Anticonvulsant levels and reloading: Difference between revisions
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===Phenytoin=== | ===Phenytoin=== | ||
====Zero Level of Initial Load==== | ====Zero Level of Initial Load==== | ||
*IV: 18mg/kg at max rate of 25mg/min | *IV: 18mg/kg at max rate of 25mg/min<ref>Osborn HH, Zisfein J, Sparano R. Single-dose oral phenytoin loading. Ann Emerg Med. 1987;16(4):407-12</ref> | ||
**PO: 18mg/kg as single dose or divided into 3 doses q2hr | **PO: 18mg/kg as single dose or divided into 3 doses q2hr<ref>Ratanakorn D, Kaojarern S, Phuapradit P, Mokkhavesa C. Single oral loading dose of phenytoin: a pharmacokinetics study. J Neurol Sci. 1997;147(1):89-92</ref> | ||
*Level above 0 (to avoid over-dosing) | *Level above 0 (to avoid over-dosing) | ||
====Subtherapeautic level >0==== | ====Subtherapeautic level >0==== | ||
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====Sheiner-Tozer Equation==== | ====Sheiner-Tozer Equation==== | ||
*may be needed to correct level in patients with low albumin or abnormal creatinine: | *may be needed to correct level in patients with low albumin or abnormal creatinine<ref>Martin E, Tozer TN, Sheiner LB, Riegelman S. The clinical pharmacokinetics of phenytoin. J Pharmacokinet Biopharm. 1977 Dec;5(6):579-96.</ref> | ||
*Corrected level = measured level/[(adjustment x albumin) + 0.1] | *Corrected level = measured level/[(adjustment x albumin) + 0.1] | ||
*adjustment is 0.2 unless patient has Creatinine clearance <20 then it is 0.1 | *adjustment is 0.2 unless patient has Creatinine clearance <20 then it is 0.1 | ||
Revision as of 02:40, 24 February 2014
Background
- IV load can be performed with phenobarbital, phenytoin, valproate, levetiracetam
- Oral loading can be spread over day or more to avoid GI upset
Dose
Dose (mg) = ideal body weight (kg) X Vd X [desired level - current level (mcg/mL)]
Volume of Distribution
| Agent |
Volume of Distribution |
| Phenytoin (dilantin) | 0.8 |
| Carbamazepine (tegretol) | 0.8 |
| Phenobarbital | 0.6 |
| Valproate (depakote) | 0.2 |
Desired Level
- Pt's optimal level = desired level
- If optimal level unknown target upper end of therapeutic range:
- Phenytoin = 20 mcg/mL
- Valproate = 100 mcg/mL
- Phenobarbital = 40 mcg/mL
- If optimal level unknown target upper end of therapeutic range:
Loading
Phenytoin
Zero Level of Initial Load
- IV: 18mg/kg at max rate of 25mg/min[1]
- PO: 18mg/kg as single dose or divided into 3 doses q2hr[2]
- Level above 0 (to avoid over-dosing)
Subtherapeautic level >0
Concentration adjusted = (concentration desired - concentration measured) x (0.8 x adjusted body weight)
Sheiner-Tozer Equation
- may be needed to correct level in patients with low albumin or abnormal creatinine[3]
- Corrected level = measured level/[(adjustment x albumin) + 0.1]
- adjustment is 0.2 unless patient has Creatinine clearance <20 then it is 0.1
Fosphenytoin
- IV: 18mg PE/kg at 100-150mg/min
See Also
Source
- ↑ Osborn HH, Zisfein J, Sparano R. Single-dose oral phenytoin loading. Ann Emerg Med. 1987;16(4):407-12
- ↑ Ratanakorn D, Kaojarern S, Phuapradit P, Mokkhavesa C. Single oral loading dose of phenytoin: a pharmacokinetics study. J Neurol Sci. 1997;147(1):89-92
- ↑ Martin E, Tozer TN, Sheiner LB, Riegelman S. The clinical pharmacokinetics of phenytoin. J Pharmacokinet Biopharm. 1977 Dec;5(6):579-96.