Trihexyphenidyl 5mg Tablets
It is used to treat Parkinson's disease.It is used to treat side effects caused by some other drugs.
Drug Class
Antiparkinsonian agent
Pharmacologic Class
Muscarinic acetylcholine receptor antagonist
Pregnancy Category
Category C
FDA Approved
Aug 1949
DEA Schedule
Not Controlled
Overview
What is this medicine?
Trihexyphenidyl is a medication used to help control muscle stiffness, tremors, and other involuntary movements. It is often prescribed for people with Parkinson's disease or for those who experience similar movement problems as a side effect of other medications.
How to Use This Medicine
Taking Your Medication
To get the most benefit from your medication, it's essential to take it as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. You can take this medication with or without food, but if it causes stomach upset, taking it with food may help.
It's also important to stay hydrated by drinking plenty of non-caffeinated liquids, unless your doctor advises you to limit your fluid intake.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry location, avoiding the bathroom. Keep all medications in a secure place, out of the reach of children and pets. When your medication is no longer needed or has expired, dispose of it properly. Do not flush it down the toilet or pour it down the drain unless instructed to do so by your doctor or pharmacist. If you're unsure about the best way to dispose of your medication, consult your pharmacist, as there may be drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To get the most benefit from your medication, it's essential to take it as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. You can take this medication with or without food, but if it causes stomach upset, taking it with food may help.
It's also important to stay hydrated by drinking plenty of non-caffeinated liquids, unless your doctor advises you to limit your fluid intake.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature in a dry location, avoiding the bathroom. Keep all medications in a secure place, out of the reach of children and pets. When your medication is no longer needed or has expired, dispose of it properly. Do not flush it down the toilet or pour it down the drain unless instructed to do so by your doctor or pharmacist. If you're unsure about the best way to dispose of your medication, consult your pharmacist, as there may be drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Take exactly as prescribed by your doctor. Do not stop taking it suddenly without consulting your doctor, as this can worsen your symptoms.
- This medication can cause dry mouth. Sucking on sugar-free candy or ice chips, or using saliva substitutes, may help.
- It can also cause blurred vision. Be careful when driving or performing tasks that require clear vision.
- Avoid overheating and stay hydrated, especially in hot weather or during exercise, as this medication can reduce sweating and increase body temperature.
- Avoid alcohol and other CNS depressants, as they can increase drowsiness and dizziness.
- Report any new or worsening side effects, especially confusion, hallucinations, difficulty urinating, or severe constipation, to your doctor immediately.
Available Forms & Alternatives
Available Strengths:
Dosing & Administration
Adult Dosing
Standard Dose:
For Parkinsonism: Initial 1 mg/day, gradually increased by 2 mg every 3-5 days to 6-10 mg/day in 3-4 divided doses. For drug-induced extrapyramidal reactions: Initial 1 mg, then 5-15 mg/day in divided doses.
Dose Range:
1 - 15 mg
Condition-Specific Dosing:
parkinsonism:
Initial 1 mg/day, increased by 2 mg every 3-5 days until optimal response, typically 6-10 mg/day. Max 15 mg/day.
drug_induced_extrapyramidal_reactions:
Initial 1 mg, then 5-15 mg/day in divided doses, adjusted based on response.
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Not established
Adolescent:
Not established
Dose Adjustments
Renal Impairment:
Mild:
Use with caution; consider lower initial doses and slower titration.
Moderate:
Use with caution; consider lower initial doses and slower titration.
Severe:
Use with caution; consider lower initial doses and slower titration due to potential for accumulation and increased sensitivity to anticholinergic effects.
Dialysis:
Not well studied; use with extreme caution and monitor closely for adverse effects.
Hepatic Impairment:
Mild:
Use with caution; monitor for increased side effects.
Moderate:
Use with caution; monitor for increased side effects.
Severe:
Use with caution; monitor for increased side effects due to potential for impaired metabolism.
Pharmacology
Mechanism of Action
Trihexyphenidyl is a synthetic anticholinergic agent that acts as a selective antagonist at muscarinic acetylcholine receptors, primarily M1 receptors, in the central nervous system. By blocking cholinergic activity in the basal ganglia, it helps to restore the balance between cholinergic and dopaminergic systems, thereby reducing the tremor and rigidity associated with Parkinson's disease and drug-induced extrapyramidal symptoms. It also exerts some direct antispasmodic effect on smooth muscle.
