Leucovorin Calcium Pharma Grade API, CAS 1492-18-8, is supplied as a non-sterile oral-grade powder and as a micronized injectable-grade powder. The molecular formula of the pentahydrate is C20H21CaN7O7·5H2O; the compound is the calcium salt of 5-formyl-5,6,7,8-tetrahydrofolic acid and is controlled against the Leucovorin Calcium monographs of USP, Ph. Eur., and JP. The commercial model designation should be selected as oral non-sterile powder, injectable non-sterile micronized powder, or injectable sterile micronized powder; this distinction drives microbiological, particulate, and particle-size controls. The API is not a finished-dosage presentation; pH adjustment, tonicity adjustment, particle-size control, and terminal sterilization are performed downstream. Oral-grade material is processed into tablets, capsules, and granules by direct compression, wet granulation, dry granulation, or roller compaction. Injectable-grade material is dissolved in Water for Injection, filtered through a sterilizing-grade membrane, and filled aseptically. In both grades, the reduced pteridine ring and 5-formyl substituent impose controls on oxygen, light, trace transition metals, and prolonged exposure to acidic or alkaline aqueous media. Packaging uses light-protective double polyethylene liners inside HDPE or aluminum drums; oral material is shipped with desiccant, and injectable material is shipped with sterile barrier closures.

What Distinguishes Leucovorin Calcium from Folic Acid in Reduced-Folate Drug Design?

Folic acid, as pteroylglutamic acid, is an oxidized precursor that requires dihydrofolate reductase–mediated conversion before it can participate in one-carbon transfer. Leucovorin calcium already contains the 5-formyl-5,6,7,8-tetrahydrofolate reduced pteridine ring and therefore bypasses that enzymatic step; this is the basis for its use in methotrexate rescue and fluorouracil potentiation. From a manufacturing standpoint, the difference is not only clinical. Folic acid is a relatively stable oxidized molecule that can be processed under ordinary light and air exposure, whereas leucovorin calcium is oxidation-prone and requires light-protective containers complying with USP <671> and nitrogen-blanketed aqueous conditions. In tablet manufacture, folic acid is commonly added as a micronized premix because the dose is in the tens of micrograms; leucovorin calcium oral doses are milligram-scale and can be processed by direct compression or granulation without the same premix challenge, but content uniformity must nevertheless be verified by USP <905> because the drug substance is present at low mass fractions in low-dose tablets. The calcium salt form provides a defined cation counterion and avoids the strongly alkaline pH adjustment that is often required to dissolve free folic acid in aqueous formulations.

Compendial quality control of the oral and injectable presentations is separated by microbiological and particulate requirements, not by chemical identity. The table below summarizes the test matrix for a dual-grade supply program. The specification values are aligned with current monograph limits; manufacturer-specific limits for particle size, residual water, and endotoxin may be narrower based on the intended formulation.

Oxidative Degradation Pathways and Moisture Control During Granulation

Wet granulation of leucovorin calcium is constrained by the same degradation chemistry that limits its aqueous shelf life. The 5-formyltetrahydrofolate ring undergoes oxidative cleavage to pterin derivatives and 10-formylfolic acid under the combined influence of dissolved oxygen, light, heat, and trace metal ions. In high-shear granulators, the impeller and chopper generate sufficient local heat to raise granule temperature by several degrees; therefore, processing is normally conducted with bowl jackets at 20–25 °C and with granulation end-point set by power consumption rather than time alone. Aqueous binder solutions are prepared near neutral pH; if a buffer is required, phosphate buffer near pH 6.8 is used because strongly acidic conditions can promote formyl-group loss. The granulation is dried in a fluid-bed dryer with inlet air temperature not exceeding 50 °C and product temperature maintained below 35 °C to prevent dehydration beyond the pentahydrate equivalence and to reduce oxidation. Dried granule moisture is controlled at 2.0–4.0% by Karl Fischer titration, a range that balances tablet hardness and dissolution. If ambient relative humidity exceeds 60%, the API and granulation are transferred under dry nitrogen purge because the powder becomes cohesive and direct compression sticking is observed on rotary tablet presses. Direct compression formulations typically combine leucovorin calcium with microcrystalline cellulose, lactose monohydrate, crospovidone, and magnesium stearate; lubricant mixing is limited to 3–5 minutes to avoid overlubrication, which reduces tablet tensile strength. Capsule filling on dosator-type machines requires a bulk density above 0.45 g/mL and a Hausner ratio below 1.35 by USP <616>; materials failing these limits are granulated by roller compaction rather than direct fill. Roller compaction is preferred when the API must be processed without water and with minimal heat.

