M onitoring of Drugs in Breast Milk

Transcription

1 ANNALS O F CLIN IC A L A N D LABORATORY SC IE N C E, Vol. 15, No. 2 Copyright 1985, Institute for Clinical Science, Inc. M onitoring of Drugs in Breast Milk STEVEN H. Y. W ONG, P h.d. Department of Laboratory Medicine, University of Connecticut School of Medicine, Farmington, CT ABSTRACT W ith the increasing popularity of breast feeding, the secretion of drugs in breast milk would be of clinical interest. The m erits of breast feeding and the composition of breast milk are outlined. The pharmacokinetics of drugs in breast milk may be described by a 3-com partm ent open model, with breast milk being the third com partm ent a deep com partm ent with lim ited capacity. R ecent clinical studies on secretion of atenolol, propranolol, propoxyphene, phenytoin, carbamazepine, and valproic acid in breast milk showed that the infant ingested dose was insignificant. Thus, nursing m others on these drug therapies should be allowed to breast feed their infants. Owing to the lack of adequate clinical data and methodology for studying the secretion of antidepressants in breast milk, there is a need for a sensitive assay. Thus, a reversed-phase high perform ance liquid chrom atography assay of imipramine and desipram ine in breast milk was outlined, w ith sensitivity of 5 (o,g p e r liter. W ith the instrum entational capability of most clinical laboratories,' it would be possible to perform drug levels m easurem ent in breast milk. In collaboration with other clinicians, a useful data base could be accumulated for making rational decisions on b reast feeding for m others on drug therapy. Introduction W ith the recent specialization of therapeutic drug m onitoring (TDM) in clinical laboratories, th ere is an increasing awareness of the role of the laboratory as well as the instrum entation capabilities needed for m onitoring drug therapies of selected patient groups such as the pediatric and oncologic p a tie n ts.14 The concern of drug secretion into breast milk evolves as a result of: increasing popularity of breast feeding, as much as 53 percent in the U nited States and 70 percent in S w eden,11 occasional case reports 100 on breast milk drug levels; increasingly available pharm acokinetic data; and the availability of instrum entation such as ch rom atography and im m unoassay to perform the quantitation with adequate specificity and sensitivity. Indeed, with m inor m odifications, the p ro ced u res w hich w ere d evelo p ed for m easuring drugs in serum, plasma or urine may also be used for b reast m ilk.4 This article attem pts to update the status of m onitoring of drugs in breast milk as follows: (1) to review the m erits of breast feeding and the composition of breast milk; (2) to outline cu rren t understanding of phar /85/ $00.90 Institute for Clinical Science, Inc.

2 MONITORING OF DRUGS IN BREAST MILK 101 macokinetics of drugs in breast milk; (3) to review several clinical studies from the author s own experience and current literature; and finally, to p resent the tech nical d etail of a rev e rsed -p h a se high p e rfo rm an ce liq u id ch ro m ato g rap h ic (HPLC) assay o f the tricyclic antidepressants in breast milk. Merits of Breast Feeding and Composition o f Breast Milk Breast feeding has been recognized as a co n v en ien t way of nourishing the infant. Besides being an ideal nutritional source, hum an breast milk is amply suitable for th e in fan t s digestive system. During the first six months, the breast milk may be the infant s only nutritional source, supplem ented by vitamin D and flu o rid e. A ccording to W ilso n,11 the advantages of breast feeding and breast milk may be sum m arized in table I. As an ideal n u trie n t for infants, the c o n stitu en ts of b reast m ilk w ould include: water, 88.1 percent, fat, 3.8 percent, protein, 0.9 percent, lactose, 7.0 percent, and ash 0.2 percent. The diam eter of the protein granules is about 300 A. For comparison, the constituents of cow s milk are: water, 87.4 percent, fat, 3.7 p ercent, protein, 3.4 percent, lactose, 4.8 percent, and ash 0.7 percent. The diam eter of the protein granule is about 800 to 1000 A. Sodium, potassium, phosphorus, and iron concentrations of breast milk are lower than those of other species. Zinc is com parable. Iodine is q u ite co n c en tra te d. B reast m ilk ph ranges probably from 6.35 to 7.65, with an average of 7.08, as compared to 6.6 for cow s m ilk.5,17 As evident later in this article, this param eter would affect drug secretion into breast milk, as indicated by the breast milk/plasma (M/P) ratios. O w ing to th e fatty acid and lipid, the q u a n tita tiv e p ro c e d u re w ould usually require extraction/clean-up steps. W hen T A B L E I Advantages o f Breast Feeding and Breast Milk* M a t e rn a l 1. M a t e r n a l b o n d i n g 2. L e s s c o s t t h a n s u b s t i t u t e p r o d u c t s 3. M ore a p p r o p r i a t e c h i l d s p a c i n g o w in g t o d e c r e a s e i n f e r t i l i t y 4. P o r t a b l e a n d r e s i s t s s p o i l a g e w h i l e i n t h e b r e a s t I n f a n t 1. I n f a n t b o n d i n g 2. D e c r e a s e i n c i d e n c e o f d i a r r h e a, w h e e z y b r o n c h i t i s a n d n e c r o t i s i n g e n t e r o c o l i t i s 3. B a c t e r i c i d a l e f f e c t o f ly s o z y m e 4. P r e s e n c e o f C3 a n d C 4 c o m p o n e n ts o f c o m p le m e n t, l a c t o f e r r i n, s e c r e t o r y I g A a n d s m a l l a m o u n ts o f IgM a n d Ig G 5. L o w e r m o r b i d i t y i n f i r s t y e a r o f l i f e 6. B i f i d u s f a c t o r s t i m u l a t e s g r o w th o f L, b i f i d u s i n g u t 7. I r o n b e t t e r a b s o r b e d a n d l e s s a n a e m i a f o u n d 8. L o w e r i n c i d e n c e o f t e t a n y o w in g t o C a /P r a t i o 9. L e s s o b e s i t y a n d l e s s c h a n c e o f m a ra s m u s 1 0. M ore d i g e s t i b l e 1 1. D e c r e a s e i n f o o d a l l e r g y ( c o m p a r e d w i t h c o w 's m i lk w h ic h h a s h i g h $ - l a c t o g l o b u l i n ) 1 2. C o m p o s i t i o n t a i l o r e d t o o r g a n d e v e l o p m e n t ( e. g., r e n a l f u n c t i o n ) a n d g r o w th ( e. g., t e r m c o m p a r e d w i t h p r e m a t u r e i n f a n t ) * R e p r i n t e d w i t h p e r m i s s i o n f r o m W i l s o n, J. T. : D r u g s i n B r e a s t M i l k. New Y o r k, A d i s, , p p com pared to the p ro ced u res for dru g m easu rem en ts in serum or u rin e, the overall recovery is lower. Pharmacokinetics of Drugs in Breast Milk According to W ilson,12 the pharm acokinetics m ay be described by a threecom partm ent open model, m odulated by the infant. The three com partm ents are: (1) central, (2) interstitial and intracellular, and (3) breast milk, postulated to be a deep com partm ent with m oderate to lim ited capacity. The pharm acokinetic factors have b een d eriv ed from data based largely on animal model studies. The relationship of blood flow to drug secretion has not been well established. In general, drug binding to milk protein is less than that of plasma protein. The extent of the non-ionized fraction, free drug crossing the biological m em brane depends on the ph of the breast milk and

