Combipen(3 lac unit+1 lac unit)/vial

Combipen is an injectable, fixed-dose combination penicillin-class antibiotic used for the treatment of moderate-to-severe bacterial infections caused by penicillin-susceptible organisms, in clinical situations where both a rapid onset of antibacterial action and sustained (depot) antibiotic blood levels are desired from a single intramuscular injection.

Established / guideline-supported uses

• Moderate-to-severe streptococcal infections susceptible to penicillin, including streptococcal pneumonia, erysipelas, cellulitis, and severe streptococcal pharyngitis/tonsillitis, when parenteral penicillin therapy is required.
• Syphilis, as a parenteral penicillin option under specialist/physician supervision, particularly where sustained tissue levels combined with an initial peak level are wanted.
• Diphtheria, as an adjunct to diphtheria antitoxin, to eradicate Corynebacterium diphtheriae and reduce the carrier state (antitoxin remains the primary life-saving treatment).
• Anthrax (cutaneous and systemic forms), as part of combination antibacterial therapy guided by a specialist, in settings where penicillin-susceptibility is confirmed or presumed.

Adjunct / combination-therapy uses

• As part of combination therapy with an aminoglycoside for selected severe susceptible infections (e.g., enterococcal or streptococcal endocarditis), under specialist supervision and local treatment protocols (the two drugs must not be mixed in the same syringe; see Interactions).

The final choice of antibiotic regimen, dose, and duration must always be individualized by the treating physician based on the site and severity of infection, culture and sensitivity results, and local antimicrobial resistance patterns.

Procaine Penicillin + Benzyl Penicillin is a fixed-dose parenteral combination containing two forms of penicillin as active ingredients:

• Procaine Penicillin (procaine benzylpenicillin) - a depot form that is slowly absorbed from the intramuscular injection site, providing sustained antibiotic blood levels over roughly 24 hours.
• Benzyl Penicillin (benzylpenicillin/crystalline penicillin G) - a rapidly absorbed, short-acting form that produces an immediate high peak antibiotic level.

The exact strength and ratio of the two components (expressed in International Units) vary by manufacturer and product presentation; the product is generally supplied as a sterile powder or pre-mixed suspension for intramuscular injection. Always confirm the exact composition and strength printed on the specific product label/pack before use.

Combipen is a combination injectable antibiotic belonging to the natural penicillin (beta-lactam) class, formulated to combine the pharmacokinetic advantages of two penicillin forms in a single intramuscular injection.

The procaine penicillin component forms a depot at the injection site and is released slowly, maintaining measurable antibiotic levels for an extended period, while the benzyl penicillin component is absorbed quickly and provides an early, higher peak concentration. Together, this allows Combipen to achieve both a fast onset of antibacterial action and prolonged antibiotic exposure from one dose, which is useful in moderate-to-severe infections due to susceptible organisms.

Combipen is administered only by deep intramuscular injection under medical supervision and is not intended for intravenous or subcutaneous use.

Combipen belongs to the natural penicillin class of beta-lactam antibiotics. It is a combination injectable antibacterial product pairing a long-acting depot penicillin (procaine penicillin) with a short-acting, rapidly absorbed penicillin (benzyl/crystalline penicillin G).

Mechanism of action

Like other penicillins, both components of Procaine Penicillin + Benzyl Penicillin exert a bactericidal effect by binding to penicillin-binding proteins (PBPs) located on the bacterial cell wall. This inhibits the transpeptidation step of peptidoglycan cross-linking, weakening the bacterial cell wall and activating autolytic enzymes, which ultimately causes bacterial cell lysis and death. Procaine Penicillin + Benzyl Penicillin is active mainly against susceptible Gram-positive organisms (e.g., streptococci) and certain other penicillin-susceptible bacteria; activity depends on local susceptibility patterns, and resistance (including via beta-lactamase production) is common in many organisms.

Pharmacokinetics

After deep intramuscular injection of Procaine Penicillin + Benzyl Penicillin, the benzyl penicillin component is absorbed rapidly, producing a high early peak serum concentration that declines over a few hours. The procaine penicillin component is absorbed slowly from the injection depot, sustaining lower but measurable serum antibiotic levels for approximately 24 hours. Both components are widely distributed in body tissues and fluids (with limited penetration into the uninflamed central nervous system), are minimally metabolized, and are eliminated mainly unchanged by renal tubular secretion and glomerular filtration; elimination is slowed in renal impairment.

