To the Editor: The recent information that methylphenobarbitone (60 mg tablets) will be unavailable after 1 January 2003 has caused anxiety in patients with epilepsy previously treated satisfactorily with this drug. The suggested substitution of phenobarbitone, primidone or a newer antiepileptic agent seems appropriate. However, patients and perhaps practitioners may assume, as my patients have, that phenobarbitone and primidone are equivalent to methylphenobarbitone on a milligram-for-milligram or a tablet-for-tablet basis. This may not be so. The equivalence is close to 30 mg of phenobarbitone for 60 mg methylphenobarbitone, and probably around 200 mg of primidone for 60 mg of methylphenobarbitone.1 Plasma phenobarbitone concentrations should be checked before and after any changeover.

In recent years, several other old, but therapeutically satisfactory, neurological drugs have also been withdrawn from the Australian market (oral neostigmine, several anticholinergic antiparkinsonian agents, ethosuximide and some phenytoin preparations, and the only ergotamine preparation not also containing caffeine).

Subject to safety issues, ethics committees usually will not approve a clinical trial of a new drug unless patients who benefit from it are guaranteed supplies until the drug is marketed. Surely similar considerations should apply for patients who have had completely satisfactory long-term responses to marketed drugs. If such drugs must be withdrawn, except for safety reasons, there should be extensive prior consultation with prescribers and patient groups, prescribers should know the situation before their patients discover it from other sources, and there should be a sufficient lead time for everyone receiving the drug to return for another prescription (and for advice) before the drug becomes unavailable (a minimum lead time of six months in the case of drugs subsidised under the Pharmaceutical Benefits Scheme).

The withdrawal of useful neurological drugs in Australia has reached the stage where therapeutic options are becoming limited. In the case of drugs required for long-term use, to protect the interests of new patients it has become necessary to consider whether the drug will continue to be available for the expected duration of the patient's therapy. In this regard, the prescriber's only guide may be the track record of the firm which markets the drug otherwise chosen.