Pharmacokinetics
Absorption:
Bioavailability:
Not precisely quantified, but well absorbed orally.
Tmax:
1-2 hours
FoodEffect:
Food may delay absorption but does not significantly affect the extent of absorption. Administering with food may reduce gastrointestinal upset.
Distribution:
Vd:
Not well established
ProteinBinding:
Not well established
CnssPenetration:
Yes
Elimination:
HalfLife:
6-10 hours (variable)
Clearance:
Not well established
ExcretionRoute:
Primarily renal excretion, with some unchanged drug and metabolites.
Unchanged:
Not precisely quantified, but a portion is excreted unchanged.
Pharmacodynamics
OnsetOfAction:
Approximately 1 hour
PeakEffect:
2-3 hours
DurationOfAction:
6-12 hours
Safety & Warnings
Side Effects
Serious Side Effects: Seek Medical Attention Immediately
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Hallucinations (seeing or hearing things that are not there)
Feeling agitated or experiencing a change in behavior
Confusion or memory problems
Trouble passing urine
Rapid heartbeat
Severe constipation or stomach pain, which may be signs of a severe bowel problem
Muscle weakness
New or worsening trouble controlling body movements
Changes in eyesight, eye pain, or severe eye irritation
Fever
Inability to sweat during activities or in warm temperatures
Enlarged pupils
Neuroleptic malignant syndrome (NMS), a severe and potentially life-threatening condition that may occur when this medication is stopped suddenly or the dose is lowered. Symptoms of NMS include:
+ Fever
+ Muscle cramps or stiffness
+ Dizziness
+ Severe headache
+ Confusion
+ Changes in thinking
+ Fast or abnormal heartbeat
+ Excessive sweating
Other Possible Side Effects
Like all medications, this drug may cause side effects in some people. While many individuals experience no side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other symptoms that bother you or do not go away, contact your doctor:
Dizziness or drowsiness
Upset stomach or vomiting
Constipation
Headache
Dry mouth
Feeling nervous or excitable
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Hallucinations (seeing or hearing things that are not there)
Feeling agitated or experiencing a change in behavior
Confusion or memory problems
Trouble passing urine
Rapid heartbeat
Severe constipation or stomach pain, which may be signs of a severe bowel problem
Muscle weakness
New or worsening trouble controlling body movements
Changes in eyesight, eye pain, or severe eye irritation
Fever
Inability to sweat during activities or in warm temperatures
Enlarged pupils
Neuroleptic malignant syndrome (NMS), a severe and potentially life-threatening condition that may occur when this medication is stopped suddenly or the dose is lowered. Symptoms of NMS include:
+ Fever
+ Muscle cramps or stiffness
+ Dizziness
+ Severe headache
+ Confusion
+ Changes in thinking
+ Fast or abnormal heartbeat
+ Excessive sweating
Other Possible Side Effects
Like all medications, this drug may cause side effects in some people. While many individuals experience no side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other symptoms that bother you or do not go away, contact your doctor:
Dizziness or drowsiness
Upset stomach or vomiting
Constipation
Headache
Dry mouth
Feeling nervous or excitable
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe confusion or disorientation
- Hallucinations (seeing or hearing things that are not there)
- Difficulty urinating or inability to urinate
- Severe constipation or abdominal pain
- Eye pain or sudden vision changes (especially blurred vision with eye pain, which could indicate acute glaucoma)
- Fever with hot, dry skin
- Rapid heartbeat
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you have been diagnosed with narrow-angle glaucoma, a condition that affects the eyes.
If you have a history of tardive dyskinesia, a severe muscle disorder.
This list is not exhaustive, and it is crucial to discuss all your medications, health conditions, and supplements with your doctor. This includes:
All prescription and over-the-counter (OTC) medications you are taking
Natural products and vitamins
Any health problems you have or have had in the past
Your doctor and pharmacist need this information to ensure it is safe for you to take this medication. Do not start, stop, or change the dose of any medication without first consulting your doctor to confirm it is safe to do so.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you have been diagnosed with narrow-angle glaucoma, a condition that affects the eyes.
