Ampicillin (250mg) + Dicloxacillin (250mg) is a fixed-dose combination of two beta-lactam antibiotics. Ampicillin is an aminopenicillin with broad-spectrum activity against many Gram-positive and Gram-negative organisms, but is susceptible to beta-lactamase degradation. Dicloxacillin is a penicillinase-resistant penicillin (isoxazolyl penicillin) that is stable against staphylococcal beta-lactamase. This combination is designed to extend the antibacterial spectrum, particularly providing coverage against beta-lactamase-producing Staphylococcus aureus, while retaining ampicillin's coverage against organisms like E. coli, H. influenzae, and Salmonella.
Adult: One capsule (Ampicillin 250mg + Dicloxacillin 250mg) every 6 hours. For severe infections, the dose may be increased to one capsule every 4-6 hours, or as per the physician's discretion based on severity and pathogen.
Note: Administer on an empty stomach, at least 1 hour before or 2 hours after meals, to ensure optimal absorption, particularly of dicloxacillin. The capsule should be swallowed whole with a full glass of water. Complete the full prescribed course even if symptoms improve.
Both components are bactericidal beta-lactam antibiotics. They inhibit the final transpeptidation step of peptidoglycan synthesis in the bacterial cell wall by binding to penicillin-binding proteins (PBPs). This leads to the activation of autolytic enzymes in the cell wall, resulting in cell lysis and death.
Pregnancy: US FDA Pregnancy Category B. Both drugs cross the placenta. Studies in animals have not shown teratogenic risk. Use during pregnancy only if clearly needed. Considered generally safe for use in pregnancy for treating susceptible infections.
Driving: Unlikely to affect the ability to drive or use machines. However, patients should be cautioned that if they experience dizziness or other CNS effects, they should avoid these activities.
| Probenecid | Decreases renal tubular secretion of both penicillins, increasing and prolonging their serum concentrations. | Moderate |
| Methotrexate | May decrease renal clearance of methotrexate, increasing its toxicity (myelosuppression, mucositis). | Major |
| Oral Contraceptives | May reduce efficacy of oral contraceptives due to altered gut flora; advise use of a non-hormonal backup method. | Moderate |
| Warfarin | May potentiate anticoagulant effect, increasing INR and risk of bleeding. Mechanism may involve gut flora alteration and protein binding displacement. | Major |
| Allopurinol | Concurrent use with ampicillin increases the incidence of skin rashes. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | In vitro synergy against some organisms (e.g., Enterococci), but physical incompatibility if mixed in same IV line. Not relevant for oral administration. | Minor |