High Doses of Drugs Extensively Metabolized by CYP3A4 Were Needed to Reach Therapeutic Concentrations in Two Patients Taking Inducers / Dos pacientes que tomaban inductores necesitaron dosis altas de medicamentos metabolizados en gran medida por el CYP3A4 para alcanzar concentraciones terapéuticas

ABSTRACT Introduction: In the last 20 years of clinical practice, the senior author has identified these 2 rare cases in which the patients needed extremely high doses of drugs metabolized by CYP3A4 to reach and maintain serum therapeutic concentrations. Methods: The high metabolic ability of these 2 patients was demonstrated by the low concentration-to-dose ratios (C/D ratios) of several drugs metabolized by CYP3A4. Results: Case 1 was characterized by a history of high carbamazepine doses (up to 2,000 mg/day) and needed 170 mg/day of diazepam in 2 days to cooperate with dental cleaning. The high activity of the CYP3A4 isoenzyme was manifested by fast metabolism for quetiapine and diazepam, which took more than 1 year to normalize after the inducer, phenytoin, was stopped. Case 2 was also very sensitive to CYP3A4 inducers as indicated by very low C/D ratios for carbamazepine, risperidone and paliperidone. The carbamazepine (2,800 mg/day) and risperidone (20 mg/day) dosages for this second patient are the highest doses ever seen for these drugs by the senior author. Risperidone induction appeared to last for many months and metabolism was definitively normal 3 years after stopping carbamazepine. On the other hand, olanzapine C/D ratios were normal for induction. Conclusions: The literature has never described similar cases of very high doses of drugs metabolized by CYP3A4. We speculate that these 2 patients may have unusual genetic profiles at the nuclear receptor levels; these receptors regulate induction of drugs.

RESUMEN Introducción: Durante sus últimos 20 años de práctica, el último autor ha identificado estos 2 infrecuentes casos que necesitaban dosis extremadamente altas de medicaciones metabolizadas por el CYP3A4 para alcanzar y mantener concentraciones séricas terapéuticas. Métodos: La gran capacidad metabólica de estos 2 pacientes se demostró por los bajos cocientes entre concentración y dosis (C/D) de varias medicaciones metabolizadas por el CYP3A4. Resultados: El caso 1 se caracterizaba por una historia de altas dosis de carbamazepina (1.500 mg/día) y la necesidad de tomar 170 mg de diazepam en 2 días para facilitar una limpieza dental. La gran actividad de la isoenzima CYP3A4 se manifestó por una gran capacidad metabólica de quetiapina y diazepam, cuya normalización tardó más de 1 año tras la toma de un inductor, fenitoína. El caso 2 tambien era muy sensible a la inducción, lo cual se demuestra por los bajos cocientes C/D de carbamazepina, risperidona y paliperidona. Las dosis de carbamazepina (2.800 mg/día) y risperidona (20 mg/día) de este segundo paciente son las más altas nunca vistas por el último autor. La inducción de risperidona duró muchos meses y su metabolismo era normal 3 años después de interrumpir la carbamazepina. El cociente C/D de olanzapina era normal para la inducción. Conclusiones: Nunca se habían descrito casos similares de dosis tan altas de medicaciones metabolizadas por el CYP3A4. Se especula con que estos pacientes podrían tener unos perfiles genéticos inusuales en los receptores nucleares que regulan la inducción de medicamentos.

High Doses of Drugs Extensively Metabolized by CYP3A4 Were Needed to Reach Therapeutic Concentrations in Two Patients Taking Inducers.

INTRODUCTION: In the last 20 years of clinical practice, the senior author has identified these 2 rare cases in which the patients needed extremely high doses of drugs metabolized by CYP3A4 to reach and maintain serum therapeutic concentrations. METHODS: The high metabolic ability of these 2 patients was demonstrated by the low concentration-to-dose ratios (C/D ratios) of several drugs metabolized by CYP3A4. RESULTS: Case 1 was characterized by a history of high carbamazepine doses (up to 2,000mg/day) and needed 170 mg/day of diazepam in 2 days to cooperate with dental cleaning. The high activity of the CYP3A4 isoenzyme was manifested by fast metabolism for quetiapine and diazepam, which took more than 1 year to normalize after the inducer, phenytoin, was stopped. Case 2 was also very sensitive to CYP3A4 inducers as indicated by very low C/D ratios for carbamazepine, risperidone and paliperidone. The carbamazepine (2,800 mg/day) and risperidone (20 mg/day) dosages for this second patient are the highest doses ever seen for these drugs by the senior author. Risperidone induction appeared to last for many months and metabolism was definitively normal 3 years after stopping carbamazepine. On the other hand, olanzapine C/D ratios were normal for induction. CONCLUSIONS: The literature has never described similar cases of very high doses of drugs metabolized by CYP3A4. We speculate that these 2 patients may have unusual genetic profiles at the nuclear receptor levels; these receptors regulate induction of drugs.

Three patients needing high doses of valproic Acid to get therapeutic concentrations.

Valproic acid (VPA) can autoinduce its own metabolism. Cases requiring VPA doses >4000 mg/day to obtain therapeutic plasma concentrations, such as these 3 cases, have never been published. Case 1 received VPA for seizures and schizophrenia and had >50 VPA concentrations in 4 years. A high dose of 5,250 mg/day of VPA concentrate was prescribed for years but this dose led to an intoxication when switched to the enterocoated divalproex sodium formulation, requiring a normal dose of 2000 mg/day. VPA metabolic capacity was significantly higher (t = -9.6; df = 6.3, p < 0.001) during the VPA concentrate therapy, possibly due to autoinduction in that formulation. Case 2 had VPA for schizoaffective psychosis with 10 VPA concentrations during an 8-week admission. To maintain a VPA level ≥50 µg/mL, VPA doses increased from 1500 to 4000 mg/day. Case 3 had tuberous sclerosis and epilepsy and was followed up for >4 years with 137 VPA concentrations. To maintain VPA concentrations ≥50 µg/mL, VPA doses increased from 3,375 to 10,500 mg/day. In Cases 2 and 3, the duration of admission and the VPA dose were strongly correlated (r around 0.90; p < 0.001) with almost no change after controlling for VPA concentrations, indicating progressive autoinduction that increased with time.