ピリメタミン
Pyrimethamine
Aminopyrimidine derivative
別名: Daraprim · Malocide · Pirimecidan · BW-50-63 · pirimetamina · pyrimethaminum · RP-4753
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Toxoplasmosis | 0.5-1 mg/kg PO once daily for 2 days, then 0.25 mg/kg PO once daily for 2 weeks | PO | once daily | 2 days, then 2 weeks | 🌎 NA |
| Toxoplasmosis | 0.25-0.5 mg/kg once daily for 28 days | PO | once daily | 28 days | 🌎 NA |
| Neospora | 1 mg/kg once daily for 28 days | PO | once daily | 28 days | 🌎 NA |
| Hepatazoon canis | 0.25-0.5 mg/kg once daily for 2-4 weeks | PO | once daily | 2-4 weeks | 🌎 NA |
| Hepatazoon americanum | 0.25 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
| Hepatazoon americanum | 0.25 mg/kg PO q24h for 14 days | PO | q24h | 14 days | 🌎 NA |
| Neosporosis | 1 mg/kg PO daily | PO | daily | — | 🌎 NA |
- Toxoplasmosis: Given with sulfadiazine at 30-50 mg/kg PO divided two to four times a day for 1-2 weeks
- Neospora: Given with trimethoprim sulfa
- Hepatazoon canis: Given with trimethoprim sulfa and clindamycin
- Hepatazoon americanum: Given with Trimethoprim/sulfa (15 mg/kg PO q12h) and clindamycin (10 mg/kg q8h). Once remission attained, decoquinate can maintain.
- Hepatazoon americanum: Given with Trimethoprim/sulfa (15 mg/kg PO q12h for 14 days) and clindamycin (10 mg/kg q8h for 14 days). Once remission attained, decoquinate can maintain.
- Neosporosis: Given with trimethoprim/sulfa (15-30 mg/kg PO twice daily).
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Toxoplasmosis | 0.5-1 mg/kg PO once daily for 2 days, then 0.25 mg/kg PO once daily for 2 weeks | PO | once daily | 2 days, then 2 weeks | 🌎 NA |
| Toxoplasmosis (enteroepithelial cycle) | 2 mg/kg, PO once daily | PO | once daily | — | 🌎 NA |
| Toxoplasmosis (extraintestinal cycle) | 0.5-1 mg/kg PO divided two to three times daily | PO | divided two to three times daily | — | 🌎 NA |
| Protozoal myocarditis | 1 mg/kg PO once daily for 3 days, then decrease dose to 0.5 mg/kg PO once a day | PO | once daily | 3 days, then ongoing | 🌎 NA |
| Toxoplasmosis | 0.5 mg/kg PO per day | PO | per day | 7-10 days | 🌎 NA |
- Toxoplasmosis: Given with sulfadiazine at 30-50 mg/kg PO divided two to four times a day for 1-2 weeks
- Toxoplasmosis (extraintestinal cycle): Combined with sulfonamides (e.g., triple sulfa, sulfadiazine) at 60 mg/kg PO or IM divided two to three times daily
- Protozoal myocarditis: Given with sulfadimethoxine 25 mg/kg PO, IV, or IM once a day
- Toxoplasmosis: Given with sulfadiazine at 30 mg/kg, PO q12h. Do not use continuously for longer than 2 weeks. Supplementation with folic acid 5 mg/day or folinic acid 1 mg/kg/day may alleviate toxicity.
鳥
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Coccidian organisms in raptors (Toxoplasmosis, Atoxoplasmosis, Sarcocystis) | 0.5 mg/kg PO twice daily for 14-28 days | PO | twice daily | 14-28 days | 🌎 NA |
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Equine protozoal myeloencephalitis | 1 mg/kg PO once a day for 90-120 days (or longer) | PO | once a day | 90-120 days (or longer) | 🌎 NA |
- Equine protozoal myeloencephalitis: Given with a sulfa or potentiated sulfa (sulfadiazine 20 mg/kg PO once or twice a day). Monitor CBC's.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
ピリメタミンは強力な抗原虫薬であり、獣医学では主に小動物のトキソプラズマ症、ネオスポラ症、Hepatozoon americanum などの重篤な原虫感染症や、馬の馬原虫性脊髄脳炎（EPM）の治療に使用されます。葉酸合成を相乗的に阻害するため、ほぼ常にサルファ剤と併用されます。
臨床のポイント： 葉酸代謝を標的とするため、特に猫において宿主の骨髄抑制が重大なリスクとなります。血液毒性を軽減するために、ホリナート（葉酸ではなく、原虫が利用できない形態）やパン酵母の補給がしばしば推奨されます。
作用機序
Pyrimethamine is a folic acid antagonist. It competitively inhibits the enzyme dihydrofolate reductase (DHFR) → blocks the reduction of dihydrofolic acid to tetrahydrofolic acid (the active form of folate) → depletes folate reserves essential for purine and pyrimidine synthesis → halts protozoal DNA and RNA synthesis.
