Acyclovir Side Effects

Acyclovir is an antiviral medication used in the treatment of different viruses including chicken pox, herpes and shingles. Though the medication can effectively treat outbreaks, it does not cure the infection. Acyclovir has been used over the years to provide treatment and though effective, it also has its side effects. It is important to understand acyclovir side effects before you start using the medication. This will prepare you physically and mentally for any of the effects.

In case you are taking the medication and notice the unwanted effects, you might want to seek medical attention immediately. This is especially the case if you are experiencing the severe side effects.

Reported Acyclovir Side Effects

Let us look at the side effects that you should pay attention to when taking Acyclovir;

Common Acyclovir Side Effects For Injections

-          Swelling, redness and pain at the area of injection

Less Common

-          Increased thirst

-          Nausea or vomiting

-          Weakness and unusual tiredness

-          Appetite loss

-          Decreased amount of urine or urination frequency

-          Stomach or abdominal pain

Rare Side effects

-          Bloody stool or urine

-          Hives

-          Trembling

-          Chills, sore, throat or fever

-          Unusual bruising or bleeding

-          Hallucinations

-          Confusion

-          Red spots in skin

-          Seizures

-          Black tarry stool

There are side effects of acyclovir that occur but do not necessarily require medical attention. Fortunately, these side effects might disappear as your body adjusts to the medication. Your health care practitioner will be in a position to explain to you different ways to deal with these side effects. The following are some of the side effects that do not need medical attention but if they persist, you might want to talk to a health care practitioner:

Common side effects

-          Generally feeling ill or discomfort (common with high dosages)

Less Common

-          Headache

-          Diarrhea

Experienced But With An Undetermined Frequency

-          Loss of hair

-          Drowsiness

-          Tingling, prickling or burning sensation

Detailed Look At Acyclovir Side Effects

The following side effects apply to Acyclovir buccal tablet, intravenous powder used in injections, intravenous solution, oral tablet, oral suspension, oral capsule and compounding powder.

Most Reported Acyclovir Side Effects

The most common reported reactions include vomiting, headache, malaise, and diarrhea.

Gastrointestinal Reaction

Most elderly subjects have reported nausea and vomiting as frequent reactions.

About 1 to 10% of patients report abdominal pain, diarrhea, nausea, vomiting, aphthous stomatitis, and gingival pain. Between 0.1 and 1% of patients report sore throat.

Renal Reactions

In rare cases, about 0.01 to 0.1% of patients experience blood urea nitrogen elevation, and creatinine elevation. In rare cases, less than 0.01% of patients have renal pain, and renal failure. There are some reactions with undetermined frequency involving renal impairment and crystalluria.

Renal pain mostly results from crystalluria and renal failure. In most cases, renal impairment can be reversed but when left unchecked; it might lead to renal failure.


Patients have reported site pain and site irritation. Some report local inflammation at areas of injection sites.  There are cases of severe local inflammations which include tissue necrosis. Buccal tablets have been found to be behind application site irritation and site pain.

Nervous system

Some of the most frequent reactions in elderly subjects include somnolence, dizziness and comas.

Common reactions in about 1 to 10% of patients include dizziness and headaches. In rare cases, below 0.01% of patients experience dysarthria, encephalopathy, convulsions, coma, and Ataxia. Other reactions with undetermined frequency include shaking, medication taste, giddiness, and taste disturbance.


Between 1 and 10% of patients experience pruritus, rashes, hives, and erythema. Uncommon reactions include accelerated hair loss and Urticaria.  Some reactions that have undetermined frequencies include Diaphoresis.

Cardiovascular Health

Though frequency has not yet been determined, some patients experience chest pain and palpitation.  There are postmarketing reports that indicate peripheral edema and hypotension.


In very rare case, less than 0.01% of patients experience leucopenia, neutropenia, thrombocytopenia, and anemia. Cases of reactions without determined frequencies include hematologic changes.


Medical practitioners have reported rare cases of liver related enzymes and reversible bilirubin. In extremely rare cases, there have been reports of jaundice and hepatitis.


There are very rare cases of anaphylaxis


There are cases of Pars planitis though the frequency has not yet been determined.

Musculoskeletal reactions

Between 0.1 and 1% off patients experience leg pain with some cases of myalgia being reported.

Genitourinary Reactions

Though the frequency is still not determined, there are reported cases of menstrual abnormalities, dysuria, anuria, hematuria and abnormal urinalysis.


Though uncommon, there are reports of Anorexia and some cases of increased thirst.


There are cases of hallucinations, confusion, agitation, aggressiveness, and psychosis especially in elderly patients. Reactions with undetermined frequency include insomnia and depression.

In conclusion

Taking Acyclovir will help in the treatment of infection and the symptoms they come with. However, the medication might have unwanted side effects that might make you uncomfortable. It is important to understand these reactions and side effects because you will be more prepared to handle them.