Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.
Allergy: Some people who are allergic to cephalosporin antibiotics also experience allergic reactions to penicillin. Before you take penicillin, inform your doctor about any previous adverse reactions you have had to medications, especially cephalosporins and other penicillins. Contact your doctor at once if you experience signs of an allergic reaction, such as skin rash, itching, difficulty breathing or swelling of the face and throat.
Antibiotic-associated colitis: This medication, like other antibiotics, may cause a potentially dangerous condition called antibiotic-associated, or pseudomembranous, colitis. Symptoms include severe, watery diarrhea that may be bloody. If you notice these symptoms, stop taking penicillin and contact your doctor as soon as possible.
Birth control: Whether penicillin decreases the effectiveness of birth control pills is controversial. Some doctors recommend adding another method of birth control for the rest of the menstrual cycle when penicillin is taken.
Kidney function: Penicillin is removed from the body by the kidneys. People with impaired kidney function are at risk of increased side effects and may need lower doses of penicillin. People with kidney disease or reduced kidney function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Overgrowth of organisms: Prolonged treatment with penicillin may allow normal fungus or types of bacteria not killed by the antibiotic to overgrow, causing unwanted infections such as yeast infections.
Pregnancy: Usual doses of penicillin appear to be safe during pregnancy.
Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking penicillin, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.