A Nurse Is Preparing To Administer Phenytoin 5 Mg/kg/day

Phenytoin, a commonly prescribed anticonvulsant, demands meticulous preparation and administration, especially when dealing with pediatric patients. Calculating and administering the correct dosage of phenytoin, such as 5 mg/kg/day, is crucial to ensure therapeutic efficacy and minimize potential adverse effects. This article delves into the essential steps and considerations a nurse must undertake when preparing and administering phenytoin at this specific dosage.

Understanding Phenytoin: An Overview

Phenytoin is an antiepileptic drug used to control seizures. It works by slowing down impulses in the brain that cause seizures. It is available in various forms, including oral capsules, tablets, and intravenous (IV) solutions. The bioavailability and pharmacokinetics of phenytoin can vary significantly between individuals, necessitating careful monitoring and dosage adjustments.

Before administering phenytoin, the nurse must have a comprehensive understanding of the drug's mechanism of action, indications, contraindications, and potential side effects. This knowledge forms the foundation for safe and effective medication administration.

Key Considerations Before Administration

• Patient Assessment: A thorough patient assessment is the cornerstone of safe medication administration. This includes reviewing the patient's medical history, current medications, allergies, and previous responses to phenytoin. Specific attention should be paid to any pre-existing conditions, such as liver or kidney disease, as these can affect phenytoin metabolism and excretion.
• Seizure History: Understanding the patient's seizure history is crucial. The nurse should document the frequency, duration, and characteristics of the patient's seizures. This information serves as a baseline for evaluating the effectiveness of phenytoin therapy.
• Baseline Laboratory Values: Obtain baseline laboratory values, including liver function tests (LFTs), renal function tests, and complete blood count (CBC). Phenytoin can affect these parameters, and monitoring them helps detect potential drug-induced toxicities.
• Pregnancy Status: Determine the patient's pregnancy status, as phenytoin can cause fetal harm. Discuss the risks and benefits of phenytoin therapy with pregnant patients or those who may become pregnant.
• Drug Interactions: Review the patient's medication list for potential drug interactions. Phenytoin interacts with a wide range of medications, including anticoagulants, antibiotics, and other antiepileptic drugs. Understanding these interactions is essential to prevent adverse effects.
• Informed Consent: Obtain informed consent from the patient or their legal guardian, explaining the purpose of phenytoin therapy, potential risks and benefits, and the importance of adherence to the prescribed regimen.

Step-by-Step Guide to Preparing Phenytoin 5 mg/kg/day

Administering phenytoin at a dosage of 5 mg/kg/day requires careful calculation and preparation to ensure accuracy and patient safety. Here is a detailed step-by-step guide:

1. Calculating the Correct Dosage

The first step is to accurately calculate the required dosage based on the patient's weight. Follow these steps:

• Obtain the Patient's Weight: Ensure the patient's weight is accurately documented in kilograms (kg). If the weight is in pounds (lbs), convert it to kilograms by dividing by 2.2 (1 kg = 2.2 lbs).

• Calculate the Daily Dosage: Multiply the patient's weight in kilograms by the prescribed dosage of 5 mg/kg/day.

  Daily Dosage (mg) = Patient Weight (kg) x 5 mg/kg/day

• Determine the Frequency of Administration: Phenytoin is typically administered in divided doses, usually two or three times per day. Divide the total daily dosage by the number of doses to determine the amount to administer per dose. For example, if administering twice daily:

  Dosage per Dose (mg) = Daily Dosage (mg) / 2

• Verify the Dosage: Double-check your calculations with another healthcare professional to ensure accuracy. Dosage errors can have serious consequences, especially in pediatric patients.

Example Calculation:

Let's say a child weighs 20 kg.

• Daily Dosage: 20 kg x 5 mg/kg/day = 100 mg/day
• If administering twice daily: 100 mg/day / 2 = 50 mg per dose

2. Selecting the Appropriate Formulation

Phenytoin is available in various formulations, including:

• Oral Suspension: Often preferred for children due to ease of administration.
• Chewable Tablets: Can be used for older children who can chew and swallow tablets.
• Capsules: Suitable for adults and older children who can swallow capsules.
• Intravenous (IV) Solution: Used for loading doses or when oral administration is not feasible.

Select the most appropriate formulation based on the patient's age, ability to swallow, and clinical condition.

