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PubMed1978

Inhibition of enzyme induction in Pseudomonas aeruginosa by exogenous nucleotides.

Alkylsufatase induction in resting cell suspensions of P. aeruginosa was inhibited by exogenously supplied adenosine or by ATP (2mM). Adenine phosphate had no effect while AMP or ADP caused a slight stimulation of induction. The inhibitory effect of ATP required the presence of added Mg2+, was not reversed by cyclic-AMP (2mM), and was independent of the nature of the inducer. Of a number of other nucleoside triphosphates tested, only UTP (2mM) acted as an inhibitor of induction. These nucleotides at external concentrations of 6mM also inhibited alkysulfatase induction in actively growing cells.

Adenosine Triphosphate↗
PubMed1979

Time-dependent kinetics. V: Time course of drug levels during enzyme induction (one-compartment model).

Equations were derived to describe the time course of drug levels during auto- and heteroinduction under a variety of input conditions. These equations were based on a pharmacokinetic theory of induction which assumes that metabolic clearance increases exponentially to a maximum value and that the rate of this increase is governed by the degradation rate constant of the induced enzyme (k'). Closed form solutions could be obtained only for intravenous single-dose (case I) and multiple-dose (case IV) administration. For each of the other cases, constant-rate intravenous infusion (case III), oral single-dose administration (case II), and multiple-dose administration (case V), an exact solution (not closed form) and an approximation (closed form) were derived. Two sets of equations were derived for each of the five cases to take into consideration the possibility of a latency term (lambda). Plots of drug amount X (or concentration C) vs. time (t) were constructed. In case I, a log X vs. t plot was convex, the slope increasing with time. In case II, X increased, reached a peak, and decayed as in case I. In case III (lambda greater than 5 ln 2V/Q) C reached a preinduction steady state before decreasing to a lower (induced) steady state. The behavior of C vs. t for cases IV and V was similar to that for case III. Determination of parameters was attempted in case III. Nonlinear least-square fitting of generated data with 3-9% error yielded reasonable estimates of k'.

Enzyme Induction↗
PubMedDate not supplied

Enzyme induction and inhibition by new antiepileptic drugs: a review of human studies.

The aim of this paper is to review a number of new antiepileptic agents (i.e. felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide) for their inducing and/or inhibitory properties in humans, mainly considering the interactions where they are involved as the cause rather than the object of such interactions. Two aspects have been particularly taken into account: the changes or absence of changes in plasma/serum concentrations of concomitant drugs and the direct or indirect evidence of induction, inhibition or lack of effect on the six major human hepatic CYP isozymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), as well as on other CYP isozymes or enzyme systems. Felbamate clearly affects the pharmacokinetics of a number of drugs, generally increasing but also decreasing their concentrations. It induces enzymes such as CYP3A4 and inhibits enzymes such as CYP2C19 and those of the beta-oxidation pathway. Topiramate is not devoid of potential interaction properties: it decreases the plasma concentrations of ethinylestradiol, induces CYP3A4 and inhibits CYP2C19. For oxcarbazepine, no inhibitory, only inductive effects have been observed thus far. Felbamate. topiramate and oxcarbazepine may induce the metabolism of steroidal oral contraceptives. In this respect, tiagabine has been studied at a rather low dose. Pharmacodynamic or pharmacokinetic interaction seems to exist between lamotrigine and carbamazepine. Lamotrigine appears to be a weak inducer of UGTs, whereas induction of CYP3A4 seems improbable as the compound does not change the concentrations of oral contraceptives or the urinary excretion of 6beta-hydroxycortisol. Zonisamide has very peculiar pharmacokinetics and an extensive metabolism. Additional information on its enzyme inducing or inhibiting properties would be necessary, as data so far collected on its effect on the pharmacokinetics of other drugs are conflicting. Gabapentin, vigabatrin and in particular levetiracetam appear to be devoid of significant enzyme inducing or inhibiting properties.

Anticonvulsants↗