Significance of milk pH in newborn infants

Impact of Milk pH and Fat Content on the Prediction of Milk-to-Plasma Ratio: Knowledge Gap and Considerations for Lactation Study Design and Interpretation

BACKGROUND AND OBJECTIVE

Different empirical lactation models have been published to predict the milk-to-plasma (M/P) ratio of drugs to gain knowledge on the extent of drug distribution to the breastmilk. M/P ratios will likely vary across the lactation period due to differences in physiological milk pH and fat content, which are not routinely reported in clinical lactation pharmacokinetic studies. This work aims to evaluate the sensitivity of two (a theory-based phase distribution and a log-transformed regression) lactation models for M/P prediction at different physiological milk pH and fat content.

METHODS

A literature search was conducted to collate reported M/P ratios for different drugs and their physicochemical parameters required for the prediction of the M/P ratio. Two distribution models were used for M/P ratio predictions. The M/P ratio of drugs was predicted under the physiological milk pHs of 6.8, 7.0, 7.2, and 7.4 and at of 1%, 3%, and 6% fat content. Calculated M/P ratios were compared with the observed M/P ratios.

RESULTS

A total of 200 M/P ratios for 130 compounds (40 acids and 90 bases) were collected from clinical studies and included in the analysis. For both model, precision decreases and bias increases outside the milk pH range 7.0-7.2 and fat contents more than 3%. Significant variability exists in the observed M/P ratios. Both milk pH and fat content are important parameters for model prediction.

CONCLUSION

Calculated M/P ratios are influenced by multiple covariates, including milk pH and fat content. The phase distribution model is less sensitive to these covariates than the log-transformed model, especially for acidic compounds. For complex matrices such as breastmilk, the actual physiological parameters of the sampled milk, at least milk fat and pH, and their distributions are required covariates to improve the prediction outcomes, design lactation pharmacokinetic studies, and inform the potential breastfed infant dose.

Human milk pH is associated with fortification, postpartum day, and maternal dietary intake in preterm mother-infant dyads

OBJECTIVE

To compare pH of human milk types (mother's own milk (MOM), pasteurized donor human milk (PDHM), fortified MOM, and fortified PDHM) fed to preterm infants.

STUDY DESIGN

This observational study consisted of 63 mother-infant dyads < 34 weeks gestation. Human milk samples (n = 245), along with maternal factors, were collected for pH analysis. pH of MOM was analyzed over the course of lactation accounting for fortification status, postpartum day, and storage conditions.

RESULTS

Mean pH of MOM was slightly acidic at 6.60 ± 0.28, which was significantly higher (p < 0.05) than other milk types. pH of MOM varied by fortification, postpartum day, and maternal vegetable/fiber intake. There was a significant interaction between fortification status and postpartum day; pH of MOM decreased over time, while pH of fortified MOM increased over time.

CONCLUSION

pH of human milk varied by type. pH of MOM was significantly associated with fortification status, postpartum day, and maternal vegetable/fiber intake.

Acidified Feedings in Preterm Infants: A Historical and Physiological Perspective

The use of acidified milk for feeding infants has a long, interesting history that appears to have developed from the use of buttermilk in Holland as early as the late 19th century for feeding infants with diarrhea. Physicians in the early 20th century assumed that the observed benefits were from buttermilk's acidity leading to the practice of acidifying infant formula. The historical and physiological perspective on the use of acidified infant formula is now especially relevant with the emergence of an acidified liquid human milk fortifier for preterm infants. Here, we review that history, with a deeper dive into the contemporary research on the use of acidified human milk fortifiers, the consequences for preterm infants, and the underlying physiological mechanisms. KEY POINTS: · In the late 19th and early 20th century acidified feedings were in common use for sick infants.. · By the mid-20th century, acidified feedings tested in preterm infants resulted in acidic physiology and poor growth.. · The current practice of acidifying feedings in preterm infants has been associated with metabolic acidosis, poor tolerance, and delayed growth..

Comparative effectiveness of liquid human milk fortifiers: A systematic review and meta-analysis

OBJECTIVE

To determine the effectiveness of liquid human milk fortifiers (HMFs) derived from exclusive HM or hydrolyzed protein on growth, necrotizing enterocolitis (NEC), or late-onset sepsis in North American very low-birth-weight (VLBW) infants compared with powder HMFs (control).

