pressure. This principle applies to any two (or more) drug classes that reduce blood pressure.