Develop. Med. Child Necrrol. 1968, 10, 497-504

Folic Acid Deficiency from Anticonvulsant Therapy

Neil Gordon

Introduction The association between megaloblastic

anaemia and anticonvulsants was first described by Mannheimer et al. in 1952, and Badenoch in 1954. Since then there have been a number of reports of pheno- barbitone, primidone and phenytoin so- dium, alone or in combination, causing macrocytosis and, more rarely, a macro- cytic anaemia. It is considered that this is due to folic acid deficiency (Girdwood and Lenman 1956, Fuld and Moorhouse 1956, Hobson et al. 1956, Hawkins and Meynell 1958). No completely satisfactory explana- tion of this megaloblastic anaemia has so far been offered. It may be that several factors are involved and acting simul- taneously. Occasionally the diet may be deficient, although this is perhaps less likely in the case of children than adults, where there are parents and teachers able to supervise the amount that is eaten. Even if the diet is adequate there is the possi- bility of defective absorption.

Meynell (1966) suggests that, as anti- convulsants transiently depress the excit- ability of the central nervous system, they may have a similar effect on the activity of the gastrointestinal tract. When patients with epilepsy with and without anaemia were given a 5 mg. test dose of folic acid

by mouth immediately after taking an anti- convulsant, serum folic acid levels taken at half-hourly intervals for two hours were significantly lowered and the urinary out- put of folic acid was as low as that obtained in untreated adult coeliac disease. If the test dose of folic acid was given two hours after the anticonvulsant, both the serum levels and urinary output approached normal values. It is claimed that the variable results reported by other workers in this field are due to the relatively large dose of folic acid given, and the lack of a fixed time relationship to the last dose of the anticonvulsant. If there is a gastro- intestinal block interfering with the absorp- tion of folic acid, it is only a transient one.

Lees (1961) also maintains that some patients suffer from a defect of intestinal absorption related to the anticonvulsants, and that this responds to cyanocobalamin and folic acid. However, his patients did have macrocytic anaemia while on these drugs, so that their condition may have differed in some way from the patients who have a deficiency of folic acid but are not anaemic.

Reynolds et al. (1965) reported on two patients who developed a macrocytic anaemia while on anticonvulsants. They were both on a rather deficient diet, so

Consultant Neurologist, Royal Manchester Children’s Hospital, Pendlebury, Manchester.

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again there may have been multiple aetiological factors. Xylose tests indicated impaired intestinal absorption and they became normal on treatment with folic acid. It is suggested that an interference with folic acid metabolism by the anti- convulsants may have damaged the intes- tinal mucosa and led to malabsorption. Also the secretion of intrinsic factor may have been reduced so that the absorptive defects are aggravated by a vitamin B,, deficiency. A direct action of the anti- convulsants on gastrointestinal function has also to be considered. Once a deficiency of folic acid or vitamin B,, has occurred, a vicious circle may arise owing to the effects of lack of these substances on intestinal absorption. Malabsorption may be a secondary factor, rather than the initial cause of the diminished serum folate level.

Others have found no evidence of mal- absorption of folic acid and have investi- gated the possibility of anticonvulsants interfering with the metabolism of folic acid (Chanarin et al. 1958). Patients with folic acid deficiency occurring during preg- nancy, or as the result of intestinal mal- absorption syndromes, cleared a small intravenous dose of the substance from their plasma very rapidly, indicating a true folic acid deficiency with depleted tissue stores. The patient being treated with primidone, on the other hand, had a normal rate of clearance of injected folic acid, suggesting that there is no tissue deficiency of folic acid. The anaemia was, therefore, ascribed to interference by the anticonvulsant drug with the action of the available folic acid on cellular metabolism. This mechanism is also supported by Girdwood (1956). About a third of the patients receiving anticonvulsants may show evidence of macrocytosis (Hawkins and Meynell 1958), but very few develop macrocytic anaemia. Perhaps the inhibitory action of anticonvulsants on folic acid

