LACTOLOGY FOUNDATION

Citric Acid (ATC A09AB04): Toxicological and Lactological Monograph

Active substance: Citric acid
ATC code: A09AB04
ATC subgroup: A09AB — Acid preparations
Therapeutic group: Digestives, including enzymes
CAS number: 77-92-9 (anhydrous citric acid)
Molecular formula: C₆H₈O₇
Molecular weight: 192.12 g/mol
WHO Defined Daily Dose (DDD): 2 g, oral administration

ATC class and general pharmacology

Citric acid is classified in the Anatomical Therapeutic Chemical (ATC) system under A09AB04, within A09AB (acid preparations), A09A (digestives, including enzymes), and A09 (digestives, including enzymes). The WHO ATC/DDD system assigns citric acid an oral Defined Daily Dose (DDD) of 2 g.

Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) is a naturally occurring weak organic tricarboxylic acid. It is widely distributed in plants and animal tissues and is also a normal intermediate of human intermediary metabolism. Its physiological importance derives principally from citrate, its conjugate base, which participates in the tricarboxylic acid (TCA or Krebs) cycle.

Unlike conventional xenobiotic drugs, citric acid is closely integrated into endogenous biochemical pathways. Citrate generated within mitochondria participates in oxidative metabolism and energy production and also serves as an intermediary substrate connecting carbohydrate, lipid, and amino-acid metabolism.

When administered orally as an acid preparation, citric acid primarily exerts physicochemical effects related to acidification and pH modification. Depending on formulation and indication, citric acid and citrate salts are also used as pharmaceutical excipients, buffering agents, alkalinizing systems, urinary pH modifiers, chelating agents, and components of effervescent medicinal preparations. Citric acid additionally has extensive use as a food acidulant and acidity regulator.

The pharmacological and toxicological behavior of citric acid is strongly influenced by formulation, concentration, route of administration, and whether it is administered as the free acid or as a citrate salt.

Following ingestion, citrate can enter normal metabolic pathways and is ultimately metabolized predominantly through the citric acid cycle. Consequently, conventional pharmacokinetic concepts such as persistent parent-drug accumulation or prolonged elimination half-life have limited relevance when citric acid is administered in ordinary physiological or therapeutic quantities.

Citric acid also possesses metal-chelating properties. Citrate can form complexes with calcium and other polyvalent cations. This property contributes to several pharmaceutical and biological applications but may become clinically relevant when very large citrate loads are introduced rapidly into the circulation, particularly in settings involving citrate-containing anticoagulant solutions rather than ordinary oral citric acid therapy.

The toxicological distinction between ordinary oral exposure to appropriately formulated citric acid and high-concentration or non-physiological exposure is therefore important.

WHO/JECFA has historically concluded that citric acid and its calcium, potassium, and sodium salts do not constitute a significant toxicological hazard to humans when used appropriately. An acceptable daily intake (ADI) was designated as “not limited”, reflecting both its established metabolic pathways and the available toxicological evidence.

Toxicological profile

General toxicity

Citric acid has a comparatively low systemic toxicological potential under normal conditions of oral exposure. Its established role in intermediary metabolism, rapid physiological utilization, and long history of dietary exposure are important components of this assessment.

Historical WHO/JECFA evaluations found no significant toxicological hazard from citric acid or its common calcium, potassium, and sodium salts. In one cited study, dogs receiving oral citric acid at approximately 1,380 mg/kg body weight/day for 112–120 days showed no clinical symptoms or evidence of renal injury. Long-term dietary studies in rats likewise did not demonstrate major systemic toxicity at the concentrations evaluated.

These observations should not, however, be interpreted to mean that citric acid is incapable of producing adverse effects. Toxicity is highly dependent upon concentration, route, dose, duration, and local tissue exposure.

Local irritant effects

The principal hazards of concentrated citric acid are local rather than systemic.

Citric acid powder and concentrated solutions can cause irritation of the eyes, respiratory tract, skin, and mucous membranes. PubChem identifies eye irritation as an important hazard, and concentrated solutions may cause substantial ocular injury. Dust inhalation can irritate the nose and throat.

Oral exposure to highly concentrated preparations may produce irritation of the oral, esophageal, or gastric mucosa, potentially presenting as burning discomfort, nausea, abdominal pain, or vomiting.

These effects are mechanistically distinct from systemic poisoning and predominantly reflect the acidity of the preparation and the duration of tissue contact.

