Prescription medication · Antiviral (Nucleoside Analog)
famciclovir
Also sold as Famvir. This medicine treats herpes infections.
Data updated 2026-05-15
- 2,678
- FDA reportsLightly reported
- 7
- InteractionsFew interactions
- 1
- Recall record
What the data shows
famciclovir (Famvir) is a prescription Antiviral (Nucleoside Analog), among the least-reported drugs the FDA tracks (2,678 FDA reports), with 7 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
famciclovir (Famvir) is a prescription Antiviral (Nucleoside Analog). This medicine treats herpes infections.
Famciclovir is an antiviral medicine. It helps to treat infections caused by certain viruses.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Generic Price
$0.24/unit
Generic Available
Yes (5 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
This medicine treats herpes infections.
Common side effects
Headache, Nausea
Key warnings
If you have kidney problems, make sure your doctor knows.
The sections below are summarized in plain English from famciclovir's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Famciclovir stops the virus from multiplying. It does this by blocking a key enzyme the virus needs to make copies of itself. This helps your body fight off the infection.
Side Effects (from patient reports)
Based on 2,678 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for famciclovir, by number of reports
- Fatigue
Fatigue
185 reports
- Diarrhoea
Diarrhoea
179 reports
- Nausea
Nausea
145 reports
- Headache
Headache
135 reports
- Pain
Pain
118 reports
- Rash
Rash
113 reports
- Dizziness
Dizziness
98 reports
- Pyrexia
Pyrexia
87 reports
- Death
Death
86 reports
- Dyspnoea
Dyspnoea
86 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for famciclovir each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where famciclovir sits
famciclovir has more FDA adverse-event reports than 16% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is famciclovir; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 2,678 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
2,678
Reports Mentioning Death
265
9.9% of reports — not proof of cause
Hospitalization Reports
836
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | FATIGUE | 185 |
| 2 | DIARRHOEA | 179 |
| 3 | NAUSEA | 145 |
| 4 | HEADACHE | 135 |
| 7 | PAIN | 118 |
| 8 | RASH | 113 |
| 9 | DIZZINESS | 98 |
| 10 | PYREXIA | 87 |
| 11 | DEATH | 86 |
| 12 | DYSPNOEA | 86 |
| 13 | PNEUMONIA | 85 |
| 14 | VOMITING | 77 |
| 15 | HERPES ZOSTER | 72 |
| 16 | ARTHRALGIA | 70 |
| 17 | FEBRILE NEUTROPENIA | 69 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
If you have kidney problems, make sure your doctor knows. Taking too much famciclovir when you have kidney problems can damage your kidneys.
Known Drug Interactions
7.2 Potential for Other Drugs to Affect Penciclovir No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine.
Mechanism: These two drugs do not have a meaningful effect on how the body breaks down or uses either medicine.
(7.2) 7.1 Potential for Famciclovir to Affect Other Drugs The steady-state pharmacokinetics of digoxin were not altered by concomitant administration of multiple doses of famciclovir (500 mg three times daily). No clinically significant effect on penciclovir pharmacokinetics was observed following multiple-dose (three times daily) administration of famciclovir (500 mg) with multiple doses of digoxin.
Mechanism: These medicines do not change each other's levels in the body when they are taken together.
7 DRUG INTERACTIONS Probenecid: May increase penciclovir levels. Concurrent use with probenecid or other drugs significantly eliminated by active renal tubular secretion may result in increased plasma concentrations of penciclovir.
Mechanism: Probenecid stops the kidneys from clearing the other medicine out of your system as quickly as usual.
7.2 Potential for Other Drugs to Affect Penciclovir No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine.
Mechanism: Studies show that theophylline does not change how the body breaks down or uses famciclovir.
7.2 Potential for Other Drugs to Affect Penciclovir No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine. Clinical interaction studies of famciclovir with cimetidine and promethazine, in vitro inhibitors of aldehyde oxidase, did not show relevant effects on the formation of penciclovir.
Mechanism: Cimetidine does not interfere with the enzymes that turn famciclovir into its active form.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
Common Questions
Can I take famciclovir if I'm allergic to penciclovir cream (Denavir)?
How quickly should I start taking famciclovir for shingles?
Can famciclovir cure herpes?
What should I do if I experience side effects while taking famciclovir?
Does famciclovir interact with other medications?
How long will I need to take famciclovir?
Can famciclovir prevent the spread of genital herpes?
What should I do if I think I have taken too much famciclovir?
Is famciclovir safe for children?
What are the common side effects of famciclovir?
Does famciclovir interact with other medications?
What drug class is famciclovir?
What pregnancy or breastfeeding source fields are listed for famciclovir?
Has famciclovir been recalled?
Active Recalls
Presence of Foreign Substance- Black hair strand found attached to a tablet in a sealed bottle.
Macleods Pharmaceuticals Ltd
Related Medications in Antiviral (Nucleoside Analog)
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albendazole
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anidulafungin
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Malarone is a drug used to prevent and treat malaria.
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Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for famciclovir: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 2,678.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 9.90%.
- benralizumab Δ 0.00 pts · 17,680 reports · Anti-IL-5R Monoclonal Antibody 9.89%death share
- doxycycline hyclate Δ 0.00 pts · 63,762 reports · Tetracycline Antibiotic (Antimalarial) 9.90%death share
- letrozole Δ 0.00 pts · 59,013 reports · Aromatase Inhibitor 9.89%death share
- eplerenone Δ 0.01 pts · 12,113 reports · Aldosterone Antagonist 9.91%death share
Medication Guides
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FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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What the FDA Data Shows for famciclovir
The FDA label for famciclovir (sold under brand names such as Famvir) classifies it as a prescription-only medication in the Antiviral (Nucleoside Analog) class. This medicine treats herpes infections. Official labeling lists 2 commonly reported side effects, including Headache, Nausea.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 2,678 voluntary reports. The database also lists 7 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated minor severity. NADAC pricing from CMS shows a generic unit cost of $0.24.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history (currently 1 recall record on file), and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. This registry does not provide medication decisions.
Last updated: January 9, 2025
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages