DRUG INTERACTIONS Foreign Language

Tetracycline + Metal-containing drugs

decreased Tetracycline Absorption

Fluoroquinolones + Metal-containing drugs

decreased Fluoroquinolones Absorption

Cholestyramine + Digoxin

decreased Digoxin Absorption

Cholestyramine + Warfarin

decreased Warfarin Absorption

Penicillamine + Metal-containing drugs

decreased Penicillamine Absorption

Sucralfate + Levothyroxine

decreased Thyroxine Absorption

Adsorbent + Any drug

decreased Drug Absorption

Cathartic + Any drug

decreased Drug Absorption

Anticholinergics (Hyoscine N-butylbromide)

decreased GI motility

Atropine + Antacid

increased Antacid Absorption

Atropine + Amphetamine

decreased Amphetamine Absorption

Nicotine + Antacid

decreased drug A

Antacid + Bisacodyl

premature liberation of Bisacodyl

Antacid + Ketoconazole

decreased Ketoconazole Absorption

Antacid + Salicylates

decreased Salicylates Absorption

Antacids

alter pH of stomach

H2RA

alter pH of stomach

PPI

alter pH of stomach

Antibiotics + Digoxin

increased Digoxin Absorption

Antibiotics

alteration of GI microbial flora

Antibiotics + OCP

decreased OCP Absorption

MAO-I (Tranylcypromine & Phenelzine)

inhibition of metabolism in intestinal cells

Epinephrine + Lidocaine

increased Lidocaine Bioavailability (a good interaction since Epinephrine is a vasoconstrictor)

Aspirin + Warfarin

Warfarin will be displaced – free drug increases

Valproic Acid + Phenytoin

Phenytoin will be displaced – risk of gingival hyperplasia

Warfarin + Phenylbutazone

Hemorrhage due to displacement

Glibenclamide + Phenylbutazone

Hypoglycaemia due to displacement

OHA (Oral Hypoglycemic Agent) + ASA

Hypoglycaemia due to displacement

Bilirubin + Salicylates

Kernicterus due to displacement

Digoxin + Quinidine

Arrhythmia due to tissue & cellular interaction

SSRI + MAO-I

Serotonin Syndrome (↑ serotonin from both drugs)

Fluoxetine (Prozac®)

SSRI (↑ serotonin)

CYP3A4 – inhibited by Grapefruit

increased drug levels (oxidation pathway)

CYP1A2 – inhibited by Cigarette smoking

increased drug levels (metabolism slowed)

Methylxanthines

↑ renal clearance via ↑ GFR & renal blood flow

Probenecid + Penicillin

decreased renal excretion of Penicillin (good interaction)

Probenecid + Indomethacin

decreased renal excretion of Indomethacin

NSAIDs + Lithium salts

decreased renal excretion of Lithium

NSAIDs + Methotrexate

decreased renal excretion of Methotrexate

Quinidine + Digoxin

decreased renal & non-renal excretion of Digoxin

Corticosteroids + ASA

increased renal excretion of ASA

Poisoning with acidic drugs (ASA, Phenobarbital)

treat with NaHCO₃ (urine alkalinizer)

Poisoning with basic drugs (Amphetamine, Ephedrine)

treat with NH₄Cl (urine acidifier)

Alcohol + Barbiturates

Increased sedation (Additive CNS depression)

Alcohol + Antihistamines (1st gen)

Increased sedation (Additive CNS depression)

Alcohol + Chloral hydrate

Increased sedation (Additive CNS depression)

Atropine + Hyoscine

Excessive anticholinergic effect

Digoxin + Quinidine

Arrhythmia (Prolonged QT interval)

Alcohol + Chlorpropamide

Increased hypoglycemic effects

Flecainide + Verapamil

Increased negative inotropic & chronotropic effects

Epinephrine + Beta-blockers

Opposing effects – Epinephrine (tachycardia) vs Beta-blockers (bradycardia)

