Little has been published on the effects of renal impairment on the pharmacokinetics of primidone. In adults on primidone monotherapy, approximately 60% of primidone is cleared via the kidney.66 In adults on polytherapy and in children, approximately 40% of primidone is cleared via the kidney.66 Another 5–10% of an administered dose of primidone is excreted via the kidney as phenobarbital.66 These observations suggest that the dosage of primidone probably should be reduced in patients with renal impairment. The amount of this reduction should be based upon a determination of the plasma concentrations of primidone and phenobarbital.
Primidone is poorly soluble in water, is 0–20% protein bound, and has a modest volume of distribution.66 Significant amounts of primidone and its metabolites (phenobarbital and phenylethylmalonamide) are lost during dialysis.67,68 Plasma concentrations of primidone and phenobarbital should be checked after hemodialysis and an additional loading dose given, if needed, following the procedure given in Correction for drug loss during hemodialysis.
Reviewed and revised February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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