Antidotes and drug-drug interactions

Objective:

This page enlists antidotes and some drug-drug interactions and provide the the reader an idea on co-administration of which drugs to be cautious.

Key words:

Antidote, drug-drug interactions, inducer, inhibitor, side effects

Antidotes of drugs

Drugs used for the reversal of the side effect or overdose of another drug.

Acetaminophen (Paracetamol): N-Acetylcysteine (NAC) Mnemonic : Acetaminophen and Acetylcysteine sounds similar.

Anticholinergics (Atropine, TCAs, Diphenhydramine): Physostigmine

Aspirin Poisoning Activated charcoal is given as soon as possible and reduces aspirin absorption. 

For moderate or severe poisoning, fluids containing sodium bicarbonate are given by vein. 

Unless there is kidney damage, potassium is added to the fluid.

Benzodiazepines (Diazepam, Lorazepam, Alprazolam): Flumazenil Mnemonic : I flew fast with my Benz.

Beta Blockers (Metoprolol, Atenolol, Propranolol) overdose: Glucagon Mnemonic : B-B-gun

Calcium Channel Blockers (Amlodipine, Verapamil, Diltiazem) Calcium Gluconate

overdose:

Carbon Monoxide (CO): 100% Oxygen

Cardiotoxicity due to chemotherapy: Dexrazoxane is a protective medicine that shields the heart and treats accidental chemotherapy leaks

Cyanide (CN): Hydroxocobalamin or Sodium Thiosulfate

Digoxin: Digibind (Digoxin Immune Fab)

Iron (ferrous): Deferoxamine [Ferrous iron (Fe²⁺) is absorbed much better in the gut than ferric iron (Fe³⁺). 

Ferrous iron is soluble and ready to cross the intestinal lining, while ferric iron must first be converted into the ferrous state by stomach acid before the body can use it]

Heparin Protamine sulfate

Magnasium sulfate Calcium gluconate

Opioids (Morphine, Heroin, Oxycodone, Fentanyl) : Naloxone Mnemonic : Na more opioids

Organophosphates (Pesticides, Nerve Agents): Atropine + Pralidoxime (2-PAM)

Warferin Vitamin K (phytonadione) Mneominc: War is not OK

Drug drug interaction

Garlic, Ginkgo and Ginseng-increase the risk of bleeding [Memory trick: Give me a G and I'll bleed-increase the risk of bleeding leads to high risk in surgery]

 *Lithium + Amiodarone:* Risk of thyroid disturbances  

- *St. John’s Wort + Fluoxetine:* Increased risk of serotonin syndrome  

- *St. John’s Wort + Methadone:* Decreased methadone levels  

- *St. John’s Wort + Digoxin, Tacrolimus, Statins (except Rosuvastatin):* Decreased drug levels  

- *St. John’s Wort + SSRIs:* Increased risk of serotonin syndrome  

- *Aspirin + Citalopram:* No significant interaction  

Drug interaction with antacid, H2 blocker and proton pump inhibitors.

Helpful video [Clear concept]

Drug that causes QT prolongation

Many common prescription drugs can cause QT prolongation, a heart rhythm risk causing delay of electrical recharging in the heart and sometimes lead to a dangerous rhythm called Torsades de Pointes.

High-Risk Drug Classes that causes QT prolongation

Antiarrhythmics: Drugs like Amiodarone and Sotalol treat irregular heartbeats but directly affect heart channels.

Class IA and III agents carry the highest direct risk because they work by blocking cardiac ion channels. 

Examples include amiodarone, sotalol, dofetilide, disopyramide, quinidine, and procainamide. 

Antibiotics: Certain antibiotics can prolong the interval, particularly when combined with electrolyte imbalances or other medications.

High-risk choices include macrolides (azithromycin, and clarithromycin, erythromycin-all the three macrolides) and 

fluoroquinolones (ciprofloxacin, levofloxacin and moxifloxacin) can increase heart risk. 

Cisapride Cisapride is a gastrointestinal prokinetic medication that increases movement in the upper and lower digestive tract. 

It can cause severe heart risks and therefore, largely withdrawn for human use, but remains widely used in veterinary medicine.

Antidepressants: Certain choices like Citalopram and tricyclic medications carry warning labels for QT changes.

Both typical and atypical antipsychotics frequently affect cardiac repolarization. 

High-risk agents include thioridazine, chlorpromazine, haloperidol (especially intravenous), ziprasidone, and quetiapine. 

Certain antidepressants like citalopram and tricyclic antidepressants (amitriptyline) also increase risk.

Antiemetics:  Anti-nausea or antiemetic drug Ondansetron  (especially when administered intravenous) can lengthen the QT interval at higher doses.

Antifungals: fluconazole (in cirrhosis) ketoconazole

general inhalation anesthetic: Halothane

Antihistamines: Diphenhydramine, Astemizole, Loratidine, Terfanadine

Methadone: used in pain management and addiction treatment  can cause QT prolongation, a serious heart rhythm risk. It blocks heart potassium channels and can lead to a dangerous heart rate called Torsades de Pointes.

Antipsychotics: Medications like Haloperidol, Quetiapine and Ziprasidone change brain chemistry and can impact heart rhythm.

Antivirals

nelfinavir

Antimalarials

chloroquine

mefloquine 

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Patients with long QT syndrome (LQTS) must avoid the medications that prolong the QT interval or trigger dangerous heart rhythms. 

Major side effects of antitubercular drug

The primary antitubercular drug that reduces visual quality is ethambutol, which can cause toxic optic neuritis, leading to blurred vision, loss of red-green color discrimination, and reduced visual acuity. Other drugs like isoniazid and linezolid (used for drug-resistant TB) can also impact vision.

Key Vision-Affecting Drugs

• Ethambutol: Main first-line culprit; causes dose-dependent optic neuropathy, blurry sight, and color blindness.

• Isoniazid: Occasionally linked to optic neuritis and retrobulbar neuritis.

• Linezolid: Second-line option that can cause bilateral progressive optic neuropathy during long-term use. [1, 2, 3, 4, 5]

Drug induced conditions

Practice questions

Alendronate should not be taken with:

A. Water

B. Vitamin C

C. Calcium or other divalent cations

D. Paracetamol

Answer: C. Calcium or other divalent cations

Alendronate should not be taken with calcium because calcium binds to Alendronate  at digestive tract, form a compound that gut cannot absorb causing  blockage from absorbing the drug and makes it fail to work.

Which drug does NOT cause QT prolongation?

A. Haloperidol

B. Erythromycin

C. Sotalol

D. Metformin

Answer: D. Metformin

Please see the above list of drugs that cause QT prolongation.

References

1. Jayasinghe, R., Kovoor, P. (2002). Drugs and the QTc interval. Australian Prescriber-an independent review. 25(3): 63-65. DOI: 10.18773/austprescr.2002.058.

Disclaimer

Most of the information in this page are collected from Google AI Overview. These are for informational purposes only. For medical advice or diagnosis, consult a professional. AI responses may include mistakes. Learn more