3 102 WONG the pka of the drugs, so that an equilibrium exists betw een the drug binding of the aqueous phase in milk and plasma. Generally, the M/P ratios are less than one for the acidic drugs and greater than one for the basic drugs. Drugs m ight be m etabolized by th e m am m ary tissue, such as th e acetylation of sulphanilam ide.10 Atenolol, Propranolol, Propoxyphene and Selected Antiepileptics As outlined in the previous section, several parameters govern drug secretion into breast milk: pka of the drugs, ph of breast milk, and protein binding. In a recent case rep o rt concerning the treatm ent of a severe hypertensive with a [3- blocker, atenolol, the plasma and breast m ilk co n cen tratio n s w ere d e te rm in e d after a single dose of 50 mg and continuous therapy of varying weekly dosages.9 The analytical procedure utilized cycloh exane/l-butanol (55:45) to extract the alkalinized plasm a, follow ed by backextraction w ith O.IN sulfuric acid.16 Aliquots w ere injected for HPLC analysis, using a W hatm an C8 column (0.46 x 25 cm) w ith acetonitrile and diluted phosphoric acid (1:9) as th e m obile phase. Flow rate was 1.2 m L p er min. D etection wavelength was set at 220 nm. After a single 50 m g dose, th e plasm a level peaked at four hours, while the breast milk level peak at about eight hours as shown by figure l. 9 The M/P ratio at four hours was 2.9. This ratio may be rationalized by the high pka of atenolol, 9.5, causing accum ulation of atenolol in breast milk as a result of ion trapping. The infant plasma level (four hours postfeeding) was less than 10 (xg per L. It was concluded that the am ount of atenolol ingested by the infant was not substantial. H ow ever, for infants w ith renal insufficiency, breast feeding by atenololtreated m others should be discouraged. Time in Hours Alter Drug Ingestion F i g u r e 1. Atenolol concentrations in maternal plasma (dotted line) and breast milk (solid line) after a single 50 m g dose. (Reprint with permission from White, W. B., Andreoli, J. W., Wong, S. H. Y., and Cohn, R. D.: Obstet. Gynec. 63:42S 44S (Suppl.), 1984.) In another clinical study involved with a B -blocker, pro p ran o lo l was used for treating hypertensive m others.6 The M/ P ratios w ere 0.33 ± The infant in g ested dose was less 0.1 p e rc e n t of m aternal dose. It was suggested that in utero exposure w ould probably be higher. The plasma and milk levels were d e te rm in e d by using b o th acidic and basic extractions, followed by reversedphase H PLC analyses with a xbondapak C-18 colum n and fluorescence detection. Propoxyphene, a widely used analgesic to relieve postpartum pain, and norpropoxyphene breast milk and plasm a co n cen tratio n s of six h ealth y nursing m o thers w ere d e te rm in e d.3 The M /P ratios of propoxyphene and norpropoxyphene w ere and The m easurem ents w ere carried out by using a C-18 column and 205 nm detection. It was concluded that the neonate would not achieve toxic plasma levels as a result of b reast feeding. Antiepileptics breast milk and plasma levels w ere recently examined in three European studies. Phenytoin and 4-OHphenytoin concentrations w ere quantitated by e ith er gas chrom atography or mass fragm entography.7 The M/P ratios

4 MONITORING OF DRUGS IN BREAST MILK 103 ran g ed from 0.06 to T he infant m ean plasma concentrations ranged from non-detected to 0.12 mg per L, in comparison to m aternal mean concentrations range of 3.23 to mg per L. It was suggested that through breast feeding, infants and small children w ould have in g ested less th an five p e rc e n t of th e dose; thus, m aternal phenytoin therapy of the nursing women m ight be allowed to continue. C arbam azepine b reast m ilk and plasma concentrations were determ ined in 19 epileptics w om en.1 After extraction with dichlorm ethane, the organic phase was evaporated and the residue was dissolved in m obile phase. A nalysis by H P