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50 Cards in this Set
- Front
- Back
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How is Phenytoin absorbed and metabolized?
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Absorbed: orally - but formulation can alter this
Metabolized: by liver p450's - excreted as glucuronide |
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What kinetics govern Phenytoin elimination? What effect can this have?
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Zero order - so its metabolizing enzymes can become saturated and half life increases.
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What is the therapeutic index of Phenytoin like? Implication?
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Very narrow - so its plasma levels must be monitored closely
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What form of phenytoin has to be used for IV administration during status epilepticus?
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Fosphenytoin
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What adverse effect of Phenytoin can occur early?
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Nystagmus
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What are the 2 most common adverse side effects of Phenytoin?
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-Diplopia
-Ataxia |
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What are 5 other adverse side effects of Phenytoin?
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-Slurred speech
-Blurred vision -Mental confusion -Hirsutism -Gingival hyperplasia |
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How can the gingival hyperplasia be avoided?
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With good dental hygiene
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What are 3 rare adverse effects of long-term phenytoin therapy?
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-Coarsening of facial features
-Mild peripheral neuropathy -Osteomalacia |
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What are 2 idiosyncratic reactions to phenytoin that would require discontinuance?
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-Exfoliative dermatitis
-Blood dyscrasias (agranulocytosis) |
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What is fetal hydantoin syndrome?
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fetal malformation in pregnant patients on phenytoin
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What is a major drug interaction seen with Phenytoin therapy?
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Stimulation of hepatic enzymes reducing other drug concentrations
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What drugs will be affected by Phenytoin's induction of P450s?
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-Carbamazepine
-Valproic acid -Ethosuximide -Anticoagulants, OCT, antibiotics |
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What drugs INHIBIT the metabolism of Phenytoin and thus increase its plasma conc?
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-Cimetidine
-Isoniazid |
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What drug INDUCES the enzymes that metabolize Phenytoin and thus decreases its plasma conc?
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Carbamazepine
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How does the absorption of CARBAMAZEPINE compare to phenytoin?
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Similar - it is well absorbed orally but significant patient variability in rate.
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What does Carbamazepine do to its metabolic enzymes? What effect does this have?
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INDUCES them - so it REDUCES its OWN plasma half life!
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How much does Carbamazepine reduce its own half life?
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From 30 hrs to less than 20 hrs
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How do you have to handle this self-induced change in Carbamazepine half life?
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Gradually adjust the dose early in therapy
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What is Carbamazepine the drug of choice for treating?
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Trigeminal neuralgia
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What other condition is treated with Carbamazepine?
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Acute Manic Episodes in Bipolar disorder
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What prodrug has similar effects to Carbamazepine?
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Oxcarbazepine
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How is Oxcarbazepine different from Carbamazepine?
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Short half-life; 1-2 hrs
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What gives the treatment effects of Oxcarbazepine?
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Its metabolite - active for 10 hrs
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Why is Oxcarbazepine possibly better than Carbamazepine?
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Less adverse side effects and less induction of metabolic enzymes.
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What are the 4 most common side effects of Carbamazepine?
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-Diplopia
-Ataxia -GI disturbance -Sedation at high doses |
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What are 3 other side effects Carbamazepine can have occasionally?
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-Water retention
-Hyponatremia -Rash/agitation in children |
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What side effects of Carbamazepine are rare?
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-Blood dyscrasias
-Severe rash |
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What drugs have increased hepatic clearance due to Carbamazepine induction of P450s?
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-Phenytoin
-Valproic acid (and others) |
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What drug increases the plasma conc of Carbamazepine by INHIBITING liver metabolism?
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Phenytoin
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What is Depakote?
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Valproic acid in a 1:1 enteric formulation with Valproate sodium
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What is the purpose of combining Valproic acid with Valproate sodium?
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It gets absorbed more slowly
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What else is Valproic acid used for other than treating seizures?
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Bipolar
Prophylaxis for migraines |
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What are the 2 most common side effects of Valproic acid?
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-GI disturbance
-Hair loss |
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What fetal malformation can Valproic acid cause?
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Spina bifida!!!
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What are the top 3 drugs for treating Absence seizures?
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-Ethosuximide
-Valproic acid -Carbamazepine |
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Why is Ethosuximide used over Valproic acid?
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Because it is safer, though it may be less effective in some patients
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What are 3 common side effects of Ethosuximide?
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-Fatigue
-Dizziness -GI disturbance |
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What are the 2 most common uses of Phenobarbital for seizures?
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-First-line drug for neonatal seizures
-Maintains control of status epilepticus |
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What is the most common adverse effect of Phenobarbital?
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Sedation
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What drug gets metabolically converted TO phenobarbital?
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Primidone
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What is Primidone used for?
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Partial and Generalized tonic-clonic seizures
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Which BDZ's are effective in short-term treatment of Status epilepticus?
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-Diazepam
-Lorazepam |
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Which BDZ is used for absence seizures?
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Clonazepam
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What is Lamotrigine again?
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A Na channel blocker (like Phenytoin and carbamazepine)
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What increases plasma levels of Lamotrigine?
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Valproic acid
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What drugs decrease plasma levels of Lamotrigine?
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-Phenytoin
-Carbamazepine |
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What drug alters GABA metabolism to increase GABA levels in the brain?
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GABApentin
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What drug inhibits GABA uptake by interacting with its transporter?
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Tiagabine
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What are 2 other antiseizure adjuncts that act by less well known mechanisms?
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-Topiramate
-Levetiracetam |