If you have a history of tardive dyskinesia, a severe muscle disorder.
This list is not exhaustive, and it is crucial to discuss all your medications, health conditions, and supplements with your doctor. This includes:
All prescription and over-the-counter (OTC) medications you are taking
Natural products and vitamins
Any health problems you have or have had in the past
Your doctor and pharmacist need this information to ensure it is safe for you to take this medication. Do not start, stop, or change the dose of any medication without first consulting your doctor to confirm it is safe to do so.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
Before operating a vehicle or engaging in any activity that requires your full attention, wait until you understand how this medication affects you. It is also crucial to discuss the use of alcohol, marijuana, or other forms of cannabis, as well as prescription or over-the-counter (OTC) medications that may cause drowsiness, with your doctor beforehand.
Do not abruptly discontinue this medication without first consulting your doctor, as this may increase your risk of experiencing side effects. If it becomes necessary to stop taking this drug, your doctor will provide guidance on how to gradually taper off the medication to minimize potential risks.
Individuals with narrow-angle glaucoma should be aware that this condition may lead to vision loss. It is vital to consult with your doctor regarding this potential risk. Additionally, adhere to your doctor's recommendations for regular eye pressure and vision checks.
There is a risk of heat stroke associated with this medication, particularly in hot weather or during physical activity. Therefore, it is crucial to exercise caution and stay hydrated. If you are 60 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor. It is essential to discuss the potential benefits and risks of this medication to both you and your baby to make an informed decision.
Before operating a vehicle or engaging in any activity that requires your full attention, wait until you understand how this medication affects you. It is also crucial to discuss the use of alcohol, marijuana, or other forms of cannabis, as well as prescription or over-the-counter (OTC) medications that may cause drowsiness, with your doctor beforehand.
Do not abruptly discontinue this medication without first consulting your doctor, as this may increase your risk of experiencing side effects. If it becomes necessary to stop taking this drug, your doctor will provide guidance on how to gradually taper off the medication to minimize potential risks.
Individuals with narrow-angle glaucoma should be aware that this condition may lead to vision loss. It is vital to consult with your doctor regarding this potential risk. Additionally, adhere to your doctor's recommendations for regular eye pressure and vision checks.
There is a risk of heat stroke associated with this medication, particularly in hot weather or during physical activity. Therefore, it is crucial to exercise caution and stay hydrated. If you are 60 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor. It is essential to discuss the potential benefits and risks of this medication to both you and your baby to make an informed decision.
Overdose Information
Overdose Symptoms:
- Severe anticholinergic crisis: dilated pupils (mydriasis), hot and dry skin, flushed face, fever, rapid heart rate (tachycardia), high blood pressure, urinary retention, decreased bowel sounds, severe confusion, delirium, agitation, hallucinations, seizures, coma, respiratory depression.
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Treatment is supportive and may include physostigmine for severe anticholinergic symptoms.
Drug Interactions
Contraindicated Interactions
- Angle-closure glaucoma (untreated or uncontrolled)
- Severe urinary obstruction (e.g., prostatic hypertrophy with retention)
Major Interactions
- Other anticholinergic drugs (e.g., atropine, benztropine, scopolamine, some antihistamines, tricyclic antidepressants): Increased risk of additive anticholinergic side effects (dry mouth, blurred vision, urinary retention, constipation, confusion, hallucinations).
- CNS depressants (e.g., alcohol, opioids, benzodiazepines, sedatives): Increased risk of additive sedation and CNS depression.
- Phenothiazines (e.g., chlorpromazine, thioridazine): May increase anticholinergic effects and potentially decrease phenothiazine levels.
- Monoamine Oxidase Inhibitors (MAOIs): Increased risk of anticholinergic effects.
Moderate Interactions
- Digoxin: Trihexyphenidyl may decrease the absorption of digoxin.
- Metoclopramide: Antagonistic effect on gastrointestinal motility.
- Potassium chloride (oral solid forms): Increased risk of gastrointestinal lesions due to delayed gastric emptying.
Minor Interactions
- Antacids: May reduce absorption if taken concurrently (separate administration by 2 hours).