L C was p erfo rm ed by using a reversed-phase Nucleosil-C 18-7 column w ith detection set at 195 nm. The carbam azepine milk concentrations ranged from 1 to 4.8 mg per L (mean concentration = 2.5 mg p er L). The M /P ratio was about Plasm a levels of seven infants w ere less than 1.5 mg per L. It was concluded that for m others u n d e r going carb am azepine therapy, b reast feeding should not be discouraged. Valproic acid breast milk and plasma concentrations w ere determ ined for 16 m others.8 Q uantitation was perform ed by using a sensitive and specific gas chrom atographic/m ass spectrom etric assay. In breast milk, the valproic acid concentrations ranged from 0.4 to 3.9 mg per L (mean = 1.9 ± 1.2 mg per L). The M/P ratios were low and ranged from to Thus, it was suggested that valproic acid treated m others should not be prohibited from breast feeding. From these recent studies, the amount of drug ingested via the m other s breast m ilk by th e infant is sm all. For the healthy infant, such drug ingestion does not seem to result in any noticeable clinical diso rd ers. H ow ever, for m others treated with atenolol, breast feeding of infants w ith renal disorder should be cautioned. Determination of Imipramine and Desipram ine in Breast Milk At present, there is a lack of information on the breast milk levels of the first g en eratio n a n tid e p re ssan ts.2 E a rlier reviews indicated that both im ipram ine and am itriptyline w ere not detected in breast milk. A closer examination of the data in d ic a te d th ese studies u tilized assays w ith inadequate sensitivity (100 jxg per L). Based upon some animal studies using rabbits, substantial amounts of am itrip ty lin e and n o rtip ty lin e w ere detected in milk. Thus, a more sensitive assay w ould be h elpful to resolve this confusion. The following procedure was modified from a previously published, sensitive, and specific reversed-phase H PLC assay of tricyclic antidepressants in plasm a.1315 To two ml of drug-free breast milk inside a series of polypropylene tubes (to p re vent drug adsorption), various amounts (50 to 1000 ng) of im ipram ine and desipram ine were added, followed by 100 xl of m ethanolic internal standard, clom i pram ine (1000 ng). These samples were alkalinzed w ith sodium hydroxide and extracted with five m L of hexane/isoamyl alcohol (99:1). T he organic phase was transferred and back-extracted with 200 jll of dil. phosphoric acid (0.05 percent). Aliquots were injected into a HPLC for rev e rsed -p h a se analysis by using a (xbondapak C-18 colum n, w ith phosp h a te /aceto n itrile (6:4) as th e m obile phase. D etection wavelength was set at 254 nm. Peak height ratios w ere linearly co rrelated to d ru g concen tratio n s in b reast m ilk (im ipram ine: Y = 3.45 x 10 3x , r = , desipramine: Y = 5.90 x 10-3 x , r = 0.996). The sensitivity was five ng for both drugs as com pared to one ng in plasma. Recovery is about 45 percent, lower than those in plasma (65 to 75 percent).15 A typical chromatogram of breast milk extract containing added im ipram ine and desipra-

5 104 WONG drugs in breast milk should be encouraged. A 3-com partm ent open m odel has b een pro p o sed for studying th e p h a r macokinetics. Recent clinical studies of two (3-blockers (atenolol and propranolol), and analgesic (propoxyphene), and three antiepileptics (phenytoin, carbamazepine, and valproic acid) indicated that the am ount of drug ingested by infant through breast feeding is low, and that breast feeding might be continued. However, for nursin g m others on atenolol therapy, caution should be taken for breast feeding an infant w ith renal disorders. In d e e d, for new ly in tro d u c ed drugs, studies of drug