metabolism is too weak to cause anaemia in the absence of certain co-factors (Todd and Dewhurst 1964). Nutrition may be of particular importance in the older patient with epilepsy, who may neglect his diet and suffer from lack of appetite. A poor intake of vitamin C and vitamin B12, as well as of folic acid, may be especially significant. Among epileptics living in a colony, Malpas et a/. (1965) found a lower in- cidence than other workers of macro- cytosis but not of low serum folate levels. They thought that the blood changes were due to the anticonvulsant therapy but that an adequate diet might prevent them. Hawkins and Meynell(l958) could find no evidence of an underlying biochemical defect causing both the epilepsy and the macrocytosis. The macrocytosis occurred as frequently among patients with a definite diagnosis, such as cerebral palsy or tuberous sclerosis, as among those with ‘idiopathic epilepsy’.

Klipstein (1964) investigated 60 epileptic patients on treatment. Subnormal serum folate levels of less than 5 .O mpg./ml. were observed in 31 of 53 patients receiving phenytoin sodium, an incidence of 58 per cent. Slight or moderate macrocytosis was observed in 71 per cent of subjects receiving phenytoin sodium who had abnormal serum folate levels, and in 18 per cent of those with normal levels. Serum B1, con- centrations were within normal limits. Plasma clearance studies after test doses of folic acid suggested that the metabolic block induced by phenytoin sodium might differ from that of primidone and barbitu- rates.

In another recent study of the effects of anticonvulsant therapy on folic acid meta- bolism Reynolds et a/. (1966) divided their 62 epileptic patients into two groups; 54 on treatment and 8 who had never had anticonvulsant therapy of any kind. None of the treated patients were anaemic, but 17 of 45 patients in whom the bone-

NEIL GORDON

marrow was examined showed megalo- blastic haemopoiesis, although in most cases there were no morphological changes in the peripheral blood. The comparative rarity of macrocytosis compared with other series has not been explained. Serum folate levels were below 5 mpg./ml. in 76 per cent of the treated patients, but with one exception the serum vitamin B,, con- centrations were within the normal range.

Clinical Findings (a) Serum Folate Estimation

The available evidence suggests that the initial symptoms of folic acid deficiency may be insidious in their onset and that anaemia is a relatively late manifestation. The only conclusive test seems to be an estimation of the serum folate level. For instance, the results of estimating the excretion of Figlu (formiminoglutamic acid) after histidine loading are variable. The compound may not be excreted in excess in megaloblastic anaemia of preg- nancy, due to slow absorption from the gut and increased utilisation for protein synthesis (Chanarin et al. 1963). Negative Figlu tests have also been reported in mengaloblastic anaemias due to anti- convulsants (Reynolds et al. 1965).

The significance of a single low serum folate level can be questioned. It certainly does not differentiate between a true deficiency of folic acid and interference with its metabolism. In some studies, levels of serum folate below 5.0 mpg./ml. are considered abnormal and no-one seems to question that levels below 2 .O mpg./ml. are abnormal. In two recent surveys on folate levels in elderly patients (Batata et al. 1967, Girdwood et al. 1967) none of the healthy controls had folate levels below 2 - 1 mpg./ml. In an estimation of vitamin levels in the blood of patients admitted to an American hospital, folate levels below 3.2 mpg./ml. were classified as abnormal (Leecry et al. 1965). The

amount of folic acid in the serum is measured microbiologically with Lacto- bacillus casei as the test organism, and there is no evidence that phenytoin sodium or primidone inhibit its growth (Kershaw and Girdwood 1964).

(b) Patients Studied So far 72 children have been studied.