3. Preparing the Medication

The preparation process varies depending on the formulation selected:

• Oral Suspension:
  • Shake the suspension well before measuring the dose to ensure uniform drug concentration.
  • Use an accurate measuring device, such as an oral syringe or calibrated spoon, to measure the prescribed dose.
  • Draw up the required amount of medication carefully, ensuring there are no air bubbles in the syringe.
• Chewable Tablets:
  • Ensure the child can chew the tablet properly before administering.
  • If necessary, the tablet can be crushed and mixed with a small amount of food or liquid to facilitate administration.
• Capsules:
  • Ensure the patient can swallow the capsule whole. Do not crush or open capsules, as this can affect the drug's release and absorption.
• Intravenous (IV) Solution:
  • Phenytoin IV should be prepared and administered according to specific guidelines due to its potential for causing hypotension and cardiac arrhythmias.
  • Dilute the phenytoin solution with normal saline (0.9% NaCl) to a concentration of no more than 5 mg/mL.
  • Administer the solution slowly, at a rate not exceeding 50 mg/minute in adults or 1-3 mg/kg/minute in children.
  • Monitor the patient's blood pressure and heart rate continuously during IV administration.

4. Verifying Compatibility

Before administering phenytoin intravenously, verify its compatibility with other IV solutions and medications. Phenytoin is incompatible with many solutions, including dextrose-containing solutions. Administering incompatible solutions can lead to precipitation and loss of drug potency.

5. Administering the Medication

• Oral Administration:
  • Position the patient upright to facilitate swallowing and prevent aspiration.
  • Administer the medication with a sufficient amount of water to ensure it is completely swallowed.
  • For children, use age-appropriate techniques to encourage cooperation and minimize distress.
• Intravenous (IV) Administration:
  • Use a dedicated IV line for phenytoin administration to avoid compatibility issues.
  • Infuse the solution slowly, monitoring the patient's vital signs closely.
  • Observe the IV site for signs of infiltration or phlebitis.

6. Documenting the Administration

Accurate documentation is essential for ensuring continuity of care and tracking the patient's response to phenytoin therapy. Document the following information:

• Date and time of administration
• Dosage administered
• Route of administration
• Patient's response to the medication
• Any adverse effects observed
• Any other relevant information

Monitoring and Managing Potential Side Effects

Phenytoin can cause a range of side effects, some of which can be serious. Close monitoring and prompt management of side effects are crucial for ensuring patient safety and adherence to therapy.

Common Side Effects

• Gingival Hyperplasia: Overgrowth of the gums, which can be minimized with good oral hygiene.
• Hirsutism: Excessive hair growth, particularly in women.
• Acne: Skin eruptions.
• Nystagmus: Involuntary eye movements.
• Ataxia: Loss of coordination.
• Drowsiness: Sedation or fatigue.
• Cognitive Impairment: Difficulty with memory and concentration.

Serious Side Effects

• Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): Severe skin reactions characterized by blistering and peeling of the skin.
• Drug-Induced Liver Injury (DILI): Liver damage caused by phenytoin.
• Blood Dyscrasias: Abnormalities in blood cell counts, such as anemia, leukopenia, or thrombocytopenia.
• Phenytoin Hypersensitivity Syndrome (PHS): A systemic reaction characterized by fever, rash, lymphadenopathy, and internal organ involvement.
• Cardiac Arrhythmias and Hypotension: Particularly with rapid IV administration.

Monitoring Strategies

• Regular Physical Examinations: Assess for signs of gingival hyperplasia, hirsutism, acne, and neurological abnormalities.
• Laboratory Monitoring: Monitor liver function tests (LFTs), complete blood count (CBC), and phenytoin serum levels regularly.
• Neurological Assessments: Evaluate for nystagmus, ataxia, and cognitive impairment.
• Skin Assessments: Monitor for signs of rash, blistering, or peeling of the skin.
• Patient Education: Educate patients and their families about the potential side effects of phenytoin and the importance of reporting any unusual symptoms promptly.

Managing Side Effects

• Gingival Hyperplasia: Emphasize good oral hygiene practices, including regular brushing, flossing, and dental check-ups.
• Hirsutism and Acne: Consider cosmetic treatments or referral to a dermatologist.
• Neurological Side Effects: Reduce the dosage of phenytoin if neurological side effects are significant.
• Serious Side Effects: Discontinue phenytoin immediately and initiate appropriate medical treatment.

Phenytoin Serum Level Monitoring

Monitoring phenytoin serum levels is an essential aspect of managing phenytoin therapy. Serum levels help ensure that the drug concentration is within the therapeutic range, minimizing the risk of toxicity and breakthrough seizures.

Therapeutic Range

The therapeutic range for phenytoin is typically 10-20 mcg/mL. However, the optimal therapeutic range can vary depending on the individual patient and their clinical condition.

Factors Affecting Serum Levels

Several factors can affect phenytoin serum levels, including:

• Dosage: Higher doses generally result in higher serum levels.
• Adherence: Non-adherence to the prescribed regimen can lead to subtherapeutic levels.
• Drug Interactions: Certain medications can increase or decrease phenytoin serum levels.
• Age: Children may require higher doses per kilogram to achieve therapeutic levels due to differences in metabolism.
• Liver and Kidney Function: Impaired liver or kidney function can affect phenytoin metabolism and excretion, leading to elevated serum levels.
• Protein Binding: Phenytoin is highly protein-bound, and conditions that affect protein binding, such as hypoalbuminemia, can alter the free (unbound) fraction of phenytoin, affecting its activity.

