PRINCIPEN '500'
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PRINCIPEN '500' (PRINCIPEN '500').
Ampicillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis and death.
| Metabolism | Ampicillin is metabolized primarily by hydrolysis to penicilloic acid; hepatic metabolism is minimal. |
| Excretion | Primarily renal (90% unchanged via glomerular filtration and tubular secretion); small amounts biliary/fecal (<5%). |
| Half-life | 0.5–1 hour; prolonged in renal impairment (up to 10 hours in anuria). |
| Protein binding | ~20% bound to serum albumin. |
| Volume of Distribution | 0.2–0.3 L/kg; limited to extracellular fluid. |
| Bioavailability | IM: 100% (complete); PO: 30–60% (acid-labile, variable). |
| Onset of Action | IM: 15–30 min; IV: immediate. |
| Duration of Action | 4–6 hours (short due to rapid renal elimination); requires frequent dosing. |
| Molecular Weight | 349.41 |
500 mg orally every 6 hours for 7-14 days for mild to moderate infections; for severe infections, 500 mg orally every 4 hours.
| Dosage form | CAPSULE |
| Renal impairment | For CrCl 30-50 mL/min: administer 500 mg every 8 hours; CrCl 10-30 mL/min: 500 mg every 12 hours; CrCl <10 mL/min: 500 mg every 24 hours. |
| Liver impairment | No specific adjustment required for hepatic impairment; caution in severe hepatic disease due to potential risk of crystalluria. |
| Pediatric use | For children >1 month: 12.5-25 mg/kg/dose orally every 6 hours; maximum 2 g/day. For neonates: 25 mg/kg/dose every 8 hours. |
| Geriatric use | Adjust based on renal function; monitor for crystalluria and superinfection; standard dosing if CrCl >50 mL/min. |
| 1st trimester | Ampicillin is generally considered safe in the first trimester; no increased risk of major birth defects has been observed in human studies. |
| 2nd trimester | Ampicillin is safe in the second trimester; placental passage occurs but therapeutic benefit outweighs risks. |
| 3rd trimester | Ampicillin is safe in the third trimester; used for group B streptococcus prophylaxis during labor. |
Clinical note
Comprehensive clinical and safety monograph for PRINCIPEN '500' (PRINCIPEN '500').
| Placental transfer | Ampicillin crosses the placenta readily; peak cord blood levels are approximately 50% of maternal serum levels within 1 hour after administration. |
| Breastfeeding | Ampicillin is excreted into breast milk in small amounts; concentrations are low and unlikely to cause adverse effects in the infant. Compatible with breastfeeding; monitor for potential gastrointestinal effects or rash in the infant. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to ampicillin or any penicillinHistory of immediate hypersensitivity reaction (e.g., anaphylaxis) to penicillins
| Precautions | Serious hypersensitivity reactions (anaphylaxis) may occur, Clostridium difficile-associated diarrhea (CDAD), Seizures may occur in patients with renal impairment or high doses, Prolonged use may result in superinfection, Risk of bleeding abnormalities with high doses |
| Food/Dietary | Avoid acidic beverages (e.g., fruit juices, soda) within 1 hour of taking ampicillin, as they may reduce absorption. Take on an empty stomach to maximize bioavailability. No specific dietary restrictions required. |
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| Lactation Rating | L1 (Safe) |
| Teratogenic Risk | Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Use only if clearly needed. No evidence of teratogenicity in first trimester; theoretical risk of diarrhea or rash in neonates if administered near term. |
| Fetal Monitoring | Monitor maternal renal function, complete blood count, and liver enzymes periodically. Observe for signs of hypersensitivity or superinfection in mother. Fetal monitoring not routinely required unless maternal infection poses risk. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies show no impairment of fertility. |
| Clinical Pearls |
| Principen '500' (ampicillin) is a penicillin-class antibiotic with activity against gram-positive cocci (except penicillinase-producing staphylococci) and some gram-negative bacilli. Use caution in patients with penicillin allergy; cross-reactivity with cephalosporins occurs in ~1% of cases. Monitor for rash, which can be maculopapular (commonly in patients with mononucleosis) or urticarial. Dose adjustment required in renal impairment (CrCl <30 mL/min). Administer on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption. Avoid concurrent use with allopurinol due to increased risk of ampicillin rash. |
| Patient Advice | Take ampicillin exactly as prescribed, even if you feel better. · Take on an empty stomach (1 hour before or 2 hours after meals) with a full glass of water. · Finish the entire course of treatment; do not stop early unless directed by your doctor. · Inform your doctor if you have a penicillin allergy, kidney disease, or mononucleosis. · Contact your doctor if you develop severe diarrhea, rash, or difficulty breathing. · Ampicillin may reduce the effectiveness of oral contraceptives; use additional birth control methods. · Store at room temperature away from moisture and heat. |