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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Carbonic Anhydrase Inhibitor [EPC]
Dichlorphenamide is a potent carbonic anhydrase inhibitor primarily used to treat primary periodic paralysis. This clinical guide provides detailed information on its mechanism, safety profile, and administration.
Name
Dichlorphenamide
Raw Name
DICHLORPHENAMIDE
Category
Carbonic Anhydrase Inhibitor [EPC]
Drug Count
3
Variant Count
4
Last Verified
February 17, 2026
RxCUI
197594, 2677447, 1661799
UNII
VVJ6673MHY
About Dichlorphenamide
Dichlorphenamide is a potent carbonic anhydrase inhibitor primarily used to treat primary periodic paralysis. This clinical guide provides detailed information on its mechanism, safety profile, and administration.
Detailed information about Dichlorphenamide
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Dichlorphenamide.
In pharmacological terms, Dichlorphenamide acts by inhibiting the enzyme carbonic anhydrase, which is found in various tissues including the kidneys, eyes, and central nervous system. By blocking this enzyme, the drug alters the balance of electrolytes and acid-base levels in the body. For patients with periodic paralysis, this mechanism helps stabilize muscle cell membranes, reducing the frequency and severity of paralytic attacks. It is important to note that Dichlorphenamide is not a cure for these genetic conditions but rather a maintenance therapy designed to improve the quality of life and functional mobility of affected individuals.
The mechanism of action for Dichlorphenamide involves the non-competitive inhibition of the enzyme carbonic anhydrase. This enzyme is responsible for the rapid conversion of carbon dioxide and water into bicarbonate and hydrogen ions. By inhibiting this process, particularly in the proximal tubules of the kidney, Dichlorphenamide increases the excretion of bicarbonate, sodium, and potassium, while decreasing the excretion of hydrogen ions. This results in a state of mild metabolic acidosis (an increase in the acidity of the blood).
In the context of periodic paralysis, the exact therapeutic mechanism is complex. Periodic paralysis is often caused by mutations in sodium, calcium, or potassium channels in muscle cells (channelopathies). These mutations lead to abnormal membrane excitability. The metabolic acidosis induced by Dichlorphenamide is thought to shift the potassium gradient and influence the opening and closing of these ion channels. By creating a more acidic environment, the drug helps to prevent the muscle cell membranes from becoming too easily depolarized (excited), which is the primary trigger for a paralytic episode. Furthermore, the drug may increase the conductance of calcium-activated potassium channels, which further stabilizes the resting potential of the muscle fiber.
Understanding how the body processes Dichlorphenamide is crucial for optimizing therapy and minimizing adverse effects.
The FDA-approved indications for Dichlorphenamide include:
Off-label uses have historically included the treatment of open-angle glaucoma and secondary glaucoma, although newer topical and oral agents have largely superseded Dichlorphenamide in ophthalmology due to a better side-effect profile.
Dichlorphenamide is currently available in the following form:
There are currently no approved liquid, injectable, or extended-release formulations of Dichlorphenamide available on the market. Patients who have difficulty swallowing tablets should consult their pharmacist or physician regarding safe administration techniques.
> Important: Only your healthcare provider can determine if Dichlorphenamide is right for your specific condition. The diagnosis of periodic paralysis requires specialized genetic testing and clinical evaluation by a neurologist or neuromuscular specialist.
The dosing of Dichlorphenamide must be highly individualized based on the patient's clinical response and tolerance. Healthcare providers typically follow a titration schedule to find the lowest effective dose.
The safety and effectiveness of Dichlorphenamide in pediatric patients (under the age of 18) have not been established through rigorous clinical trials. While some specialists may use it off-label for children with severe periodic paralysis, this must be done under the strict supervision of a pediatric neurologist. Dosing in these cases is usually weight-based and started at very low levels.
Since Dichlorphenamide is primarily excreted by the kidneys, its use in patients with renal impairment requires extreme caution. In patients with mild to moderate renal dysfunction, lower starting doses and slower titration are necessary. Dichlorphenamide is generally contraindicated in patients with severe renal impairment (GFR < 30 mL/min) or end-stage renal disease, as the risk of life-threatening metabolic acidosis is unacceptably high.
