Usage
Amoxycillin is prescribed for a wide range of bacterial infections, including:
- Upper Respiratory Tract Infections: Tonsillitis, pharyngitis, sinusitis, otitis media.
- Lower Respiratory Tract Infections: Bronchitis, pneumonia.
- Genitourinary Tract Infections: Cystitis, urethritis, pyelonephritis.
- Skin and Soft Tissue Infections: Impetigo, cellulitis, abscesses.
- Gastrointestinal Infections: Helicobacter pylori infections (in combination with other medications).
- Other Infections: Endocarditis prophylaxis (prevention), Lyme disease (early stage).
Pharmacological Classification: β-lactam antibiotic, aminopenicillin.
Mechanism of Action: Amoxycillin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), which are enzymes involved in the cross-linking of peptidoglycans. This leads to cell wall instability and bacterial lysis.
Alternate Names
Amoxicillin (International Nonproprietary Name - INN), Amoxycillin Trihydrate.
Brand Names: Amoxil, Trimox, Moxatag (extended-release), and various others depending on the region. Amoxycillin is also available in combination formulations with clavulanate potassium (e.g., Augmentin, Co-amoxiclav).
How It Works
Pharmacodynamics: Amoxycillin exerts its bactericidal effect by disrupting cell wall synthesis, leading to bacterial death. It is effective against a broad spectrum of Gram-positive and Gram-negative bacteria.
Pharmacokinetics:
- Absorption: Amoxycillin is well-absorbed orally, with bioavailability around 75-90%. Food does not significantly affect absorption.
- Distribution: It is widely distributed throughout the body, achieving therapeutic concentrations in various tissues and fluids, including the lungs, middle ear, and urine.
- Metabolism: Minimal hepatic metabolism.
- Elimination: Primarily renal excretion, with a half-life of approximately 1-1.5 hours. Dose adjustments are required in patients with renal impairment.
Mode of Action: Amoxycillin binds to and inactivates PBPs, leading to inhibition of peptidoglycan cross-linking and disruption of cell wall synthesis, causing bacterial cell death.
Elimination Pathways: Primarily excreted unchanged in the urine via glomerular filtration and tubular secretion.
Dosage
Standard Dosage
Adults:
- Mild to Moderate Infections: 250-500 mg every 8 hours or 500-875 mg every 12 hours.
- Severe Infections: 875 mg every 12 hours or 500 mg every 8 hours.
Children:
- Children > 3 months and < 40 kg: 20-40 mg/kg/day divided every 8 hours or 25-45 mg/kg/day divided every 12 hours.
- Children < 3 months: 30 mg/kg/day divided every 12 hours.
Pediatric Safety Considerations: Monitor for diarrhea, as it may indicate superinfection.
Special Cases:
- Elderly Patients: Dose adjustments generally not necessary unless renal impairment is present.
- Patients with Renal Impairment: Dosage reduction required based on creatinine clearance.
- Patients with Hepatic Dysfunction: No adjustment typically needed.
- Patients with Comorbid Conditions: Consider drug interactions and monitor for adverse events.
Clinical Use Cases
Dosages for clinical situations such as intubation, surgical procedures, mechanical ventilation, ICU use, and emergency situations vary widely depending on the specific indication, patient factors, and institutional guidelines. Consult specific protocols and infectious disease experts as required.
Dosage Adjustments
Adjustments are based on creatinine clearance (CrCl). Refer to specific dosing guidelines and consider consultation with a nephrologist or pharmacist for complex cases.
Side Effects
Common Side Effects
- Nausea
- Vomiting
- Diarrhea
- Rash
Rare but Serious Side Effects
- Clostridioides difficile-associated diarrhea (CDAD)
- Anaphylaxis (severe allergic reaction)
- Stevens-Johnson Syndrome (SJS)
- Toxic Epidermal Necrolysis (TEN)
- Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)
- Cholestatic jaundice
Long-Term Effects
With appropriate use, long-term side effects are rare. Prolonged use can lead to antibiotic resistance and increased risk of superinfections, including fungal infections like thrush.
