Page 13 - RxExam's Naplex Theory Review Part-1

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Drug Interactions with Phenytoin:

Carbamazepine May increase the metabolism of Phenytoin (Dilantin) by its
enzyme induction property.

Estrogen and other oral May cause failure of contraception because of induction of
contraceptives metabolism of oral contraceptive by Phenytoin (Dilantin).

Amiodarone May raise the serum concentration and toxic effects of
Phenytoin (Dilantin).

Fluconazole, Miconazole Concurrent use of azoles with Phenytoin (Dilantin) may inhibit the
and Ketoconazole metabolism and increase the toxicities of Phenytoin (Dilantin).

Methadone Phenytoin (Dilantin) may accelerate the metabolism of Methadone
and precipitate withdrawal symptoms in opioid dependent patients.

Omeprazole May inhibit the metabolism of Phenytoin (Dilantin) by CP450
inhibition and result in a higher plasma concentration of Phenytoin
(Dilantin).

Antacids + Sucralfate May reduce the absorption of Phenytoin (Dilantin) and decrease
its bioavailability.

Valproic acid May displace Phenytoin (Dilantin) from protein-binding, inhibit its
metabolism and increase its toxic effects.

Theophylline May increase the clearance and decrease the pharmacological
effects of Theophylline.

Digoxin May increase the serum concentration of Digoxin (Lanoxin) up to
50 to 60%. The serum concentration of Digoxin (Lanoxin) should
be monitored.
Class IC Antiarrhythmic Agents:

Dose Special Notes

Flecainide For PSVT and PAF: 1). Flecainide (Tambocor) is indicated for the prevention of:
(Tablet) 50 to 100 mg PO
bid. a). Paroxysmal supraventricular tachycardias (PSVT), including
atrioventricular nodal reentrant tachycardia, atrioventricular reentrant
For sustained VT: tachycardia and other supraventricular tachycardias of unspecified
150 mg PO bid.
mechanism associated with disabling symptoms.
b). Paroxysmal atrial fibrillation/flutter (PAF) associated with disabling
symptoms.

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