Pentrexyl 500 mg capsules – ampicillin, an antibiotic for bacterial infections

Pentrexyl is a medicine in the form of hard capsules containing ampicillin – an antibiotic from the group of broad-spectrum penicillins. Ampicillin kills bacteria that are sensitive to it and is used to treat various bacterial infections.

Each capsule contains 500 mg of ampicillin (as ampicillin trihydrate). The medicine is made by Galenika AD Belgrade and is taken by mouth, half an hour to one hour before a meal. Like other antibiotics, Pentrexyl does not work against viral infections such as the common cold or flu.

What is Pentrexyl used for and how should it be taken correctly?

Key information about the medicine

What is Pentrexyl used for?

According to the package leaflet and the summary of product characteristics, ampicillin is used to treat bacterial infections caused by ampicillin-sensitive micro-organisms, such as:

• ear, throat and nose infections;
• bronchitis, pneumonia and other chest infections;
• urinary tract infections;
• sexually transmitted infections (e.g. gonorrhoea) and gynaecological infections;
• skin and soft tissue infections;
• gastrointestinal infections, including enteric fevers;
• more serious infections such as sepsis (bacteria in the blood), peritonitis, endocarditis and meningitis – here the doctor decides whether the antibiotic needs to be given by injection.

How is Pentrexyl taken and dosed?

Always take the medicine exactly as prescribed by your doctor. Swallow the capsules whole with enough liquid, half an hour to one hour before a meal. Spread the doses evenly through the day (for example before each meal and at bedtime).

Usual doses for adults (including the elderly) according to the summary of product characteristics:

• Doses below 500 mg cannot be given with this capsule – a medicine of a suitable strength and form is used for them.
• In severe infections the doctor may prescribe higher doses or ampicillin by injection.
• The duration of treatment is decided by the doctor. Take the medicine until the end of the prescribed course.

Special patient groups

• Children: according to the leaflet, adults and children over 10 years take the usual dose of 250 mg to 750 mg four times a day, and children under 10 years half the adult dose four times a day. The dose for a child is always decided by the doctor (the capsule contains 500 mg).
• Elderly patients: the usual adult doses apply.
• Impaired kidney function: in severe impairment (creatinine clearance below 10 mL/min) the doctor reduces the dose or extends the interval between doses. Patients on dialysis take an additional dose after dialysis, as instructed by the doctor.

Contraindications – when the medicine must not be used

• allergy (hypersensitivity) to ampicillin or any of the excipients;
• allergy to other beta-lactam antibiotics – penicillins or cephalosporins.

Precautions and warnings

Talk to your doctor before taking the medicine if:

• you have previously had a skin rash or swelling of the face or neck after taking an antibiotic;
• you are already taking another antibiotic;
• you have infectious mononucleosis or a weakened immune system;
• you have leukaemia (especially lymphatic) – the risk of skin rash is increased;
• you have impaired kidney function.

Prolonged use may lead to overgrowth of resistant micro-organisms. Ampicillin can cause false-positive results of urine glucose tests performed with chemical methods – tell your doctor or the laboratory that you are taking it.

Interactions with other medicines, food and drink

• other antibiotics – bacteriostatic antibiotics may interfere with the action of ampicillin;
• probenecid (for gout) – slows the excretion of ampicillin and increases its blood levels;
• allopurinol (for gout) – increases the likelihood of allergic skin reactions;
• oral contraceptives – ampicillin may reduce their effectiveness; an additional contraceptive method (e.g. a condom) is needed, and your doctor or pharmacist will tell you for how long;
• food: the capsules are taken half an hour to one hour before meals.

Pregnancy and breast-feeding

• Pregnancy: ampicillin has been used for a long time and its use in pregnancy is well studied; according to the summary of product characteristics, when an antibiotic is needed during pregnancy, ampicillin may be considered appropriate. Take it only on your doctor's advice.
• Breast-feeding: small amounts of the medicine may pass into breast milk. Consult your doctor before use.