While the drug is not heavily metabolized by the liver, patients with severe hepatic insufficiency should avoid Dichlorphenamide. Hepatic impairment can lead to electrolyte imbalances and ammonia accumulation; since Dichlorphenamide also affects electrolytes and acid-base balance, it may precipitate hepatic encephalopathy (brain dysfunction due to liver failure).
Geriatric patients (aged 65 and older) should be started on the lowest possible dose. This population is more susceptible to the cognitive side effects of the drug, such as confusion and memory loss, and is more likely to have age-related declines in kidney function.
If you miss a dose of Dichlorphenamide, take it as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not double the dose to make up for a missed one, as this can increase the risk of acute metabolic acidosis or severe paresthesia.
Signs of a Dichlorphenamide overdose may include severe drowsiness, nausea, vomiting, dizziness, ataxia (loss of muscle coordination), and signs of severe metabolic acidosis (such as rapid breathing, confusion, or heart palpitations).
In the event of a suspected overdose:
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop the medication without medical guidance, as sudden discontinuation can lead to a rebound increase in paralytic attacks.
Dichlorphenamide is associated with several common side effects, many of which are related to its action as a carbonic anhydrase inhibitor.
> Warning: Stop taking Dichlorphenamide and call your doctor immediately if you experience any of these serious symptoms.
Prolonged use of Dichlorphenamide requires ongoing monitoring for chronic conditions:
As of 2026, the FDA has not issued a specific Black Box Warning for Dichlorphenamide. However, the drug carries significant warnings regarding metabolic acidosis and sulfonamide-related hypersensitivity that are treated with the same level of clinical gravity as a boxed warning.
Report any unusual symptoms to your healthcare provider. Your doctor may perform regular blood tests to check your electrolyte levels and acid-base balance while you are taking this medication.
Dichlorphenamide is a high-alert medication due to its systemic effects on the body's acid-base balance and electrolyte levels. It should only be prescribed by physicians familiar with the management of periodic paralysis. Patients must be aware that this medication can interact with many other drugs and requires regular laboratory monitoring.
No FDA black box warnings for Dichlorphenamide. However, the clinical risks of metabolic acidosis and sulfonamide sensitivity are paramount.
To ensure safety, healthcare providers will require the following tests periodically:
Dichlorphenamide can cause significant drowsiness, confusion, and visual disturbances. Patients should not drive, operate heavy machinery, or engage in hazardous activities until they are certain the medication does not impair their mental or physical abilities. This is especially important during the first few weeks of treatment or after a dose increase.
Alcohol should be avoided or strictly limited while taking Dichlorphenamide. Alcohol can worsen the central nervous system side effects (such as dizziness and confusion) and can also contribute to metabolic acidosis and dehydration, increasing the risk of kidney stones.
Do not stop taking Dichlorphenamide abruptly. Sudden discontinuation can cause a rapid shift in electrolyte balance and may lead to a severe rebound of paralytic attacks. If the drug must be stopped, your doctor will provide a tapering schedule to slowly reduce the dose.
> Important: Discuss all your medical conditions with your healthcare provider before starting Dichlorphenamide, especially if you have a history of kidney disease, lung disease, or liver problems.
For each major interaction, the mechanism typically involves either an additive effect on the same physiological pathway (e.g., both drugs causing acidosis) or competition for renal excretion. Management usually involves avoiding the combination or performing more frequent blood chemistry monitoring.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter pain relievers like aspirin or cold medicines.
Dichlorphenamide must NEVER be used in the following circumstances:
Conditions requiring a careful risk-benefit analysis include:
Patients should be aware of cross-sensitivity between Dichlorphenamide and other sulfonamide-derived drugs, including:
> Important: Your healthcare provider will evaluate your complete medical history, including your kidney function and allergy profile, before prescribing Dichlorphenamide.
Dichlorphenamide is classified as Pregnancy Category C (under the older FDA system). There are no adequate and well-controlled studies in pregnant women. Animal studies have shown that high doses of carbonic anhydrase inhibitors can cause fetal abnormalities, including limb defects. Dichlorphenamide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. If a woman becomes pregnant while taking this drug, she should immediately consult her neurologist and obstetrician to discuss a management plan.