Monitoring
Baseline Monitoring
Ophthalmic examination (intraocular pressure)
Rationale: To rule out or monitor for narrow-angle glaucoma, which is a contraindication or requires careful management.
Timing: Prior to initiation of therapy.
Urinary function assessment
Rationale: To assess for pre-existing urinary retention or prostatic hypertrophy, which can be exacerbated.
Timing: Prior to initiation of therapy.
Baseline motor symptoms (tremor, rigidity, bradykinesia)
Rationale: To establish a baseline for assessing therapeutic efficacy.
Timing: Prior to initiation of therapy.
Routine Monitoring
Efficacy (reduction in tremor, rigidity, dystonia)
Frequency: Regularly during dose titration and periodically thereafter.
Target: Optimal symptom control with tolerable side effects.
Action Threshold: Lack of efficacy or worsening symptoms may require dose adjustment or alternative therapy.
Anticholinergic side effects (dry mouth, blurred vision, constipation, urinary retention, cognitive impairment, confusion, hallucinations)
Frequency: Regularly, especially during dose titration and in elderly patients.
Target: Minimal to no intolerable side effects.
Action Threshold: Presence of significant or intolerable side effects may require dose reduction or discontinuation.
Mental status and cognitive function
Frequency: Periodically, especially in elderly patients.
Target: Stable cognitive function.
Action Threshold: New onset or worsening confusion, disorientation, or hallucinations may require dose adjustment or discontinuation.
Intraocular pressure (for patients at risk of glaucoma)
Frequency: Periodically, as clinically indicated.
Target: Within normal limits.
Action Threshold: Elevated pressure requires ophthalmological consultation.
Symptom Monitoring
- Dry mouth
- Blurred vision
- Constipation
- Urinary hesitancy or retention
- Dizziness
- Lightheadedness
- Nausea
- Vomiting
- Tachycardia
- Nervousness
- Insomnia
- Confusion
- Disorientation
- Hallucinations
- Memory impairment
Special Patient Groups
Pregnancy
Category C. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Limited human data are available.
Trimester-Specific Risks:
First Trimester:
Potential for fetal harm cannot be ruled out; animal studies show some adverse effects at high doses.
Second Trimester:
Limited data; monitor for maternal anticholinergic effects.
Third Trimester:
Potential for anticholinergic effects in the neonate if used close to delivery.
Lactation
Unknown if excreted in human milk. Due to potential for anticholinergic effects in the infant (e.g., sedation, constipation) and potential for reduction in milk supply, use with caution or consider an alternative. Monitor breastfed infant for anticholinergic effects.
Infant Risk:
Risk L3 (Moderate concern) - potential for anticholinergic effects (sedation, constipation, urinary retention) and theoretical risk of decreased milk production.
Pediatric Use
Safety and efficacy have not been established in pediatric patients. Use is generally not recommended.
Geriatric Use
Elderly patients are particularly susceptible to the anticholinergic side effects of trihexyphenidyl, including confusion, hallucinations, memory impairment, urinary retention, constipation, and falls. Start with lower doses and titrate slowly. Monitor closely for cognitive and psychiatric adverse events.
Clinical Information
Clinical Pearls
- Titrate the dose slowly to minimize anticholinergic side effects, especially in elderly patients.
- Administer with food if gastrointestinal upset occurs.
- Monitor for signs of central anticholinergic syndrome (e.g., confusion, delirium, hallucinations), particularly in susceptible individuals.
- Abrupt discontinuation can lead to a worsening of Parkinsonian symptoms or withdrawal symptoms.
- Patients should be advised to avoid activities requiring mental alertness (e.g., driving) until they know how the drug affects them.
- Regular dental check-ups are important due to dry mouth increasing the risk of dental caries.
Alternative Therapies
- Other anticholinergic agents (e.g., benztropine, procyclidine)
- Dopamine agonists (e.g., pramipexole, ropinirole, rotigotine)
- Levodopa/carbidopa
- Amantadine
- MAO-B inhibitors (e.g., selegiline, rasagiline)
- COMT inhibitors (e.g., entacapone, tolcapone)
- Deep Brain Stimulation (DBS) for advanced Parkinson's disease
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (generic 5mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about this medication, don't hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When reporting the incident, be prepared to provide details about the medication taken, the amount, and the time it occurred.