secretion in breast m ilk w ould be n e e d e d to estab lish rational guidelines for nursing m others treated on these drug therapies. Acknowledgment The author is indebted to Mr. Elliot Cazes for technical assistance. References F i g u r e 2. Chromatogram of a breast milk extract containing 100 xg per L each of imipramine and desipramine. (Peak identification: 1 = desipramine; 2 = imipramine; and 3 = internal standard, clomipramine). m ine is shown in figure 2. This procedure m ight also be used for assaying am itriptyline and nortriptyline in breast milk. Conclusions M onitoring of drugs in breast milk has been readily achieved by either gas or liquid chrom atography which offers specificity and sensitivity. W ith the increasing popularity of breast feeding and the increasing num ber of new drugs which may be used for long term drug therapy for lactating m others, the studies on the infant exposure to b o th new and old 1. F r o e s c h e r, W., E i c h e l b a u m, M., N i e s e n, M., D i e t r i c h, K., and R a u s c h, P.: Carbamazepine levels in breast milk. Ther. Drug Monit. 6: , J o b e, P. C.: Psychoactive substances and antiepileptic drugs. Drugs in Breast Milk. Wilson, J. T., ed. New York, Adis, 1981, pp K u n k a, R. L., V e n k a t a r a m a n a n, R., S t e r n, R. M., and L a d ik, C. F.: Excretion of propoxyphene and norpropoxyphene in breast milk. Clin. Pharmacol. Ther. 35: , M a n k o, J. F.: Analytical procedures. Drugs in Breast M ilk. Wilson, J. T., ed. New Y o rk, Adis, , p p R a s m u s s e n, F.: The mechanism of drug secretion into milk. Dietary Lipids and Postnatal D evelopment. Galli, C., Jacini, G., and Pecile, A., eds. New York, Raven Press, 1973, pp S m i t h, M. X, L i v i n g s t o n e, I., H o o p e r, W. D., E a d i e, M. J., and T r i g g s, E. J.: Propranolol, propranolol glucuronide, and naphthoxylactic acid in breast m ilk and plasm a. Ther. Drug Monit. 5:87-93, S t e e n, B., R a n e, A., L o n n e r h o l m, G., F a l k, O., E l w i n, C., and S j o q v i s t, F.: Phenytoin excretion in hum an breast m ilk and plasm a le v e ls in nursed infants. Ther. Drug Monit. 4: , v o n U n r u h, G. E., F r o e s c h e r, F. W., H o f f m a n n, F., a n d N i E S E N, M V a l p r o i c a c i d i n b r e a s t

6 milk: How much is really there? Ther. Drug Monit. 6: , W h i t e, W. B., A n d r e o i.i, J. W., W o n g, S. H. Y., and C o h n, R. D.: Atenolol in human plasma and breast m ilk. O b stet. G ynec. 6 3 :4 2 S -4 4 S (Suppl.), W i l s o n, J. T.: Pharmacokinetics of drug excretion. Drugs in Breast Milk. Wilson, J. T., ed. New York, Adis, 1981, pp W i l s o n, J. T.: Prevalence and advantages of breast feeding. Drugs in Breast Milk. Wilson, J. T., ed. New York, Adis, 1981, pp W i l s o n, J. T.: Production and characteristics of breast milk. Drugs in Breast Milk. Wilson, J. T., ed. New York, Adis, 1981, pp W o n g, S. H. Y.: Antidepressants. Therapeutic Drug M onitoring and Toxicology by Liquid MONITORING OF DRUGS IN BREAST MILK 105 Chrom atography. W ong, S. H. Y., ed. N ew York, Marcel Dekker, 1985, pp W o n g, S. H. Y.: Conclusion: Current status and future developm ents. Therapeutic Drug Monitoring and Toxicology by Liquid Chromatography. Wong, S. H. Y., ed. N ew York, Marcel Dekker, 1985, pp W o n g, S. H. Y., and M c C a u l e y, T.: Reversed phase high-performance liquid chromatographic analysis of tricyclic antidepressants in plasma. J. Liquid Chromatogr. 4: , Y e e, Y. G., R u b i n, P., and B l a s c h k e, T. F.: Atenolol determination by high-performance liquid chromatography and fluorescence detection. J. Chromatogr. 171: , Y u r c h a k, A. M. and J u s k o, W. J. : Theophylline secretion into breast milk. Pediatrics 5 7 : , 1976.