Driving and using machines

• According to the leaflet, Pentrexyl does not affect the ability to drive or use machines.

Possible side effects

• Stop taking the medicine and seek medical help immediately if you notice signs of an allergic reaction: difficulty breathing or swallowing, swelling of the face, lips, tongue or throat; intense itching with a red rash; blisters in the mouth, on the eyes or genitals, peeling skin (rare: erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis).
• Rare reactions for which you should see a doctor: severe stomach cramps and watery, severe diarrhoea, possibly with blood, and fever (pseudomembranous or haemorrhagic colitis); yellowing of the skin or whites of the eyes, pale stools and dark urine (hepatitis, cholestatic jaundice); unusual bleeding or bruising; fever, sore throat, mouth ulcers, frequent infections; tiredness and shortness of breath with pale skin; fever, rash and changes in urination (interstitial nephritis). Some of these reactions can appear several weeks after the end of treatment.
• Other side effects: stomach upset, nausea, vomiting and diarrhoea (usually settle without changing the dose); occasionally skin rash, itching and hives; temporary changes in blood counts and a temporary increase in liver enzymes.

Overdose, missed dose and stopping treatment

• Overdose: nausea, vomiting and diarrhoea may occur. Contact a doctor, pharmacist or the nearest hospital immediately and take the pack with you, even if you feel well.
• Missed dose: take it as soon as you remember; if it is almost time for the next dose, skip the missed one. Never take a double dose.
• Stopping treatment: do not stop taking the medicine because you feel better – if you stop too early, the infection may come back.

Related information

For additional care and support of the gut flora during and after antibiotic treatment, see also the category Products with probiotics – products from this category do not replace the medicine prescribed for you.

Composition, pack and manufacturer

• Active substance: ampicillin 500 mg per capsule (as ampicillin trihydrate).
• Excipients – capsule content: magnesium stearate; microcrystalline cellulose. Capsule body: gelatin; titanium dioxide (E171); black iron oxide (E172). Capsule cap: gelatin; titanium dioxide (E171); indigo carmine (E132); erythrosine (E127).
• Appearance: opaque hard gelatin capsule (No. 0) with a grey body and red cap, filled with white to yellowish-white powder.
• Pack: PVC-Al/PVC blister with 8 capsules; 2 blisters (16 capsules) per box.
• Marketing authorisation holder and manufacturer: Galenika AD Beograd, Batajnički drum b.b., Belgrade, Serbia.
• Authorisation number: 515-01-03912-21-001 of 16.08.2022.

Storage

• Store below 30 °C, in the original package to protect from light and moisture.
• Shelf life: 3 years. Do not use after the expiry date stated on the pack.
• Keep out of the sight and reach of children. Return unused medicines to a pharmacy that collects them.

Frequently asked questions

Is Pentrexyl taken before or after food?

Before food. The capsules are swallowed whole with enough liquid, half an hour to one hour before a meal, evenly spread through the day.

Can I take Pentrexyl if I am allergic to penicillin?

No. Pentrexyl contains ampicillin, which is a penicillin, so it is contraindicated in allergy to penicillins, and also to cephalosporins and other beta-lactam antibiotics.

Does ampicillin affect the contraceptive pill?

Yes, it may reduce its effectiveness. An additional contraceptive method, e.g. a condom, is needed during treatment; your doctor or pharmacist will tell you for how long.

Why is ampicillin not recommended in mononucleosis?

In infectious mononucleosis and lymphatic leukaemia, skin rash occurs much more often after ampicillin, so its use should be avoided if these conditions are suspected.

Sources

• ALIMS – Package leaflet Pentrexyl 500 mg (PIL, Serbian)
• ALIMS – Summary of product characteristics Pentrexyl 500 mg (SmPC, Serbian)

Sources checked on: 25.10.2026.