Gastrointestinal effects

Therapeutic or dietary quantities of citric acid are generally well tolerated. Excessive oral intake, particularly in concentrated acidic formulations, may cause gastrointestinal discomfort, nausea, abdominal irritation, or diarrhea.

Patients with pre-existing mucosal disease, severe gastroesophageal reflux, oral ulceration, or other conditions in which acidic substances aggravate symptoms may experience greater local intolerance.

Dental effects

Frequent or prolonged exposure of teeth to acidic preparations may promote dental enamel erosion. This effect is attributable primarily to repeated low-pH contact with the tooth surface rather than systemic toxicity.

Accordingly, chronic exposure to acidic drinks, lozenges, solutions, or medicinal formulations containing substantial quantities of citric acid may have greater dental relevance than an equivalent dose consumed rapidly and with limited dental contact.

Electrolyte and metabolic considerations

Citric acid itself is an endogenous metabolic intermediate and ordinary oral exposure does not normally produce clinically important systemic acid-base disturbances.

However, adverse metabolic effects may occur under unusual circumstances involving very large quantities, impaired metabolism, abnormal routes of exposure, or citrate-containing formulations accompanied by substantial electrolyte loads.

The toxicity of citrate salts must also be distinguished from that of free citric acid. Sodium, potassium, or other citrate preparations can produce adverse effects attributable partly or predominantly to their associated cations. For example, excessive potassium citrate exposure carries risks different from those of citric acid alone.

Similarly, rapid systemic citrate exposure, particularly from citrate-containing anticoagulant solutions used in transfusion or extracorporeal procedures, can bind ionized calcium and contribute to hypocalcemia. This phenomenon should not be extrapolated directly to ordinary oral administration of citric acid.

Genotoxicity, carcinogenicity, and reproductive toxicity

Citric acid is a normal metabolic intermediate and has not demonstrated a toxicological profile suggestive of clinically meaningful carcinogenic risk under normal conditions of exposure. Its extensive physiological occurrence and long-established metabolic fate are central to regulatory assessments of its safety.

WHO/JECFA placed particular emphasis on these well-established metabolic pathways when concluding that citric acid and its common salts do not represent a significant toxicological hazard to humans.

There is likewise no established evidence that normal therapeutic or dietary exposure to citric acid produces clinically significant reproductive toxicity.

Toxicological summary

Lactation pharmacology and infant exposure

The lactation assessment of citric acid differs substantially from that of conventional pharmaceutical xenobiotics because citrate is an endogenous physiological metabolite.

Citric acid/citrate participates normally in maternal intermediary metabolism and is therefore fundamentally different from a foreign drug requiring hepatic detoxification and subsequent elimination.

Transfer into human milk

Dedicated pharmacokinetic studies quantifying the transfer of therapeutic oral citric acid into human milk are extremely limited. Consequently, conventional lactation parameters such as a formal milk-to-plasma ratio (M/P ratio), absolute infant dose (AID), and relative infant dose (RID) have not been established for citric acid as a discrete therapeutic agent.

The absence of these measurements should not be interpreted as evidence of hazardous milk transfer.

Instead, exposure assessment must consider that citrate is part of normal human metabolism. An administered quantity of citric acid enters physiological metabolic pathways rather than persisting as an unusual xenobiotic with prolonged systemic circulation.

LactMed provides indirect but clinically useful evidence from preparations containing citric acid. For an oral cellulose–citric acid product, LactMed reports no published maternal milk levels, infant levels, adverse effects in breastfed infants, or effects on lactation. The database considers the combination acceptable during breastfeeding because relevant gastrointestinal absorption from that particular formulation is not expected to result in breast-milk exposure.

LactMed has also evaluated a vaginal contraceptive combination containing lactic acid, citric acid, and potassium bitartrate. It notes that these ingredients are normal components of maternal blood, that systemic absorption following vaginal administration should be minimal, and that no special precautions are required during breastfeeding. No published adverse effects in breastfed infants or effects on milk production were identified in that assessment.

These findings cannot be used to calculate an RID for orally administered citric acid, but they support the broader biological conclusion that ordinary maternal exposure is unlikely to generate clinically significant toxic exposure in a breastfed infant.

Relative infant dose

A conventional numerical RID cannot presently be assigned.

This limitation has two components:

First, adequate published measurements of maternal milk concentrations following isolated therapeutic citric acid administration are unavailable.

Second, citrate is an endogenous metabolite, making the distinction between drug-derived citrate and physiological citrate difficult and of limited clinical relevance at ordinary exposure levels.

Therefore, assigning an estimated percentage RID without direct pharmacokinetic evidence would imply a degree of precision that the literature does not support.

