Lack of efficacy (ectoparasite) - flea: in adverse event reports for animal drugs

Clinical sign, a VeDDRA term

In plain words: the product did not have the expected effect: fleas.

Read this first. FDA says this about the data:

An API dataset query result cannot be used to estimate the risk associated with the product or compare one drug or device product with another. When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event. This dataset should not be the sole source of information for clinical decision-making or other assumptions about the safety or effectiveness of a product. The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.
FDA Center for Veterinary Medicine publishes these words. Source: Adverse Event Reports for Animal Drugs and Devices, read on 2 Oct 2026. The data have the reports that FDA received through 26 Jun 2026.

This page is not veterinary advice. For an animal that is ill, speak to a veterinarian.

Contacting a veterinarian How to report to FDA

From February 1995 to June 2026, FDA received 65,571 adverse event reports for animal drugs that list this sign. That is 4.8% of the 1,378,761 reports that FDA received from January 1987 to June 2026. In the 12 months to June 2026, FDA received 6,828 reports that list this sign.

Of the 65,571 reports, 82.3% are about dogs. A report can list more than one sign and more than one drug. A report is not proof that a drug caused a sign.

By number of reports in all years, this sign is number 6 of 1,149 clinical signs with a page. Reports that list this sign rose by 34.1% in the 12 months to June 2026, compared with the 12 months before. Reports for all animal drugs fell by 4.6% in the same periods. The newest months can get more reports in a later update. Reports about dogs are 82.3% of the reports that list this sign, and 72.6% of all reports.

Drug pages with reports that list this sign

The table has every drug page with 20 or more reports that list this sign, in order of name. No count decides which drug is in the table. The table has 57 drug pages.

Show the 57 drug pages

Drug pages with 20 or more reports that list this sign, in order of name
Active ingredients	Reports that list the sign
(S) - methoprene	907
Afoxolaner	4,273
Afoxolaner + Moxidectin + Pyrantel Pamoate	372
Amoxicillin Trihydrate + Clavulanate Potassium	25
Carprofen	54
Cefovecin sodium	45
Cefpodoxime proxetil	28
Cephalexin	42
Cyclosporine	28
Diphenhydramine	166
Emodepside + Praziquantel	26
Enalapril Maleate	27
Eprinomectin + Esafoxolaner + Praziquantel	213
Fluralaner	18,184
Fluralaner + Moxidectin	675
Furosemide	33
Gabapentin	38
Hydroxyzine	28
Imidacloprid	2,668
Imidacloprid + Moxidectin	2,411
Insulin	39
Ivermectin	429
Ivermectin + Praziquantel + Pyrantel Pamoate	38
Ivermectin + Pyrantel Pamoate	450
Levothyroxine sodium	26
Lotilaner	586
Lotilaner + Moxidectin + Praziquantel + Pyrantel Pamoate	85
Lufenuron	104
Lufenuron + Milbemycin Oxime	806
Lufenuron + Milbemycin Oxime + Praziquantel	275
Lufenuron + Praziquantel	127
Maropitant	24
Meloxicam	20
Metronidazole	22
Milbemycin Oxime	107
Milbemycin Oxime + Praziquantel	123
Milbemycin Oxime + Spinosad	7,201
Moxidectin	64
Moxidectin + Pyrantel Pamoate + Sarolaner	21
Nitenpyram	6,744
Oclacitinib	242
Phenobarbital	55
Pimobendan	40
Piperonyl Butoxide	28
Piperonyl Butoxide + Pyrethrins	32
Praziquantel	33
Praziquantel + Pyrantel Pamoate	45
Prednisolone	32
Prednisolone + Trimeprazine Tartrate	34
Prednisone	158
Pyrantel Pamoate	25
Pyrantel Pamoate + Sarolaner	1,753
Sarolaner	1,066
Sarolaner + Selamectin	706
Selamectin	5,679
Spinosad	14,082
Tramadol	41

The openFDA records give the value "MSK" for the brand name and for the manufacturer name of each drug. FDA says that MSK means "masked". So the site cannot count a report for a brand. A report can name more than one drug.

An API dataset query result cannot be used to estimate the risk associated with the product or compare one drug or device product with another.
The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.
FDA Center for Veterinary Medicine. Source: Adverse Event Reports for Animal Drugs and Devices

Ingredients, all combinations

The list has every active ingredient with 20 or more reports that list this sign, in order of name. It has 46 ingredients.

