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Drug Interactions in Clinical Dentistry

This section covers the important interactions that may occur between drugs a patient is taking for non-dental conditions and common antimicrobials, analgesics, local anaesthetic and antianxiety preparations prescribed or used in clinical dentistry.

Common drug interactions that could have serious consequences are identified. It is important that dentists are aware of potential drug interactions.

Interactions with Antibiotics

Drug Interacting Drug Effects and Recommendations
Penicillins, Cephalosporins Bacteriostatic antibiotics ex. macrolides, tetracyclines, clindamycin Bacteriostatic antibiotics may interfere with the action of bactericidal antibiotics. Consult with other practitioner for optimal therapy.
Penicillins, Cephalosporins, Tetracyclines, Ciprofloxacin Oral contraceptives Stimulation of oestrogen. Elimination may decrease effectiveness of the contraceptive agent, advice patient accordingly.
Penicillins, Cephalosporins Probenecid Urinary excretion of the antibiotic is retarded. Consult with physician for appropriate dosage schedule.
Penicillins Enoxaparin, Heparin High dose penicillin can increase the bleeding, advice to use cautiously.
Methotrexate Urinary excretion of Methotrexate may be inhibited, advice to use cautiously.
Ampicilin Allopurinol High incidence of skin rash has been reported. Substitute ampicillin by amoxicillin.
Atenolol Atenolol concentrations may be reduced.
Cephalosporins Drugs that cause nephrotoxicity or ototoxicity ex. aspirin, aminoglycosides, amphotercin B, cisplastin cephalosporins. Additive toxicity may occur. Cephalexine and cefoxitin are apparently safe.
Clindamycin, Macrolides, Tetracyclines Bactericidal antibiotics ex. penicillins, cephalosporins. The action of bactericidal antibiotics may be inhibited. Avoid concurrent use.
Clindamycin Erythromycin, Clarithrimycin, Azithromycin Antagonism can occur between these drugs. Avoid concurrent use. Do not use one agent for antibiotic prophylaxis after recent use of the other.
Kaolin Absorption of clindamycin is reduced.
Macrolides Chloramphenicol, Clindamycin, Lincomycin Erythromycin and other Macrolides may interfere with the antibacterial effects of the other agents. Avoid concurrent use.
Digoxin Absorption of digoxin with poor bioavailabity is increased. Advise patient accordingly.
Erythromycin, Clarithromycin Cisapride The antimicrobial drugs impair the metabolism of second drug. Serious cardiac toxicity is possible. Avoid concurrent use.
Alfentanil, Bromocryptine, Caffeine, Carbamazepine, Corticosteroid, cyclosporine, midazolam, theophylline drugs, warfarin, valproic acid Erythromycin and clarithromycin may interfere with the metabolism of theses drugs. Use IV agents cautiously.
HMG-CoA reductase inhibitors Erythromycin and clarithromycin interfere with the metabolism of these drugs possibly causing rhabdomyolysis. Avoid concurrent use.
Erythromycin Drugs that cause ototoxicity or especially hepatotoxicity ex. furosemide, flurouracil The use of erythromycin for prophylaxis endocarditis is probably not a problem. Increased risk of ototoxicity and hepatotoxicity may warrant consultation with the physician.
Tetracyclines Antacids, Bismuth, Calcium, Iron, Magnesium or Zinc salts, H2 antihistamines Absorption of antacids is impaired. Space administration schedules to avoid simultaneous ingestion.
Lithium salts Plasma Li+ concentrations may be increased. Advise patient accordingly.
Anisinodine, Warfarin In patients with poor dietary habits vitamin K, tetracyclines may increase the effects of oral anticoagulant, advice to use cautiously.
Doxycycline Barbitrurates, Alcohol, Carbamazepine, Phenytoin Hepatic clearance of doxycycline is increased. Adjust dosage upwards or use alternative tetracycline.
Oxytetracycline Insulin Hypoglyceamic action of oxytetracycline reduces the insulin requirements.
Metronidazole Alcohol Alcohol metabolism is altered, leading to build up of acetaldehyde.
Cimetidine Hepatic clearance of metronidazole is decreased.
Barbiturates, Phenytoin Hepatic clearance of metronidazole is decreased. Consider increasing dose if therapy proves to be sub optimal. However, metronidazole may decrease phenytoin which may warrant physician's consultation.
Warfarin Hepatic clearance of warfarin is decreased. Consult physician for full course therapy.
Lithium Renal toxicity of lithium may occur.

Interactions with Analgesics

Drug Interacting drug Effect and recommendation
Aspirin and other NSAIDs NSAIDs  The ulcerogenic and platelet- inhibiting effects of these drugs are increased, but not the analgesia. Aspirin may decrease the effect of some NSAIDs. Avoid concurrent use but ensure optimal NSAID therapy.
Drugs that cause nephrotoxicity and ototoxicity (ex. aminoglycosides, cyclosporine, furosemide, vancomycin)     Short courses for pain relief are probably of little concern, but avoid or minimize concurrent use.
Antidiabetic drug (insulin or oral agents) Hypoglycemic effect is enhanced.      
Anti-cancer drugs ex. methotrexate NSAIDs reduce  the  clearance of methotrexate out of the body from the kidneys.  This can lead to having too much methotrexate in  blood.
Alcohol, corticosteroids Combination may result in gastrointestinal ulceration and bleeding. Corticosteroids may also increase salicylate clearance.
ACE inhibitors, Beta- blockers, Diuretics Hypotensive effects may be reduced.
Aspirin, other NSAIDs and acetaminophen Anticoagulants and thrombolytics, broad- spectrum beta lactam antibiotics Combination may result in increased bleeding, especially with aspirin. Cautious use of acetaminophen is acceptable(<2g/day).
Aspirin Valproic acid Increased plasma concentration of valproic acid and additive anti-platelet effects may increase tendency to bleed. Advice to use cautiously.
  Carbonic anhydrase inhibitor Increased CNS toxicity from aspirin or the carbinic anhydrase inhibitor may result.
Antacids, Griseofluvin Salicylate concentrations reduced.
Ibuprofen Digoxin Ibuprofen decreases digoxin concentrations. Substitute acetamoniphen to avoid possibility of increased toxicity.
Acetaminophen Alcohol   Acetaminophen hepatotoxicity is more likely in chronic alcoholics.
Cholestyramine   Concurrent ingestion inhibits acetaminophen absorption.
Beta blockers, Barbiturates, Phenytoin Alteration of acetaminophen metabolism may increase risk of hepatotoxicity. Advice to use cautiously.
Opioids analgesics and agonists-antagonists Alcohol, CNS depressants, local anaesthetics, antidepressants, antipsychotics, centrally acting antihypertensives, antihistamines, cimetidine, MgSO4 Increased CNS and respiratory depression may occur. Use cautiously, perhaps in reduced dosage.
Antimuscaranics, antidiarrheals, antihypertensive Opioids increase the effects of these drugs.
Naltrexone, opoid agonist- antagonists These drug block the analgesic effect of opioids. Substitute with ibuprofen or similar NSAID for pain.
MAO inhibitors, procarbazine Meperidine results in marked toxicity and is absolutely contraindicated. Use other opioids cautiously.

Interactions with Local Anaesthetics

Drug Interacting Drug Effect and Recommendation
Local anaesthetics Alcohol, CNS depressants, antidepressants, antipsychotics, opioids, centrally acting hypertensives, antihistamines (parentral) Increased CNS and respiratory depression may occur.
Antiarrhythmic drugs Increased cardiac depression may occur.
Anticholinestarases Local anaesthetics may antagonises the effects of anticholinesterases on muscle contractility. Treat myasthenic patients after consultation with the physician.
Amides Amiodarone, beta blocker, cimetidine Metabolism of amides in the liver is reduced.
Esters Anticholinesterases, sulfonamides Metabolism of esters is reduced. Inhibition of sulfonamide action may occur.
Adrenergic vasoconstrictor Inhalation anaesthetic Increased possibility of cardiac arrythmia exists with some agents. Consult with anaesthesiologists.
Methyl dopa, tricyclic antidepressants Sympathomimetics effects may be enhanced.
Beta blockers, adrenergic neoron blockers, entacapone Hypertensive and/or cardiac reactions are more likely.
Antipsychotics Vasoconstrictor action is inhibited, which may lead to hypotensive responses.

Interactions with Anti Anxiety-Sedatives

Drug Interacting Drug Effects and recommendation
Barbiturates, benzodiazepines, chloral hydrate, propofol, hydroxyzine Alcohol, CNS depressants, antidepressants, antipsychotics, opioids, centrally acting hypertensives, antihistamines (parentral) Increased CNS and respiratory depression may occur.
Barbiturates, benzodiazepines, propofol Antihypertensives, antipsychotics, IV opioids, lithium Intravenous administration in patients receiving these medications can lead to hypotension.
Barbiturates Barbiturates simulate metabolism of many drugs. Avoid multidose use.
Antipsychotics Increased tendency for hypothermia. Evaluate temperature as needed.
Chloramphenicol, valproic acid Metabolism of barbiturates decreased. Avoid multidose use. Advise patient of possible post sedation drowsiness.
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