It is not known whether Dichlorphenamide is excreted in human milk. However, many sulfonamides are excreted in breast milk and can pose a risk of kernicterus (a type of brain damage) in newborns, particularly those who are premature or have jaundice. Because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Dichlorphenamide is not FDA-approved for use in children under 18 years of age. The safety profile and appropriate dosing have not been established. In rare cases where it is used off-label, pediatric patients must be monitored extremely closely for growth retardation and chronic metabolic acidosis, which can affect bone development.
Clinical studies of Dichlorphenamide did not include sufficient numbers of subjects aged 65 and over to determine if they respond differently than younger subjects. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range. This reflects the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy. Geriatric patients are at a significantly higher risk for confusion and falls while taking this medication.
As the kidneys are the primary route of elimination, any degree of renal impairment will increase the systemic exposure to Dichlorphenamide. For patients with mild to moderate impairment, dosing should be infrequent and monitored with regular blood gas or bicarbonate checks. The drug is contraindicated in severe renal impairment.
Dichlorphenamide should be avoided in patients with marked hepatic impairment. The drug's effect on electrolytes can trigger an increase in blood ammonia levels, which the impaired liver cannot process, leading to hepatic coma. There are no specific dose adjustment guidelines for Child-Pugh classifications; avoidance is generally recommended in moderate to severe cases.
> Important: Special populations require individualized medical assessment and more frequent laboratory monitoring to ensure safety.
Dichlorphenamide is a potent inhibitor of the enzyme carbonic anhydrase (CA). It acts primarily on CA II (found in the cytoplasm) and CA IV (found on the luminal membrane) of cells in the proximal convoluted tubule of the kidney. By inhibiting these enzymes, the drug prevents the reabsorption of bicarbonate (HCO3-). This leads to an increase in urinary excretion of bicarbonate, sodium, and potassium. The resulting systemic effect is a hyperchloremic metabolic acidosis. In muscle tissue, this acidosis is believed to stabilize the sarcolemmal membrane potential by modulating pH-sensitive ion channels, thereby preventing the episodes of inexcitability that characterize periodic paralysis.
The onset of action for Dichlorphenamide occurs within 30 to 60 minutes of oral administration. The peak effect on urinary electrolyte excretion is typically seen within 2 to 4 hours. The duration of action for a single dose is approximately 6 to 12 hours. Unlike some other diuretics, the body does not usually develop a rapid tolerance to the acidifying effect of Dichlorphenamide, making it suitable for long-term maintenance therapy.
| Parameter | Value |
|---|---|
| Bioavailability | High (estimated >80%) |
| Protein Binding | Moderate |
| Half-life | 12 - 15 hours |
| Tmax | 1 - 2 hours |
| Metabolism | Minimal hepatic metabolism |
| Excretion | Renal (primarily unchanged) |
Dichlorphenamide is classified as a Carbonic Anhydrase Inhibitor. It is pharmacologically related to other CAIs such as Acetazolamide and Methazolamide. Within the therapeutic area of periodic paralysis, it is currently the only FDA-approved medication specifically indicated for both hyperkalemic and hypokalemic forms.
Medications containing this ingredient
Common questions about Dichlorphenamide
Dichlorphenamide is primarily used to treat a group of rare genetic conditions known as primary periodic paralysis, which includes both the hypokalemic and hyperkalemic forms. These conditions cause episodes of extreme muscle weakness or temporary paralysis. The medication works by inhibiting an enzyme called carbonic anhydrase, which helps stabilize muscle cell membranes and reduces the frequency of these attacks. While it was once used for glaucoma, its main clinical focus today is neuromuscular management. It is a long-term maintenance therapy rather than a treatment for acute attacks.
The most common side effects reported by patients taking Dichlorphenamide include paresthesia (a tingling or 'pins and needles' sensation in the hands, feet, or face) and cognitive impairment, often described as 'brain fog.' Many patients also experience a metallic taste in their mouth, fatigue, and nausea. These side effects are often dose-dependent and may improve as the body adjusts to the medication. However, if cognitive issues like confusion or memory loss become severe, a dose reduction may be necessary. Always report these symptoms to your doctor to ensure the dose is appropriate for you.