Serum folate levels of 2 to 5 mpg./ml. have been considered of doubtful significance and levels below 2 mpg. definitely ab- normal. The children had all been on treatment with primidone, phenytoin sodium and phenobarbitone, sometimes in combination and sometimes combined with other drugs. Attention was only paid to these three drugs so that the results could be comparable to previous studies on the role of anticonvulsants in causing serum folate deficiency. The possible role of other drugs has so far not been in- vestigated. Epileptic seizures had been present for periods ranging from 6 months to 12 years and in most cases treatment had been given continuously for some years. For this preliminary study the children were selected because of their poor response to antiepileptic treatment, the purpose of the investigation being to obtain further information on the possible incidence of folic acid deficiency among children on treatment with anticonvulsants. It was considered that such a deficiency was most likely to be present among children who had had intensive anticonvulsant treat- ment for a considerable period but were still having fits. Their ages ranged from 7 months to 184 years, with an average of 10 years. There were 46 boys and 26 girls. With the exception of 9 children at Coulthurst School for epileptic children in the David Lewis Colony and 2 children at Condover Hall Special School for blind children, they were attending the Royal Manchester Children’s Hospital, Booth

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Hall Children’s Hospital, Manchester, or the Duchess of York Hospital for Babies, Manchester. Investigations done to help exclude any progressive cerebral disease had been negative, although in some cases the past history suggested the possibility of brain damage.

(c ) Merifal State The mental state and behaviour of this

group of children were very variable and the contributing factors complex. The incidence of fits, particularly if severe and frequent, must be relevant and complicat- ing emotional disturbances are often present. However, more attention needs to be paid to the effects of intensive drug therapy. It is well known that barbiturates often make the hyperkinetic child more restless and teachers of children with epilepsy may complain that they are over- sedated. Although a clinical impression, three of these children in particular, who had low serum folate levels of 1.84, 2-08 and 2.02 mpg./ml., have shown evidence over a period of years of a gradual deterioration in their intellectual capacities. This has been too slow to suggest any recognised type of cerebral degeneration, such as a lipid storage disease. It may be due to the occurrence of fits and their associated anoxia, but the possible role of drug toxicity certainly cannot be dismissed without further study. Two patients with folate levels of 2 . 8 and 1.8 mpg./ml., both aged 14. spontaneously complained of increasingly defective memory, which was making their school work more difficult.

(d) Laborator! Inwstigatioris There were 110 children (15 per cent)

with serum folate levels per ml. below 2 m:Lg. : 13 (1 8 per cent) between 2 and 3 mpg.: 25 (35 per cent) between 3 and 5 rn:*g., and 23 (32 per cent) with levels above 5 mpg.!ml. The percentage of 68 with levels below 5 mpg./ml. is in close

accord with Reynolds et af. (1966) who found that 76 per cent of their patients had similarly low values. All the children with levels below 2 mpg./ml., 7 with levels between 2 and 3 mpg./ml. and 4 with levels between 3 and 4 mpg./ml. have been treated with folk acid in daily doses of 5 to 15 mg. The follow-up of these patients is still proceeding and so far the longest a patient has been on treatment with folic acid is 18 months; 4 patients have only just started treatment. The fits became significantly more frequent in 2 children but this did not necessitate stop- ping the treatment, and there was a marked reduction in the fits in 2 children. The follow-up is not long enough to establish if this is an effect of the folic acid or results from the natural history of the disease. On the evidence of parents and teachers, the mental state of 3 children improved while on this vitamin and none became worse. In 7 cases, the serum folate level was re-estimated after 3-12 months while the patients were still taking bar- biturates or hydantoins. The original folate levels were all above 2 mpg./ml. blood and none of them showed a further significant fall-in fact, the level had risen considerably in 3 cases. The level of vitamin B,, in the serum was estimated in 29 of the patients and was above 120 mpg./ml. blood in all of them. None of the children were anaemic. Absolute values were estimated in addition to full blood counts in 44 children. Only the mean corpuscular volume showed any significant change. This was 90 cp. or over in 35 children, 12 of whom had values of 100 cp. or over. The absence of anaemia may only reflect that the patients’ diet was adequate and that they were healthy, so that there were no additional factors causing the folk acid deficiency to become so severe that a macrocytic anaemia resulted.

