Monopen

Indications

Benzyl Penicillin (also called Penicillin G) is an injectable antibiotic used for serious infections caused by bacteria that are sensitive to penicillin. These include pneumonia, throat and skin infections caused by streptococci, meningitis, infection of the heart valves (endocarditis), septicaemia, syphilis, gonorrhoea caused by sensitive strains, diphtheria, tetanus, gas gangrene, anthrax and leptospirosis. It may be given before hospital transfer when meningococcal infection is suspected.

How It Works

Benzyl Penicillin stops bacteria from building their cell walls. The weakened bacteria burst and die. It does not work against viral infections such as colds or flu.

Dosage and Administration

As prescribed. It is given by a doctor or nurse as an injection into a vein (slow injection or drip) or into a muscle. The dose, how often it is given and for how long depend on the infection, its severity, body weight and kidney function. Children's doses are worked out by weight. It is usually given every 4 to 6 hours.

Interactions

• Probenecid raises penicillin levels in the blood.
• Penicillin can increase the effects and side effects of Methotrexate.
• Tetracycline and some other bacteriostatic antibiotics may reduce its effect.
• It may change the effect of blood thinners such as Warfarin; extra blood tests may be needed.

Contraindications

Allergy to penicillin or any other penicillin-type antibiotic. Tell the doctor about any allergy to Cephalosporin antibiotics or other beta-lactams, as cross-allergy can occur.

Side Effects

Common: pain or swelling at the injection site, rash, itching, nausea and diarrhoea. When used for syphilis or leptospirosis, fever, chills, headache and muscle aches can appear in the first hours (a short-lived reaction to dying bacteria).

Get urgent medical help if you have: swelling of the face, lips, tongue or throat, wheezing, trouble breathing or collapse (serious allergic reaction, anaphylaxis); a severe rash with blisters or peeling; severe or bloody diarrhoea during or after treatment; or fits (seizures), which are more likely with very high doses or kidney problems.

Pregnancy and Lactation

Penicillins are generally considered safe in pregnancy and during breastfeeding when needed. Small amounts pass into breast milk; watch the baby for diarrhoea, thrush or rash and tell the doctor.

Precautions and Warnings

• Always tell staff about any past reaction to penicillin before receiving it.
• The dose is reduced in severe kidney disease.
• Very high doses contain significant sodium or potassium, which matters for people with heart or kidney problems.
• Long courses can lead to thrush or other resistant infections.
• It must never be injected into the spine (intrathecal use) unless a specialist specifically directs it.

Overdose

As it is given in hospital, overdose is uncommon. Very high levels can cause agitation, confusion, twitching and seizures, especially with kidney failure. Doctors stop the medicine and give supportive treatment; dialysis may help.

Therapeutic Class

Penicillin antibiotic (beta-lactam).

Storage

Store unopened vials below 25°C in a dry place, away from light and out of the reach of children. Once mixed, the solution should be used straight away or as directed by the pharmacist or product leaflet.