It is generally advised to avoid or strictly limit alcohol consumption while taking Dichlorphenamide. Alcohol can significantly worsen the drug's side effects on the central nervous system, leading to increased dizziness, drowsiness, and confusion. Furthermore, alcohol can contribute to dehydration and metabolic acidosis, both of which increase the risk of developing kidney stones while on this medication. Since both alcohol and Dichlorphenamide affect your body's internal balance, combining them can lead to unpredictable and potentially dangerous results. Discuss your alcohol intake with your healthcare provider for personalized safety advice.
The safety of Dichlorphenamide during pregnancy has not been well-established in humans, and it is generally only used if the benefits to the mother clearly outweigh the potential risks to the fetus. Animal studies have suggested that high doses of similar medications can cause birth defects. Because periodic paralysis is a complex condition, pregnant patients or those planning to become pregnant must have a detailed discussion with their neurologist and obstetrician. There may be alternative management strategies or specific monitoring required during pregnancy. Never start or stop this medication during pregnancy without direct medical supervision.
While Dichlorphenamide begins to affect the body's chemistry within an hour of the first dose, its full therapeutic effect in reducing the frequency of paralytic attacks may take several days or even weeks to become apparent. Doctors typically start with a low dose and gradually increase it based on how many attacks the patient continues to have. Patients are encouraged to keep a 'paralysis diary' to track their symptoms during the first month of treatment. This helps the healthcare provider determine if the medication is working and if the dosage needs adjustment. Consistency in taking the medication is key to its effectiveness.
No, you should not stop taking Dichlorphenamide suddenly unless specifically instructed by your doctor in an emergency. Abruptly stopping the medication can cause a rapid shift in your blood's acid-base balance and electrolyte levels, which may trigger a severe rebound of muscle weakness or paralytic attacks. If the medication needs to be discontinued due to side effects or other reasons, your doctor will usually provide a tapering schedule to slowly lower the dose. This allows your body to safely readjust its metabolic processes. Always consult your healthcare team before making any changes to your treatment regimen.
If you miss a dose of Dichlorphenamide, take it as soon as you remember. However, if it is almost time for your next scheduled dose, you should skip the missed dose and simply take the next one at the regular time. Do not take two doses at once to make up for the missed one, as this increases the risk of side effects like severe tingling or metabolic acidosis. To help prevent missed doses, try using a pill organizer or setting a daily alarm on your phone. If you frequently miss doses, talk to your doctor about the best way to stay on your treatment schedule.
Dichlorphenamide is actually more commonly associated with weight loss rather than weight gain. The medication can cause a decrease in appetite and changes in how food tastes (dysgeusia), which often leads to reduced caloric intake. Additionally, the metabolic changes and mild acidosis caused by the drug can alter the way the body processes energy. If you notice significant or rapid weight loss while taking Dichlorphenamide, you should discuss this with your healthcare provider. They may suggest nutritional adjustments or evaluate whether the dose is too high for your body weight.
Dichlorphenamide has several significant drug interactions that require careful management. It should never be taken with high doses of aspirin, as this can lead to life-threatening toxicity. It also interacts with other diuretics, corticosteroids, and certain seizure medications like topiramate. Because it affects potassium levels, any other drug that changes potassium must be monitored closely. It is vital to provide your doctor and pharmacist with a complete list of all medications, including over-the-counter drugs and herbal supplements, to prevent dangerous interactions. Your doctor will use this list to ensure Dichlorphenamide is safe for you.
As of 2026, Dichlorphenamide is available as a generic medication, although it may still be sold under the brand name Keveyis in some regions. Because it is used for a very rare condition, it may not be stocked at all local pharmacies and might need to be ordered through a specialty pharmacy. The availability of a generic version has helped make the treatment more accessible, but costs can still vary significantly depending on insurance coverage. Patients should check with their insurance provider and pharmacy regarding the most cost-effective way to obtain this specialized medication.