The results of this preliminary study suggest that deficiency of folic acid may be

NEIL GORDON

a frequent finding among children on pro- longed anticonvulsant therapy, and that, in view of the possible harmful effects of this deficiency, the level of folic acid should be checked at intervals when barbiturates or hydantoin derivatives are given for any length of time.

Discussion Folic acid is essential to the formation of

nucleic acid. The folk acid co-enzymes participate in reactions leading to syn- thesis of purines and of thymine, the methylated pyrimidine of deoxyribonucleic acid ; this emphasises the fundamental role of folic acid in the growth and reproduction of cells. Folic acid co-enzymes are un- doubtedly required throughout the body, and in folic acid deficient monkeys a con- siderable decrease in the rate of synthesis of nucleoprotein has been found (Harper 1959). Folic acid is also related to choline synthesis and to amino-acid metabolism, and it is interesting in this connection to speculate whether deficiency of folic acid may be related to the increased amino- aciduria often found among epileptic patients taking anti-convulsants (Gordon and Wilson 1963).

The anticonvulsant drugs may act as competitive inhibitors of some cellular enzyme systems, and there are similarities in the molecular structure of phenobarbi- tone, phenytoin sodium, primidone and folic acid. In phenytoin there is a five- membered hydantoin ring and in primidone and phenobarbitone a six-membered pyri- midine ring. The pyrimidine ring is an essential part of the structure of folic acid. Substances may, therefore, resemble natural vitamins sufficiently to replace them as prosthetic groups in enzyme systems, but are unable to perform their essential functions (Hawkins and Meynell 1958, Kershaw and Girdwood 1964).

The lack of such an essential and ubiqui- tous substance as folic acid may well

interfere with growth and development, but there is no definite evidence of this. Hansen et al. (1964) report a patient who developed a macrocytic anaemia due to folic acid deficiency and died from broncho- pneumonia following an accident. At autopsy, degenerative changes were found in the cerebellum, spinal cord and spinal root pouches, but there was no proof that these were the result of folic acid deficiency. When folic acid deficiency is demonstrated in patients on anticonvulsants, the question of the effect of this on the incidence of the epileptic seizures also arises. Chanarin et al. (1960) suggested that in one patient with a megaloblastic anaemia due to folic acid deficiency, the fits might have been precipitated by giving folic acid. They considered it was unproven that barbitu- rates produced their anticonvulsant action by interfering with folic acid metabolism and that this action was counteracted by giving large doses of folic acid. A possible explanation suggested was the depression of all cell function by folk acid deficiency so that the cells of the brain were incapable of massive simultaneous discharge. This might only become possible when this interference had been overcome by ade- quate doses of folic acid.

Reynolds et al. (19663) support a rela- tionship between the therapeutic and anti- folate action of anticonvulsants. In view of the essential role of folic acid in protein synthesis, this may reduce the energy utilisation of neurones or the production of transmitter substances and so help to prevent epileptic seizures. Reynolds et al. (1966~) found that there was an improve- ment in the mental state of many of their patients on anticonvulsants when they were given folic acid. This took the form of an increase in alertness, speed of thought and action, drive, interest, confidence and sociability. They also suggest that a dis- turbance in folic acid and vitamin B1, metabolism, resulting from anticonvulsant

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therapy may result in more serious psychia- tric disorders. In a longer follow-up study (Reynolds 1967) 26 patients were studied. All were taking two or more anticonvulsant drugs and had serum folate levels of less than 5 m ~ g . h i l . The anticonvulsants were continued in the same dosage and folic acid, 5 mg. three times a day, was added. There was a definite improvement in the mental state of 22 of the patients but in 13 the frequency or severity of the fits in- creased and necessitated stopping the vitamin in 9. The same effects were recorded in 6 patients when vitamin B,, was also given by intramuscular injection, with a suggestion that a more sustained response i n the mental state was obtained by treatment with both vitamins.

