Osteomalacia barbiturates

CARBONIC ANHYDRASE INHIBITORS ANTIEPILEPTICS- BARBITURATES, PHENYTOIN Risk of osteomalacia Barbiturates and phenytoin have a small risk of causing osteomalacia this may be t by acetazolamide-induced urinary excretion of calcium Be aware... 

Chronic acetazolamide therapy is associated with greater spinal bone mineral density. This is probably the result of metabolic acidosis urine calcium is increased and serum phosphate reduced. Osteomalacia has been reported during long-term therapy in combination with barbiturates in two patients. 

Anticonvulsants (barbiturates and phenytoin) and other drugs that induce liver enzymes (such as rifampicin) can accelerate the hepatic catabolism of vitamin D and can lead to reduced serum concentrations of calcifediol and osteomalacia. Prophylactic vitamin D treatment of patients taking long-term enzyme inducers can be helpful and should be given at least in cases of anticonvulsant-drug-induced osteomalacia (74,75). 

Uncertain. Mild osteomalacia induced by antiepileptics is a recognised phenomenon (see also Vitamin D substances + Phenytoin and Barbiturates , p.l291). It seems that this is exaggerated by acetazolamide, which increases urinary calcium excretion, possibly by causing systemic acidosis, which results from the reduced absorption of bicarbonate by the kidney. The changes in the antiepileptic levels are not understood. 

The long-term use of phenytoin, phenobarbital, or primidone can disturb vitamin D and calcium metabolism and may result in osteomalacia. There are a few reports of patients taking vitamin D supplements who responded poorly to vitamin replacement while taking phenytoin or barbiturates. Serum phenytoin levels are not altered by vitamin D. 

---