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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Generic drug name: penicillin g
Brand name(s):
GENERIC: not available FAMILY: Penicillins
Find the drug label by searching at DailyMed.

Generic drug name: penicillin v
Brand name(s): PEN VEE K
GENERIC: not available FAMILY: Penicillins
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

There was no evidence of toxicity in animal studies. Use during pregnancy only for clear medical reasons. Tell your doctor if you are pregnant or thinking of becoming pregnant before you take this drug.

Breast-feeding Warning

Penicillin G is excreted in human milk. You should consult with your doctor if you are planning to nurse.

Safety Warnings For This Drug [top]

Antibiotic-Associated Diarrhea

Antibiotic-associated diarrhea (AAD) is quite common and its incidence varies from 5% to 20% of patients depending on which antibiotic they are taking, although practically all antibiotics have been associated with AAD. Fortunately, most cases are mild and self-limited, ending with the cessation of use of the offending antibiotic. The antibiotics most commonly associated with this mild form of AAD include ampicillin, amoxicillin, cephalosporins and clindamycin.[1] There have been studies in children or adults in which the use of prophylactic yogurt in people using antibiotics has significantly reduced the occurrence or severity of AAD.[2],[3] However, 10% to 20% of all patients who get AAD (0.5% to 4% of patients using antibiotics) will get the more severe form of AAD known as pseudomembranous colitis (see below). If you are taking any antibiotic and develop diarrhea after starting to use the drug, call your physician to discuss whether another antibiotic should be used and to discuss the need for rehydration due to the fluid loss from the diarrhea.

Pseudomembranous colitis has been reported with nearly all antibacterial agents and may range in severity from mild to life-threatening. Therefore, it is important to consider this diagnosis in patients who present with diarrhea subsequent to the administration of antibacterial agents.

Because antibiotic therapy has been associated with severe colitis, which may end fatally, it should be reserved for serious infections where less toxic antimicrobial agents are inappropriate, as described in the INDICATIONS AND USAGE section. It should not be used in patients with nonbacterial infections such as most upper respiratory tract infections. Treatment with antibacterial agents alters the normal flora of the colon and may permit over-growth of clostridia. Studies indicate that a toxin produced by Clostridium difficile is one primary cause of "antibiotic-associated colitis."

After the diagnosis of pseudomembranous colitis has been established, therapeutic measures should be initiated. Mild cases of pseudomembranous colitis usually respond to drug discontinuation alone. In moderate to severe cases, consideration should be given to management with fluids and electrolytes, protein supplementation, and treatment with an antibacterial drug that is clinically effective against C. difficile colitis.

Diarrhea, colitis, and pseudomembranous colitis have been observed to begin up to several weeks following cessation of therapy.

Facts About This Drug [top]

Penicillin is used to treat some infections caused by bacteria, including strep throat, some other oral (mouth) infections, and skin infections. Your doctor might prescribe oral penicillin for you to take at home if you have just gotten out of the hospital and were getting antibiotic shots while there. Penicillin will not help if you have a cold or the flu.

If you are taking penicillin by mouth, penicillin V is the better form to take because your body absorbs it better. If you have kidney...

Penicillin is used to treat some infections caused by bacteria, including strep throat, some other oral (mouth) infections, and skin infections. Your doctor might prescribe oral penicillin for you to take at home if you have just gotten out of the hospital and were getting antibiotic shots while there. Penicillin will not help if you have a cold or the flu.

If you are taking penicillin by mouth, penicillin V is the better form to take because your body absorbs it better. If you have kidney damage, you may need to take less than the usual adult dose.

Before You Use This Drug [top]

Do not use this drug if you have or have had:

Tell your doctor if you have or have had:

  • pregnancy or are breast-feeding
  • allergies to drugs
  • general history of other allergies
  • stomach or intestinal disease
  • kidney disease
  • bleeding disorder
  • heart disease
  • high blood pressure
  • infectious mononucleosis
  • cystic fibrosis

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • Check with your doctor if there is no improvement within a few days.
  • If you get severe diarrhea, check with your doctor before taking any antidiarrheals.
  • If you plan to have any surgery, including dental, tell your doctor that you take this drug.
  • Possibly use an alternate or additional method of contraception if taking estrogen-containing oral contraceptives.
  • Caution diabetics: These drugs may interfere with glucose urine tests.

How to Use This Drug [top]

  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • Penicillin G should be taken with water only. Do not eat or drink for about an hour before taking this medication.
  • Penicillin V can be taken with or without food.
  • Take this drug for the prescribed length of time. If you stop too soon, your symptoms could come back.
  • Store tablets at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Keep out of reach of children.

Interactions with Other Drugs [top]

The following drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods are listed in Evaluations of Drug Interactions 2003 as causing “highly clinically significant” or “clinically significant” interactions when used together with any of the drugs in this section. In some sections with multiple drugs, the interaction may have been reported for one but not all drugs in this section, but we include the interaction because the drugs in this section are similar to one another. We have also included potentially serious interactions listed in the drug’s FDA-approved professional package insert or in published medical journal articles. There may be other drugs, especially those in the families of drugs listed below, that also will react with this drug to cause severe adverse effects. Make sure to tell your doctor and pharmacist the drugs you are taking and tell them if you are taking any of these interacting drugs:

ALDACTONE, aspirin—high dose, cholestyramine, COUMADIN, enalapril, estrogen-containing oral contraceptives, GARAMYCIN, gentamicin, GENUINE BAYER ASPIRIN, heparin, methotrexate, potassium supplements, QUESTRAN, spironolactone, VASOTEC, warfarin.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • severe asthma (wheezing)
  • extreme weakness
  • nausea or vomiting
  • pain, cramps, or bloating in the abdomen or stomach
  • severe, watery diarrhea (may contain blood)
  • fever
  • increased thirst
  • abnormal weakness or tiredness
  • abnormal weight loss
  • skin rash, hives, or itching
  • sore throat
  • seizure
  • decreased amount of urine
  • depression
  • pain at site of injection
  • unusual bleeding or bruising
  • yellow eyes or skin
  • lightheadedness or fainting
  • puffiness or swelling around face
  • decrease in blood pressure
  • red or scaly skin
  • joint pain

Call your doctor if these symptoms continue:

  • mild diarrhea
  • nausea or vomiting
  • sore mouth or tongue
  • white patches on mouth or tongue
  • vaginal itching and discharge

last reviewed April 30, 2021