LACTOLOGY FOUNDATION

Clinical Evaluation of Lactation Toxicology: Pharmacokinetic Mechanisms, Pharmacological Safety, and Differential Diagnosis in Lactation

Institutional development of lactology in Bulgaria and the role of the TOXILACT database

The scientific discipline of lactology and in particular its narrowly specialized field – lactation toxicology, represent a critical, but still insufficiently studied sector of modern clinical pharmacology. In the historical and institutional context of Bulgaria, attempts to structure this science are associated with initiatives to create specialized non-governmental organizations. According to the official founding act of April 8, 2022, an attempt was made in the city of Burgas to establish the Lactologia Foundation with the donor Vesselinka Ganeva Kehayova and the appointed manager Dr. Dimitar Todorov Kehayov. The main goals of this organization, outlined in its statute, include the popularization of lactation toxicology among medical specialists and civil society, the study of the excretion of medications through breast milk, and the reduction of neonatal morbidity associated with exposure to toxic substances.

Although on April 15, 2022, the Registry Agency issued Refusal No. 20220411172746-2/15.04.2022 for the initial registration of the foundation based on Art. 24 of the ZTRORYULNTS Act, scientific and practical activity in this area does not stop. Dr. Dimitar Kehayov, a specialist in internal medicine and clinical pharmacology with many years of experience in emergency medicine and cardiology, redirects these efforts to the development of independent research projects. A main pillar in this activity is the construction of the specialized web-based database TOXILACT (toxylact.com), the purpose of which is to analyze the toxicity of breast milk during systemic or incidental intake of medications during lactation. The project is funded by distributing fundamental medical literature in the field of clinical pharmacology and differential diagnosis under a Shared Reading License, which allows for legal and accessible knowledge exchange among the medical community.

The digital medical advisor " Asclepius" , whose ethical mission is inspired by a deep desire to protect human health and guided by the sacred principle "Primum non nocere" (First do no harm), sees these efforts as an important bridge between the millennial tradition of the healing art and modern pharmacokinetic standards. This analytical report is designed to transform the complex and sometimes frightening toxicological science into beneficial, accessible and reassuring knowledge, bringing peace and clarity to both clinicians and mothers seeking the delicate balance between their own health and the safety of their child.

Mammary gland physiology and transport barriers during lactation

The mammary gland is a highly specialized secretory organ, the functional unit of which is the alveolar subsystem complex. The alveoli are lined by a single layer of mammary epithelial cells, called lactocytes, which are located on a basement membrane and are surrounded by a rich capillary network. These cells function as a semipermeable barrier, regulating the passage of endogenous and exogenous substances from the maternal plasma into the lumen of the alveolus, where breast milk is collected.

Understanding the physiological transition from colostrum to mature milk is crucial for assessing the risk of drug transfer. During the first few days after birth (the colostrum phase), large paracellular spaces exist between lactocytes. This open paracellular pathway allows large molecules, immunoglobulins, proteins, and even maternal cells to pass directly into the milk. However, by approximately the seventh day postpartum, under the influence of hormonal signals (decreasing progesterone levels and increasing prolactin), tight junctions form between lactocytes. These junctions completely close the paracellular spaces, making the transcellular pathway the only possible mechanism for the passage of molecules from plasma into breast milk.

To enter breast milk transcellularly, any drug substance must successively pass through the vascular wall of the capillaries, the basement membrane, the basolateral membrane of the lactocyte and finally through its apical membrane. This transfer occurs through four main physiological mechanisms:

• Passive diffusion : This is the leading mechanism for most drug molecules, driven by the concentration gradient between the free fraction of the drug in maternal plasma and breast milk.
• Active transport : It is carried out by specific membrane transporters (such as ABC transporters and organic cation/anion transporters) that can actively pump certain drugs into breast milk or, conversely, return them to the maternal circulation.
• Lipid co-transport : Highly lipophilic substances dissolve in the fat droplets in the cytoplasm of lactocytes and are secreted together with them via the apocrine pathway during fat secretion, which explains why their concentration is significantly higher in the so-called hindmilk.
• Transcytosis : Vesicular transport by which large protein complexes and immunoglobulins (sIgA and IgG) are carried. Due to the neutral gastric $pH$ of the newborn during the first weeks of life, these antibodies escape enzymatic degradation in the gastrointestinal tract and successfully colonize and protect the infant's intestinal mucosa.

