Phenytoin TDM Flashcards

1
Q

What types of seizures is phenytoin used for?

A

Tonic-clonic
Focal

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2
Q

Is phenytoin an enzyme inducer or inhibitor?

A

Inducer, so the affected drug dose needs to be increased

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3
Q

What is the therapeutic range for phenytoin?

A

10-20mg/L

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4
Q

What protein does phenytoin bind to, what form of phenytoin is the active form?

A

It binds to albumin, and only free unbound phenytoin is the active form

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5
Q

What can hypoalbuminaemia cause in relation to phenytoin?

A

It can cause an increase in the free active form of phenytoin, leading to toxicity

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6
Q

What are the side effects of phenytoin?

A

Agranulocytosis
Blood/skin disorders
Slurred speech
Ataxia
Peripheral neuropathy
Increased risk of fractures due to enhanced vit. D metabolism

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7
Q

What 2 parameters do you always measure when checking serum phenytoin levels?

A

Albumin concentration
Renal function

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8
Q

Which drugs increase serum phenytoin levels?

A

Enzyme inhibitors like -
Amiodarone
Antifungals - miconazole, ketoconazole, fluconazole
Chloramphenicol
Acute alcohol
Omeprazole
Nifedipine
Diltiazem

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9
Q

What drugs decrease serum phenytoin levels?

A

Enzyme inducers like -
Chronic alcohol
Smoking
Rifampicin
St Johns wort

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10
Q

What should you monitor when using phenytoin?

A

ADRs
LFTs
FBC
Blood/skin disorders

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11
Q

What are the signs of phenytoin overdose?

A

Ataxia
Respiratory depression
Involuntary eye movements - nystagmus
Difficulty speaking

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12
Q

When should you check serum phenytoin levels after any dose changes?

A

14 days after

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