penicillin G benzathine
(redirected from Megacillin)penicillin G benzathine
Pharmacologic class: Penicillin
Therapeutic class: Anti-infective
Pregnancy risk category B
Action
Inhibits biosynthesis of cell-wall mucopeptide; kills penicillin-susceptible bacteria during active multiplication stage
Availability
Suspension for I.M. injection: 600,000 units/ml in 1-, 2-, and 4-ml prefilled syringes
Indications and dosages
➣ Upper respiratory infections
Adults: 1.2 million units I.M. as a single dose
Children weighing 27 kg (60) or more: 900,000 units I.M. as a single dose
Infants and children weighing less than 27 kg (60 lb): 300,000 to 600,000 units I.M. as a single dose
➣ Early syphilis (primary, secondary, or latent)
Adults: 2.4 million units I.M. as a single dose
Children: 50,000 units/kg I.M. as a single dose, increased as needed up to adult dosage
➣ Congenital syphilis
Children younger than age 2: 50,000 units/kg I.M. as a single dose
➣ Late (tertiary) syphilis and neurosyphilis
Adults: 2.4 million units I.M. q week for up to 3 weeks, after aqueous penicillin G or procaine penicillin therapy
➣ Gummas and cardiovascular syphilis
Adults: 2.4 million units I.M. q week for 3 weeks
➣ Yaws, bejel, and pinta
Adults: 1.2 million units I.M. as a single dose
➣ Prophylaxis of rheumatic fever and glomerulonephritis
Adults: After acute attack, 1.2 million units I.M. q month or 600,000 units q 2 weeks
Contraindications
• Hypersensitivity to penicillins, beta-lactamase inhibitors (piperacillin/tazobactam), or benzathine
Precautions
Use cautiously in:
• severe renal insufficiency, significant allergies, asthma
• pregnant or breastfeeding patients.
Administration
• Before giving, ask patient about allergy to penicillin, beta-lactamase inhibitors, and benzathine. Be aware that cross-sensitivity to cephalosporins and imipenem also may occur.
☞ Do not give intravenously
• Inject deep I.M. into upper outer quadrant of buttock in adult or mid-lateral thigh in infant or small child. Don't inject into gluteal muscle in child younger than age 2. Rotate injection sites with repeated doses.
☞ Keep epinephrine and emergency equipment at hand in case of anaphylaxis.
• Be aware that Hoigne's syndrome (transient bizarre behavior and neurologic reactions) may immediately follow I.M. injection.
• Know that in syphilis treatment, Jarisch-Hersheimer reaction (fever, chills, headache, sweating, malaise, hypotension or hypertension) may occur 2 to 12 hours after therapy begins and usually subsides within 24 hours.
Adverse reactions
CNS: headache, lethargy, hallucinations, anxiety, neuropathy, fatigue, nervousness, tremors, euphoria, asthenia, Hoigne's syndrome, cerebrovascular accident, seizures, coma
CV: hypotension, pulmonary hypertension, vasodilation, vasovagal reaction, syncope, palpitations, tachycardia, cardiac arrest, pulmonary embolism
EENT: blurred vision, vision loss, laryngeal edema
GI: nausea, vomiting, diarrhea, epigastric distress, abdominal pain, colitis, blood in stool, glossitis, pseudomem-branous colitis
GU: hematuria, proteinuria, urogenic bladder, erectile dysfunction, priapism, nephropathy, renal failure
Hematologic: hemolytic anemia, leukopenia, thrombocytopenia
Metabolic: hypernatremia, hyper-kalemia
Respiratory: dyspnea, hypoxia, apnea, pulmonary embolism
Skin: rash, urticaria, sweating
Other: fever, superinfection, injection site reactions and pain, Jarisch-Hersheimer reaction, anaphylaxis, serum sickness
Interactions
Drug-drug. Aspirin, probenecid: increased penicillin blood level Erythromycins, tetracyclines: decreased antimicrobial activity of penicillin
Hormonal contraceptives: decreased contraceptive efficacy
Drug-diagnostic tests. Alanine aminotransferase, blood urea nitrogen, creatinine, eosinophils, granulocytes, hemoglobin, platelets, potassium, white blood
cells: increased levels
Direct Coombs' test: positive result
Sodium: decreased level
Urine glucose, urine protein: false-positive results
Patient monitoring
☞ Watch closely for anaphylaxis and serum sickness.
• In long-term therapy, monitor electrolyte levels and CBC with white cell differential; watch for electrolyte imbalances and blood dyscrasias.
• Assess neurologic status, especially for seizures and decreasing level of consciousness.
☞ Watch for evidence of superinfection and pseudomembranous colitis.
Patient teaching
☞ Teach patient to recognize anaphylaxis symptoms and to contact emergency medical services immediately if these occur.
☞ Tell patient drug may cause diarrhea. Instruct him to immediately report severe, persistent diarrhea, and fever.
• Urge patient to complete entire course of therapy as prescribed, even after symptoms improve.
• Advise patient to contact prescriber if infection symptoms get worse.
• Tell female patient that drug may make hormonal contraceptives ineffective. Advise her to use barrier birth control if she wishes to avoid pregnancy.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.