Chicken Pox Medication Side Effects

The Centers for Disease Control and Prevention recommend prescription antiviral medications for the treatment of chicken pox in high risk patients. According to University of Alabama Medical School Professor Richard J. Whitely, M.D., in the 2008 edition of "Harrison's Principles of Medicine," doctors typically prescribe one of three drugs: acyclovir, valacylclovir or famciclovir. All three target the way that the virus that causes chicken pox virus, varicella-zoster, replicates within the body, so they produce similar side effects.

Nausea and Vomiting

In clinical trial data submitted to the Food and Drug Administration, the manufacturer of acyclovir, Glaxo-Smith Kline, reported that nausea and vomiting was the most common side effect seen in adults. Approximately 2.7 percent of patients treated with oral acyclovir complained of nausea or vomiting, compared with 0.7 percent of patients treated with a placebo. Nausea and vomiting have also been associated with valacyclovir, famciclovir and the intravenous form of acyclovir. Eating prior to taking the medication does not appear to reduce the risk of stomach upset.

Diarrhea

Diarrhea was the most common side effect seen in children treated with oral acyclovir for chicken pox. According to Glaxo-Smith Kline, approximately 3.2 percent of children who took acyclovir developed diarrhea, compared to 2.2 percent of children who took a placebo. Similar rates of diarrhea were described by the makers of famciclovir and valacyclovir. The makers of famciclovir, Novartis Pharmaceutical Corporation, report that their product contains lactose, which can cause diarrhea in lactose-intolerant patients. People who have difficulty digesting lactose should choose other drugs.

Headache

In clinical trials for famciclovir, Novartis Pharmaceutical Corporation disclosed that nearly 23 percent of treated patients reported headaches, compared to about 18 percent of patients who received a placebo. In a few cases---about 2.6 percent of patients---headache was accompanied by the sensation of numbness or tingling. The incidence of migraine was less than one percent and did not differ between treated patients and placebo patients. The risk of headache may be greatest for children treated with acyclovir. In clinical studies in patients between 2 and 18 years, Glaxo Smith Kline reported that the incidence of headache was 17 percent among patients treated with valacyclovir, compared to 3 percent in patients treated with a placebo.

Other Side Effects

Less common side effects of antiviral drugs include dizziness, fatigue, agitation, joint or muscle pain, hair loss and changes in vision. These side effects usually subside when the medication is discontinued, but adults and caregivers of children who experience them should contact their doctors for advice. In rare cases, antiviral medications can cause serious allergic reactions, so it's better to err on the side of caution.