August 30, 2016
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Famvir Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 8/5/2015

Famvir (famciclovir) is an antiviral drug used to treat infections caused by herpes viruses, including genital herpes, cold sores, shingles, and chicken pox. Famvir is available in generic form. Common side effects of Famvir include headache, nausea, stomach pain, gas, diarrhea, tired feeling, dizziness, sleepiness, itching or skin rash, or numbness or tingly feeling.

Dosing for Famvir varies. The recommended doses are: recurrent genital herpes: 1,000 mg every 12 hours for one day; recurrent cold sores: 1,500 mg as a single dose; suppression of recurrent genital herpes: 250 mg twice daily; shingles: 500 mg every 8 hours for 7 days; and HIV-infected patients (cold sores or genital herpes): 500 mg twice daily for 7 days. Before taking Famvir, tell your doctor if you are also taking probenecid (Benemid). If you are using probenecid, you may not be able to use Famvir, or you may need dosage adjustments or special tests during treatment. During pregnancy, Famvir should be used only when prescribed. It is not known if this medication passes into breast milk. It may have undesirable effects on a nursing infant. Consult your doctor before breast-feeding.

Our Famvir (famciclovir) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Patient Information in Detail?

Easy-to-read and understand detailed drug information and pill images for the patient or caregiver from Cerner Multum.

Famvir in Detail - Patient Information: Side Effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using famciclovir and call your doctor at once if you have a serious side effect such as:

  • urinating less than usual or not at all;
  • weakness, confusion, increased thirst, loss of appetite, vomiting, pounding heartbeats or fluttering in your chest; or
  • swelling, weight gain, feeling short of breath.

Less serious side effects may include:

  • nausea, gas, stomach pain;
  • diarrhea,
  • headache, tired feeling;
  • dizziness, sleepiness;
  • mild itching or skin rash; or
  • numbness or tingly feeling.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Famvir (Famciclovir)

What is Patient Information Overview?

A concise overview of the drug for the patient or caregiver from First DataBank.

Famvir Overview - Patient Information: Side Effects

SIDE EFFECTS: Headache, nausea, and diarrhea may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including: mental/mood changes (such as agitation, slowed thinking, confusion, hallucinations), dizziness, drowsiness, change in the amount of urine, yellowing eyes/skin, easy bruising/bleeding.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire patient information overview for Famvir (Famciclovir)

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Famvir FDA Prescribing Information: Side Effects
(Adverse Reactions)


Acute renal failure is discussed in greater detail in other sections of the label [see WARNINGS AND PRECAUTIONS].

The most common adverse events reported in at least 1 indication by > 10% of adult patients treated with FAMVIR are headache and nausea.

Clinical Trials Experience in Adult Patients

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Immunocompetent patients

The safety of FAMVIR has been evaluated in active-and placebo-controlled clinical studies involving 816 FAMVIR-treated patients with herpes zoster (FAMVIR, 250 mg three times daily to 750 mg three times daily); 163 FAMVIR-treated patients with recurrent genital herpes (FAMVIR, 1000 mg twice daily); 1,197 patients with recurrent genital herpes treated with FAMVIR as suppressive therapy (125 mg once daily to 250 mg three times daily) of which 570 patients received FAMVIR (open-labeled and/or double-blind) for at least 10 months; and 447 FAMVIR-treated patients with herpes labialis (FAMVIR, 1500 mg once daily or 750 mg twice daily). Table 2 lists selected adverse events.

Table 2 : Selected Adverse Events (all grades and without regard to causality) Reported by ≥ 2% of Patients in Placebo-Controlled Famvir Trials*

Events Incidence
Herpes Zoster† Recurrent Genital Herpes‡ Genital Herpes-Suppression§ Herpes Labialis‡
Nervous System
Headache 22.7 17.8 13.5 5.4 39.3 42.9 8.5 6.7
Paresthesia 2.6 0.0 0.0 0.0 0.9 0.0 0.0 0.0
Migraine 0.7 0.7 0.6 0.6 3.1 0.0 0.2 0.0
Nausea 12.5 11.6 2.5 3.6 7.2 9.5 2.2 3.9
Diarrhea 7.7 4.8 4.9 1.2 9.0 9.5 1.6 0.8
Vomiting 4.8 3.4 1.2 0.6 3.1 1.6 0.7 0.0
Flatulence 1.5 0.7 0.6 0.0 4.8 1.6 0.2 0.0
Abdominal Pain 1.1 3.4 0.0 1.2 7.9 7.9 0.2 0.4
Body as a Whole
Fatigue 4.4 3.4 0.6 0.0 4.8 3.2 1.6 0.4
Skin and Appendages
Pruritus 3.7 2.7 0.0 0.6 2.2 0.0 0.0 0.0
Rash 0.4 0.7 0.0 0.0 3.3 1.6 0.0 0.0
Reproductive (Female)
Dysmenorrhea 0.0 0.1 1.8 0.6 1.6 6.3 0.4 0.0
* Patients may have entered into more than one clinical trial.
†7 days of treatment
‡1 day of treatment
§daily treatment

Table 3 lists selected laboratory abnormalities in genital herpes suppression trials.

Table 3 : Selected Laboratory Abnormalities in Genital Herpes Suppression Studies*

Parameter Famvir
(n = 660) †
(n = 210) †
Anemia ( < 0.8 x NRL) 0.1 0.0
Leukopenia ( < 0.15 x NRL) 1.3 0.9
Neutropenia ( < 0.8 x NRL) 3.2 1.5
AST (SGOT) ( > 2 x NRH) 2.3 1.2
ALT (SGPT) ( > 2 x NRH) 3.2 1.5
Total Bilirubin ( > 1.5 x NRH) 1.9 1.2
Serum Creatinine ( > 1.5 x NRH) 0.2 0.3
Amylase ( > 1.5 x NRH) 1.5 1.9
Lipase ( > 1.5 x NRH) 4.9 4.1
* Percentage of patients with laboratory abnormalities that were increased or decreased from baseline and were outside of specified ranges.
†n values represent the minimum number of patients assessed for each laboratory parameter.
NRH = Normal Range High.
NRL = Normal Range Low.

HIV-infected patients

In HIV-infected patients, the most frequently reported adverse events for FAMVIR (500 mg twice daily; n=150) and acyclovir (400 mg, 5x/day; n=143), respectively, were headache (17% vs. 15%), nausea (11% vs. 13%), diarrhea (7% vs. 11%), vomiting (5% vs. 4%), fatigue (4% vs. 2%), and abdominal pain (3% vs. 6%).

Postmarketing Experience

The adverse events listed below have been reported during postapproval use of FAMVIR. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure:

Blood and lymphatic system disorders: Thrombocytopenia

Hepatobiliary disorders: Abnormal liver function tests, cholestatic jaundice

Nervous system disorders: Dizziness, somnolence

Psychiatric disorders: Confusion (including delirium, disorientation, and confusional state occurring predominantly in the elderly), hallucinations

Skin and subcutaneous tissue disorders: Urticaria, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema (e.g., face, eyelid, periorbital, and pharyngeal edema), leukocytoclastic vasculitis

Cardiac disorders: Palpitations

Read the entire FDA prescribing information for Famvir (Famciclovir)

Famvir - User Reviews

Famvir User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Famvir sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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