Pen-G10 lac unit/vial

Pen-G (penicillin G) is a natural, narrow-spectrum beta-lactam antibiotic administered by injection. It is indicated for the treatment of infections caused by susceptible strains of specific microorganisms, as established by culture and susceptibility testing where possible.

Established / guideline-supported uses

• Streptococcal infections, including pharyngitis/tonsillitis, erysipelas, cellulitis, scarlet fever, and streptococcal bacteremia caused by susceptible group A beta-hemolytic streptococci
• Pneumococcal infections (pneumonia, empyema, bacteremia) caused by susceptible Streptococcus pneumoniae
• Meningococcal meningitis and meningococcemia caused by susceptible Neisseria meningitidis
• Syphilis (all stages, including neurosyphilis and congenital syphilis) caused by Treponema pallidum — Pen-G (aqueous crystalline form) is the treatment of choice for neurosyphilis and is the only recommended treatment in pregnancy
• Clostridial infections, including gas gangrene and tetanus, usually as an adjunct to antitoxin and surgical management
• Diphtheria, as an adjunct to diphtheria antitoxin, to prevent the carrier state
• Anthrax (cutaneous and systemic), as part of combination therapy per public health guidance
• Listeria monocytogenes infections, including meningitis, often combined with an aminoglycoside
• Fusospirochetal infections of the oropharynx (Vincent's infection) in severe cases
• Rat-bite fever and Pasteurella infections caused by susceptible organisms
• Actinomycosis, usually as prolonged therapy after an initial course of high-dose Pen-G

Adjunct / combination uses

• Enterococcal endocarditis and other severe enterococcal infections, typically combined with an aminoglycoside for synergy (enterococci are only moderately susceptible to Pen-G alone)

Pen-G is not effective against beta-lactamase–producing organisms (including most Staphylococcus aureus) or gram-negative bacilli, and should be reserved for confirmed or strongly suspected susceptible infections in line with local antibiotic stewardship practice.

Each vial of Benzyl Penicillin for injection contains Benzyl Penicillin (penicillin G), commonly supplied as the sodium or potassium salt, as a sterile powder for reconstitution. Strength is expressed in International Units (IU) per vial (common presentations include 1 million IU, 5 million IU and 10 million IU vials); local formulations in Bangladesh are typically available as Benzyl Penicillin sodium/potassium injection.

Pen-G, also known as penicillin G, is the original natural penicillin derived from Penicillium mould cultures. It belongs to the natural penicillin subclass of beta-lactam antibiotics and is bactericidal against a defined range of gram-positive and a few gram-negative and anaerobic organisms.

Because it is inactivated by gastric acid, Pen-G is given only by intravenous (IV) or intramuscular (IM) injection, in hospital or supervised clinical settings, and is not available as an oral formulation.

Natural Penicillin — Beta-lactam antibiotic. Pen-G is classified under the penicillin class of antimicrobial agents.

Benzyl Penicillin exerts a bactericidal effect by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs) located on the inner bacterial cell membrane, inhibiting the transpeptidation (cross-linking) step of peptidoglycan synthesis in the growing cell wall. This weakens the cell wall and activates autolytic enzymes, ultimately causing bacterial cell lysis and death, particularly in actively dividing organisms.

Benzyl Penicillin has poor oral bioavailability and is destroyed by gastric acid, which is why it is administered parenterally. After IM or IV administration it distributes widely into most body tissues and fluids; CSF penetration is low in the absence of meningeal inflammation but increases when the meninges are inflamed, allowing use in bacterial meningitis. It is largely eliminated unchanged by the kidneys via glomerular filtration and active tubular secretion, giving it a short elimination half-life in patients with normal renal function.

Pen-G powder for injection must be reconstituted with an appropriate sterile diluent immediately before use (see Reconstitution) and administered by a healthcare professional.

• For IV use, give by slow intermittent infusion over 15–30 minutes, or as a continuous infusion; do not give as a rapid IV bolus
• For IM use, inject deep into a large muscle mass, rotating injection sites to reduce local pain and irritation
• Do not mix Pen-G in the same syringe or IV line as aminoglycoside antibiotics, as they are chemically incompatible
• Complete the full prescribed course and duration even if symptoms improve early

The following are well-recognized, clinically significant interactions with Pen-G:

• Probenecid: blocks renal tubular secretion of Pen-G, raising and prolonging its blood levels; sometimes used intentionally to boost penicillin levels, but requires dose awareness
• Aminoglycosides (e.g., gentamicin): synergistic antibacterial effect when co-administered clinically, but the two drugs are physically/chemically incompatible and must not be mixed in the same syringe or infusion line
• Tetracyclines and other bacteriostatic antibiotics: may antagonize the bactericidal action of Pen-G by slowing bacterial cell division; concurrent use is generally avoided
• Methotrexate: Pen-G can reduce renal clearance of methotrexate, increasing the risk of methotrexate toxicity; concurrent use requires monitoring
• Hormonal contraceptives: a theoretical reduction in contraceptive efficacy has been reported with penicillins; an additional non-hormonal contraceptive method may be advised during treatment

As with other penicillins, adverse effects of Pen-G range from mild local reactions to rare but serious systemic reactions.