I n the patients whose fits became worse on treatment with folic acid the vitamin ~ v a s stopped after periods varying from 10 days to 22 months, and in a notoriously variable condition like epilepsy it is difficult to be sure if the increase in the severity and frequency of the fits was definitely the result of the folic acid ?I upp leme nt s. However, there is supporting evidence for the improvement in the mental state. Herbert (1962) persuaded a colleague to take a diet deficient in folic acid. After 4--5 months, the volunteer became forgetful, irritable and suffered fromsleeplessness, but these symptoms were rapidly relieved bq giving folic acid by mouth. Hawkins and Meynell (1958) noted a marked decrease in the incidence of fits after treat- ment of macrocytic anaemia with folic acid, and, occasionally, an improvement in the EEG as well. They maintain that the deficiency of folic acid may be a factor in lowering the threshold for the cerebral discharge producing the epileptic attacks. However, correcting a deficiency of folic acid would only be removing one possible factor leading to the fits and would not affect the original cause of the epilepsy.

A related problem has been raised by

Kohler (1966). Anticonvulsant drugs given to expectant mothers may adversely affect the foetus. Two patients are described whose babies died at 2 days old. Both mothers were taking primidone and pheny- toin sodium, in addition to other drugs. At necropsy, both infants were found to be severely anaemic. There was extensive intracranial haemorrhage without evidence of trauma or asphyxia. It is suggested that the drugs caused disastrous damage to the foetal haemopoietic tissues, while the mothers showed no noticeable effect. Hibbard and Smithells (1965) have shown that the mothers of malformed babies are five times more likely to demonstrate defective folate metabolism than those of normal babies. Folic acid deficiency during pregnancy seems to predispose to foetal malformation, particularly of the central nervous system, and this possibility must be considered when any woman on treat- ment with anticonvulsants becomes preg- nant.

Low serum folate levels can be found in hospital patients not on treatment with anticonvulsants. Grant et al. (1965) exam- ined patients with peripheral neuropathy or myelopathy attending a neurological hospital during a period of one year. Seven patients were found to show evidence of folate deficiency with macrocytosis and megaloblastic anaemia. It is possible that the neurological abnormalities were re- lated to the deficiency but unproven. In some of the cases the neurological disease may have caused the folate deficiency by interfering with appetite.

If folic acid is so necessary for protein synthesis, may this lack not be particularly deleterious in children whose cells are dividing very rapidly, and, in the case of the brain, laying down patterns of be- haviour and the foundation of future skills? Deoxyribonucleic acid (DNA) is now thought to transmit the genetic code to the more labile ribonucleic acid (RNA). The

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latter influences the building up of com- plex molecules, and, if an environmental stimulus transmuted into an electrical impulse, were to alter the sequence of bases in a particular RNA molecule, this might cause structural modifications in the cells and permanently alter their physical proper- ties. A ‘memory trace’ would then exist (Lancet 1965). An increase in RNA has been found in normal cells in response to learn- ing (Gaito 1963) and RNA supplements improve learning and retention in rats (Cook 1964). There is no doubt that patients on large doses of anti-epileptic

drugs do sometimes complain of defective memory, but whether this is related to an interference with the synthesis of neuclei acids by folic acid deficiency must be a matter for further study. It does raise the question whether folic acid supplements should not be given to patients on anti- epileptic treatment, especially during the growing years. If significantly low levels are found these must be rectified, regard- less of the possible relationship between the therapeutic and antifolate action of these drugs. As yet there is no definite proof that this relationship is of significance.

SUMMARY Folic acid deficiency may result from treatment with various antiepileptic drugs. This

seems more likely to be due to an interference with folic acid metabolism than to defective absorption. Seventy-two patients on such treatment were studied. Eleven had serum folate levels below 2 mpg. per ml., 13 between 2 and 3 mpg., 25 between 3 and 5 mpg. and 23 above 5 mpg. per ml. The possible results of this deficiency are discussed, with particular reference to the role of folic acid in protein synthesis. Low folate levels over a long period in a growing child may well have a deleterious effect. Folate levels must also be watched when pregnant women are taking anticonvulsants.