METHODS

Prospective trials published between 2009 and 2020 were systematically reviewed, and meta-analysis was conducted by using a random-effects model.

RESULTS

Five studies were identified for up to 591 participants across 39 centers. Study treatments included whey or casein hydrolysate HMF and exclusive HM HMF. Infants fed whey or casein hydrolysate HMF had growth differences compared with the control. No differences were found across treatments in regard to NEC or sepsis.

CONCLUSION

Very low-quality evidence suggests greater linear growth in VLBW infants fed whey hydrolysate liquid HMF, as well as greater weight gain in those fed casein hydrolysate HMF, compared with the control. Additional prospective, multicenter randomized controlled trials are needed to confirm these estimates because of sparsity of evidence. There is insufficient evidence to support HMF decisions regarding NEC or late-onset sepsis prophylaxis.

Composition of human breast milk in acute kidney injury

BACKGROUND

Breastfeeding is a widely encouraged practice due to its benefits for mother and the infant. Little is known about the impact of disease states, such as kidney dysfunction and childbirth complications, on the composition of breast milk.

METHODS

We describe a case of a 35-year-old woman who suffered a postpartum hemorrhage, was administered a contrast dye prior to computer tomography, and developed an acute kidney injury. Using nuclear magnetic resonance spectrometry, we measured composition of milk in acute kidney injury. The amount of dye secreted into milk was determined using a spectroscopic assay.

RESULTS

Here we show that acute kidney injury results in changes in milk composition, but it does not significantly affect major macronutrients. We also determine that iodinated computer tomography contrast dye does not accumulate in milk in appreciable amounts.

CONCLUSION

Acute kidney injury has impact on breast milk. Intravenous administration of computer tomography contrast dye does not result in significantly elevated levels in milk.

Effects of Oketani Breast Massage on Breast Pain, the Breast Milk pH of Mothers, and the Sucking Speed of Neonates

PURPOSE

This study was done to test the effects of Oketani breast massage on breast pain and breast milk pH of mothers, and sucking speed of neonates.

METHODS

A nonequivalent control group and a pretest-posttest design was used. Postpartum mothers complaining of breast pain were recruited at a postpartum care center. The application of Oketani breast massage by an Oketani massage therapist was the experimental treatment. The control group received the conventional massage technique from a nurse at the postpartum care centre. The collected data were analysed using a chi2-test and a t-test with the SPSS WIN 12.0 program.

RESULTS

The participants were homogeneous in age, gestation period, and birth weight. Breast pain (t=8.384, p<.001) was significantly relieved, and breast milk pH (t=4.793, p<.001) was significantly increased in the experimental group compared to the control group. The sucking speed of the neonates in the experimental group was significantly increased compared to the control group (t=9.920, p<.001).

CONCLUSION

These findings indicate that Oketani breast massage is effective in relieving breast pain and increasing breast milk pH as well as the sucking speed of neonates.

Modelling of the passage of drugs into milk

Pharmacokinetic modelling of plasma to milk transfer of drugs has assisted our understanding of the milk to plasma ratio (M/P) and pitfalls associated with it. The most useful way of measuring M/P ratios is, however, by model independent analysis. Physiological models have been proposed to enable the prediction of M/P ratios. The most accurate in prospective performance is the log-transformed phase distribution model. This model, developed by stepwise multiple linear regression analysis, also assists in the understanding of the relative contribution of the various physiological factors involved in the distribution of drugs into milk.