Common

• Pain, redness, or induration at the IM injection site; phlebitis at the IV site
• Nausea, vomiting, diarrhea
• Rash or urticaria

Serious (uncommon to rare)

• Hypersensitivity reactions ranging from urticaria to anaphylaxis (see Contraindications and Precautions)
• Jarisch-Herxheimer reaction — a transient reaction (fever, chills, headache, myalgia, worsening of skin lesions) occurring within hours of the first dose when treating syphilis; this is not a drug allergy and usually resolves spontaneously
• Neurotoxicity/seizures with very high doses, especially in patients with renal impairment
• Electrolyte disturbances (hyperkalemia or hypernatremia) with high-dose potassium or sodium Pen-G salts, particularly in renal impairment or cardiac disease
• Interstitial nephritis, hemolytic anemia, and reversible bone marrow suppression (rare)
• Clostridioides difficile–associated diarrhea/colitis from disruption of normal gut flora

Pregnancy: Pen-G is widely used in pregnancy and is considered the treatment of choice for maternal syphilis, as no adequate alternative exists for preventing congenital syphilis; penicillin-allergic pregnant patients requiring treatment for syphilis should be desensitized rather than given an alternative antibiotic. For other indications in pregnancy, Pen-G should be used only if clearly needed, with the potential benefit weighed against any potential risk; consult a physician before use.

Lactation: Pen-G passes into breast milk in small amounts. It is generally considered compatible with breastfeeding, but the breastfed infant should be monitored for diarrhea, oral thrush, or skin rash; consult a physician if any of these occur.

• Before starting Pen-G, tell your physician about any previous allergic reaction to penicillins, cephalosporins, or other beta-lactam antibiotics; although cross-reactivity with cephalosporins is now considered lower risk than once believed, caution is warranted in patients with a history of severe penicillin allergy
• Use with caution in patients with renal impairment, as high doses can accumulate and cause neurotoxicity, including seizures; dose adjustment is required (see Dosage and Administration)
• High-dose IV Pen-G salts contain significant amounts of potassium or sodium; use with caution in patients with renal impairment, heart failure, or conditions requiring fluid/electrolyte restriction
• When treating syphilis, patients should be counseled about the possible Jarisch-Herxheimer reaction shortly after the first dose (see Side Effects)
• Prolonged use may result in overgrowth of non-susceptible organisms, including fungi; monitor for signs of superinfection
• Take exactly as prescribed by your physician; do not stop, extend, skip doses, or share this medicine with others without medical advice

Overdose of Pen-G, particularly in patients with renal impairment, can cause neuromuscular irritability, confusion, and seizures due to accumulation of the drug. There is no specific antidote; treatment is supportive. Excess drug can be removed by hemodialysis in severe cases. If an overdose is suspected, seek immediate medical attention or contact emergency services/a poison control center without delay.

Store the unreconstituted powder at room temperature (below 30°C), away from light and moisture. Once reconstituted, use the solution promptly as directed on the product label or by the pharmacist, and discard any unused portion after the specified time. Keep out of reach of children.

• Renal impairment: dose or dosing interval reduction is required, as Pen-G is primarily renally eliminated and accumulation raises the risk of neurotoxicity/seizures (see Dosage and Administration)
• Hepatic impairment: no specific dose adjustment is generally required, as Pen-G is mainly eliminated renally rather than hepatically
• Elderly: use with attention to age-related decline in renal function; dose adjustment may be needed
• Pediatric and neonatal patients: see Pediatric Uses

Duration of Pen-G therapy depends on the indication: typically 7–10 days for streptococcal pharyngitis/soft tissue infection (10 days to help prevent rheumatic fever), 10–14 days for pneumococcal or meningococcal infections, and 10–14 days (or longer per specialist protocol) for neurosyphilis. Treatment duration for endocarditis, actinomycosis, or other severe/deep-seated infections may extend to several weeks under specialist supervision. Always complete the full course as directed by the prescribing physician, even if symptoms improve earlier.

Pen-G powder for injection must be reconstituted with an appropriate sterile diluent (such as sterile water for injection or sodium chloride injection, per the product's package insert) immediately before administration. Gently swirl (do not vigorously shake) to dissolve completely, inspect the solution for particulate matter or discoloration, and use only clear solutions. Reconstitution should be performed by a healthcare professional under aseptic conditions, and any unused reconstituted solution should be discarded after the time specified on the product label.

Natural Penicillins (Beta-lactam antibiotics)

Benzyl Penicillin is a bactericidal beta-lactam antibiotic that binds penicillin-binding proteins to inhibit bacterial cell wall (peptidoglycan) synthesis, leading to cell wall weakening, activation of autolytic enzymes, and bacterial cell death.

B

Pen-G is well established and commonly used in pediatric and neonatal patients for susceptible infections, including streptococcal disease, congenital syphilis, meningococcal disease, and clostridial infections, under specialist or hospital supervision.

• Dosing is weight-based (units/kg/day) and divided according to age-appropriate dosing intervals; neonatal dosing further depends on postnatal age and birth weight
• Safety and efficacy for indications and dosing regimens not specifically studied in neonates or infants have not been established; use should follow recognized pediatric/neonatal dosing protocols
• Renal function is immature in neonates, so dosing intervals are adjusted accordingly to avoid drug accumulation