Interpreting Serum Levels

• Subtherapeutic Levels: May indicate non-adherence, inadequate dosage, or drug interactions. Increase the dosage or address adherence issues as appropriate.
• Therapeutic Levels: Indicate that the drug concentration is within the desired range. Continue monitoring and adjust the dosage as needed based on clinical response.
• Toxic Levels: May indicate overdosage, impaired metabolism, or drug interactions. Reduce the dosage or discontinue phenytoin if necessary.

Timing of Serum Level Monitoring

• Initial Monitoring: Check phenytoin serum levels after initiating therapy and after any dosage adjustments.
• Routine Monitoring: Monitor serum levels periodically, especially in patients with fluctuating seizure control, impaired liver or kidney function, or those taking interacting medications.
• Symptom-Based Monitoring: Check serum levels if the patient develops signs or symptoms of phenytoin toxicity.

Special Considerations for Pediatric Patients

Administering phenytoin to pediatric patients requires special considerations due to age-related differences in pharmacokinetics and pharmacodynamics.

Dosage Adjustments

Children often require higher doses of phenytoin per kilogram compared to adults to achieve therapeutic serum levels. This is due to differences in metabolism and volume of distribution.

Formulation Selection

Oral suspensions and chewable tablets are generally preferred for children due to ease of administration. However, ensure the child can chew the tablet properly before administering.

Monitoring for Side Effects

Children may be more susceptible to certain side effects of phenytoin, such as gingival hyperplasia and cognitive impairment. Close monitoring and early intervention are essential.

Parent Education

Provide comprehensive education to parents or caregivers about phenytoin therapy, including proper administration techniques, potential side effects, and the importance of adherence to the prescribed regimen.

Potential Drug Interactions

Phenytoin interacts with a wide range of medications, and these interactions can significantly affect its serum levels and therapeutic effects. Understanding these interactions is crucial for preventing adverse outcomes.

Drugs That Increase Phenytoin Levels

• Cimetidine: Inhibits phenytoin metabolism.
• Isoniazid: Inhibits phenytoin metabolism.
• Fluconazole: Inhibits phenytoin metabolism.
• Ketoconazole: Inhibits phenytoin metabolism.
• Valproic Acid: Displaces phenytoin from protein binding sites, increasing the free fraction.

Drugs That Decrease Phenytoin Levels

• Carbamazepine: Induces phenytoin metabolism.
• Rifampin: Induces phenytoin metabolism.
• Phenobarbital: Induces phenytoin metabolism.
• Folic Acid: May decrease phenytoin levels.

Drugs Affected by Phenytoin

• Warfarin: Phenytoin can alter the metabolism of warfarin, affecting its anticoagulant effect.
• Oral Contraceptives: Phenytoin can decrease the effectiveness of oral contraceptives.
• Digoxin: Phenytoin can decrease digoxin levels.

Always review the patient's medication list carefully for potential drug interactions and adjust the dosage of phenytoin or other medications as necessary.

Patient Education and Counseling

Effective patient education and counseling are essential for promoting adherence to phenytoin therapy and minimizing the risk of adverse outcomes.

Key Points to Cover

• Purpose of Phenytoin Therapy: Explain why the patient is taking phenytoin and what it is expected to achieve.
• Dosage and Administration: Provide clear instructions on how to take phenytoin, including the correct dosage, frequency, and timing of administration.
• Potential Side Effects: Discuss the potential side effects of phenytoin and what to do if they occur.
• Drug Interactions: Explain the importance of informing healthcare providers about all medications the patient is taking, including over-the-counter drugs and herbal supplements.
• Importance of Adherence: Emphasize the importance of taking phenytoin exactly as prescribed and not missing doses.
• Monitoring: Explain the need for regular monitoring, including physical examinations, laboratory tests, and serum level monitoring.
• Lifestyle Considerations: Discuss any lifestyle considerations, such as avoiding alcohol and driving until seizure control is established.
• Emergency Information: Provide information on what to do in case of a seizure or other medical emergency.

Encourage patients to ask questions and address any concerns they may have. Provide written materials to reinforce the information discussed.

Conclusion

Preparing and administering phenytoin 5 mg/kg/day requires meticulous attention to detail and a thorough understanding of the drug's pharmacokinetics, pharmacodynamics, and potential side effects. Nurses play a critical role in ensuring the safe and effective use of phenytoin by accurately calculating dosages, selecting appropriate formulations, monitoring for adverse effects, and providing comprehensive patient education. By adhering to best practices and staying informed about the latest evidence-based guidelines, nurses can help optimize patient outcomes and improve the quality of life for individuals with seizure disorders.