Famciclovir Side Effects

Medically reviewed by Drugs.com. Last updated on Aug 22, 2024.

Applies to famciclovir: oral tablet.

Common side effects of famciclovir

Some side effects of famciclovir may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common side effects

• cramps
• diarrhea
• headache
• heavy bleeding
• nausea
• stomach pain

Less common side effects

• bloated, full feeling
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feeling
• confusion as to time, place, or person
• excess air or gas in the stomach or intestines
• hives or welts
• holding false beliefs that cannot be changed by fact
• itching skin
• mood or mental changes
• passing gas
• rash
• redness of skin
• seeing, hearing, or feeling things that are not there
• unusual excitement, nervousness, or restlessness
• unusual tiredness or weakness
• vomiting

Incidence not known

• sleepiness or unusual drowsiness

Serious side effects of famciclovir

Along with its needed effects, famciclovir may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking famciclovir:

Incidence not known

• black, tarry stools
• bleeding gums
• blistering, peeling, or loosening of the skin
• blood in urine or stools
• chills
• clay-colored stools
• cough
• dark urine
• dizziness
• fever
• joint or muscle pain
• loss of appetite
• pinpoint red spots on the skin
• red, irritated eyes
• sore throat
• sores, ulcers, or white spots in the mouth or on the lips
• unpleasant breath odor
• unusual bleeding or bruising
• vomiting of blood
• yellow eyes or skin

For healthcare professionals

Applies to famciclovir: oral tablet.

General adverse events

Famciclovir is generally well tolerated. The most common side effects reported in at least 1 indication by greater than 10% of patients are headache and nausea.^[Ref]

Nervous system

• Very common (10% or more): Headache (up to 39.3%)
• Common (1% to 10%): Migraine (up to 3.1%), paresthesia (up to 2.6%)
• Frequency not reported: Insomnia
• Postmarketing reports: Dizziness, somnolence^[Ref]

Confusion and bradykinesia developed in an 80-year-old woman who received famciclovir for acute herpes zoster. The dosage administered was clinically appropriate and adjusted to her estimated creatinine clearance. Although herpes zoster may sometimes elicit neurological complications and cannot be ruled out as a contributing factor, the patient's mobility problems and mental deterioration corresponded temporally with drug administration (onset within 48 and 72 hours, respectively, of initiation and reinstitution of therapy).^[Ref]

Gastrointestinal

• Very common (10% or more): Nausea (up to 13%)
• Common (1% to 10%): Diarrhea (up to 9%), abdominal pain (up to 7.9%), vomiting (up to 5%), elevated lipase (greater than 1.5 times normal range high [NRH]; 4.9%), flatulence (up to 4.8%), elevated amylase (greater than 1.5 times NRH; 1.5%)
• Rare (less than 0.1%): Pancreatitis
• Frequency not reported: Dyspepsia, anorexia^[Ref]

An isolated case of acute necrotic-hemorrhagic pancreatitis occurred in a kidney graft recipient who was treated with famciclovir for severe hepatitis B infection. The author could not identify any other etiologic factor for the pancreatitis, although some possible predisposing factors were noted, including the patient's liver insufficiency and renal dysfunction.^[Ref]

Genitourinary

• Common (1% to 10%): Dysmenorrhea (up to 7.6%)^[Ref]

Other

• Common (1% to 10%): Fatigue (up to 4.8%)
• Frequency not reported: Injury, back pain, viral infection (including influenza, influenza-like symptoms, and symptoms of a cold), asthenia, fever^[Ref]

Dermatologic

• Common (1% to 10%): Pruritus (up to 3.7%), rash (up to 3.3%)
• Postmarketing reports: Urticaria, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema (e.g., face, eyelid, periorbital, and pharyngeal edema), leukocytoclastic vasculitis^[Ref]

Hematologic

• Common (1% to 10%): Neutropenia (less than 0.8 times normal range low [NRL]; 3.2%), leukopenia (less than 0.75 times NRL; 1.3%)
• Uncommon (0.1% to 1%): Anemia (less than 0.8 times NRL; 0.1%)
• Postmarketing reports: Thrombocytopenia^[Ref]

Hepatic

• Common (1% to 10%): Elevated ALT (greater than 2 times NRH; 3.2%), elevated AST (greater than 2 times NRH; 2.3%), elevated total bilirubin (greater than 1.5 times NRH; 1.9%)
• Postmarketing reports: Cholestatic jaundice, abnormal liver function tests^[Ref]

Renal

• Uncommon (0.1% to 1%): Elevated serum creatinine (greater than 1.5 times NRH; 0.2%)
• Frequency not reported: Acute renal failure^[Ref]

Cardiovascular

• Postmarketing reports: Palpitations

Psychiatric

• Postmarketing reports: Confusion (including delirium, disorientation, and confusional state occurring predominantly in the elderly), hallucinations

Respiratory

• Frequency not reported: Upper respiratory tract infection, pharyngitis^[Ref]

Further information

Famciclovir side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer