Fluconazole (FLZ) in conjunction with Pyrimethamine (Pirimecidan; 4 nM–4 μM; 24 h; LLC-MK2 cells with T. gondii) suppresses T. gondii activity for FLZ concentrations of 0, 0.05, 0.1, 0.5, 1.0, and 3.0 μM, respectively, with IC50 values of 0.23, 0.19, 0.23, 0.34, 0.14, and 0.19 μM[1].

The combination of fluconazole and sulfadiazine with pyrimethamine (Pirimecidan; 1 mg/kg; ig; daily, for 10 d; female CF1 mice with T. gondii xenograft) enhances protection against death[1].

Cell Viability Assay[1]
Cell Types: LLC-MK2 cells with T. gondii
Tested Concentrations: 4 nM-4 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: Inhibited T. gondii activity and diminished parasite proliferation index.

Animal/Disease Models: Female CF1 mice (18-22 g ; 4-6 week of age) with T. gondii xenograft[1]
Doses: po (oral gavage); daily, for 10 days
Route of Administration: 1 mg/kg; 10 mg/kg (Fluconazole ), 40 mg/kg (Sulfadiazine)
Experimental Results: Increased mouse survival compared to treatment with SDZ/PYR alone.

Absorption, Distribution and Excretion
Well absorbed with peak levels occurring between 2 to 6 hours following administration
The concentration of chloroquine, dapsone and pyrimethamine in plasma and milk were measured following the coadministration of a single dose of chloroquine and Maloprim to lactating women. The milk to plasma area under the concentration-time curve (AUC) ratio ranged from 1.96 to 4.26 for chloroquine, 0.22 to 0.45 for dapsone and 0.46 to 0.66 for pyrimethamine. Assuming a daily milk ingestion of 1 l by the infant, the maximum percentage of the maternal dose for chloroquine, dapsone and pyrimethamine in milk was 4.2%, 14.3% and 45.6%, respectively, over a 9 day period.
Pyrimethamine is excreted into milk. It is estimated that approximately 3-4 mg of the drug would be ingested by a nursing infant over the first 48-hour period following administration of a single 75-mg oral dose to the mother.
In this study, the kinetics of pyrimethamine elimination via the urine was investigated. The experiments were carried out on six healthy male volunteers aged 23-32 years. The drug was administered orally (p.o.) in a single dose at three different concentrations i.e.: 50, 75 and 100 mg. The concentration of the drug in the urine was determined via the modified method of Bonini et al. and Garber et al. It was found that 13.4 +/- 1.3% of the dose eliminated via the urine was in unchanged form. The process of pyrimethamine elimination may be described according to an open kinetic two-compartmental model: the formula showing the course of pyrimethamine elimination over time has been given. Several examples of the quantitative exposure test have been proposed, which allow the calculation of the drug dose absorbed and thus the degree of toxicity to be determined. This test can also be useful in a controlled clinical setting.
A pharmacokinetic study of pyrimethamine was carried out in 4- (103-115 g) and 12-week-old (260-280 g) white male Wistar rats fed a standard diet containing 24% protein, and a low-protein diet containing 8% protein. After intragastric administration of the drug in a single dose of 40 mg/kg body weight, the concentrations of pyrimethamine in the blood were determined at different time points from 15 min to 20 hours post-dose. On the basis of the results obtained, a number of parameters characterizing the course of absorption and elimination of the drug from the blood were calculated. The majority of parameters were dependent on both age and type of diet. The greatest bioavailability was observed in the 4-week-old rats: for the animals fed the low-protein diet, the area under the concentration-time curve (AUC) amounted to 593.0 and for those on the standard diet the AUC was 503.1. In the older rats, this parameter was 339.3 and 228.1 respectively. The k(e) values were lower in the younger rats (i.e. 0.0121 hr(-1) and 0.0135 h(-1)) than in the older animals (i.e. 0.0164 h(-1) and 0.0193 hr(-1) respectively). The elimination half-life (t1/2) was higher in the 4-week-old rats (i.e. 57.1 hr; 8% protein, and 51.2 hr; 24% protein) than in the 12-week-old animals (i.e. 42.4 hr; 8% protein, and 36.0 hr; 24% protein).
For more Absorption, Distribution and Excretion (Complete) data for Pyrimethamine (10 total), please visit the HSDB record page.

---

Metabolism / Metabolites
Hepatic
Pyrimethamine is metabolized to several unidentified metabolites. About 5% of a dose of sulfadoxine is present in plasma as an acetylated metabolite and about 2-3% is present as the glucuronide.
Hepatic
Half Life: 96 hours

---

Biological Half-Life
96 hours
Pyrimethamine reportedly has an average plasma half-life of 111 hours (range: 54-148 hours). The plasma half-life of sulfadoxine reportedly averages 169 hours (range: 100-231 hours).
To determine pyrimethamine levels in sera, cerebrospinal fluid, and ventricular fluid in infants, specimens were examined from 37 infants, ages 10 days to 1.5 yr, receiving pyrimethamine 1 mg/kg of body weight daily for 2 months followed by the same dosage each Monday, Wednesday, and Friday for treatment of suspect or proven congenital toxoplasmosis. The pyrimethamine half-life obtained from serum of 9 babies was 64 hr, which was significantly different than for 2 infants taking phenobarbital (33 hr).
A pharmacokinetic study of pyrimethamine was carried out in 4- (103-115 g) and 12-week-old (260-280 g) white male Wistar rats fed a standard diet containing 24% protein, and a low-protein diet containing 8% protein. After intragastric administration of the drug in a single dose of 40 mg/kg body weight, the concentrations of pyrimethamine in the blood were determined at different time points from 15 min to 20 hours post-dose...The elimination half-life (t1/2) was higher in the 4-week-old rats (i.e. 57.1 hr; 8% protein, and 51.2 hr; 24% protein) than in the 12-week-old animals (i.e. 42.4 hr; 8% protein, and 36.0 hr; 24% protein).

Toxicity Summary
Pyrimethamine inhibits the dihydrofolate reductase of plasmodia and thereby blocks the biosynthesis of purines and pyrimidines, which are essential for DNA synthesis and cell multiplication. This leads to failure of nuclear division at the time of schizont formation in erythrocytes and liver.

---

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No adverse reactions in breastfed infants have been reported and it is acceptable in nursing mothers. In HIV-infected women, elevated viral HIV loads in milk were decreased after treatment with chloroquine to a greater extent than other women who were treated with the combination of sulfadoxine and pyrimethamine. It has been suggested that maternal pyrimethamine clearance might be increased during lactation, but data are insufficient to make a definitive conclusion.
◉ Effects in Breastfed Infants
Administration of pyrimethamine to mothers of 26 predominantly breastfed infants 2 to 6 months old who were infected with malaria was curative in the infants.] The regimen consisted of 75 mg followed by a subsequent dose of 50 to 75 mg 4 to 7 days later. The efficacy apparently is related to breastfeeding habits, because infants in another tribal group who breastfed their infants less extensively were not protected. No adverse effects were reported in these infants.
A case report indicates that a maternal dose of 75 mg orally followed by 25 mg weekly cured malaria in her breastfed infant and protected her infant against becoming infected with malaria for 6 months. After the mother missed taking her dose for 2 weeks, the infant developed symptoms of malaria.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

---

Protein Binding
87%

---

Interactions
Although the clinical importance is unclear, mild hepatotoxicity has been reported in some patients receiving pyrimethamine and lorazepam concomitantly.
Although the clinical importance is unclear, p-aminobenzoic acid (PABA) reportedly interferes with the action of pyrimethamine and probably should not be used in patients receiving pyrimethamine.
An increased incidence and severity of adverse effects has been reported when chloroquine was used concomitantly with the fixed combination of sulfadoxine and pyrimethamine compared with use of the fixed combination alone. Sulfadoxine and pyrimethamine is compatible with quinine and with other anti-infectives.
Concomitant use of pyrimethamine or sulfadoxine and pyrimethamine with other antifolate agents (e.g., sulfonamides, co-trimoxazole, trimethoprim) is not recommended since such use may increase the risk of bone marrow suppression. If signs of folate deficiency develop, pyrimethamine or sulfadoxine and pyrimethamine should be discontinued and leucovorin administered (if necessary) until normal hematopoiesis is restored.
For more Interactions (Complete) data for Pyrimethamine (6 total), please visit the HSDB record page.

---

Non-Human Toxicity Values
LD50 Rat intraperitoneal 70 mg/kg
LD50 Mouse intraperitoneal 74 mg/kg
LD50 Mouse oral 92 mg/kg

[1]. Aikawa M, et, al. Studies on nuclear division of a malarial parasite under pyrimethamine treatment. J Cell Biol. 1968 Dec;39(3):749-54.
[2]. Martins-Duarte ÉS, et, al. Toxoplasma gondii: the effect of fluconazole combined with sulfadiazine and pyrimethamine against acute toxoplasmosis in murine model. Exp Parasitol. 2013 Mar;133(3):294-9.

Therapeutic Uses
Although pyrimethamine has been used alone for suppression or chemoprophylaxis of malaria in travelers, the drug is no longer recommended by the US Centers for Disease Control and Prevention (CDC) or other experts for prevention of malaria. The manufacturer states that pyrimethamine should only be used for suppression or chemoprophylaxis of malaria caused by Plasmodium known to be susceptible to the drug. However, resistance to pyrimethamine is prevalent worldwide and the drug alone is not a suitable chemoprophylaxis regimen for travelers to most areas of the world. /Included in US product labeling/
Pyrimethamine is used in conjunction with sulfadiazine or, alternatively, clindamycin, atovaquone, or azithromycin for the treatment of toxoplasmosis caused by Toxoplasma gondii. /Included in US product labeling/
Oral or parenteral leucovorin is used with pyrimethamine in these regimens to prevent pyrimethamine-induced adverse hematologic effects. /Included in US product labeling/
Although co-trimoxazole generally is considered the drug of choice for the treatment of GI infections caused by Isospora belli, pyrimethamine has been used for the treatment of isosporiasis in some patients (e.g., HIV-infected patients) when co-trimoxazole was contraindicated, including those with sulfonamide sensitivity. /NOT included in US product labeling/
For more Therapeutic Uses (Complete) data for Pyrimethamine (16 total), please visit the HSDB record page.

---

Drug Warnings
High dosages of pyrimethamine may result in adverse nervous system effects including ataxia, tremors, seizures, and respiratory failure. Headache, light-headedness, insomnia, depression, malaise, fatigue, and irritability have been reported rarely with pyrimethamine. Reversible hyperesthesia has been reported rarely with sulfadoxine and pyrimethamine. Other adverse nervous system effects reported with sulfonamides or pyrimethamine include peripheral neuritis, hallucinations, tinnitus, vertigo, muscle weakness, nervousness, and polyneuritis.
Sensitivity reactions, occasionally severe (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, anaphylaxis) have been reported with pyrimethamine, especially when the drug was used with a sulfonamide. Severe, sometimes fatal, hypersensitivity reactions have occurred with the fixed-combination preparation of sulfadoxine and pyrimethamine. In most reported cases, fatalities resulted from severe cutaneous reactions, including erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis. Pulmonary hypersensitivity reactions and a fatal reaction involving the skin, liver, and kidneys also have been reported. Fatal hepatitis also has been reported with the fixed-combination drug.
Severe reactions to sulfadoxine and pyrimethamine have occurred in travelers who received 2-9 doses of the drug for prophylaxis of malaria, but have not been reported to date following a single dose of the drug such as that used in the treatment of malaria. It is estimated that the incidence of severe cutaneous adverse reactions ranges from 1/8000 to 1/5000 and that the incidence of fatal cutaneous reactions ranges from 1/25,000 to 1/11,000 in US travelers receiving chemoprophylaxis with sulfadoxine and pyrimethamine.
Anorexia, abdominal cramps, diarrhea, and vomiting may occur with high dosages of pyrimethamine. Anorexia and vomiting may be minimized by reducing dosage of pyrimethamine or by administering the drug with meals. Atrophic glossitis or gastritis also has been reported with high dosages of pyrimethamine. Other adverse GI effects reported with sulfonamides or with pyrimethamine include stomatitis, nausea, abdominal pain, and feeling of fullness.
For more Drug Warnings (Complete) data for Pyrimethamine (21 total), please visit the HSDB record page.

---

Pharmacodynamics
Pyrimethamine is an antiparasitic compound commonly used as an adjunct in the treatment of uncomplicated, chloroquine resistant, P. falciparum malaria. Pyrimethamine is a folic acid antagonist and the rationale for its therapeutic action is based on the differential requirement between host and parasite for nucleic acid precursors involved in growth. This activity is highly selective against plasmodia and Toxoplasma gondii. Pyrimethamine possesses blood schizonticidal and some tissue schizonticidal activity against malaria parasites of humans. However, the 4-amino-quinoline compounds are more effective against the erythrocytic schizonts. It does not destroy gametocytes, but arrests sporogony in the mosquito. The action of pyrimethamine against Toxoplasma gondii is greatly enhanced when used in conjunction with sulfonamides.

C12H13CLN4

248.71

248.082

58-14-0

Pyrimethamine-d3;1189936-99-9

4993

Crystals
White scored tablets contains 25 mg pyrimethamine /Daraprim/

1.4±0.1 g/cm3

368.4±52.0 °C at 760 mmHg

233-234°C

176.6±30.7 °C

0.0±0.8 mmHg at 25°C

1.667

1.03

2

4

2

17

243

0

ClC1C([H])=C([H])C(=C([H])C=1[H])C1C(N([H])[H])=NC(N([H])[H])=NC=1C([H])([H])C([H])([H])[H]

WKSAUQYGYAYLPV-UHFFFAOYSA-N

InChI=1S/C12H13ClN4/c1-2-9-10(11(14)17-12(15)16-9)7-3-5-8(13)6-4-7/h3-6H,2H2,1H3,(H4,14,15,16,17)

5-(4-chlorophenyl)-6-ethylpyrimidine-2,4-diamine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (10.05 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (10.05 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

 (Please use freshly prepared in vivo formulations for optimal results.)