Changes in milk pH and bicarbonate during 20 days of lactation in the guinea pig

Milk samples were obtained from lactating albino guinea pigs after 4 to 6 h of separation from their offspring. The samples were collected in 5-ml glass vials and capped immediately. They were transported rapidly to a pH-gas analyzer for measurements of pH, bicarbonate, base excess, and partial pressure of CO2. Eight guinea pigs were sampled daily for 20 d for a total of 160 observations. Analysis of variance indicated animal and day differences. Regression analyses over days revealed equations of best fit to be quadratic, although stepwise trends were observed in the data as well. The quadratic model for pH was Y(pH) = 6.996 - .057X + .002X2, where X was day of lactation (R2 = .54). The model for bicarbonate was Y (-HCO3 in milliequivalents per liter) = 8.896 - .659X + .0202X2 (R2 = .60). For base excess, the model was Y (in milliequivalents per liter) = -22.65 - 1.99X + .069X2 (R2 = .58). The model for partial pressure of CO2 was Y (millimeters of Hg) = 38.63 + 1.06X - .080X2 (R2 = .33). Decreases in pH and bicarbonate were parallel to changes in mammary epithelial cells of guinea pigs in which degeneration of mechanisms responsible for two important ingredients relating to milk volume occur. These have been identified previously as reductions in lactose and potassium. Synthesis of the enzyme carbonic anhydrase with its resultant bicarbonate production may be related in some way to these components of milk secretion.

Midazolam and nitrazepam in the maternity ward: milk concentrations and clinical effects

1. In a randomized study of 22 patients in a maternity ward, the residual concentrations of two hypnotics, midazolam 15 mg p.o. and nitrazepam 5 mg p.o., in early breast milk and plasma were measured 7 h after intake on day 2 to day 6 postpartum. Milk pH, milk fat and binding to plasma proteins were also investigated. Sleep variables were scored on questionnaires. 2. No measurable (less than 10 nmol l-1) concentrations of drug in milk were found in the group receiving 15 mg midazolam at night, either after the first night or after the fifth night. Additional investigations in two mothers demonstrated that midazolam and its hydroxymetabolite disappeared rapidly from milk with undetectable levels after 4 h. The mean (s.d.) milk to plasma ratio for midazolam was 0.15 (0.06) in six paired samples. It may be assumed that practically no midazolam is transferred via early milk to the baby if the baby is nursed more than 4 h after tablet intake. 3. Milk nitrazepam concentrations increased significantly from the first (30 nmol l-1) to the fifth morning (48 nmol l-1) in the group receiving 5 mg nitrazepam at night. The mean (s.d.) milk to plasma ratio of nitrazepam after 7 h was 0.27 (0.06) in 32 paired samples, and did not vary from day 1 to day 5. Plasma protein binding of nitrazepam in puerperal women was found to be lower than that in plasma of healthy controls. The average amount of nitrazepam received by the breast-fed baby in the morning was calculated to increase from 1 to 1.5 micrograms 100 ml-1 breast milk, from days 1 to 5. In the mothers nitrazepam was associated with better hypnotic effect, but a higher incidence of complaints than midazolam. 4. Milk pH, assuming anaerobic conditions, was found in 10 women to average 6.91 +/- 0.09 (s.d.) on days 2-6 postpartum, which is less than previously reported. 5. It is concluded that both hypnotics may be used safely for a few days in the maternity ward. However, possible long-term effects in the suckling infant of small doses of benzodiazepines ingested with breast milk remain to be investigated.

Prediction of drug distribution into human milk from physicochemical characteristics

Decisions about the safety of breast feeding during maternal ingestion of drugs require knowledge of the amount of drug which might be present in the milk. For many drugs this has not been studied, and mothers are usually advised against breast feeding. In many cases this is undoubtedly unnecessary, as the total dose to which the baby is exposed is often negligible. It would be very helpful, therefore, to be able to predict the approximate amount of drug which might be present in milk. Existing theory of pH partitioning enables estimation of the distribution of unbound drug, i.e. milk: plasma unbound ratios. However, these ratios are poor estimates of the concentration ratios for whole milk, because whole milk contains proteins and lipid in which drugs will distribute in amounts which depend on their particular physicochemical properties. To predict the milk: plasma concentration ratios for whole milk the amount of drug present in the protein and lipid phases must be considered along with the unbound drug distribution. A 'phase distribution model' has therefore been developed which permits estimation of whole milk: plasma concentration ratios. The model requires a knowledge of the unbound drug concentration ratio, the plasma and milk unbound fractions and the milk lipid: ultrafiltrate partition coefficient. Evaluation of the model by comparison of predicted whole milk ratio values with literature milk: plasma area under the curve (AUC) ratios indicated a trend to overprediction for acidic and neutral drugs and underprediction for basic drugs. Transformation of the phase distribution equation by taking logarithms results in a relationship which can be analysed by multiple linear regression to derive predictive equations for acidic and basic drugs which take into account the relative contributions of each component of the model. Regression of the logarithms of the literature milk: plasma AUC values against the independent variables resulted in good correlations for acidic and basic drugs. The independent variables explained 93.1% and 82.9% of the variance in the values for acidic and basic drugs, respectively, with random scatter of residuals. The equations, together with those to predict unbound fractions of drug in milk and milk lipid: ultrafiltrate partition coefficients, enable the ratio of the milk: plasma AUCs to be estimated for any acidic or basic drug for which the distribution into human milk is not known, using the pKa, octanol: water partition coefficient and plasma protein binding values of the drug. The data set for neutral drugs (n = 3) was too small to develop a correlation equation.(ABSTRACT TRUNCATED AT 400 WORDS)

