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phenytoin
generic
Black Box Warnings .
Cardiovascular Risk with Rapid Infusion
IV infusion should not exceed 50 mg/min in adults or 1-3 mg/kg/min (or 50 mg/min, whichever is slower) in peds pts; incr. risk severe hypotension and cardiac arrhythmias above recommended infusion rate, but events also reported at or below recommended rate; monitor cardiac adverse events during and after IV infusion; IV infusion rate reduction or D/C may be necessary; EDITORIAL NOTE: expert guidelines suggest slower rates of 25-50 mg/min (healthy adults), 10-20 mg/min (elderly or cardiac dz), <1 mg/kg/min (peds pts), and 0.5 mg/kg/min (neonates) may decr. risk of tissue or vascular injury, hypotension, or other adverse events
Adult Dosing .
Dosage forms: ER CAP: 100 mg, 200 mg, 300 mg; CHEWABLE: 50 mg; SUSP: 25 mg per mL; INJ: various
Special Note
- [formulation clarification]
- Info: phenytoin ER caps contain 8% less drug than chewable tabs and susp; monitor closely and consider dose adjustment if switching between products
status epilepticus
- [15-20 mg/kg/dose IV x1]
- Max: 50 mg/min IV; Info: may give additional 10 mg/kg/dose IV x1 after 20min if no response to initial dose; begin maint. dose for seizure disorder 12-24h after loading dose
seizure disorder
- [immediate-release form]
- Dose: 300-400 mg/day PO/IV divided bid-tid; Start: 100 mg PO/IV tid; Max: 600 mg/day for maint. tx; 50 mg/min IV; Alt: 4-7 mg/kg/day PO/IV divided bid-tid; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in elderly pts and CYP2C9 intermediate or poor metabolizers; dose adjustment may be needed during pregnancy and/or postpartum; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [extended-release form]
- Dose: 300-400 mg/day ER PO divided bid-tid; Start: 100 mg ER PO tid; Max: 600 mg/day for maint. tx; Alt: 4-7 mg/kg/day ER PO divided bid-tid; Info: may consider load of 15-20 mg/kg ER PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in elderly pts and CYP2C9 intermediate or poor metabolizers; dose adjustment may be needed during pregnancy and/or postpartum; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; if stable on bid-tid ER dosing, then may switch to qd ER dosing; do not open ER cap; taper dose gradually to D/C
seizure prophylaxis, neurosurgery-associated
- [4-7 mg/kg/day IV divided bid-tid]
- Start: 10-20 mg/kg/dose IV x1; Max: 600 mg/day for maint. tx; 50 mg/min IV; Info: consider low start dose in elderly pts and CYP2C9 intermediate or poor metabolizers
renal dosing
- [see below]
- renal impairment: no adjustment; Info: do not give oral loading regimen
- HD/PD: no adjustment; no supplement; Info: do not give oral loading regimen
hepatic dosing
- [see below]
- hepatic impairment: not defined; Info: do not give oral loading regimen
Peds Dosing .
- Dosage forms: ER CAP: 100 mg, 200 mg, 300 mg; CHEWABLE: 50 mg; SUSP: 25 mg per mL; INJ: various
Special Note
- [formulation clarification]
- Info: phenytoin ER caps contain 8% less drug than chewable tabs and susp; monitor closely and consider dose adjustment if switching between products
status epilepticus
- [15-20 mg/kg/dose IV x1]
- Max: 1500 mg/day; 3 mg/kg/min IV up to 50 mg/min; Info: may give additional 10 mg/kg/dose IV x1 after 20min if no response to initial dose; begin maint. dose for seizure disorder 12-24h after loading dose
seizure disorder
- [immediate-release form, <6 mo]
- Dose: 4-8 mg/kg/day PO/IV divided bid-tid; Start: 5 mg/kg/day PO/IV divided bid; Max: 300 mg/day for maint. tx; 3 mg/kg/min IV up to 50 mg/min; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [immediate-release form, 6 mo-3 yo]
- Dose: 8-10 mg/kg/day PO/IV divided bid-tid; Start: 5 mg/kg/day PO/IV divided bid-tid; Max: 300 mg/day for maint. tx; 3 mg/kg/min IV up to 50 mg/min; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [immediate-release form, 4-6 yo]
- Dose: 7.5-9 mg/kg/day PO/IV divided bid-tid; Start: 5 mg/kg/day PO/IV divided bid-tid; Max: 300 mg/day for maint. tx; 3 mg/kg/min IV up to 50 mg/min; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [immediate-release form, 7-9 yo]
- Dose: 7-8 mg/kg/day PO/IV divided bid-tid; Start: 5 mg/kg/day PO/IV divided bid-tid; Max: 300 mg/day for maint. tx; 3 mg/kg/min IV up to 50 mg/min; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [immediate-release form, 10-16 yo]
- Dose: 6-7 mg/kg/day PO/IV divided bid-tid; Start: 5 mg/kg/day PO/IV divided bid-tid; Max: 300 mg/day for maint. tx; 3 mg/kg/min IV up to 50 mg/min; Info: may consider load of 15-20 mg/kg/dose IV x1 or 15-20 mg/kg PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; taper dose gradually to D/C
- [immediate-release form, >16 yo]
- see Adult Dosing
- [extended-release form, 7-9 yo]
- Dose: 7-8 mg/kg/day ER PO divided bid-tid; Start: 5 mg/kg/day ER PO divided bid-tid; Max: 300 mg/day for maint. tx; Info: may consider load of 15-20 mg/kg ER PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; if stable on bid-tid ER dosing, then may switch to qd ER dosing; do not open ER cap; taper dose gradually to D/C
- [extended-release form, 10-16 yo]
- Dose: 6-7 mg/kg/day ER PO divided bid-tid; Start: 5 mg/kg/day ER PO divided bid-tid; Max: 300 mg/day for maint. tx; Info: may consider load of 15-20 mg/kg ER PO divided in 3 doses given 2h apart, then start maint. dose after 12-24h; consider low start dose in CYP2C9 intermediate or poor metabolizers; adjust dose no more frequently than q7-10 days based on tx response and serum levels; if divided doses unequal, give larger dose qhs; if stable on bid-tid ER dosing, then may switch to qd ER dosing; do not open ER cap; taper dose gradually to D/C
- [extended-release form, >16 yo]
- see Adult Dosing
renal dosing
- [see below]
- renal impairment: no adjustment; Info: do not give oral loading regimen
- HD/PD: no adjustment; no supplement; Info: do not give oral loading regimen
hepatic dosing
- [see below]
- hepatic impairment: not defined; Info: do not give oral loading regimen