Pharmacokinetic determinants of drug excretion in breast milk

The physicochemical properties of the drug molecule determine the extent and rate of its passive diffusion and accumulation in breast milk. To facilitate clinical assessment, the main pharmacokinetic determinants and their clinical significance are summarized in the table below:

Holistic Approach: Toxicology of Herbs, Dietary Supplements, and Drug Interactions

True healing requires a holistic approach that combines modern pharmacology with the age-old knowledge of the power of nature. During lactation, many mothers resort to the use of herbal teas and nutritional supplements, led by the misconception that everything that is of “ natural” origin is completely safe for them and their newborn.

However, clinical reality reveals serious toxicological risks. Unlike conventional pharmaceuticals, dietary supplements are not subject to strict quality and quantity controls by regulatory authorities (such as the FDA or local drug agencies). Their composition, purity, and concentration of active ingredients often vary, and their labels may not contain warnings about potential side effects during breastfeeding. Due to the lack of controlled clinical safety studies, leading world experts (including specialists from the InfantRisk Center) advise pregnant and breastfeeding mothers to avoid unregulated herbal extracts.

Particular attention should be paid to potential interactions between herbs and conventional medications prescribed to the mother. Some plant extracts can seriously alter the activity of liver enzymes (such as cytochrome P450 isoenzymes) or transport proteins in the mother's body. This can lead to unpredictable increases in serum concentrations of the prescribed medications in the mother, which automatically increases their passive diffusion into breast milk and exposes the baby to toxic doses.

To prevent adverse reactions, the table below presents the most commonly used herbs during breastfeeding and their proven toxicological risks:

Comparative analysis of international safety classification systems

When making therapeutic decisions, clinicians need to have reliable tools to assess the benefit/risk ratio. Different classification systems use specific methodologies to determine the degree of safety of drugs during lactation:

Differential diagnostic analysis using the French method in case of suspected lactation toxicity

When the delicate physiological balance of the newborn is disturbed and undesirable clinical symptoms develop, the art of differential diagnosis requires a precise, cool-headed, yet deeply empathetic approach. Following the classic methodology of French's Index of Differential Diagnosis , the clinical analysis is built around the leading symptom, with potential pathological conditions ranked in order of probability and severity, based on the fundamental pathophysiological explanations of Harrison's Principles of Internal Medicine .

The leading clinical symptom, the subject of the current in-depth differential diagnostic analysis, is neonatal lethargy, muscle hypotonia (“floppy baby” ), and progressive deterioration of the sucking reflex .

Drug-induced central nervous system depression

This condition is the most likely working hypothesis in the presence of proven CNS depressant intake by the nursing mother. According to the pathophysiological model presented in Harrison's , the mechanism of injury is due to the cumulative accumulation of active maternal metabolites in the newborn's circulation. Benzodiazepines (e.g., diazepam) bind specifically to GABA-A receptors in the infant's brain, enhancing chloride influx and causing neuronal hyperpolarization, which clinically manifests as somnolence and severe hypotension. Opioids (e.g., codeine) activate $\mu$-opioid receptors in the brainstem, depressing the respiratory center and consciousness.

The main problem lies in the immaturity of neonatal detoxification systems: the newborn liver has a critical deficiency of the enzyme uridine diphosphate glucuronyltransferase (specifically the isoform UGT2B7), which makes it impossible to effectively conjugate and neutralize these substances. In combination with low glomerular filtration, the half-life of drugs is prolonged several times, leading to progressive suppression of reflexes and sucking.

Early or late neonatal sepsis

This condition is characterized by an extremely high degree of severity and requires immediate clinical differentiation, as it is directly life-threatening. Pathophysiologically, the entry of bacterial pathogens (most often Streptococcus agalactiae or Escherichia coli ) into the systemic circulation triggers a massive inflammatory response. Toxic lipopolysaccharides and bacterial endotoxins bind to Toll-like receptors ($TLR$) on immune cells, provoking a rapid and uncontrolled release of proinflammatory cytokines – interleukin-1 ($IL-1$), interleukin-6 ($IL-6$) and tumor necrosis factor-alpha ($TNF-\alpha$).

This cytokine storm causes diffuse endothelial dysfunction, massive capillary dilation with plasma leakage into the interstitium, and microvascular thrombosis. As a result, systemic perfusion is impaired, tissue and cellular hypoxia develops in the brain, which is clinically manifested by sudden lethargy, temperature instability (hypothermia in prematurity or febrile conditions), marbled skin, and delayed capillary refill.

