Ampicillin (250mg) + Cloxacillin (250mg) is a fixed-dose combination of two beta-lactam antibiotics belonging to the penicillin class. Ampicillin is an aminopenicillin with a broad spectrum of activity against many Gram-positive and Gram-negative organisms but is susceptible to beta-lactamase degradation. Cloxacillin is a penicillinase-resistant penicillin (isoxazolyl penicillin) that is stable against staphylococcal beta-lactamase, providing coverage against penicillin-resistant staphylococci. This combination is designed to extend the antibacterial spectrum, particularly targeting infections where Staphylococcus aureus (including penicillinase-producing strains) is suspected alongside other susceptible organisms. It is bactericidal and acts by inhibiting bacterial cell wall synthesis.
Adult: One capsule (Ampicillin 250mg + Cloxacillin 250mg) every 6 hours. For severe infections, the dose may be increased to 2 capsules every 6 hours, as per physician advice. Must be taken on an empty stomach (1 hour before or 2 hours after food).
Note: ORAL: Swallow the capsule whole with a full glass of water. MUST be taken on an empty stomach: at least 1 hour before or 2 hours after meals to ensure adequate absorption. The course should be completed even if symptoms improve to prevent resistance and relapse.
Both ampicillin and cloxacillin are bactericidal beta-lactam antibiotics. They inhibit the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls by binding to and inactivating penicillin-binding proteins (PBPs). This inhibition leads to the activation of autolytic enzymes (autolysins) in the cell wall, resulting in cell lysis and death.
Pregnancy: US FDA Pregnancy Category B. Both drugs cross the placenta. Studies have not shown a clear risk of major birth defects. Use during pregnancy only if clearly needed. Generally considered safe for use in pregnancy for treating susceptible infections.
Driving: Unlikely to affect the ability to drive or use machines. However, if the patient experiences dizziness or other CNS effects (rare), they should avoid these activities.
| Probenecid | Decreases renal tubular secretion of penicillins, increasing and prolonging serum concentrations. Can be used therapeutically. | Moderate |
| Methotrexate | May decrease renal clearance of methotrexate, increasing risk of methotrexate toxicity (myelosuppression, mucositis). | Major |
| Oral Contraceptives | May reduce efficacy of oral contraceptives due to altered gut flora and possibly other mechanisms. Advise use of a non-hormonal backup method. | Moderate |
| Warfarin | May potentiate anticoagulant effect, increasing INR and risk of bleeding. Mechanism may involve alteration of gut flora reducing vitamin K production. | Major |
| Allopurinol | Co-administration with ampicillin increases the incidence of skin rash, especially in patients with hyperuricemia. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | In vitro synergy against some organisms (e.g., Enterococci), but physical incompatibility if mixed in same IV line. Can be administered separately. | Minor |
| Tetracyclines, Chloramphenicol, Sulfonamides | Bacteriostatic antibiotics may antagonize the bactericidal effect of penicillins. Avoid concurrent use unless clearly indicated. | Moderate |