Is switching from brand name to generic formulations of phenobarbital associated with loss of antiepileptic efficacy?: a pharmacokinetic study with two oral formulations (Luminal® vet, Phenoleptil®) in dogs

Table 1 Pharmacokinetic parameters of phenobarbital following oral administration of 100 mg Luminal® vet or Phenoleptil® in a group of 8 dogs

Parameter	Luminal® vet	Phenoleptil®	P
T_max (h) observed	3.75 ± 0.79	2.75 ± 0.37	0.2275
T_max (h) calculated	5.97 ± 1.33	2.64 ± 0.51	0.0588
C_max (μg/ml) observed	10.9 ± 0.92	10.5 ± 0.77	0.2426
C_max (μg/ml) calculated	10.3 ± 0.92	10.0 ± 0.85	0.2569
T_0.5 (h)	50.3 ± 3.1	52.9 ± 2.8	0.2348
AUC_(0-119) (μg ml^-1 h) observed	644 ± 52.5	618 ± 44.5	0.1499
AUC∞ (μg ml^-1 h) calculated	807 ± 66.8	781 ± 54.0	0.2961
Relative bioavailability (AUC_{Phenoleptil®} /AUC_{Luminal® vet})	0.98 ± 0.031
	(range: 0.90-1.15; 90% CI: 0.92-1.04)
Relative C_max observed (C_{max, observed Phenoleptil®}/ C_{max, observed Luminal® vet})	0.96 ± 0.031
	(range: 0.85-1.05; 90% CI: 0.90-1.03)
Relative C_max calculated (C_{max, calculated, Phenoleptil®)}/C_{max, calculated, Luminal® vet})	0.97 ± 0.028
	(range: 0.81-1.08; 90% CI: 0.92-1.03)

All data are shown as means ± SEM; for ratios also the range and 90% confidence intervals (90% CI) are shown. Abbreviations: T_max, time to reach peak plasma concentration; C_max, peak plasma concentration; t_0.5, elimination half-life in plasma; AUC, area under the plasma concentration curve.

ISSN: 1746-6148