Granule-based oral powders are prepared by fluid-bed top-spray granulation using a binder solution of povidone K30 or hydroxypropyl cellulose in water. The spray rate is adjusted so that the bed relative humidity remains below 50–55% and the product temperature remains below 35 °C; higher spray rates produce particle agglomeration and increase residual moisture above the 4.0% limit. The granules are sized through a 0.8–1.0 mm screen and lubricated with sodium stearyl fumarate when magnesium stearate is incompatible with the formulation. Dissolution testing is performed using USP <711> Apparatus II at 50 rpm in 900 mL degassed water, with sampling at 15, 30, and 45 minutes; the finished tablet is expected to release not less than 75% of the labeled amount by 30 minutes unless the approved label specifies an alternative.

When Sterile Filtration Replaces Terminal Heat Treatment for Aqueous Injectable Formulations

Leucovorin calcium injection is prepared as a sterile solution by aseptic filtration rather than by autoclaving because the tetrahydrofolate ring degrades under moist heat. The injectable-grade API is dissolved in Water for Injection that has been purged with nitrogen to reduce dissolved oxygen below 2 mg/L; the solution is adjusted to pH 6.5–8.0 with sodium hydroxide or hydrochloric acid, and tonicity is adjusted with sodium chloride. The solution is filtered through a 0.22 µm polyethersulfone or polyvinylidene fluoride membrane filter at 15–25 °C into sterilized amber glass vials that meet light transmission specifications of USP <660> and USP <671>. Headspace oxygen is reduced by nitrogen overlay to below 2% v/v before stoppering. Terminal sterilization is not the default cycle because even 121 °C for 15 minutes produces measurable increases in related substances; if terminal sterilization is nevertheless proposed, the cycle must be supported by stability data showing that total degradation products remain within monograph limits. The injectable-grade powder is not expected to be sterile unless procured under a sterile grade; non-sterile powder is rendered sterile by the validated filtration process. For this reason, bacterial endotoxin control in the API is critical, because endotoxins are not removed by 0.22 µm filtration; limits are assigned from the maximum human dose and the USP <85> threshold, and depyrogenation of all contact surfaces is required before filling. The filling line is operated under ISO 14644-1 Class 5 or equivalent EU GMP Grade A. The solution is light-sensitive; compounding under amber lighting or low-actinic white light reduces photodegradation and protects the 5-formyl group.

Leucovorin calcium is not directly interchangeable with levoleucovorin calcium on an equal-weight basis. Leucovorin is a racemic mixture at C6, containing the active (6S)-5-formyltetrahydrofolate and the inactive (6R) form, whereas levoleucovorin calcium is the isolated active diastereomer. Consequently, the total amount of active folate per milligram differs by approximately one-half; the substitution must be performed according to approved labeling and not by simple weight equivalence. Compared with sodium folinate, the calcium salt contributes calcium ions that may interact with phosphate-buffered parenteral fluids; compatibility with calcium-containing admixtures and phosphate-containing admixtures must be assessed separately using visual inspection, turbidity measurement, and subvisible particle counts under USP <788>. Oral-grade leucovorin calcium is also not a direct-compression premix; it requires blending, granulation, and lubrication steps as described above. The API is manufactured in accordance with ICH Q7 and regional GMP regulations, including 21 CFR 210/211 for finished-product processing; finished-product manufacturers are responsible for process validation, cleaning validation, and stability studies under ICH Q1A(R2).