Combipen must be administered only by a trained healthcare professional, by deep intramuscular injection into a large muscle (e.g., the gluteal region), using a technique that avoids injection into or near a nerve or blood vessel.

• Before injecting, the syringe plunger should be gently withdrawn (aspirated) to confirm the needle is not in a blood vessel, as inadvertent intravascular or intravenous administration of procaine-containing penicillin can cause severe adverse reactions, including cardiorespiratory collapse.
• If supplied as a powder, reconstitute strictly as directed on the product label immediately before use (see Reconstitution).
• If supplied as a pre-mixed suspension, shake well before drawing up the dose to ensure a uniform suspension.
• Do not administer Combipen intravenously or subcutaneously.
• Administer in a setting where facilities for managing anaphylaxis (e.g., epinephrine/adrenaline, resuscitation equipment) are immediately available.

Clinically significant interactions with Combipen include:

• Probenecid: Competitively inhibits renal tubular secretion of penicillins, increasing and prolonging blood levels of Combipen; this combination may occasionally be used intentionally under medical supervision to boost antibiotic exposure.
• Aminoglycosides (e.g., gentamicin): May act synergistically against certain susceptible organisms when used together clinically, but must never be physically mixed in the same syringe or infusion, as penicillins can inactivate aminoglycosides on direct contact.
• Bacteriostatic antibiotics (e.g., tetracyclines, chloramphenicol, macrolides): May theoretically antagonize the bactericidal action of Combipen if given concurrently; combined use should be guided by a physician.
• Methotrexate: Penicillins may reduce renal clearance of methotrexate, increasing the risk of methotrexate toxicity; concurrent use requires close monitoring.
• Hormonal contraceptives: Some antibiotics, including penicillins, have been reported rarely to reduce the efficacy of combined oral contraceptives; an additional non-hormonal contraceptive method may be advised during treatment.

Possible side effects of Combipen include:

Common

• Pain, induration, or sterile abscess at the intramuscular injection site.
• Mild gastrointestinal upset (nausea, diarrhea).

Hypersensitivity reactions

• Skin rash, urticaria, pruritus.
• Serious allergic reactions, including anaphylaxis and angioedema, which can be life-threatening and require immediate medical attention (see Contraindications and Precautions).

Procaine-related (non-allergic) reaction

• A transient reaction sometimes called a "Hoigne syndrome" or immediate procaine-related CNS reaction can occur within seconds to minutes of injection, causing anxiety, fear, agitation, hallucinations, or seizure-like activity. This is distinct from a true allergic reaction and is thought to be related to inadvertent intravascular entry of procaine or its systemic absorption; it usually resolves within 15-30 minutes but should be evaluated by a healthcare professional and distinguished from anaphylaxis.

Less common / serious

• Clostridioides difficile-associated diarrhea/colitis, which can range from mild to severe and may occur during or after treatment.
• Jarisch-Herxheimer reaction (fever, chills, myalgia) when Combipen is used to treat spirochetal infections such as syphilis.
• Blood dyscrasias (rare) with prolonged high-dose therapy.

Natural penicillins as a class have a long history of clinical use in pregnancy and are generally considered among the antibiotics of choice when a penicillin is indicated, including for certain infections in pregnancy. However, formal safety data specifically for the combined Combipen product (including its procaine component) in pregnancy are limited. Combipen should be used during pregnancy only if clearly needed and if the potential benefit justifies the potential risk to the fetus; use only under the direct advice and supervision of a physician.

Penicillins are excreted in small amounts in breast milk. Combipen should be used with caution during breastfeeding, and the infant should be monitored for possible effects such as diarrhea, rash, or allergic sensitization. Consult a physician before use while breastfeeding.

• Anaphylaxis risk: Serious and occasionally fatal hypersensitivity reactions have occurred with penicillins. Combipen should be administered only in a setting where facilities for the immediate management of anaphylaxis (e.g., epinephrine/adrenaline, oxygen, resuscitation equipment) are available. Before starting therapy, ask the patient about any prior penicillin or cephalosporin allergy.
• Intramuscular use only: Combipen must never be given intravenously or into a blood vessel; always aspirate before injecting to avoid inadvertent intravascular administration, which can cause serious cardiorespiratory and neurological reactions.
• Procaine-related reaction: Patients may experience a transient, non-allergic anxiety/agitation reaction immediately after injection (see Side Effects); inform patients this may occur and is usually self-limiting, but should still be assessed by a healthcare professional to rule out anaphylaxis.
• Renal impairment: Use with caution and adjusted dosing in patients with significant renal impairment, due to the risk of accumulation and neurotoxicity (including seizures) at high doses.
• Superinfection: Prolonged use may result in overgrowth of non-susceptible organisms, including Clostridioides difficile; evaluate any significant or persistent diarrhea during or after treatment.
• Antibiotic stewardship: Take Combipen exactly as prescribed by your physician; do not stop, extend, skip doses, or share this medicine with others without medical advice.