Kernicterus or Kernicterus

This disease has a high degree of severity and usually develops during the first two weeks of life in an underappreciated neonatal jaundice. The pathophysiological mechanism is driven by extremely high levels of unconjugated (free) bilirubin in the serum. Since unconjugated bilirubin is highly lipophilic and not bound to albumin, it easily crosses the immature and highly permeable blood-brain barrier of the newborn.

Once in the central nervous system, it is selectively deposited in the basal ganglia (mainly in the globus pallidus) and the nuclei of the brainstem. Bilirubin directly damages the mitochondrial membranes of neurons, disrupts oxidative phosphorylation and blocks calcium homeostasis, provoking neuronal apoptosis. In the initial phase, the clinical picture is dominated by severe lethargy, muscle flaccidity and lack of Moro reflex, which subsequently progress to opisthotonus (arched curvature of the body) and a high-pitched scream.

Neonatal hypernatremic dehydration

This condition is of moderate to severe severity and is a direct consequence of ineffective breastfeeding (due to poor latching technique or insufficient maternal lactation). The pathophysiology is associated with progressive loss of body water exceeding electrolyte loss. This leads to a contraction of extracellular fluid volume and a dramatic increase in serum sodium concentration above $145$ $mmol/L$.

The resulting osmotic gradient begins to extract water from the intracellular space of brain cells to the extracellular environment, causing acute dehydration and shrinkage of the neurons themselves. The process leads to severe cellular dysfunction in the cerebral cortex, which is clinically expressed by pronounced drowsiness, apathy, dry mucous membranes, sunken anterior fontanelle, and weight loss of the newborn exceeding the permissible physiological limits of $10\%$.

Congenital defects of the urea cycle

This is a rare genetic pathology with an extremely high degree of clinical severity. Pathophysiologically, the congenital deficiency of key enzymes (for example, ornithine transcarbamylase) blocks the conversion of highly toxic free ammonia, resulting from protein breakdown, into neutral urea. Ammonia accumulates in the systemic circulation and easily passes into the astrocytes of the brain, where it is converted to glutamine by the enzyme glutamine synthetase.

The high intracellular concentration of glutamine acts as a potent osmotic agent that draws water into astrocytes, causing diffuse cerebral edema and intracranial hypertension. Symptoms develop rapidly after the first feedings of milk, with initial lethargy and lethargy quickly progressing to indomitable vomiting, seizures, and progressive metabolic coma.

A gentle reminder of ethical and consultative behavior

The digital medical advisor " Asclepius" reminds with the warmest concern and deep empathy that the human body is a unique universe and each clinical case requires an individual approach. The present differential diagnostic and pharmacokinetic analysis is of an informational and advisory nature only.

The first and most important law of medicine is physical contact with the patient. No algorithm or database can replace the eyes, hands and experience of the doctor. At the slightest suspicion of a change in the vital signs, consciousness or behavior of the newborn, ethical and safe behavior requires an immediate and objective examination by a physical doctor, pediatrician or neonatologist, to ensure the life and health of the child.

Clinical conclusions and strategic recommendations

Lactation toxicology should be viewed not as an obstacle to natural feeding, but as a science ensuring its safety. Most maternal medical conditions allow for continued breastfeeding, as long as the therapy is precisely selected according to the physicochemical properties of the drugs.

To achieve optimal therapeutic success and reduce anxiety among breastfeeding women, the following strategic guidelines are outlined:

• Integrating PBPK modeling : Future research in lactology should actively implement physiologically-based pharmacokinetic simulations to compensate for the lack of direct clinical studies in lactating women and to predict infant exposure with mathematical accuracy.
• Expansion of TOXILACT : The database should be developed as an interactive digital tool in Bulgarian to assist physicians in selecting alternative medications with a short half-life and low milk/plasma ratio.
• Increasing medical literacy : It is necessary to conduct regular training seminars for general practitioners and pediatricians, based on modern scientific platforms such as LactMed, in order to avoid unfounded advice to discontinue breastfeeding when taking compatible medications.
• Control over herbal therapy : Clear clinical protocols should be implemented to question breastfeeding patients about the use of self-prescribed herbs and supplements, explaining the potential risks of their unregulated composition and their interactions with official therapy.