Diet and faecal flora in the newborn: casein and whey proteins

Despite the extensive modifications of cows' milk to make an infant formula resemble human breast milk, we showed in a previous study that the faecal flora of breast fed babies still differs substantially from that of formula fed babies. This paper describes the effects that differences in the distribution of whey proteins and caseins exert on the faecal flora. Faecal flora was examined in 33 babies receiving a whey formula, 29 babies receiving a casein formula, and 38 breast fed babies. Subsequently fewer babies in each group were studied at weeks 7, 11, and 15. More whey fed babies were colonised with bifidobacteria at 14 days compared with the casein fed group, more casein fed babies were colonised with bacteroides (at 14 days), and more had a dominant growth of enterococci (at week 7). It seems therefore that during the first two months that the whey predominant formula induced a faecal flora generally closer to that of breast fed babies than did a casein formula.

Relationship between human milk lipid-ultrafiltrate and octanol-water partition coefficients

The distribution into human milk lipid of 16 drugs with widely varying lipophilicity is reported. There is a high degree of correlation between milk lipid-ultrafiltrate and octanol-water partition coefficients, measured at 37 degrees C, provided digoxin and prednisolone are excluded. These steroid-based molecules may interact with free fatty acids in milk, forming micelles and thus perturbing the milk lipid-ultrafiltrate relationship. Equations are described which enable estimation of drug distribution into milk for lipid-soluble drugs, based on drug pKa and octanol-water partition coefficients.

The binding of drugs to major human milk whey proteins

The binding of nine drugs of diverse physicochemical characteristics to major human milk whey proteins is reported. This group included acids, bases and neutral drugs. No drug bound to alpha-lactalbumin, which is the protein present in greatest concentrations in mature milk. Four drugs, diclofenac, phenytoin, prednisolone and warfarin, bound to albumin but to a much lesser extent than in plasma, consistent with quantitatively less albumin in milk. None of the basic drugs studied bound to albumin. Five drugs, atenolol, diclofenac, prednisolone, propranolol and warfarin, bound to lactoferrin though the extent was minimal except for diclofenac. This group included acids, bases and neutral drugs.

Drugs in human milk. Clinical pharmacokinetic considerations

Drugs ingested by a lactating mother would be expected to appear in human milk to some extent and be ingested by a breast-feeding infant. Drugs pass from maternal plasma into milk by passive diffusion and are distributed within the aqueous, protein and lipid phases of milk. Distribution into milk will be affected by physiochemical characteristics of the drug: acid-base characteristics, relative protein binding in plasma and milk, and lipid solubility, as well as milk composition. The milk-to-plasma concentration ratio is the most commonly quoted index of drug distribution into human milk. However, calculation of the daily infant dose of drug ingested in milk, and from this the dose in milk relative to the maternal dose on a weight-adjusted basis, is a more relevant indicator of infant exposure to a drug. This is particularly true for drugs with a high volume of distribution, for which only a small proportion of the mother's dose is contained within the plasma and available for distribution into milk. A better indication of infant exposure to a drug is the steady-state plasma drug concentration in a breast-feeding infant, the major determinants of which are the dose rate (via milk) and the oral availability and clearance in the infant. Although in neonates the rate of absorption may be different from adults, there is little evidence that its extent is significantly different. Clearance, however, is impaired in very young infants, particularly if premature. The decreased clearance would result in a proportional increase in steady-state plasma concentrations in the breast-feeding infant. Consideration of the dose ingested in milk and the approximate clearance in infants of different ages allows estimation of likely steady-state plasma concentrations in breast-feeding infants. From these considerations, recommendations regarding the safety of drugs during breast-feeding can be made. Drugs which are very toxic or have dose-independent toxicity should be considered separately. Recommendations regarding 'social' drugs such as nicotine, alcohol, caffeine and theobromine are particularly difficult, as doses are uncontrolled and vary variable.