Overdosage with Combipen, particularly in patients with renal impairment, may cause neuromuscular hyperexcitability, confusion, and seizures due to high penicillin levels, as well as exaggerated procaine-related CNS effects (anxiety, hallucinations). Electrolyte disturbances may occur if a potassium- or sodium-containing penicillin salt is given in very high doses to patients with renal impairment.

There is no specific antidote for penicillin overdose. If an overdose is suspected, seek immediate medical attention or contact a poison control center; management is supportive and may include seizure control and, in severe renal impairment, hemodialysis to help remove the drug. Do not attempt to manage a suspected overdose at home.

Store at room temperature (below 30°C), away from light and moisture, unless the specific product label directs refrigeration. Once reconstituted, use the suspension within the time specified on the product label and discard any unused portion. Keep out of reach of children.

• Renal impairment: Use Combipen with caution and reduced dose/frequency, as accumulation can increase the risk of neurotoxicity (see Dosage and Overdose Effects).
• Hepatic impairment: No specific dose adjustment is well established; use with physician judgment as the drug is primarily renally eliminated.
• Elderly: Age-related decline in renal function should be considered when dosing; monitor renal function and adjust dose as needed.
• Neonates and young infants: Use only under specialist supervision with weight-based dosing; safety and dosing recommendations for very young infants/neonates are not as well established as for older children and adults.
• Known penicillin allergy: Combipen must not be used in patients with a history of penicillin hypersensitivity (see Contraindications).

The duration of treatment with Combipen depends on the specific infection being treated and the patient's clinical response, and should be determined by the prescribing physician. As a general principle, treatment is continued for at least 48-72 hours after the patient becomes afebrile or shows clear clinical improvement, and for a minimum of 10 days for streptococcal infections (to reduce the risk of rheumatic fever/glomerulonephritis) unless a physician directs otherwise. Longer courses (e.g., 10-14 days or more) may be required for syphilis, diphtheria, or anthrax, as directed by a specialist. The full prescribed course must always be completed even if symptoms improve earlier.

If Combipen is supplied as a sterile powder for injection, reconstitute only with the diluent specified on the product label (e.g., water for injection or the manufacturer-supplied diluent), using aseptic technique.

• Add the diluent slowly to the vial and swirl/shake gently until a uniform, milky suspension is obtained; avoid vigorous shaking that causes excessive foaming.
• Inspect the reconstituted suspension; it should be used only if it is a uniform suspension without visible particulate matter or contamination.
• Use the reconstituted suspension promptly (within the time window stated on the product label) and discard any unused portion; do not store reconstituted suspension for later use unless the label specifically permits it.
• Do not mix Combipen with other drugs (e.g., aminoglycosides) in the same syringe or vial.

If the product is supplied as a ready-to-use suspension, shake well before use; no reconstitution is required.

Penicillins - natural (beta-lactam) antibacterials; combination depot/short-acting penicillin injectable.

Procaine Penicillin + Benzyl Penicillin acts by inhibiting bacterial cell wall synthesis. Both the procaine penicillin and benzyl penicillin components bind to penicillin-binding proteins (transpeptidases) on the bacterial cell membrane, blocking the final cross-linking step of peptidoglycan synthesis. This weakens the rigid bacterial cell wall and triggers autolytic enzymes within the bacterial cell, leading to cell lysis and bactericidal killing of susceptible, actively dividing organisms. The combination provides a rapid initial peak level (from the benzyl penicillin component) together with sustained lower-level antibiotic exposure (from the slowly-absorbed procaine penicillin depot).

B

Use of Combipen in children should be guided by a pediatrician, with weight-based dosing individualized to the specific infection and its severity. It has established use in children for susceptible streptococcal infections, diphtheria (with antitoxin), and other indications under specialist guidance, similar to adult indications but with pediatric weight-based dosing.

Safety and efficacy of Combipen in neonates and very young infants are not as well established as in older children and adults; use in this age group should be reserved for specialist-directed treatment with close monitoring, particularly given the theoretical risk of procaine-related neurological effects and the need for careful renal-function-based dosing in neonates.