Penicillin G (Potassium, Sodium) Injection

Penicillin G injection is used to treat a broad range of serious bacterial infections caused by organisms susceptible to penicillin. PENICILLIN G POTASSIUM for Injection is approved for the following conditions:

• Septicemia (bloodstream infection), empyema, pneumonia, pericarditis, endocarditis, and meningitis caused by susceptible streptococci, staphylococci (non-penicillinase-producing), and Streptococcus pneumoniae
• Anthrax (Bacillus anthracis)
• Actinomycosis — both cervicofacial and thoracic/abdominal forms
• Botulism (as adjunctive therapy to antitoxin), gas gangrene, and tetanus (as adjunctive therapy to human tetanus immune globulin)
• Diphtheria — as adjunctive therapy to antitoxin and to prevent the carrier state
• Erysipelothrix endocarditis
• Fusospirochetosis (severe infections of the mouth, lower respiratory tract, and genital area, including Vincent's infection)
• Listeria infections, including meningitis and endocarditis
• Pasteurella infections, including bacteremia and meningitis
• Haverhill fever and rat-bite fever
• Disseminated gonococcal infections caused by penicillin-susceptible Neisseria gonorrhoeae
• Syphilis — including congenital syphilis and neurosyphilis (Treponema pallidum)
• Meningococcal meningitis and/or septicemia (Neisseria meningitidis)
• Gram-negative bacillary bacteremias — though penicillin G is noted to not be the drug of choice for these infections

Penicillin G kills bacteria by blocking the construction of their cell walls. Bacteria need a strong, intact cell wall to survive — without it, they fall apart. Penicillin G targets specific proteins (penicillin-binding proteins) that bacteria use to build and maintain that wall, causing the bacteria to die. It is most effective against bacteria that are actively growing and dividing.

Penicillin G is only effective against bacteria that are susceptible to it. Some bacteria produce an enzyme called penicillinase (beta-lactamase) that breaks down penicillin and makes them resistant — those strains will not respond to this drug.

Penicillin G Potassium for Injection is always given by a healthcare professional — never self-administered. It is given intravenously (into a vein) or intramuscularly (into a muscle), and in some cases directly into specific body spaces such as the pleural cavity (intrapleural) or spinal canal (intrathecal). Doses are given frequently — typically every 2 to 6 hours — because penicillin G clears from the body quickly.

• The 20 million unit vial is for intravenous infusion only
• Doses and frequency are tailored to the specific infection, its severity, and the patient's kidney function
• Treatment should continue for at least 48 to 72 hours after symptoms resolve; strep throat infections require at least 10 days of treatment to prevent rheumatic fever
• Always follow your prescriber's instructions for the full course — stopping early can allow the infection to return or worsen

Penicillin G injection is generally well tolerated, but side effects can occur. Common ones include:

• Allergic reactions — ranging from mild hives and itching to severe anaphylaxis
• Nausea, vomiting, or gastrointestinal irritation
• Diarrhea, which can sometimes signal a serious gut infection (C. difficile)
• Pain, phlebitis (vein inflammation), or irritation at the injection site
• Fever or chills — particularly the Jarisch-Herxheimer reaction in patients being treated for syphilis
• Black or hairy tongue
• Headache and muscle aches (with Herxheimer reaction)

Seek immediate medical attention if you experience difficulty breathing, throat tightening, widespread skin blistering or peeling, seizures, confusion, severe diarrhea, or signs of kidney injury (blood in urine, decreased urination). These are serious reactions that need prompt care.

The biggest risk with penicillin G is a severe, potentially life-threatening allergic reaction called anaphylaxis. It can cause throat swelling, a sudden drop in blood pressure, and difficulty breathing. This risk is higher if you've had a prior penicillin or cephalosporin allergy, or if you react to many different allergens. Rare but severe skin reactions — including Stevens-Johnson syndrome and toxic epidermal necrolysis (widespread skin breakdown) — have also been reported and require stopping the drug immediately.

