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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Penoxsulam is a sulfonamide herbicide used primarily for weed control in rice crops and aquatic environments. This guide details its toxicological profile and safety protocols.
Name
Penoxsulam
Raw Name
PENOXSULAM
Category
Other
Drug Count
3
Variant Count
3
Last Verified
February 17, 2026
About Penoxsulam
Penoxsulam is a sulfonamide herbicide used primarily for weed control in rice crops and aquatic environments. This guide details its toxicological profile and safety protocols.
Detailed information about Penoxsulam
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Penoxsulam.
While this profile follows a clinical drug information format, it is vital to understand that Penoxsulam is not a therapeutic medication. There are no FDA-approved indications for human consumption, and it is never prescribed for the treatment of any medical condition. Instead, its 'clinical' relevance pertains to occupational medicine, environmental health, and toxicology. Healthcare providers may encounter Penoxsulam in the context of accidental exposure, agricultural runoff, or the management of patients who work in industrial or agricultural settings where this substance is utilized. As of 2026, Penoxsulam remains a cornerstone in global rice production and aquatic weed management, marketed under various brand names such as Grasp, Granite, and Galleon.
At the molecular level, Penoxsulam functions by binding to the acetolactate synthase (ALS) enzyme, also known as acetohydroxyacid synthase (AHAS). This enzyme is the first common step in the production of the three essential branched-chain amino acids. By inhibiting this enzyme, Penoxsulam effectively halts protein synthesis and cell division in susceptible plant species. This leads to a cessation of growth within hours of application, though visible symptoms such as chlorosis (yellowing of leaves) and necrosis (death of tissue) may take several days or weeks to appear.
From a mammalian toxicological perspective, the mechanism of action is significantly different. Because mammals lack the target enzyme, the primary concerns regarding Penoxsulam exposure involve non-specific cellular interactions, metabolic stress, or irritation of mucosal membranes. Research into the molecular targets of Penoxsulam in mammals has shown no significant binding to human neurotransmitter receptors, ion channels, or common metabolic enzymes, which accounts for its classification as a low-risk substance for general toxicity.
Although Penoxsulam is not administered as a drug, its behavior within biological systems has been extensively studied through animal models (rats, rabbits, and dogs) to establish safety margins for human exposure.
Penoxsulam is utilized in several distinct sectors, each governed by specific regulatory standards:
Penoxsulam is formulated for industrial and agricultural use in several concentrations and delivery systems:
> Important: Only your healthcare provider or a qualified toxicologist can determine the clinical significance of Penoxsulam exposure in a human context. This substance is an herbicide and is not for human consumption.
Because Penoxsulam is not a medication, there is no therapeutic 'dosage' for humans. Instead, regulatory bodies like the EPA and the World Health Organization (WHO) establish exposure limits to ensure public safety. For adults, the Reference Dose (RfD)—the amount a human can be exposed to daily without appreciable risk—is typically set based on the No Observed Adverse Effect Level (NOAEL) from animal studies.
In agricultural settings, the application rate for the herbicide itself varies. For example, in rice crops, the typical application rate is 0.031 to 0.045 lbs of active ingredient per acre.
Penoxsulam is not approved for pediatric use in any capacity. Children are considered a sensitive population due to their developing metabolic systems and higher surface-area-to-mass ratio. Regulatory safety factors often include an additional 10x safety margin (FQPA Safety Factor) to protect infants and children from potential residues in food or environmental exposure. There is no 'safe' dose for a child to ingest; any ingestion should be treated as a potential poisoning event.
In the event of accidental toxic exposure, certain physiological factors may influence how the body processes Penoxsulam.
Since Penoxsulam is primarily excreted through the kidneys, individuals with pre-existing renal disease (reduced GFR) may experience slower clearance of the compound if absorbed systemically. However, no specific adjustment protocols exist because the substance is not used therapeutically.
While hepatic metabolism is a secondary clearance route, severe liver dysfunction could theoretically prolong the presence of Penoxsulam metabolites in the blood. Clinical management focuses on supportive care rather than dose adjustment.
Elderly individuals may be more susceptible to the irritant effects of Penoxsulam, particularly regarding skin and respiratory exposure, due to age-related changes in tissue integrity and pulmonary function.