RBSUME Carence en acide folique provenant d’un traitement anticonvulsif

La carence en acide folique peut &re le rtsultat d’un traitement par certains medicaments anti-comitiaux. Ceci parait plus vraisemblablement dii A une interftrence avec le mCta- bolisme de l’acide folique plut6t qu’d une absorption dtfectueuse. On a Ctudit 72 malades qui suivaient ces traitements. Onze malades avaient des taux striques d’acide folique infkrieurs B 2 pg./ml., 13 avaient des taux compris entre 2 et 3 pg./ml., 25 avaient des taux compris entre 3 et 5 pg. et 23 avaient des taux supkrieurs A 5 pg./ml. On discute des rksultats possibles de cette dtficience avec rtfdrence particulibre au r81e de l’acide folique dans la synthbse des prottines. Une rtduction des taux d’acide folique pendant une longue pCriode chez un enfant en pleine croissance pourrait bien avoir un effet nocif. I1 apparait Cgalement ntcessaire de surveiller les taux d’acide folique chez les femmes enceintes prenant des anticonvulsifs.

RESUMEN Una dejiciencia de cicido fdlico como consecuencia de terapkutica nnticonvulsivante

Una deficiencia de icido folico puede resultar de tratamiento con una variedad de drogas antiepilkpticas. Parece que esto resulta mis probablemente de interferencia con el metabo- lis model Bcido folico que de absorci6n defectiva. Se estudiaron setenta y dos enfermos que recibian este tratamiento. Once tenian una cantidad de Bcido folico en suer0 de debajo de 2 mpg./ml, 13 tenian una cantidad de entre 3 y 5 mpg./ml, y 23 tenian una cantidad de encima de 5 mpg./ml. Se discuten 10s resultados posibles de esta diferencia, con referencia

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especial a1 papel del acido folico en la sintesis de proteinas. Valores bajos de acido folico durante un periodo prolongado en un niiio creciente podrian tener un efecto deletkreo. Es necesario tambien observar valores de acido folico cuando mujeres embarazadas toman anticonvulsivantes.

REFERENCES Badenoch, J . (1954) ’The use of labelled vitamin B.12 and gastric biopsy in the investigation of anaemia.’

Pror. roj‘. Soc. Med., 47, 426. Batata, M., Spray, G. H., Bolton, F. G.. Higgins, G., Wollner, L. (1967) ‘Blood and bone marrow changes

in elderly patients with special reference to folk acid, vitamin B.12 iron and ascorbic acid.’ Brit. med. J., ii, 667.

Chanarin, 1. . Elmes, P. C., Mollin, D. L. (1958) ‘Folic acid studies in megaloblastic anaemia due to pheno- barbitone.’ Brit. med. J . , ii, 80.

Laidlaw, J . , Longbridge, L. W., Mollin, D. L. (1960) ‘Megaloblastic anaemia due to phenobarbitone.’ Brit. med. J. , i, 1099.

-- Rothman, D., Watson-Williams, E. J. (1963) ‘Normal forminoglutamic acid excretion in megaloblastic anaemia in pregnancy.’ Lancet, i, 1068.

Cook, L. (Ed.) (1964) Animal Behaviour and Drug Action. Ciba Foundation and the Co-Ordinating Committee for Symposia on Drug Action and the Pharmacological Society. London: Churchill.

Fuld, H., Moorhouse, E. H. (1956) ‘Observations on megaloblastic anaemia after primidone.’ Brit. med. J., i , 1021.

Gaite, J . (1963) ‘D.N.A. and R.N.A. as memory molecules.’ Psychol. Rev., 70, 471. Girdwood, R. H. (1956) ‘The megaloblastic anaemias.’ Qrrart. J. Med., 25. 87.

