1. Clinical Overview
Amoxycillin is a broad-spectrum, bactericidal, beta-lactam antibiotic belonging to the aminopenicillin class. It is a semi-synthetic derivative of ampicillin with enhanced oral bioavailability. It acts by inhibiting bacterial cell wall synthesis, leading to osmotic lysis and cell death. It is effective against a wide range of Gram-positive and some Gram-negative bacteria, but is susceptible to degradation by beta-lactamases. It is a first-line agent for many common infections in the Indian context.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentrations are achieved within 1-2 hours post oral administration. | The bactericidal effect persists for approximately 6-8 hours, necessitating dosing every 8 hours for most infections. | Approximately 74-92% following oral administration, not significantly affected by food. |
2. Mechanism of Action
Amoxycillin is a bactericidal antibiotic. It binds to specific penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. This binding inhibits the final transpeptidation step of peptidoglycan synthesis in the bacterial cell wall, a critical component for cell wall structural integrity. The inhibition leads to the activation of autolytic enzymes (autolysins) in the cell wall, resulting in lysis and death of the bacterium.
3. Indications & Uses
- Acute bacterial sinusitis
- Acute otitis media
- Community-acquired pneumonia (mild to moderate)
- Acute exacerbation of chronic bronchitis
- Uncomplicated skin and skin structure infections
- Uncomplicated urinary tract infections (UTIs)
- Dental infections (e.g., periodontitis, dental abscess)
- Pharyngitis/Tonsillitis (caused by Streptococcus pyogenes)
4. Dosage & Administration
Adult Dosage: 250-500 mg orally every 8 hours. For severe infections: 500-875 mg every 12 hours or 500 mg every 8 hours. Maximum daily dose: 3-4 grams.
Administration: Can be taken with or without food. Taking with food may reduce GI upset. Capsule/Tablet: Swallow whole with a full glass of water. Do not crush or chew sustained-release formulations. Suspension: Shake the bottle well before each use. Use the measuring device provided. Complete the full prescribed course even if symptoms improve.
5. Side Effects
Common side effects may include:
- Diarrhea (may indicate pseudomembranous colitis)
- Nausea
- Vomiting
- Abdominal discomfort
- Skin rash (non-allergic, maculopapular)
- Oral or vaginal candidiasis (thrush)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Probenecid | Decreases renal tubular secretion of amoxycillin, increasing and prolonging its blood levels. | Moderate |
| Methotrexate | Amoxycillin may reduce renal clearance of methotrexate, increasing risk of methotrexate toxicity (bone marrow suppression, mucositis). | Major |
| Allopurinol | Concomitant use increases the incidence of non-allergic skin rash. | Moderate |
| Oral Contraceptives | Potential for reduced efficacy of oral contraceptives; advise use of a backup non-hormonal contraceptive method. | Moderate |
| Warfarin and other Coumarin Anticoagulants | May potentiate anticoagulant effect, increasing INR and risk of bleeding. Monitor INR closely. | Major |
| Other Bacteriostatic Antibiotics (e.g., Tetracyclines, Chloramphenicol) | Theoretically may reduce the bactericidal effect of amoxycillin (antagonism). | Moderate |
7. Patient Counselling
- DO complete the entire course of medication as prescribed, even if you feel better.
- DO take the medicine at evenly spaced intervals for best effect.
- DO inform your doctor if you have a history of allergies, especially to penicillin or cephalosporins.
- DO inform your doctor about all other medicines, vitamins, and herbal products you are taking.
- DONT skip doses. If you miss a dose, take it as soon as you remember. If it's almost time for the next dose, skip the missed dose and continue your regular schedule. Do not double the dose.
- DONT share your medicine with anyone else.
- DONT use it for viral infections like the common cold or flu.
8. Toxicology & Storage
Overdose: Primarily gastrointestinal (severe nausea, vomiting, diarrhea). May lead to electrolyte imbalances. In patients with renal impairment, high doses can cause CNS effects including confusion, lethargy, myoclonic jerks, and seizures.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Keep in the original container tightly closed. Keep out of reach of children. For reconstituted oral suspension: Store in a refrigerator (2-8°C). Do not freeze. Shake well before use. Discard any unused suspension after 7 days (check manufacturer's label).