Do NOT use Aciclovir if:

• you are allergic to any ingredient in Aciclovir or to valacyclovir

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Aciclovir. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are pregnant, planning to become pregnant, or are breast-feeding
• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you have kidney problems or a weakened immune system.

Some medicines may interact with Aciclovir. Tell your health care provider if you are taking any other medicine, especially any of the following:

• Medicines that may harm the kidney (eg, aminoglycoside antibiotics [eg, gentamicin], amphotericin B, cyclosporine, nonsteroidal anti-inflammatory drugs [NSAIDs] [eg, ibuprofen], tacrolimus, vancomycin) because the risk of kidney side effects may be increased. Ask your doctor if you are unsure if any of your medicines might harm the kidney.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Aciclovir may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Aciclovir may cause drowsiness, dizziness, vision changes, or lightheadedness. These effects may be worse if you take it with alcohol or certain medicines. Use Aciclovir with caution. Do not drive or perform other possibly unsafe tasks until you know how you react to it.
• Aciclovir may cause dizziness, lightheadedness, or fainting; alcohol, hot weather, exercise, or fever may increase these effects. To prevent them, sit down or stand up slowly, especially in the morning. Sit or lie down at the first sign of any of these effects.
• Aciclovir may cause you to become sunburned more easily. Avoid the sun, sunlamps, or tanning booths until you know how you react to Aciclovir. Use a sunscreen or wear protective clothing if you must be outside for more than a short time.
• Aciclovir is not a cure for genital herpes and will not prevent the virus from spreading. Avoid sexual intercourse when sores are present to prevent infecting your partner. You can also be contagious and spread the herpes virus but not have any signs or symptoms at all. This is called asymptomatic viral shedding.
• Lab tests, including kidney function and serum urea nitrogen (BUN), may be performed while you use Aciclovir. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Use Aciclovir with caution in the elderly; they may be more sensitive to its effects, especially confusion, drowsiness, or hallucinations.
• Aciclovir is not recommended for use in children younger than 2 years old as safety and effectiveness for children have not been confirmed.
• Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Aciclovir while you are pregnant. Aciclovir is found in breast milk. If you are or will be breast-feeding while you use Aciclovir, check with your doctor. Discuss any possible risks to your baby.

All medicines may cause side effects, but many people have no, or minor, side effects.

Check with your doctor if any of these most common side effects persist or become bothersome:

Diarrhea; general body discomfort; headache; nausea/vomiting.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); aggressive behavior; blood in the urine; confusion; decreased consciousness; decreased urination; hallucinations; lower back pain; mental or mood changes; red, swollen, blistered, or peeling skin; seizures; unusual bruising or bleeding.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.