Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For acyclovir, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to acyclovir or valacyclovir. Also tell your health care professional if you are allergic to any other substances, such as foods, sulfites or other preservatives, or dyes.

Pregnancy—Acyclovir has been used in pregnant women and has not been reported to cause birth defects or other problems. However, studies have not been done in humans. Studies in rats and rabbits have shown that acyclovir given by injection may keep the fetus from becoming attached to the lining of the uterus (womb). However, acyclovir has not been shown to cause birth defects or other problems in mice given many times the usual human dose, or in rats or rabbits given several times the usual human dose.

Breast-feeding—Acyclovir passes into breast milk. However, it has not been reported to cause problems in nursing babies.

Children—A limited number of studies have been done using oral acyclovir in children, and it has not caused different effects or problems in children than it does in adults.

Older adults— Agitation, confusion, dizziness, and drowsiness may be especially likely to occur in elderly patients who are usually more sensitive than younger adults to the central nervous system effects of acyclovir.

Other medicines—Although certain medicines should not be used together at all, in many cases two different medicines may be used together even if an interaction might occur. In these cases, changes in dose or other precautions may be necessary. If you are taking acyclovir it is especially important that your health care professional know if you are taking any of the following:

• Carmustine (e.g., BiCNU) or
• Cisplatin (e.g., Platinol) or
• Combination pain medicine containing acetaminophen and aspirin (e.g., Excedrin) or other salicylates or
• Cyclosporine (e.g., Sandimmune) or
• Deferoxamine (e.g., Desferal) (with long-term use) or
• Gold salts (medicine for arthritis) or
• Inflammation or pain medicine, except narcotics, or
• Lithium (e.g., Lithane) or
• Methotrexate (Mexate) or
• Other medicine for infection or
• Penicillamine (e.g., Cuprimine) or
• Plicamycin (e.g., Mithracin) or
• Streptozocin (e.g., Zanosar) or
• Tiopronin (Thiola)—Concurrent use of these medicines with acyclovir may increase the chance for side effects, especially when kidney disease is present

Other medical problems—The presence of other medical problems may affect the use of acyclovir. Make sure you tell your doctor if you have any other medical problems, especially:

• Dehydration or
• Kidney disease—Dehydration or kidney disease may increase blood levels of acyclovir, increasing the chance of side effects

• Nervous system problems—Acyclovir may make these problems worse