Background Determination of the plasma concentration of free phenytoin (CpFL) could improve seizure control and prevent adverse effects.
Purpose To evaluate the safety profile of patients treated with phenytoin using CpFL.
Material and methods Prospective study (2013–2014) in a hospital. Collected data: demographics, doses, CpFL, creatinine clearance (Clcr), serum albumin (g/dL), degree of intoxication, days of hospitalisation and concomitant medication. Phenytoin therapeutic range, CPFL: 1–2.5 μg/mL. Moderate intoxication, CpFL 2.5–3.0 μg/mL and severe, CpFL >3.0 μg/mL. To determine renal clearance, we used CKD-EPI. Moderate renal impairment was defined as Clcr 20–50 mL/min. Polymedicated patients: >5 drugs. Statistical analysis: Spearman correlation and the χ2 test.
Patients 93 (cases 192; phenytoin levels/patient 1–6). Men 51.6%. Age 58 years (range 27–84). Daily dose 299 mg/day. CpFL 1.1 μg/mL. Clcr 51.7 mL/min. Serum albumin 3.6 g/dL. Levels in the therapeutic range: 49.5% (95/192), 32.8% (63/192) were suboptimals and 17.7% were toxic (34/192) (CpFL 3.8 μg/mL; range 2.6–5.7 μg/mL). Intoxication, moderate was 64.7% and severe 35.3%. Average age (Intoxicated patients) 71 years. Clcr 38.9 mL/min. Serum albumin 3.4 g/dL. Three patients were hospitalised. Polymedicated patients: 71% vs. 50% for the rest. Patients with drugs that bind over 70% to plasma proteins: 48%. Patients >70 years had a higher risk of intoxication (p = 0.033). We observed an inverse correlation between CpFL and Clcr (Spearman rho: -0.562; p = 0.04) and with albumin (Spearman rho: -0.623; p < 0.01). In relation to moderate intoxication, the plasma concentration of phenytoin had a value 23% higher than CpFL.
Conclusion Elderly patients, polymedicated patients and those with moderate renal insufficiency and hypoalbuminaemia presented a higher risk of phenytoin toxicity. It would be advisable to be careful with these patients because in our study efficacy/toxicity is correlated better with CpFL.
No conflict of interest.
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.