Thiazide diuretics + Digoxin

Hypokalemia leads to increased Digoxin toxicity

Naloxone + Opioid Analgesics

Antagonistic effect – reversal of opioid action

Smoking Cessation

Increases concentration of substrate drugs of CYP1A2

Clozapine + Haloperidol

Changes metabolism upon stopping/starting one

Trimethoprim + Sulfamethoxazole

Combined bactericidal action through folic acid inhibition

Penicillin + Gentamicin

Synergistic antipseudomonal activity

Trimethoprim + Sulfamethoxazole

Greater than additive bactericidal effect

Amoxicillin + Clavulanic Acid

Increased Amoxicillin effect (β-lactamase inhibition)

Ampicillin + Sulbactam

Increased Ampicillin effect

Piperacillin + Tazobactam

Increased Piperacillin effect

Levodopa + Carbidopa

Increased Levodopa effect (prevents peripheral breakdown)

Phenoxybenzamine + Catecholamines

Antagonism (for pheochromocytoma)

Warfarin + Vitamin K

Antidote for Warfarin toxicity

Heparin + Protamine SO₄

Antidote for Heparin toxicity

Opioids + Naloxone

Antidote for Opioid toxicity

Atropine + Neostigmine

Antidote for Atropine toxicity

Benzodiazepine + Flumazenil

Antidote for Benzodiazepine toxicity

Procaine + Sulfonamides

Antagonism of Sulfonamide’s antibacterial activity

Penicillin + Erythromycin

Antagonism (Bactericidal + Bacteriostatic interaction)

Black Cohosh + Antihypertensive

Increased effect of antihypertensive (hypotension)

Coenzyme Q10 + Warfarin

Vitamin K antagonism; increased INR & risk of bleed

Dong Quai + β-blockers

Increased β-blocker levels; increased hypotension

Dong Quai + Benzodiazepines

Increased Benzodiazepine levels; increased drowsiness & CNS depression

Echinacea + Immunosuppressants (e.g. monoclonal antibodies)

Decreased immunosuppression

Ephedrine (Ma Huang) + β-blockers

Sympathomimetic effect; hypertension

Ephedrine (Ma Huang) + MAOIs

Increased & prolonged sympathomimetic effect; hypertensive crisis

Ephedrine + Corticosteroids

Decreased corticosteroid levels; reduced steroid effectiveness

Evening Primrose Oil + Antiplatelets

Both are antiplatelets; increased risk of bleeding

Evening Primrose Oil + Phenothiazines

Reduced seizure threshold; risk of seizures

Ginkgo biloba + Warfarin/Heparin

Both have blood thinning effect; increased bleeding risk

Ginseng + MAOIs

Increased GABA metabolism & dopamine levels; may cause mania symptoms

Kava-Kava + Acetaminophen

Increased potential for hepatotoxicity (elevated LFTs, hepatic failure)

Kava-Kava + Azole Antifungals

Increased risk of hepatic toxicity (enzyme interaction)

Kava-Kava + Statins

Increased risk of hepatic toxicity

Kava-Kava + Barbiturates

Increased GABA receptor affinity; increased CNS depression

Kava-Kava + Levodopa

Dopamine blockade; decreased effectiveness of Levodopa

Soy + Levothyroxine

Decreased Levothyroxine levels; may cause hypothyroid symptoms

St. John’s Wort + Irinotecan

Reduced levels of active Irinotecan metabolite; decreased myelosuppression

St. John’s Wort + Digoxin

Decreased concentration of Digoxin in blood

Valerian + Sedatives

Increased CNS depression; drowsiness and sedation

Valerian + Benzodiazepines

Displacement + additive CNS depression; increased drowsiness

Ginger/Garlic/Feverfew + Warfarin

Direct platelet inhibition; increased bleeding risk

Wheatgrass + Warfarin

Antagonistic effect due to Vitamin K content; inadequate anticoagulation