• C. difficile colitis: Antibiotic use can disrupt normal gut bacteria, allowing C. difficile to overgrow and cause dangerous diarrhea or colitis — even weeks after finishing treatment
• Neurotoxicity: Very high intravenous doses can cause seizures, confusion, muscle twitching, and coma — risk is higher with kidney impairment
• Electrolyte disturbance: Large IV doses of penicillin G potassium can raise blood potassium levels (hyperkalemia) to dangerous levels
• Kidney injury: High doses can cause renal tubular damage and interstitial nephritis (kidney inflammation)
• Jarisch-Herxheimer reaction: Patients treated for syphilis or other spirochetal infections may develop fever, chills, flushing, and rapid heartbeat within hours of starting treatment — this usually resolves within 24 hours

Several drugs can interact with penicillin G and either reduce its effectiveness or change how it is cleared from the body:

• Probenecid — blocks the kidney's removal of penicillin, raising blood levels and prolonging its action; sometimes used intentionally but needs prescriber awareness
• Aspirin, indomethacin, phenylbutazone, sulfonamides, thiazide diuretics, furosemide, and ethacrynic acid — these drugs compete with penicillin for kidney excretion, potentially prolonging its half-life
• Bacteriostatic antibiotics (chloramphenicol, erythromycins, sulfonamides, tetracyclines) — these slow bacterial growth rather than killing bacteria outright, which may reduce penicillin G's ability to work effectively; concurrent use is generally avoided
• Dextrose-containing solutions — may be contraindicated as a diluent in patients with a corn allergy

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Tell your doctor if you have ever had an allergic reaction — especially anaphylaxis or hives — to any penicillin or cephalosporin antibiotic
• Tell your doctor about all drug allergies; people who react to many allergens are at higher risk for penicillin reactions
• Tell your care team if you have kidney disease — penicillin G is cleared primarily by the kidneys, and doses must be adjusted in severe kidney impairment
• Tell your doctor if you have both kidney and liver disease — additional dose adjustment may be needed
• Inform your care team if you are pregnant — penicillin G crosses the placenta
• Tell your doctor if you are breastfeeding — penicillin G is excreted into breast milk
• This product should not be used in children who require less than one million units per dose
• Newborns, premature infants, and older adults eliminate penicillin more slowly and require careful dose monitoring
• Tell your doctor if you have a corn allergy, as some diluent solutions contain dextrose derived from corn

Taking massive doses of intravenous penicillin G — particularly in patients with severe kidney impairment — can cause serious neurological effects including agitation, confusion, hallucinations, stupor, coma, muscle twitching, seizures, and a dangerous rise in blood potassium (hyperkalemia). If overdose is suspected, penicillin G is stopped, and supportive care is provided. In some cases, hemodialysis (a kidney-filtering procedure) may be used to help remove penicillin from the blood, though its effectiveness for this purpose is uncertain.

Penicillin G kills susceptible bacteria by preventing them from building intact cell walls, causing them to rupture and die. It is most effective against bacteria that are actively dividing. To maintain the drug's effectiveness and reduce the development of resistant bacteria, it should only be used for infections proven or strongly suspected to be caused by penicillin-susceptible organisms.

Penicillin G is rapidly absorbed after intramuscular or intravenous administration, with peak blood levels occurring immediately after IV injection. It distributes widely throughout body tissues — including the lungs, liver, kidneys, muscle, and bone — but penetrates poorly into the eyes, brain, and prostate unless inflammation is present; with inflamed meninges, penetration into the cerebrospinal fluid improves. Penicillin G is excreted primarily by the kidneys (58–85% unchanged in urine), with a half-life of about 42 minutes in adults with normal kidney function. Clearance is slower in newborns, premature infants, and people with kidney impairment, which requires dose adjustment in those groups.

Store dry powder at 20º to 25ºC (68º to 77ºF). refrigerator at 2° to 8°C (36° to 46°F). refrigerated, penicillin solutions may be stored for seven days without loss of potency.