Prediction of drug concentrations in human skim milk from plasma protein binding and acid-base characteristics

1. Protein binding in human skim milk of a series of seven drugs with diverse plasma protein binding and acid-base characteristics, was measured by ultrafiltration. 2. A mathematical relationship between plasma and skim milk unbound fractions was established using measured values from this study along with values from the literature. 3. The relationship enables prediction of unknown protein binding values of drugs in skim milk from known plasma protein binding values. 4. Knowledge of milk protein binding enables a more accurate assessment of total milk concentrations than is available from existing theory which is limited to prediction of unbound drug.

Principles of drug biodisposition in the neonate. A critical evaluation of the pharmacokinetic-pharmacodynamic interface (Part I)

Rational pharmacotherapy is dependent upon an understanding of the clinical pharmacokinetic and pharmacodynamic properties of the drugs employed. Although the available data on drug biodisposition and action in the neonate have increased considerably in the last few years, pharmacokinetic-pharmacodynamic interactions for many drugs remain poorly understood. The ontogeny of drug absorption, distribution, metabolism, and elimination are addressed in this review. Drug absorption from any site depends upon both the physicochemical properties of the drug and a variety of patient factors. Absorption of orally administered drugs may be affected by changes in gastric acidity and emptying time as well as by bile salt pool size, bacterial colonisation, and extraintestinal disease states such as congestive heart failure. Factors affecting drug absorption following intramuscular, percutaneous, and rectal administration are also discussed. Drug distribution in the neonate is influenced by a variety of important and predictable age-dependent factors. The developmental aspects of protein binding and body water compartments are described. Additionally, hepatic drug metabolism assumes an important role in understanding the pharmacokinetic and pharmacodynamic properties of many compounds. Certain biotransformation pathways, including hydroxylation by the P450 mono-oxygenase system and glucuronidation, demonstrate only limited activity at birth, while other pathways, such as sulphate or glycine conjugation, appear very efficient at birth. Elimination of drugs excreted unchanged in the urine is dramatically reduced in the newborn, compared with older infants and children, due to immaturity of both glomerular filtration and tubular secretory processes. The glomerular filtration rate remains markedly reduced prior to 34 weeks gestational age, increasing as a function of post-conceptual age until adult values are achieved by approximately 2.5 to 5 months of age. Tubular secretory capacity is also limited at birth, approaching adult values by approximately 7 months of age. Published reports describing the pharmacokinetics and pharmacodynamics of commonly used drugs in the neonatal period, as well as differences in drug biodisposition among premature infants, full term neonates, and older infants and children, are reviewed. Our recommendations for neonatal drug therapy are based upon a critical interpretation of these data, an understanding of fetal development and maturational processes, and an understanding of how disease states may affect drug biodisposition in the neonate.

Milk pH, acid base status, and growth in babies

Metabolic acidosis is common in babies fed cows' milk-based formulae. Therefore the effects of adding alkaline salts (sodium and potassium citrate) to a demineralised whey formula were studied in vitro and in 26 low birthweight babies fed on the formula or formula plus citrate. The alkali altered the pH and titratable acidity to a value nearer human milk but it increased the buffering capacity to a value further away. This may effect the bacterial flora of the intestine. The babies fed on formula plus citrate did not make greater gains in weight, length, head circumference, skinfold thickness, or midarm muscle circumference, although they had a greater blood base excess. Some of these babies developed a mild metabolic alkalosis and 3 had hyponatraemia despite their increased sodium intakes. These babies also had lower levels of plasma transferrin but showed no differences in urea, albumin, cholesterol, and calcium levels. No baby fed on the demineralised whey formula without added citrate had a base deficit exceeding 5 mmol/l; late metabolic acidosis is less common in babies fed on this formula and the routine addition of alkali can have untoward metabolic effects.