Show the 46 ingredients

Reports by species

Dog82.3%53,948
Cat17.4%11,414
Other0.2%159
Rabbitunder 0.1%12
Ferretunder 0.1%5
Foxunder 0.1%2

The share is of the 65,571 reports that list this sign. The sign is in 5.4% of all reports about the species dog. The sign is in 7.6% of all reports about the species cat.

Reports by month and by year

Reports for each month, Jul 2021 to Jun 2026. The month is the month in which FDA received the report.

FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.

Reports that list Lack of efficacy (ectoparasite) - flea, by the year in which FDA received them
Year	Reports
2026	3,301
2025	5,490
2024	5,296
2023	3,966
2022	3,273
2021	3,599
2020	3,622
2019	2,991
2018	2,612
2017	2,499
2016	3,992
2015	4,700
2014	3,695
2013	4,188
2012	3,733
2011	2,807
2010	1,787
2009	1,117
2008	601
2007	214
2006	120
2005	44
2004	46
2003	17
2002	162
2001	654
2000	1,021
1999	9
1997	3
1996	3
1995	9

What these reports record

Outcome at the time of the report

Reports with this sign
All reports

Recovered/Normal3.8%2,475, All reports: 20.7%
Recovered with Sequela[recovered, with a lasting effect]2.3%1,524, All reports: 2.3%
Ongoing31.7%20,755, All reports: 17.4%
Died0.2%127, All reports: 4.9%
Euthanized0.1%72, All reports: 1.5%
Outcome Unknown50.8%33,296, All reports: 22.7%

An outcome in a report is not proof that the drug caused it. The person who sends the report gives the outcome. Each share is of the 65,571 reports that list this sign.

Age of the animal

Reports with this sign
All reports

Under 1 year7.7%5,059, All reports: 9.5%
1 to 3 years24.6%16,143, All reports: 23.9%
4 to 7 years24.1%15,773, All reports: 20.2%
8 to 11 years15.6%10,237, All reports: 15.4%
12 years and over8.6%5,658, All reports: 10.7%
Age not given19.4%12,701, All reports: 20.3%

The outcome is for the full report, not for this sign only.

Next in the A to Z list of signs

Lack of efficacy (bacteria) - Ehrlichia[the product did not have the expected effect: Ehrlichia bacteria]
Lack of efficacy (bacteria) - NOS[the product did not have the expected effect: target not specified]
Lack of efficacy (ectoparasite) - Demodex[the product did not have the expected effect: Demodex]
Lack of efficacy (ectoparasite) - ear mite[the product did not have the expected effect: ear mites]
Lack of efficacy (ectoparasite) - lice[the product did not have the expected effect: lice]
Lack of efficacy (ectoparasite) - mite NOS[the product did not have the expected effect: mite NOS]
Lack of efficacy (ectoparasite) - NOS[the product did not have the expected effect: target not specified]
Lack of efficacy (ectoparasite) - Sarcoptes[the product did not have the expected effect: Sarcoptes]

All clinical signs

Cite this page

Pet Drug Reports. Lack of efficacy (ectoparasite) - flea: adverse event reports for animal drugs. https://petdrugreports.com/reaction/lack-of-efficacy-ectoparasite-flea/ Source: FDA Center for Veterinary Medicine, openFDA Animal and Veterinary adverse event reports, export of 30 Oct 2026. Reports received through 26 Jun 2026.

Where the data come from

The counts come from the openFDA Animal and Veterinary adverse event files, export of 30 Oct 2026. The files have the reports that the FDA Center for Veterinary Medicine received through 26 Jun 2026. The files mask brand and manufacturer names. The site counts a drug by the active ingredients that each record gives, and gives no count to a brand, an application or a company. Ingredient names and the lists of approved products follow the FDA Green Book of 2 Nov 2026. The site counts the different spellings of one VeDDRA term together.

The site does not publish report text, lot numbers or details of a reporter. FDA's record is the authority. See how the site counts reports, the data sources and the corrections page.

Questions about this sign

What does this term mean in a report?: In plain words: the product did not have the expected effect: fleas. It is a term from VeDDRA, the list of terms that FDA and drug companies use to code a report. The person who coded the report selected the term.
How does the count of the latest 12 months compare with the 12 months before?: FDA received 6,828 reports in the 12 months to June 2026. It received 5,092 reports in the 12 months before. FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.
How many of these reports have a serious flag?: Of the 58,029 reports that say if the event was serious, 15.4% have the serious flag. The person who sends a report sets the flag.
Does a drug in the table cause this sign?: The reports do not show that. A report can name more than one drug. FDA states this about the data.
When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event.
The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.
FDA Center for Veterinary Medicine. Source: Adverse Event Reports for Animal Drugs and Devices