Medicines & Supplements A to Z > Unasyn


Last updated on 06/07/2021.

Overview   |   Dosage   |    Side Effects   |   Precautions  |   Tips  |   Where To Buy  

GENERIC NAME: Sultamicillin (Ampicillin + Sulbactam)


DRUG CLASS: Antibiotics

SUB CLASS: Penicillins, Beta-lactamase inhibitors

USED FOR: Respiratory tract infections, urinary tract infections (UTIs), intra-abdominal infections, gonorrhoea, skin and soft tissue infections, bone and joint infections

– 375 mg (tablets)
– 750 mg (injections)

What is Unasyn for?

Unasyn is a combination antibiotic used for treating bacterial infections involving the abdomen, urinary tract, respiratory tract or skin and soft tissues. Unasyn contains sultamicillin, which is rapidly metabolized by enzymes into Ampicillin and Sulbactam in your body. Ampicillin belongs to a class of medications called penicillins, which kills bacteria by interrupting the integrity of bacterial cell walls. Sulbactam belongs to a class of medications called beta-lactamase inhibitors, which prevents bacteria from destroying Ampicillin. Unasyn does not work for virus or fungus infections.

How to use it?

Unasyn may be taken orally as a tablet, or injected through a needle into a vein or muscle as directed by your doctor. Your doctor will advise you on the dosage and frequency depending on your infection. The maximum dosage is 12 g Unasyn (equivalent to 8 g Ampicillin and 4 g Sulbactam) daily.

What are the side effects of Unasyn?

Common side effects of Unasyn include anemia, insomnia, headache, diarrhea, constipation, gastrointestinal discomfort, nausea and vomiting, and allergic skin reactions.

Who should not take Unasyn?

– People allergic to any component of the formulation.
– People who are allergic to beta-lactams, e.g. Penicillins and Cephalosporins.

Pharmacist Tips:

– Antibiotics like Ampicillin may reduce the effectiveness of oral contraceptives. Consider using another form of contraception while taking Unasyn.
– Report severe diarrhea and ask your doctor or pharmacist before taking antidiarrheal medicines.
– Drink plenty of water to replace any lost fluids due to diarrhoea.
– If you experience symptoms like skin rash, report to your doctor immediately.

Common dosing schedule:
Unasyn is commonly administered every 6-12 hours.

This schedule is for reference only, adjustments may be made according to individual needs.

Some common medications Unasyn may interact with:
– Warfarin and other anticoagulants
– Oral contraceptives, e.g. Desogestrel, Drospirenone, Levonorgestrel

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Unasyn in Hong Kong?

In Hong Kong, Unasyn is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.

For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at

Need more information?

For detailed information about the use of Unasyn in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.