Omnipen (ampicillin) online antibiotic prescription available

If you are suffering from a bacterial infection, Omnipen (ampicillin) can help. Get a new prescription or refill of Omnipen from a caring, board-certified doctor online.*

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Treats UTIs, respiratory infections, and more

Available as an oral capsule, liquid suspension, or powder for injection

Follow full course for effective bacterial infection treatment

*Prescriptions are provided at the doctor’s discretion. Learn more about our controlled substances policy and how you can save up to 80% with our prescription discount card.

About Omnipen (ampicillin)

Omnipen is a penicillin antibiotic that fights bacterial infections. Like other antibiotic medicines, Omnipen is not effective against fungal or viral infections.

Omnipen is used to treat or prevent bacterial infections, including bladder infections, pneumonia, and others. Omnipen is available only by prescription. It is available in a generic formulation as well as under different brand names, including ampicillin.

Omnipen may be prescribed as an oral capsule, liquid suspension, or powder for injection. It’s always important to follow the specific instructions on your prescription, as they can vary based on the formulation and dosage prescribed.

If you're prescribed Omnipen, be sure to complete the full course of the antibiotic unless your doctor specifically tells you to stop. If you don’t complete your prescription, the antibiotic may not fully treat your bacterial infection.

Omnipen uses

There are several FDA-approved uses for Omnipen

Your doctor may prescribe ampicillin for any of the following reasons, or other reasons not listed here. If you have questions about why a medication is prescribed, ask your online doctor or pharmacist.

  • Respiratory tract infections

    Ampicillin is FDA-approved to treat respiratory infections caused by S. pneumoniae, Staphylococcus aureus, H. influenzae, and Group A Streptococci. These infections include the following:

  • Urinary tract infections

    Ampicillin is FDA-approved to treat UTIs caused by sensitive strains of E. coli and Proteus mirabilis.

  • Gastrointestinal infections

    Ampicillin is FDA-approved to treat gastrointestinal infections caused by Salmonella typhi (typhoid fever), other Salmonella spp., and Shigella spp. (dysentery).

Omnipen side effects

  • The side effects associated with taking Omnipen are typically mild. Most Omnipen side effects are associated with gastrointestinal discomfort.

    Omnipen has some common side effects. They may include:

    • Nausea, vomiting, or upset stomach

    • Itching or skin rash

    • Swollen, black, or "hairy" tongue

    Other side effects, which are less common but might be more severe, could include:

    • Severe stomach pain

    • Watery or bloody diarrhea

    • Joint pain

    Tell your doctor if you notice any adverse effects, or if you develop any other new or concerning symptoms.

How to take Omnipen

Your doctor will provide you with instructions on how to take your Omnipen prescription. Be sure to read your prescription label and follow the instructions. Call your doctor if you have any questions.

Omnipen can come in different forms and doses, so be sure to follow the specific instructions on your prescription. The initial dose for ampicillin tablets can range from 250 mg to 500 mg, while the oral suspension ranges from 125 mg to 250 mg. Take ampicillin on an empty stomach with a full glass of water.

Omnipen can cause unusual results with certain lab tests. Tell your doctor that you're taking ampicillin before medical tests.

What to avoid while taking Omnipen

Omnipen has 50 drug interactions. Don’t change what you are taking without checking with your doctor or pharmacist. That includes other medications or supplements, as well as over-the-counter drugs. 

Possible drug interactions with Omnipen include:

  • Metoprolol Succinate ER (metoprolol)

  • Oral contraceptives

  • Omeprazole

  • Simvastatin

  • Warfarin

Avoid taking anti-diarrhea medicine without your doctor's approval.

Alcohol does not interact with ampicillin. However, drinking alcohol can make it harder for your body to fight an infection. Ask your doctor for medical advice before drinking alcohol.

Medication alternatives to Omnipen

If your healthcare provider prefers to put you on another treatment altogether, they may suggest another penicillin antibiotic or an antibiotic medication in another drug class. Here are some common doctor-recommended alternatives based on your health issue:

Omnipen prescription FAQs

  • How much does Omnipen cost?

    Depending on your pharmacy, Omnipen costs around $26 for 10 powder injections without insurance. Fortunately, generic brands, such as ampicillin, may offer an affordable alternative. Price may vary depending on your insurance coverage.

  • How can I refill my Omnipen prescription?

    Omnipen is only available by prescription, so you will need to see a board-certified doctor to get a refill on your prescription. To get started, book a virtual appointment with one of our top rated board-certified doctors. After a qualifying evaluation, your prescription will be sent to your local pharmacy for pickup.

  • What is Omnipen used for?

    Omnipen is used to treat a wide variety of bacterial infections, including urinary tract infections and respiratory infections

  • Who should not take ampicillin?

    Avoid taking ampicillin if you:

    • Have had an allergic reaction to cephalosporin antibiotic medicines

    • Are currently taking allopurinol

    • Have kidney disease

    Tell your doctor if you have any allergies to food or drugs.

  • What happens if I miss a dose of Omnipen?

    If you miss a dose of Omnipen, take the missed dose as soon as you remember. Skip the missed dose if it's almost time for your next dose. Avoid taking two doses to make up for a missed dose.

  • What happens if I take too much Omnipen?

    If you've taken too much Omnipen, contact your local poison control center or seek immediate medical attention.

3 simple steps to request your Omnipen prescription today 

Step 1: Book an appointment

Step 1

Book an Omnipen prescription request appointment.

Book a same day appointment from anywhere.

Step 2: Visit with a doctor on your smartphone

Step 2

Talk to your medical provider regarding your Omnipen prescription.

Visit with a doctor on your smartphone or computer.

Step 3: pick up at local pharmacy

Step 3

Pick up your Omnipen prescription.

We can send prescriptions to any local pharmacy.

Omnipen prescription pricing details

How pricing works

To get a new or refill on your Omnipen prescription, join our monthly membership and get discounted visits.

Paying with insurance



First month free



30 days of free membership

  • Same-day appointments 7 days a week

  • Unlimited messages with your Care Team

  • Prescription discount card to save up to 80%

  • Exclusive discounts on lab tests

  • Free memberships for your family

  • Cancel anytime

Visit price with insurance

Often the same as an office visit. Most patients with in-network insurance pay $30 or less!

  • We accept these insurance plans and many more:

    • Humana
    • Aetna
    • Cigna

Paying without insurance



First month free



30 days of free membership

  • Same-day appointments 7 days a week

  • Unlimited messages with your Care Team

  • Prescription discount card to save up to 80%

  • Exclusive discounts on lab tests

  • Free memberships for your family

  • Cancel anytime

Visit price without insurance

Initial visits are $129.

Book an appointment

If we're unable to treat you, we'll provide a full refund.


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PlushCare content is reviewed by MDs, PhDs, NPs, nutritionists, and other healthcare professionals. Learn more about our editorial standards and meet the medical team. The PlushCare site or any linked materials are not intended and should not be construed as medical advice, nor is the information a substitute for professional medical expertise or treatment.