If you are an agricultural worker or applicator, specific safety protocols must be followed to minimize exposure:
This concept does not apply to Penoxsulam as it is not a scheduled medication. In the context of an agricultural application schedule, missing a scheduled application may result in poor weed control but has no clinical health implications for the user.
An 'overdose' of Penoxsulam refers to acute toxic exposure via ingestion, inhalation, or massive dermal contact.
> Important: Follow the instructions provided by your healthcare provider or poison control center in the event of exposure. Do not attempt to self-treat accidental poisoning.
While Penoxsulam is classified by the EPA as having low acute toxicity (Category III or IV for most routes), exposure can still result in uncomfortable symptoms. These are most commonly seen in occupational settings where concentrated forms of the chemical are handled.
In cases of higher-level exposure, such as accidental spills or prolonged contact without PPE, more systemic symptoms may occur:
While Penoxsulam is not highly toxic, certain symptoms indicate a severe reaction or a massive exposure that requires emergency intervention.
> Warning: Stop using the product and call a doctor or emergency services immediately if you experience any of the following:
Chronic exposure studies in animals have been conducted to determine the potential for long-term health effects in humans. In two-year feeding studies in rats, the primary findings at very high doses included:
As Penoxsulam is not a pharmaceutical drug, it does not carry FDA Black Box Warnings. However, it carries 'Signal Words' required by the EPA on its labeling. Most Penoxsulam formulations carry the signal word 'CAUTION,' which is the lowest level of toxicity warning, indicating that the product is slightly toxic or relatively non-toxic.
Report any unusual symptoms or suspected exposure events to your healthcare provider or the National Poison Control Center at 1-800-222-1222.
Penoxsulam is an agricultural chemical and should never be used in a manner inconsistent with its labeling. The primary safety concerns involve environmental protection and the prevention of accidental human exposure. It is crucial to recognize that while Penoxsulam has a low mammalian toxicity profile, the solvents and surfactants (inert ingredients) in the final product may have their own safety profiles that require attention.
There are no FDA black box warnings for Penoxsulam. It is regulated by the EPA under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), not as a human medication.
Individuals with a history of sensitivity to sulfonamide compounds (such as 'sulfa drugs') should exercise extreme caution. While cross-reactivity between sulfonamide herbicides and sulfonamide antibiotics is not well-documented, the structural similarity (the SO2NH2 group) suggests a theoretical risk of cross-sensitivity in highly predisposed individuals.
Penoxsulam is highly toxic to certain aquatic plants and can be mobile in soil. It has the potential to leach into groundwater, especially in areas with permeable soils and high water tables. It must not be applied directly to water except as specified for aquatic weed control.
For general agricultural workers, routine medical monitoring (like blood tests) is not typically required for Penoxsulam use. However, in cases of significant chronic exposure, a healthcare provider might suggest:
Penoxsulam exposure is not known to cause impairment of the central nervous system (CNS) that would interfere with the ability to drive or operate heavy machinery. However, if an individual experiences secondary symptoms like headache or dizziness following exposure, they should cease these activities until symptoms resolve.
There are no known direct interactions between Penoxsulam and alcohol. However, alcohol consumption can dehydrate the body and potentially complicate the clinical picture in the event of an accidental poisoning.
If you choose to stop using Penoxsulam, do not pour the remaining product down the drain or into the trash. It must be disposed of according to local, state, and federal regulations for hazardous waste. Empty containers should be triple-rinsed and recycled or disposed of in a sanitary landfill as directed by the product label.
> Important: Discuss all your medical conditions and potential occupational risks with your healthcare provider before working with Penoxsulam.
In the context of human biology, there are no 'contraindicated' drug-drug interactions because Penoxsulam is not a drug. However, in the context of agricultural chemistry, Penoxsulam should not be mixed with certain other chemicals that could create hazardous reactions or neutralize its efficacy:
From a toxicological standpoint, if a person is exposed to Penoxsulam while taking certain medications, there could be theoretical concerns:
There are no known food interactions with Penoxsulam. It is not affected by grapefruit juice, dairy, or high-fat meals. However, the EPA sets 'Maximum Residue Limits' (MRLs) for Penoxsulam on food crops (like rice) to ensure that dietary intake remains far below any level that could cause interaction with human physiology.
There is no data suggesting that herbal supplements like St. John's Wort or Ginkgo Biloba interact with Penoxsulam. Because Penoxsulam does not significantly utilize the CYP3A4 pathway for metabolism, the risk of supplement-induced metabolic interference is extremely low.