~ Lenman, J . A. R. (1956) ‘Megaloblastic anaemia occurring during primidone therapy.’ Brit. rned. J.,

~- Thomson, A. D., Williamson, J . (1967) ‘Folate status in the elderly.’ Brit. rned. J., ii, 670. Gordon, N.. Wilson, V. K. (1963) ‘Abnormal amino acid excretion in cerebral disease.’ Develop. Med.

Grant, H. C., Hoffbrand. A. V., Wells, D. G. (1965) ‘Folate deficiency and neurological disease.’ Lancet,

Hansen, H. A., Nordquist, P., Samander, P. ( 1964) ‘Megaloblastic anaemia and neurological disturbances

Harper, H. A. ( 1 959) Review of Physiological Chemistry. Los Altos, California: Lange Medical Publications. Hawkins, C. F., Meynell, M. H. (1958) ‘Macrocytosis and macrocytic anaemia caused by anticonvulsant

Herbert, V. (1962) ‘Experimental nutritional folate deficiency in man.’ Trans. Ass. Amer. Phycns., 75, 307. Hibbard, E. D., Smithells, R. W. (1965) ’Folic acid nietabolisni and human embryopathy.’Lancer, i, 1254. Hobson, Q. J . G., Selwyn, J. G., Mollin, D. L. (1956) ‘Megaloblastic anaemia due to barbiturates.’Lanrer,

Kershaw, P. W., Girdwood, R. H. (1964) ‘Some investigations of folk acid deficiency.’ Scot. rned. J., 9, 201. Klipstein. F. A. (1964) ‘Subnormal serum folate and macrocytosis associated with anticonvulsant drug

Kohler, H. G. (1966) ‘Haemorrhage in the newborn of epileptic mothers.’ Lancet, i, 267. Lanret, Leading Article (1965) ‘Memory molecules.’ Lancet, ii, 1281. Lees, F. (1961) ‘Radioactive vitamin B12 absorption in the megaloblastic anaemia caused by anticonvulsant

Leevy, C . M., Cardi, L., Frank, O., Gellone, R., Baker, H. (1965) ‘Incidence and significance of hypo-

Malpas, J. S., Spray, G. H.. Witts, L. J. (1966) ‘Serum folk acid and vitamin B12 levels in anticonvulsant

Mannheimer, E.. Pakesch, F., Reimer, E. F., Vetter, H. (1952) ‘Die hamatologischen Komplikationen der

Meynell. M. H. (1966) ‘Megaloblastic anaemia in anticonvulsant therapy.’ Lancet, i, 487. Reynolds, E. H. (1967) ’Effects of folk acid on the mental state and fit-frequency of drug-treated epileptics.’

- Hallpike, J . F., Phillips, B. M., Matthews, D. M. (1965) ‘Reversible absorptive defects in anticonvulsant

- - - Chanarin, I . , Milner, G., Matthews, D. M. (1966) ‘Anticonvulsant therapy, folk acid and vitamin B12

- - ~ Milner, G., Matthews, D. M., Chanarin, I . (1966) ‘Anticonvulsant therapy, megaloblastic haemo-

Todd, J., Dewhurst, K. (1964) ‘Macrocytosis and megaloblastic anaemia due to anticonvulsant drugs.’

i , 146.

Child Nerirol., 5, 586.

ii, 763.

combined with folk acid deficiency.’ Acta med. Scand., 176, 243.

drugs.’ Qrrarf. J . Med., 27, 45.

ii, 1079.

therapy.’ Blood, 23, 68.

drugs.’ Quart. J . Med., 30, 231.

vitaminaemia in a randomly selected municipal hospital population.’ Amer. J. din . Nufr., 17, 259.

therapy.’ Brit. med. J.. i, 955.

Epilepsiebehandlung mit Hydantoinkorpern.’ Med. Klin., 47, 1397.

Lnncet, i, 1086.

megaloblastic anaemia.’ J . clitr. Path., 18, 593.

metabolism and mental symptoms.’ Epilepsia, 7, 261.

poiesis and folic acid metabolism.’ Quarf. J . Med., 35, 521.

Brit. J . din. Prart., 18, 479.

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