Phenobarbital antagonists

Drugs that may affect itraconazole include antacids, carbamazepine, didanosine, H2 antagonists, hydantoins, macrolide antibiotics, nevirapine, phenobarbital, phenytoin, protease inhibitors, proton pump inhibitors, and rifamycins. 

Initially, this individual had been given phenobarbital, the GABAergic drug it had done nothing for his seizures. However, when he received carbamazepine, the Na" channel antagonist, his seizures stopped immediately. As long as he was on this medication he had no seizures. 

Three studies examined the mediating effect of phenobarbital on white phosphorus-induced liver function impairment. Pre-treatment with four or five intraperitoneal injections of phenobarbital showed no effect on white phosphorus-induced triglyceride accumulation at 12 hours after white phosphorus administration (Pani et al. 1972), but had an antagonistic effect on white phosphorus-induced increases in BSP retention at 24 hours after treatment with white phosphorus (Hurwitz 1972). The antagonistic effect of phenobarbital pretreatment on white phosphorus-induced BSP retention disappeared by 48 hours after white phosphorus administration. Another study conducted by Hurwitz (1972) showed the antagonistic effect of 4 daily intraperitoneal post-treatments with phenobarbital on white phosphorus-induced mortality. 

Chlorinated hydrocarbon pesticides are esterase- and SER-stimulat-ing, like phenobarbital, chlorcyclizine, and certain other drugs, and antagonistic to organic phosphates, presumably by reinforcing available esterase supply. 

Drugs. Antiepilepsy drugs, particularly phenytoin, primidone and phenobarbital, occasionally cause a macrocytic anaemia that responds to folic acid. This may be due to enzyme induction by the antiepileptics increasing the need for folic acid to perform hydroxylation reactions (see Epilepsy) but other factors such as reduced absorption may be involved. Administration of folic acid causes a recurrence of seizures in some patients. Some anti-malarials, e.g. pyrimethamine, may interfere with conversion of folates to the active tetrahydrofolic acid, causing macrocytic anaemia. Methotrexate, another folate antagonist, may cause a megaloblastic anaemia especially when used long-term for leukaemia, rheumatoid arthritis or psoriasis. 

Treatment of icteric episodes with phenobarbital (3 x 20-60 mg/day) together with phototherapy (430-470 nm, 8-12 hr/day) and/or plasmapheresis is indicated. Cholestyramine (3x4 g/day) or cholestipol (3x5 g/day) may be used to treat pruritus. Qther recommended effective antipruritics are naloxone (2-3 x 0.4 mg/day, i.v.) or naltrexone (2-4 x 25-50 mg/day), which act as opi-oidergic neurotransmitters. (69) It is also possible to use the 5-HT3 antagonist ondansetron (3 x 4.8 mg/day, i.v. or orally). (64) Refractory cholestasis pruritus has recently been treated successfully with dronabinol (50) and also with sertraline. Administration of ursodeoxycholic acid (22, 53), medium-chain fatty acids, PUFA (65) and fat-soluble vitamins (especially vitamin K) is recommended. (s. pp 6, 47) (s. tab. 13.11)... 

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