Phenobarbital Digitoxin

The principal precaution with use of the bile acid resins is the possibility of impaired absorption of other drugs given orally at the same time. Cholestyramine and colestipol can bind many other drugs, such as digitoxin, phenobarbital, chlorothiazide, and warfarin, and delay or prevent their absorption. For this reason, other drugs should always be taken at least 1 hour before or 4 to 6 hours after the resin. The resins can also decease absorption of fat-soluble vitamins. 

Phenobarbital Bishydroxy coumarin, digitoxin, phenylbutazone, phenytoin... 

Thus, in patients taking digitoxin, who then start therapy with phenobarbital, (CYP3A4 inducer), the blood level of digitoxin decreases by about half. The dose would then need to be raised to compensate, but if the phenobarbital was stopped, the induction would decline and toxicity would ensue if there was no readjustment of the dose. 

Phenobarbital and other barbiturates1 Barbiturates, chloramphenicol, chlorpromazine, cortisol, coumarin anticoagulants, desmethylimipramine, digitoxin, doxorubicin, estradiol, phenylbutazone, phenytoin, quinine, testosterone... 

Diazoxide Diflunisal Digitoxin Pentobarbital Phenobarbital Phenylbutazone Warfarin ... 

The metabolism of digitoxin can be increased, with resulting increasing dosage requirements, by enzyme-inducing drugs (200). For example, phenobarbital 100 mg daily reduces steady-state serum digitoxin concentrations by 50%. 

For thyroxine measurement linearity was obtained between 25 and 400 nmol/1, for lidocaine between 5 and 50 pmol/1, i.e., in the clinically relevant range. Lidocaine has been determined in plasma samples with a measuring time of 15 min per sample. The method is also applicable to other haptens such as digitoxin, theophylline, and phenobarbital. Increasing the sensitivity up to that of conventional RIA should make this kind of assay of practical utility. 

Blood levels of digitoxin can be halved by phenobarbital and its effects may be expected to be reduced accordingly. However, another study found that phenobarbital did not affect digitoxin, digoxin or acetyldigitoxin pharmacokinetics. 

Phenobarbital 60 mg three times daily for 12 weeks, halved the steady-state plasma levels of digitoxin 100 mierogiams daily. In associated studies the half-life of digitoxin deereased from 7.8 to 4.5 days during phenobarbital treatment. In another study the rate of eonversion of digitoxin to digoxin ineieased from 4% to 27% in one patient who took phenobarbital 96 mg daily for 13 days. 

Phenobarbital and other barbiturates are well-known potent liver enzyme inducers which, it would seem, can increase the metabolism and conversion of digitoxin to digoxin. The lack of interaction in one study may possibly have been because the barbiturate was taken for a relatively short time. ... 

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