Penoxsulam is not known to interfere with common clinical laboratory tests, such as:
However, in a toxicology screening, specialized liquid chromatography-mass spectrometry (LC-MS) would be required to detect Penoxsulam in blood or urine, as it will not show up on a standard 10-panel drug screen.
If interactions were to occur, they would likely be pharmacokinetic in nature, specifically involving renal clearance. Because Penoxsulam is an organic acid, it may compete for organic anion transporters (OATs) in the kidney tubules. This could theoretically lead to a slight increase in the plasma concentration of other drugs that rely on the same transport system, such as methotrexate or certain penicillins.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, especially if you work in an industry where you are exposed to agricultural chemicals.
There are several scenarios where exposure to Penoxsulam is strictly contraindicated due to the risk of adverse health or environmental outcomes:
These are conditions where the risk of using or being near Penoxsulam may be higher, requiring a careful risk-benefit analysis by an occupational health specialist:
Patients should be aware of potential cross-sensitivity with other members of the sulfonamide chemical family. This includes not only other herbicides like Florasulam or Metsulfuron-methyl but also, theoretically, certain medications. If you have had a severe reaction to a 'sulfa' drug, discuss this with your employer or healthcare provider before handling Penoxsulam.
> Important: Your healthcare provider will evaluate your complete medical history and occupational risks before determining if it is safe for you to work with substances like Penoxsulam.
Penoxsulam has been evaluated in developmental toxicity studies to determine its safety for pregnant women. In studies using pregnant rats and rabbits, Penoxsulam did not cause birth defects (teratogenicity) even at doses that were toxic to the mother. The EPA has determined that there is no evidence of increased susceptibility of the fetus to Penoxsulam. However, as a precaution, pregnant women should minimize exposure to all agricultural chemicals. The substance is generally classified in a category equivalent to FDA Category B or C—meaning animal studies show no risk, but human studies are lacking.
It is not known whether Penoxsulam is excreted in human breast milk. However, given its relatively low molecular weight and moderate protein binding, small amounts could theoretically pass into milk following a significant exposure. Because the compound has low acute toxicity, the risk to a nursing infant is likely low, but breastfeeding mothers who work with the chemical should exercise extra caution and practice rigorous hygiene (showering and changing clothes) before nursing.
Penoxsulam is not for use in or on children. While it is used in some turf applications (like golf courses), the residue levels allowed by the EPA are calculated to be safe for children playing on treated grass after the spray has dried. There are no clinical conditions in children for which Penoxsulam is a treatment.
In animal studies, older subjects did not show a significantly different toxicological profile compared to younger adults. However, in humans, the elderly may be at higher risk for complications from accidental exposure due to a higher prevalence of pre-existing kidney or heart disease. Occupational health assessments for older workers should focus on their ability to safely use PPE and their overall renal clearance capacity.
As the kidneys are the primary route of elimination for absorbed Penoxsulam, individuals with impaired renal function (CrCl < 30 mL/min) should be monitored more closely in the event of an accidental poisoning. There are no established dose-adjustment guidelines as it is not a medication.
Liver disease is not expected to significantly impact the safety of Penoxsulam exposure, as hepatic metabolism is a minor pathway. However, general health status should always be considered in the context of chemical safety.
> Important: Special populations require individualized medical assessment and should consult with a specialist in occupational medicine or toxicology.
Penoxsulam is a potent inhibitor of the enzyme acetolactate synthase (ALS). In plants, this enzyme is located in the chloroplasts and is essential for the production of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine. Penoxsulam binds to the ALS enzyme, preventing the conversion of pyruvate to acetolactate (in the valine/leucine pathway) or the conversion of pyruvate and alpha-ketobutyrate to acetohydroxybutyrate (in the isoleucine pathway). This blockage leads to a rapid depletion of essential proteins, stopping plant growth almost immediately. In mammals, this pathway does not exist, providing the biochemical basis for its low toxicity.
