1. Clinical Overview
Amoxycillin is a broad-spectrum, bactericidal, beta-lactam antibiotic belonging to the aminopenicillin class. It is a semisynthetic 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 primary care setting.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentrations are achieved within 1-2 hours post oral administration. | Approximately 6-8 hours, necessitating dosing every 8 hours for most infections. | Approximately 74-92% when administered orally, unaffected by food. |
2. Mechanism of Action
Amoxycillin 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 structural component. 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 otitis media (caused by susceptible strains of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis)
- Acute bacterial sinusitis
- Community-acquired pneumonia (mild to moderate)
- Acute exacerbation of chronic bronchitis
- Uncomplicated skin and skin structure infections
- Acute uncomplicated cystitis
- Pharyngitis/Tonsillitis (caused by Streptococcus pyogenes)
4. Dosage & Administration
Adult Dosage: Mild to Moderate Infections: 250-500 mg orally every 8 hours. Severe Infections/Respiratory Infections: 500-875 mg every 12 hours or 500 mg every 8 hours.
Administration: May be taken with or without food. Taking with food may reduce gastrointestinal upset. Capsules/Tablets should be swallowed whole with a full glass of water. The oral suspension must be shaken well before each use. Complete the entire prescribed course even if symptoms improve.
5. Side Effects
Common side effects may include:
- Diarrhea (may be mild to moderate)
- 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. | Major |
| Allopurinol | Concomitant use increases the incidence of non-allergic skin rash. | Moderate |
| Oral Contraceptives | May reduce efficacy of oral contraceptives due to altered enterohepatic circulation; advise use of a non-hormonal backup method. | Moderate |
| Warfarin and other Anticoagulants | May potentiate anticoagulant effect, increasing risk of bleeding; monitor INR closely. | Major |
| Other Bacteriostatic Antibiotics (e.g., Tetracyclines, Chloramphenicol) | May theoretically antagonize the bactericidal effect of amoxycillin. | Moderate |
7. Patient Counselling
- DO complete the full course of therapy as prescribed, even if you feel better.
- DO take the medicine at evenly spaced intervals (e.g., every 8 hours).
- DO inform your doctor if you have a history of allergies, especially to penicillin or cephalosporins.
- DO report severe diarrhea, abdominal cramps, or blood/mucus in stool immediately.
- DO use an additional, non-hormonal form of contraception if you are on oral contraceptive pills.
- DON'T share your medication with others.
- DON'T save leftover antibiotics for future use.
- DON'T skip doses.
8. Toxicology & Storage
Overdose: Primarily gastrointestinal (severe nausea, vomiting, diarrhea). With massive overdose, particularly in renal impairment, CNS effects such as agitation, confusion, behavioral changes, dizziness, and seizures may occur. Crystalluria leading to renal toxicity is possible.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Keep away from children. For reconstituted oral suspension: Store in a refrigerator (2-8°C). Do not freeze. Shake well before use. Discard any unused portion after 7 days (check manufacturer's label as it may vary from 7-14 days).