Metabolic acidosis and infant feeding

Most cows' milk based formulae for infant feeding present a greater acid load to the infant than breast milk. To determine the effect of this difference the acid base state of 180 healthy term infants was measured on the sixth day of life and related to the type of feed. Those infants fed on cows' milk formula (SMA) had a mean pH of 7-34 +/- 0-05 and a base deficit of 8-8 +/- 3-1, while those fed on breast milk had a mean pH of 7-38 +/- 0-05 and a base deficit of 5-6 +/- 3-1. The difference between the two groups of infants was significant for both these measurements. Metabolic acidosis was defined as a base deficit greater than 10 mmol/l. Seventy-four per cent of the 34 infants who were acidotic at six days were bottle-fed. There was a significant correlation between the pH of the feed and the degree of acidosis in the infant as measured by the base deficit. The findings suggest that when breast milk is not available a pH-adjusted milk formula would be desirable for preventing and treating neonatal metabolic acidosis.

Gastric pH and microflora of normal and diarrhoeic infants

The microflora and pH of gastric contents were determined in breast-fed and in bottle-fed normal infants, in well nourished infants with acute diarrhoea and in infants with chronic diarrhoea and protein-calorie malnutrition. The last group of infants was reevaluated after recovery from diarrhoea and protein-calorie malnutrition. A bactericidal pH effect below 2-5 was observed. Bottle-fed controls had low pH values and low bacterial concentrations, whereas infants with chronic diarrhoea and protein-calorie malnutrition had high pH values and bacterial overgrowth, essentially of Gram-negative bacilli. After recovery, the only remaining alteration was the frequent isolation of yeast-like fungi in low concentrations. Infants with acute diarrhoea, except for the isolation more frequently of yeast-like fungi, presented no alterations; this seems to indicate that pH alterations and Gram-negative bacilli overgrowth occurred during the evolution of the disease to a chronic state. Breast-fed normal infants had hydrogen-ion concentrations similar to those of the chronic diarrhoea group, but without Gram-negative bacilli overgrowth, suggesting that other factors, besides pH, regulate bacterial growth in the gastric contents of these groups of infants.

Inhibition of Escherichia coli by bovine colostrum and post-colostral milk. II. The bacteriostatic effect of lactoferrin on a serum susceptible and serum resistant strain of E. coli

Two strains of Escherichia coli were inhibited by complement-inactivated cow serum and to a lesser extent by precolostral calf serum devoid of specific antibodies. They were not inhibited by undiluted colostral whey or milk but colostral whey became bacteriostatic after dialysis or dilution in Kolmer saline and addition of precolostral calf serum or lactoferrin. The inhibition in all these fluids was due to iron-binding proteins (transferrin or lactoferrin). Undiluted dialysed milk was not inhibitory because of its low content of lactoferrin but became inhibitory after addition of 1 mg/ml of lactoferrin. The lack of inhibition in undiluted whey is due to the high concentration of citrate in colostral whey (and milk) and it is suggested that citrate competes with the iron-binding proteins for iron and makes it availabe to the bacteria. Addition of bicarbonate, which is required for the binding of iron by transferrin and lactoferrin, can overcome the effect of citrate; hence, the bacteriostatic effect of cow serum and precolostral calf serum is due to the presence of both transferrin and bicarbonate as well as the low lefel of citrate.

Breast milk substitute: a bacteriological study

The increased susceptibility of infants fed on cows' milk preparations has been attributed, at least in part, to differences in the nature of the large-bowel content-owing to the acidity of the faeces and their high content of Lactobacillus bifidus. In an attempt to mimic these features of the breastfed infant in one who is fed artificially, a breast milk substitute was devised which resembles breast milk in several important ways. When this material was fed to newborn infants the faeces developed the characteristics of those of the breast-fed child.