Pharmacologic class (EPC) · 3 drug pages

Histamine-1 receptor inhibitor: adverse event reports filed with FDA

7,029 reports list a drug in this class as a suspect or interacting product, 2005–2026.

Read first · FDA's statement on these data

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product. openFDA, FDA

FDA adds: "There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event." The information in these reports "cannot be used to estimate the incidence of these events."

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

7,029
reports across the class: 0% of all reports; 100
reports, 12 months to June 2026: 117 in the 12 months before; 3.1%
marked serious by the reporter: 57.4% across all reports; 3
drugs with a page: brand and generic names counted separately

Histamine-1 receptor inhibitor is a pharmacologic class (an FDA Established Pharmacologic Class) with 3 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 7,029 adverse event reports received by FDA, 0% of the database, from April 2005 to June 2026.

100 reports arrived in the 12 months to June 2026, down 15% from 117 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 3.1% of the class's reports are marked serious, 0.5% record death among the outcomes and 1.1% record hospitalisation, as reported.

Across the class the reactions recorded most often are treatment failure (61.9%), drug ineffective (12%) and eye irritation (8.7%). The class median share shown beside each term is the middle value across the member drugs; it is the comparison used on every drug page in this class.

The members table is ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Drugs in the class

Drug	Name type	Reports	Latest 12 months	Marked serious	Top term recorded
ZaditorKetotifen fumarate	brand	3,290	3	1.6%	Treatment failure
Olopatadine hydrochloride	generic	2,404	61	6.1%	Treatment failure
AlawayKetotifen fumarate	brand	1,335	36	1.7%	Eye irritation

Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Reports by month, five years

FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

Reactions recorded across the class

share of class reports recording the termmedian drug in the class

Treatment failurethe treatment did not work61.9%4,351
Drug ineffectivethe medicine did not work as expected12%841
Eye irritationeye irritation8.7%612
Eye paineye pain3.4%238
Ocular hyperaemiaa red eye2.9%203
Eye pruritus2.6%183
Instillation site pain1.8%127
Vision blurredblurred vision1.6%115
Hypersensitivityan allergic-type reaction1.5%108
Condition aggravatedthe condition being treated got worse1.4%97
Eye swellinga swollen eye1%71
Lacrimation increasedwatery eyes0.8%54
Product quality issuea problem with the product itself0.8%54
Dry eyedry eye0.8%53
No adverse eventno adverse event was reported0.5%36
Expired product administeredthe product was used past its expiry date0.5%35
Eyelid oedemaa swollen eyelid0.5%35
Headachehead pain0.5%33
Product delivery mechanism issue0.5%33
Burning sensationa burning feeling0.5%32
Drug hypersensitivityan allergic-type reaction to a medicine0.4%31
Instillation site irritation0.4%30
Dizzinesslight-headedness or unsteadiness0.4%26
Eye discharge0.4%26
Inappropriate schedule of product administrationthe product was taken at the wrong times0.4%26

Solid bar: share of all class reports. Hollow bar: the median share across the 3 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death0.5%33

Life-threatening0.2%12

Hospitalisation (initial or prolonged)1.1%78

Disability0.1%6

Congenital anomaly0.1%4

Other serious2.5%177

Not serious96.9%6,809

Patient age

Under 20.1%4

2 to 110.5%35

12 to 170.3%20

18 to 442.1%148

45 to 645.6%394

65 to 743.9%276

75 and over4.6%322

Age not given82.9%5,830

Who reported

Physician2.8%194

Pharmacist0.5%37

Other health professional13%913

Lawyer0%1

Consumer or non-health professional83.3%5,854

Not given0.4%30

Grey bar: all 20,646,523 reports in the database. Outcome flags are as the reporter set them and are not verified by FDA.

Questions about Histamine-1 receptor inhibitor reports

Which drugs are in the Histamine-1 receptor inhibitor class on this site?

Zaditor, Olopatadine hydrochloride and Alaway. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

7,029 reports through June 2026, 100 of them in the latest 12 months. A report listing two drugs of the class counts once for each.

What reactions are recorded most often?

treatment failure (61.9%), drug ineffective (12%), eye irritation (8.7%), eye pain (3.4%) and ocular hyperaemia (2.9%).

Can the members table be used to rank the drugs?

No. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." Drugs differ in how many people take them, in the conditions they treat, in time on the market and in how diligently reports are collected.

How do I report an adverse event?

Through FDA MedWatch (Form FDA 3500, or 1-800-FDA-1088) or to the manufacturer. See the guide on how to report.

Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A class is the Established Pharmacologic Class most often attached to a drug's reports by openFDA's label harmonisation, or from the NDC Directory where reports carry none. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.

Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.