3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexenyl) -nona-2,4,6,8-tetraenoic acid
2.促進表皮細胞分裂活動之正常，抑制面皰形成。
3.侵入面皰周圍之厚壁，解除角化層，消除面皰。
4.本劑療效可深入皮膚深處，根治面皰、青春痘、粉刺。
Absorption
C max is approximately 347 ng/mL. T max is 1 or 2 h. Orally, tretinoin is well absorbed into systemic circulation.
Distribution
Vd is not yet determined. Tretinoin is more than 95% protein bound (primarily to albumin). Binding remains constant over the concentration range of 10 to 500 ng/mL.
Metabolism
CYP-450 (CYP3A4, 2C8, and 2E) enzymes have been implicated in the oxidative metabolism of tretinoin. Metabolites are 13-cis retinoic acid, 4-oxo trans retinoic acid, 4-oxo cis retinoic acid, 4-oxo trans retinoic acid glucuronide. Metabolites have been identified in plasma and urine. Tretinoin's activity is primarily caused by the parent drug. There is evidence that tretinoin induces its own metabolism.
Elimination
Tretinoin's t ½ is 0.5 to 2 h. 63% is excreted in urine and 31% in feces.
Peak
1 to 2 h.
Agents known to cause pseudotumor cerebri (eg, tetracycline)
The risk of this condition occurring may be increased.
Antifibrinolytic agents (eg, aminocaproic acid, aprotinin, tranexamic acid)
Fatal thrombotic complications have been reported.
Benzoyl peroxide, cosmetics with drying effects, resorcinol, salicylic acid, soaps, or sulfur
May result in significant skin irritation.
CYP-450
Elimination may be altered by agents that inhibit or induce CYP-450 enzymes.
Photosensitizers (eg, fluoroquinolones, phenothiazines, sulfonamides, tetracyclines, thiazide diuretics)
May augment photosensitivity.
Vitamin A
Because symptoms of hypervitaminosis A may be exacerbated, do not give with vitamin A.
2. 若顯著的紅斑或刺激，則減少施藥的次數，或暫時停止給藥。
3. 告訴病人經常會發生輕微的螯刺和溫暖，而乾燥和脫皮是所期望的。
4. 告訴病人，不要和具有乾燥作用的局部外用製劑(如酒精，收斂劑，摩擦的肥皂或清潔劑，化妝品一起使用)，因為會產生過度的乾燥。
5. 通知病人，在治療的早期會發生暫時性的情況惡化，是由於藥物作用在較深部，先前眼睛看不見的損傷處。
6. 警示病人，減少曝露於陽光或太陽燈下，因為會發生對光敏感的反應。實驗動物研究顯示，tretinoin曝露於紫外光下，有致腫瘤的可能，雖然這種作用的意義對人類而言，不太清楚。
7. 濕疹病人要小心使用，因曾發生嚴重的刺激。