Adverse Drug Reactions (ADR)
Anaphylaxis, SJS/TEN, DRESS, CDAD, severe hepatitis, and hematological abnormalities require immediate medical attention.
Contraindications
- History of serious hypersensitivity reaction to amoxycillin, any penicillin, or cephalosporin.
Drug Interactions
- Allopurinol: Increased risk of rash.
- Probenecid: Increases amoxycillin serum levels.
- Oral Contraceptives: May decrease efficacy of oral contraceptives, though this interaction is considered weak.
- Warfarin: May enhance anticoagulant effect.
- Methotrexate: May increase methotrexate toxicity.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: B (old FDA classification). Generally considered safe for use during pregnancy.
- Breastfeeding: Amoxycillin is excreted in breast milk in low concentrations and is generally considered compatible with breastfeeding.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial cell wall synthesis.
- Side Effects: Nausea, vomiting, diarrhea, rash. Rare but serious: anaphylaxis, SJS/TEN.
- Contraindications: Hypersensitivity to penicillins or cephalosporins.
- Drug Interactions: Allopurinol, probenecid, warfarin, oral contraceptives, methotrexate.
- Pregnancy & Breastfeeding: Generally safe.
- Dosage: Varies by infection severity and patient age/renal function.
- Monitoring Parameters: Renal function (in patients with pre-existing renal disease or receiving high doses), liver function (if indicated), signs of hypersensitivity, resolution of infection.
Popular Combinations
- Amoxycillin + Clavulanate Potassium: Clavulanate is a beta-lactamase inhibitor that extends the spectrum of activity of amoxycillin.
- Amoxycillin + Clarithromycin + Lansoprazole/Omeprazole: Used for H. pylori eradication.
Precautions
- General Precautions: Assess for penicillin allergy before administration. Monitor for signs of superinfection.
- Specific Populations: Standard dosage adjustments for renal impairment and pediatric patients. Use with caution in patients with infectious mononucleosis.
- Lifestyle Considerations: No specific lifestyle restrictions usually required.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Amoxycillin?
A: The dosage varies based on age, weight, infection type, and severity. See the detailed Dosage section above.
Q2: What are the most common side effects of amoxycillin?
A: The most common side effects are gastrointestinal, including nausea, vomiting, and diarrhea. Rash can also occur.
Q3: Is amoxycillin safe to use during pregnancy?
A: Amoxycillin is generally considered safe during pregnancy. However, always consult with a healthcare provider for guidance.
Q4: Can I take amoxycillin if I’m allergic to penicillin?
A: No, Amoxycillin is a penicillin antibiotic and should not be taken if you have a penicillin allergy.
Q5: How long does it take for amoxycillin to start working?
A: You may start to feel better within a few days, but it’s crucial to complete the entire course of antibiotics as prescribed.
Q6: Can amoxycillin be used to treat viral infections?
A: No, amoxycillin is only effective against bacterial infections.
Q7: What should I do if I miss a dose of amoxycillin?
A: Take the missed dose as soon as you remember. However, if it’s close to the time for your next dose, skip the missed dose and continue your regular dosing schedule. Do not double the dose.
Q8: Can I drink alcohol while taking amoxycillin?
A: While moderate alcohol consumption is unlikely to cause a direct interaction with amoxycillin, it’s generally advisable to avoid or limit alcohol while taking any medication.
Q9: Should I take amoxycillin with food?
A: Amoxycillin can be taken with or without food, as it does not significantly affect absorption.
Q10: What should I do if I experience severe diarrhea while taking amoxycillin?
A: Severe diarrhea, especially if bloody or accompanied by fever, could indicate Clostridioides difficile infection (CDI). Contact your doctor immediately if you experience these symptoms.
