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

Anticoagulants: Vitamin K, Fresh Frozen Plasma

Fresh Frozen Plasma is the liquid, pale-yellow portion of human blood separated from a whole blood donation and rapidly frozen. It contains vital proteins and clotting factors (such as factors II, VII, IX, and X) that help the blood to clot. It replaces missing or depleted coagulation factors when a patient experiences severe bleeding or an overdose of a blood-thinning medication.

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 : (My) Benz flew me fast.

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

Cholinergics Atropine, Pralidoxime (2-PAM)

Drugs and compounds that mimic or enhance the action of the neurotransmitter acetylcholine. Direct-Acting Cholinergic Agonists: Nicotine, Pilocarpine, Bethanechol, Carbachol; Indirect-Acting Cholinergics (Acetylcholinesterase Inhibitors): Donepezil, Rivastigmine, Galantamine, Pyridostigmine & Neostigmine.

Direct-Acting Cholinergic Agonists

These drugs bind directly to cholinergic receptors to trigger a response.

Nicotine: Found in tobacco products, it is the most widely consumed direct-acting cholinergic agonist.

Pilocarpine: A natural alkaloid used as eye drops to treat glaucoma or dry mouth.

Bethanechol: A synthetic choline ester prescribed to stimulate bladder and gastrointestinal smooth muscle after surgery or urinary retention.

Carbachol: Used in eye drops during eye surgery to constrict the pupil.

Indirect-Acting Cholinergics (Acetylcholinesterase Inhibitors) These drugs block the enzyme acetylcholinesterase, increasing acetylcholine levels at nerve synapses.

Donepezil: A widely prescribed reversible inhibitor used to manage cognitive symptoms in Alzheimer's disease.

Rivastigmine: Another common reversible inhibitor delivered orally or via skin patch for Alzheimer's and dementia.

Galantamine: A reversible medication used to treat mild-to-moderate Alzheimer's disease.

Pyridostigmine & Neostigmine: Reversible agents primarily used to treat muscle weakness in Myasthenia Gravis.

Cyanide (CN): Hydroxocobalamin, amyl nitrite 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]

Ethylene glycol Fomepizole, ethanol

Insulin Glucose

Isoniazid Pyridoxine

Heparin Protamine sulfate

Hydrofluoric acid: Calcium gluconate

Magnasium sulfate Calcium gluconate

Methanol Ethanol

Methamoglobin Methylene blue

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

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

Serotonine reuptake inhibitors Cycloheptadine

Selective serotonin reuptake inhibitors (SSRIs) work by increasing the levels of serotonin—a key chemical messenger—in the brain. Common examples include sertraline, fluoxetine, and citalopram. Cycloheptadine is a first-generation antihistamine that reduces the effects of histamine by binding to the H1 receptor and stabilising it in an inactive form. Cycloheptadine also has antiserotonin activity and therefore given in a serotonin reuptake inhibitor overdose to treat serotonin syndrome by blocking excess serotonin receptors [Australian Medical Handbook].

Sulfonylurea Octreotide, glucose

Octreotide is a synthetic hormone analog that copies natural somatostatin, primarily used to treat acromegaly severe diarrhea from  certain neuroendocrine tumors (such as carcinoid tumors and VIPomas), and bleeding stomach blood vessels by reducing excess growth hormone levels, and to control severe diarrhea and flushing. It blocks extra growth hormone and gut hormones. 

Sulfonylureas are a class of oral prescription medications used to treat type 2 diabetes by binding to specific receptor sites on the pancreas, close ATP-sensitive potassium channels, open calcium channels to trigger  more insulin release. They help lower blood sugar levels, are taken as pills, and cost less than many newer diabetes drugs. Octreotide is given in a sulfonylurea overdose to stop the pancreas from releasing too much insulin and causing dangerous, repeating low blood sugar. 

Tricyclic antidepressant Sodium bicarbonate

Tricyclic antidepressant (TCA) drug "I Tri Desi Clone for Ami and Nori

Tricyclic antidepressant (TCA) drugs Try Cloning Depressed for Ami and Nori

Doxepin, Protriptyline, Amoxapine, Dosulepin / Dothiepin.

I — Imipramine, Tri — Trimipramine, Desi — Desipramine, Clone — Clomipramine, Ami — Amitriptyline, Nori — Nortriptyline.
Most TCAs names are comprising with the generic suffix -ipramine (e.g., Imipramine, Trimipramine, Desipramine, Clomipramine)-triptyline (e.g., Amitriptyline, Nortriptyline)

Mirtazapine and Mianserin are classified as a tetracyclic antidepressant (TeCA) or a noradrenergic and specific serotonergic antidepressant (NaSSA).

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 

Queensland University of Technology (QUT) has departments: Arts, Botany, C, Department, English, Fungology, History, Math, Natriuretic, Psycology

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

Drug-Induced Color Syndromes

Black syndrome: Mincocycline toxicity

Purple toe syndrome: Warfarin toxicity

Purple glove-Phenytoin

Bronze baby syndrome-Photherapy

Black color tongue-Bismuth

Green Urine Syndrome

Cause: Propofol, Methylene Blue

Yellow Vision Syndrome

Cause: Digoxin toxicity

Orange Body Fluid Syndrome/Orange urine

Cause: Rifampicin

Black Hairy Tongue Syndrome

CareCraft Nursing

antibiotic use

Al content

Scott Dugdale Holiday Bells

Drug-Induced Color Syndromes: Learn the color, remember the drug!

Brown Teeth Syndrome

Not every adverse drug reaction is just an "allergy." Some are life-threatening syndromes that every healthcare professional should recognize early.