When combined with sulfonamides (which inhibit dihydropteroate synthase earlier in the pathway), it produces a synergistic, sequential blockade of the folate synthesis pathway.
安全性・警告
禁忌
- Known hypersensitivity to pyrimethamine
- Preexisting hematologic disorders (use with extreme caution)
- Pregnancy (potentially teratogenic, weigh risks vs. benefits)
- Pregnancy (teratogenic)
- Pre-existing bone marrow suppression
有害事象
- Small animals: Anorexia, malaise, vomiting, depression
- Small animals: Bone marrow depression (anemia, thrombocytopenia, leukopenia)
- Cats: Highly susceptible to adverse reactions (noted 4-6 days after starting combination therapy)
- Horses: Leukopenias, thrombocytopenia, and anemias
- Bone marrow suppression (anemia, leukopenia, thrombocytopenia)
- Lethargy
注意事項
Hematologic Toxicity: Hematologic effects can develop rapidly. Frequent monitoring is recommended, particularly if therapy persists longer than 2 weeks. Oral administration of folinic acid, folic acid, or Brewer's yeast has been suggested to alleviate adverse effects.
Feline Sensitivity: Some clinicians recommend avoiding its use in cats entirely because of its adverse effect profile.
Pregnancy: Pyrimethamine is teratogenic in rats and fetal abnormalities have been seen in foals. FDA Category C. Weigh risks against benefits. Excreted in maternal milk; consider using milk replacer.
医薬品相互作用
Reportedly antagonistic towards the activity of pyrimethamine; clinical significance is unclear.
Synergistic with pyrimethamine in activity against toxoplasmosis and malaria.
Use with pyrimethamine/sulfa is not recommended in humans as adverse effects may be additive, however, this combination has been used clinically in horses.
May increase folate deficiency
May increase folate deficiency
監視
- CBC with platelet count (frequent monitoring recommended)
- Clinical efficacy
- Signs of abnormal bleeding or lassitude
- Complete Blood Count (CBC) every 1-2 weeks
- Appetite and body weight
- Signs of bleeding, bruising, or lethargy
薬物動態
半減期
吸収
No pharmacokinetic data located for veterinary species. In humans, well absorbed from the gut after oral administration.
分布
Distributed primarily to the kidneys, liver, spleen, and lungs. Crosses the blood-brain barrier. Volume of distribution is about 3 L/kg. 80% bound to plasma proteins. Enters milk in levels greater than serum.
代謝
Unknown how or where the drug is metabolized, but metabolites are found in the urine.
消失
Excreted in the urine.
過剰投与
Reports of acute overdosage in animals were not located. In humans, signs include vomiting, nausea, anorexia, CNS stimulation (including seizures), and hematologic effects.
Treatment recommendations:
- Standard procedures to empty the gut or prevent absorption.
- Parenteral barbiturates for seizures.
- Folinic acid for hematologic effects.
- Long-term monitoring (at least 1 month) of renal and hematopoietic systems.
製品
製剤
- Tablets: 25 mg
- 25 mg tablet
ヒト用医薬品
- Pyrimethamine Tablets: 25 mg; Daraprim® (GlaxoSmithKline); (Rx)
- Daraprim 25 mg tablets
規制ステータス
Often used under the cascade from human medicine.
Listed as a Pharmacy (P) medicine in the provided monograph.
規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Store tablets in tight, light-resistant containers. Tablets may be crushed to make oral suspensions. If cherry syrup, corn syrup, or sucrose-containing liquids are used, store the suspension at room temperature and discard after 7 days (sugars adversely affect stability).
飼主向け情報
重要： この薬は重篤な寄生虫感染症の治療に使用され、慎重なモニタリングが必要です。
- 指示通りに投与してください： 最大の効果を得るために、他の抗生物質（サルファ剤など）と一緒に投与されることがよくあります。投与を飛ばさないでください。
- 副作用に注意： ペットが元気消失、食欲不振、嘔吐を示したり、異常な出血やあざ（歯茎の蒼白や皮膚の赤い斑点など）の兆候が見られた場合は、すぐに獣医師に連絡してください。
- 猫への投与の難しさ： 市販の錠剤は25mgであり、猫への正確な投与が非常に困難です。また、錠剤は猫にとって味が悪いです。正確で簡単な投与を確実にするために、獣医師は特別に調剤された液体やカプセルを推奨することがあります。
- 妊娠に関する警告： 飼い主様が妊娠している場合はこの薬に触れないでください。また、獣医師の明確な指示がない限り、妊娠中のペットには使用しないでください。
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