In plant species, the dose-response relationship is very sharp; even low concentrations (in the parts per billion range in water) can inhibit growth. In mammals, the pharmacodynamic effects are non-specific and only occur at very high concentrations. There is no evidence of 'tolerance' development in mammals, although weed species can develop resistance to ALS inhibitors through genetic mutations in the ALS enzyme site.
| Parameter | Value (Mammalian Model) |
|---|---|
| Bioavailability | 30% - 50% (Oral) |
| Protein Binding | ~40% - 60% |
| Half-life | 2 - 6 hours |
| Tmax | 1 - 2 hours |
| Metabolism | Minimal (Hydroxylation) |
| Excretion | Renal 70%, Fecal 30% |
Penoxsulam belongs to the Sulfonamide Herbicide class. Within this group, it is specifically a Triazolopyrimidine. It is related to other herbicides like Diclosulam and Florasulam. It is NOT related to the sulfonamide class of antibiotics (like sulfamethoxazole) in terms of therapeutic use, although they share a similar chemical backbone.
Common questions about Penoxsulam
Penoxsulam is a selective herbicide used to control broadleaf weeds and sedges in rice crops and aquatic environments. It is not a human medication and is never prescribed to patients for any medical condition. Instead, it works by inhibiting the ALS enzyme in plants, which is necessary for their growth but absent in humans. It is commonly found in products used by farmers and professional lake managers. If you see it listed on a product, it is intended for weed control only.
The most common side effects in humans are related to direct contact during application. These include mild skin irritation, redness, and itching at the site of contact. If the mist is inhaled, it may cause a temporary sore throat or cough. Eye contact can lead to stinging and redness. These symptoms are generally mild and go away once the person washes the affected area and moves to fresh air.
Since Penoxsulam is an herbicide and not a medication you 'take,' there is no direct interaction with alcohol. However, you should never ingest Penoxsulam under any circumstances. If you have been accidentally exposed to the chemical, it is best to avoid alcohol until you are sure you are not experiencing any toxic effects. Alcohol can mask symptoms of poisoning or worsen dehydration. Always prioritize safety and follow the advice of a poison control center.
Animal studies have shown that Penoxsulam does not cause birth defects or developmental issues at doses that are not toxic to the mother. However, there is very little data on the effects of Penoxsulam in pregnant women. To be safe, pregnant women should avoid handling this chemical or entering areas where it has recently been sprayed. If you are pregnant and work with herbicides, talk to your doctor about ways to minimize your exposure. Always wear the recommended protective gear.
In the plants it targets, Penoxsulam stops growth within a few hours of application. However, because it works by slowly starving the plant of essential amino acids, you won't see the weeds die immediately. It usually takes 1 to 3 weeks for the plants to turn yellow and eventually turn brown and die. This process depends on the weather and how fast the plants are growing. For humans, there is no 'work' time as it has no therapeutic effect.
This question does not apply to Penoxsulam because it is not a medication that humans take. If you are using it as an herbicide, you can stop using it at any time without any risk of withdrawal or health effects. However, stopping an application program in a rice field or pond may allow weeds to grow back quickly. If you have been accidentally exposed, 'stopping' simply means removing yourself from the area and washing your skin thoroughly.
Because Penoxsulam is not a medicine, there is no such thing as a 'missed dose' for a patient. If you are an agricultural applicator and you miss a scheduled spray, you should consult the product label to see if you can still apply it. Most labels have specific windows of time based on the growth stage of the rice or the weeds. Do not try to 'double up' the concentration of the spray, as this can damage the crops or the environment.
There is no evidence that exposure to Penoxsulam causes weight gain in humans. Chronic animal studies showed that at very high doses, some animals actually lost weight or gained less weight than normal due to the stress of the chemical. In the low amounts that a person might be exposed to through the environment, no change in body weight is expected. It does not affect the hormones or metabolic pathways that typically lead to weight gain.
You should never 'take' Penoxsulam. If you are taking other medications and are accidentally exposed to Penoxsulam, the risk of a dangerous interaction is very low. Penoxsulam does not interfere with most common drugs like blood pressure medicine or heart pills. However, if you are taking 'sulfa' antibiotics, you might be more likely to have an allergic skin reaction. Always tell your doctor about your work environment and any chemicals you handle.
Yes, Penoxsulam is available in various generic formulations now that the original patents have expired. It is sold by many different agricultural chemical companies under different brand names. The active ingredient 'Penoxsulam' will always be listed on the label regardless of the brand. When buying a generic version, ensure the concentration of the active ingredient is correct for your specific needs, whether for a lawn, a rice field, or a pond.