Potential effects in the breastfed infant

No specific pattern of adverse reactions in breastfed infants attributable to maternal therapeutic citric acid exposure has been established.

Theoretical infant exposure resulting from modest changes in maternal citrate metabolism would be expected to be small relative to normal endogenous metabolic handling.

Moreover, citrate itself is not intrinsically foreign to the infant. Infants possess metabolic pathways for citrate utilization, and citrate-containing preparations have been administered directly to pediatric patients in appropriate clinical contexts.

For perspective, a WHO/JECFA review described a randomized trial in infants and children under 36 months in which an oral rehydration solution containing citrate at approximately 1.9 g/L was administered without adverse effects attributable to citrate; the citrate-containing group also recovered from acidosis more rapidly. This represents direct pediatric oral exposure rather than exposure through breast milk and therefore should not be interpreted as a lactation study, but it provides supportive toxicological context.

Effects on lactation and milk production

No evidence has established that therapeutic citric acid suppresses lactogenesis, decreases milk production, alters prolactin physiology, or otherwise adversely affects breastfeeding performance.

LactMed reports no relevant published evidence of effects on lactation or breast milk for the citric-acid-containing preparations it evaluates.

The evidence base remains limited, however, and absence of published adverse effects should be distinguished from proof derived from controlled lactation trials.

Lactological safety assessment and clinical recommendations

Citric acid can be regarded as presenting a low lactational toxicological concern when used orally in conventional therapeutic quantities and appropriate formulations.

This assessment rests primarily on physiological and toxicological considerations rather than extensive direct milk pharmacokinetic studies.

Citric acid is a normal metabolic intermediate, does not have a recognized tendency toward bioaccumulation, enters established metabolic pathways, and has low systemic toxicity at ordinary oral exposure levels. WHO/JECFA has historically assigned citric acid and its common salts an ADI of “not limited,” reflecting their low toxicological concern and well-characterized metabolism.

Available LactMed assessments of citric-acid-containing products are also reassuring. No specific adverse effects in breastfed infants or detrimental effects on lactation have been documented in the cited evaluations, although direct data for isolated oral citric acid remain sparse.

Clinical recommendations

Breastfeeding interruption is not generally warranted solely because a mother receives an appropriately formulated oral citric acid preparation at conventional therapeutic doses.

No pharmacological rationale exists for routine “pump and discard” procedures following ordinary therapeutic exposure.

No specific timing of breastfeeding relative to a maternal citric acid dose is generally required because citric acid is rapidly incorporated into normal physiological metabolism and there is no established clinically relevant post-dose peak in human milk requiring avoidance.

Routine infant laboratory monitoring is not indicated after conventional maternal exposure.

For a healthy term infant, specific clinical surveillance beyond normal pediatric observation is generally unnecessary.

Greater caution is appropriate when citric acid is part of a multi-ingredient medicinal product. In such cases, lactation compatibility should be determined by the complete formulation rather than by citric acid alone. A product containing citric acid together with another pharmacologically active substance may have a completely different lactation risk profile.

Likewise, citrate salts should be evaluated according to both the citrate component and the associated ion. Sodium citrate, potassium citrate, calcium citrate, and other citrate compounds should not automatically be treated as pharmacologically identical to citric acid.

Particular clinical assessment may be appropriate in mothers with severe renal dysfunction, major electrolyte abnormalities, significant acid-base disturbances, or unusual high-dose exposure. In such circumstances, the underlying disease, electrolyte component, dose, and accompanying medications may be more clinically important than citric acid itself.

Accidental ingestion of a highly concentrated preparation should be managed according to the actual exposure and maternal clinical condition. Lactation management in significant poisoning should be individualized, particularly if the mother requires additional medications or intensive medical treatment.

Overall lactological assessment

Conclusion

Citric acid (ATC A09AB04) is compatible with breastfeeding when used in appropriate therapeutic formulations and conventional doses.

The confidence of this conclusion derives more from its endogenous physiological role, established metabolic fate, low systemic toxicological potential, extensive history of human exposure, and available indirect lactation evidence than from dedicated studies measuring citric acid concentrations in human milk.

A quantitative RID cannot currently be provided and should not be artificially estimated in the absence of appropriate pharmacokinetic data.

The clinically important distinction is between ordinary therapeutic exposure, which presents low lactological concern, and excessive, concentrated, unusual-route, or multi-ingredient exposure, for which risk assessment should consider the formulation, dose, route, maternal clinical status, and accompanying pharmacologically active substances.