Penicillin G Benzathine: Uses, How It's Given, Dosing & Side Effects

Penicillin G benzathine is an antibiotic used to treat infections caused by bacteria that are sensitive to this medication. It may be prescribed for throat infections, such as tonsillitis or pharyngitis, as well as sexually transmitted infections, such as syphilis.

This medication is given as an injection directly into the muscle, usually in the gluteal muscle, by a nurse at a hospital, clinic, or other healthcare facility. A doctor may recommend using an anesthetic, such as lidocaine, to help reduce discomfort during the injection.

Penicillin G benzathine can cause pain, redness, and swelling at the injection site. It can also cause allergic reactions, which may include trouble breathing and swelling of the face or throat, so the injection should always be given under medical supervision.

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What it is used for

Penicillin G benzathine is indicated for the treatment of diseases caused by bacteria that are sensitive to penicillin G benzathine, including:

  • Infections caused by group A Streptococcus bacteria, as long as the infection has not spread to the blood;

  • Upper respiratory tract infections, such as mild to moderate tonsillitis or pharyngitis, or skin infections;

  • Sexually transmitted infections caused by bacteria from the Treponema species, such as syphilis, yaws, endemic syphilis, or pinta.

This medication may also be used to prevent a kidney disease called acute glomerulonephritis. It may also be used to help prevent rheumatic disease and recurrences and/or late neurological complications of rheumatic fever.

Is penicillin G benzathine used for urinary tract infections?

Penicillin G benzathine is not indicated for urinary tract infections, as it mainly works against gram-positive bacteria that are sensitive to penicillin. Urinary tract infections are usually caused by gram-negative bacteria that require specific antibiotics.

Is penicillin G benzathine used for the flu?

Penicillin G benzathine is not used for the flu, as it is an antibiotic that works against bacteria. The flu is caused by viruses, which are not affected by antibiotics.

How to use it

Penicillin G benzathine should be administered by a nurse at a hospital or health clinic. It is given as an injection directly into the gluteal muscle in adults, or into the outer thigh muscle in babies up to 2 years old.

The injection should be given slowly and continuously. Different injection sites may be used to help reduce pain and prevent the needle from clogging.

Penicillin G benzathine can cause pain and discomfort at the injection site, which may last up to one week. To help relieve this discomfort, the doctor may combine it with an anesthetic such as lidocaine and recommend a warm compress.

Dosing table

The recommended doses of penicillin G benzathine vary according to the infection being treated and age:

Type of infection Age and dose
Respiratory or skin infections caused by group A Streptococcus Children up to 27 kg: single dose of 300,000 to 600,000 units
Older children: single dose of 900,000 units
Adults: single dose of 1,200,000 units (2 mL)
Latent, primary, and secondary syphilis Single dose of 2,400,000 units (4 mL)
Late latent and tertiary syphilis 2,400,000 units (4 mL), once a week, for 3 weeks
Congenital syphilis Children under 2 years old: single dose of 50,000 units per kg of body weight
Children 2 to 12 years old: single dose, as recommended by a doctor
Yaws, bejel, and pinta Single dose of 1,200,000 units (2 mL)
Rheumatic fever and glomerulonephritis prophylaxis 1,200,000 units (2 mL), every 4 weeks

The effect of penicillin G benzathine usually begins within 24 to 48 hours after the injection. However, infection symptoms may take a few days to improve completely.

How long does penicillin G benzathine stay in the blood?

Penicillin G benzathine stays in the blood for about 2 to 4 weeks. It gradually releases penicillin G to maintain a long-lasting effect against sensitive bacteria.

Possible side effects

Some of the most common side effects that may occur during treatment with penicillin G benzathine are:

  • Headache;

  • Nausea and vomiting;

  • Diarrhea;

  • Oral and genital yeast infection.

Some rare side effects may include redness or blisters on the skin, swelling or formation of a lump at the injection site, itching, fluid retention, stomach pain, palpitations, and a sudden feeling of warmth or tingling.

Other possible effects include anxiety, dizziness, drowsiness, muscle or joint pain, and decreased blood pressure.

Penicillin G benzathine can cause serious allergic reactions, including anaphylactic shock. Symptoms may include trouble breathing, a feeling that the throat is closing, and swelling in the mouth, tongue, or face, which require immediate medical care.

For this reason, penicillin G benzathine should be given under the supervision of a healthcare professional so that emergency care can be provided immediately if needed.

Does penicillin G benzathine reduce the effect of birth control?

Penicillin G benzathine does not directly interfere with the effect of oral birth control. However, it may cause an imbalance in the gut flora and diarrhea, which may reduce hormone absorption and, as a result, decrease the effectiveness of the birth control pill.

In this case, using an additional contraceptive method, such as condoms, is recommended during treatment with penicillin G benzathine to help prevent pregnancy.

Who should not use it

Penicillin G benzathine should not be used by people who are allergic to penicillin G benzathine or other penicillins, such as ampicillin, carbenicillin, ticarcillin, or piperacillin; cephalosporins, such as cefuroxime, cefdinir, or cefprozil; or fluoroquinolones, such as levofloxacin, for example.

In addition, penicillin G benzathine should be used with caution in people with asthma, epilepsy, kidney disease, or heart disease. It should also be used with caution by people who take medications such as methotrexate, mycophenolate mofetil, probenecid, or tetracyclines.

Can pregnant women take penicillin G benzathine?

Penicillin G benzathine may be used during pregnancy only under medical guidance. It may be indicated to treat bacterial infections that can affect the mother or baby, such as syphilis.

In these cases, the doctor evaluates the risks and benefits before prescribing it to help ensure safety for the pregnant woman and the fetus.