This infographic highlights six important drug-induced syndromes every nurse, physician, pharmacist, and healthcare student should know:

• Red Man Syndrome – Vancomycin

• Gray Baby Syndrome – Chloramphenicol

• Purple Glove Syndrome – IV Phenytoin

• Blue Baby Syndrome – Nitrates/Nitrites

• Cheese Reaction – MAOIs + Tyramine-rich foods

• Stevens–Johnson Syndrome (SJS) – Sulfa drugs, anticonvulsants, NSAIDs

Early recognition, prompt discontinuation of the offending drug, and timely intervention can significantly improve patient outcomes.

As healthcare professionals, our knowledge is one of the strongest tools we have to ensure patient safety. Continuous learning transforms small observations into life-saving actions.

Which of these drug-induced syndromes have you encountered in your clinical practice? 

Red Man Syndrome

Red Man Syndrome is a reaction that occurs mainly during rapid infusion of the antibiotic Vancomycin. It is not a true allergy, but rather a rate-dependent histamine release reaction.

Why It Happens

• When Vancomycin is infused too quickly, it causes mast cells and basophils to release histamine.

• This leads to skin redness and itching, mainly on the face, neck, and upper chest.

Symptoms

• Flushing or redness of the skin especially face, neck and upper torso

• Itching (pruritus) or burning sensation

• Dizziness or low blood pressure in some cases

• Chest or back pain (rare)

How to Manage

• Stop or slow the infusion immediately.

• Give an antihistamine such as diphenhydramine (e.g., Benadryl).

• Once symptoms improve, restart the infusion slowly.

Prevention

• Always infuse Vancomycin slowly, usually over 1 to 2 hours.

• In patients with a previous reaction, premedicate with an antihistamine.

Key Point

Red Man Syndrome is an infusion-related reaction — not a true drug allergy. It can be prevented by slowing the Vancomycin infusion and using antihistamines if needed. 

Drug-induced syndromes 💊⚠️

🔴 Red Man Syndrome – Associated with vancomycin rapid infusion;

Manifests as;

1. itchy (pruritic) erythematous rash on the face, neck, and upper torso,

2. hypotension

🔵Blue Baby Syndrome – Drug-induced methemoglobinemia (e.g., nitrates, nitrites, benzocaine).

Manifests as;

1. cyanosis unresponsive to oxygen therapy

2. rapid breathing

3. lethargy

⚫ Gray Baby Syndrome – Direct administration of chloramphenicol in infants, especially premature neonates.

Manifests as;

1. ashen-gray skin color (cyanosis)

2. abdominal distension, vomiting

3. limp body (flaccidity)

4. respiratory distress

5. hypothermia

🟡 Serotonin Syndrome – Commonly caused by combining medications, such as mixing antidepressants (SSRIs, SNRIs) with other drugs like migraine medications (triptans), pain meds (tramadol); look for agitation and hyperreflexia/clonus.

⚪ Neuroleptic Malignant Syndrome (NMS) – Caused by antipsychotics; presents with "Tetrad" of symptoms,

1. high fever > 38°C

2. muscle rigidity

3. altered mental status (confusion/delirium)

4. autonomic instability (tachycardia, labile blood pressure)

SCARs ( Severe Cutaneous Adverse Reactions): SJS/TEN/DRESS SYNDROMES

🟠 Stevens–Johnson Syndrome (SJS) / Toxic Epidermal Necrolysis (TEN) – Commonly linked to antiepileptics and sulfa drugs, can also caused by infections such as mycoplasma pneumoniae and herpes simplex virus

Manifests as;

1. severe, painful blistering

2. detachment of the skin and mucous membranes.

Note-

SJS: Affects < 10% of body surface area.

SJS/TEN Overlap: Affects 10–30% of body surface area.

TEN: Affects > 30% of body surface area.

🟢 DRESS Syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms) Often due to phenytoin or allopurinol; characterized by eosinophilia.

Manifests as;

1. high fever, rash, itching

2. facial edema

3. enlarged lymph nodes.

💡 Early recognition + prompt drug withdrawal can save lives. 

Drugs That Cause Urine Discoloration

Certain medications can change the color of urine, usually harmless but sometimes alarming to patients.

1. Red / Pink / Reddish-Brown Urine

• Rifampicin / Rifampin → red-orange urine

• Phenazopyridine (urinary analgesic) → orange-red urine

• Warfarin (rare, due to hematuria in overdose)

• Beets / beetroot (not a drug, but dietary)

• Senna / anthraquinone laxatives → reddish-brown urine

2. Brown / Tea-Colored Urine

• Metronidazole (rare) → dark brown

• Chloroquine / Primaquine → brownish discoloration

• Nitrofurantoin (long-term use) → dark brown

• Levodopa / methyldopa → brown urine

• Rhabdomyolysis-inducing drugs → myoglobinuria

3. Blue / Green Urine

• Methocarbamol → green urine

• Propofol infusion (rare, green)

• Amitriptyline → blue-green urine

• Indomethacin → greenish urine

• Methylene blue (used diagnostically) → blue/green urine

4. Yellow / Bright Yellow Urine

• Riboflavin (Vitamin B2) → bright fluorescent yellow

• Phenazopyridine → orange-yellow (urinary analgesic)

5. Orange Urine

• Rifampicin / Rifapentine → orange-red

• Phenazopyridine → orange

• Sulfasalazine → orange urine

6. Purple Urine

• Indwelling catheter + UTI + phenols → “purple urine bag syndrome” (rare, elderly)

• Most urine discoloration from drugs is benign and reversible

• Red / brown urine → always rule out hematuria or myoglobinuria if clinically suspicious

• Patients on rifampicin should be warned about red-orange urine

Rifampicin = red-orange; Phenazopyridine = orange-red; Nitrofurantoin = brown; Methylene blue = blue-green; Riboflavin = bright yellow 

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.

Characteristic side effects

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