XTRALITE

Indications

• Acne vulgaris
• Acute promyelocytic leukemia (APL)
• Cytotoxic responsive malignancies

Dosage

Children: For children, consult local protocols or BNF for Children for specific dosing regimens.

Adults: For acute promyelocytic leukemia, the recommended dose is 45 mg/m2 daily in two divided doses for a maximum duration of 90 days.

Mechanism of action

Tretinoin exerts its pharmacological effects by binding to and activating retinoic acid receptors (RARs) and retinoid X receptors (RXRs) in the nucleus. This binding induces transcriptional regulation of genes involved in cell differentiation and proliferation. In skin conditions, it enhances keratinocyte turnover and reduces inflammation, while in APL, it promotes differentiation of leukemic cells.

Pharmacodynamics

Tretinoin promotes cell production, proliferation, and differentiation, primarily affecting epidermal cells. Topically, it regulates epidermal turnover and collagen synthesis, thereby preventing collagen degradation and enhancing skin appearance. It also exhibits antineoplastic effects by inducing cytodifferentiation in tumor cells, particularly in APL, leading to decreased proliferation of leukemic cells.

Pharmacokinetics

Tretinoin is well absorbed after oral administration, with peak plasma concentrations occurring within 1-2 hours. It is extensively metabolized in the liver, primarily through oxidation and conjugation, yielding several active and inactive metabolites. The elimination half-life ranges from 0.5 to 2 hours, and its metabolites are excreted in urine. The pharmacokinetics may be affected by liver function, necessitating caution in hepatic impairment.

Contra-indications

• Pregnancy
• Breastfeeding
• Hypersensitivity to tretinoin
• History of depression or severe neuropsychiatric reactions

Adverse effects

• Headache
• Dizziness
• Nausea
• Vomiting
• Abdominal pain
• Dry skin
• Erythema
• Chills
• Insomnia
• Intracranial hypertension
• Visual impairment
• Emotional lability
• Increased risk of thromboembolism
• Hypercalcemia
• Tinnitus
• Skin reactions

Interactions

• Tretinoin and vitamin A: Severe (increases risk of vitamin A toxicity)
• Tretinoin and posaconazole: Moderate (increases risk of tretinoin toxicity)

Precautions

• Caution in hepatic impairment
• Monitor haematological and coagulation profile, liver function, serum calcium, and plasma lipids before and during treatment
• Risk of neuropsychiatric reactions; advise patients to seek medical attention for mood changes

Pregnancy

Tretinoin is teratogenic; avoid use during pregnancy.

Breast-feeding

Avoid; discontinue breastfeeding during treatment.

Storage

Store in a cool, dry place away from direct sunlight.

Formulations

• Capsules (75 mg)
• Solution for injection
• Topical formulations (cream or gel)

Indications

• Eczema
• Psoriasis
• Contact dermatitis
• Allergic dermatitis
• Seborrheic dermatitis

Dosage

Children: Refer to specific product information or clinical guidelines for appropriate dosing in children, as it varies by formulation and condition treated.

Adults: Refer to specific product information or clinical guidelines for appropriate dosing, as it varies by formulation and condition treated.

Mechanism of action

Acetonide exerts its effects by binding to glucocorticoid receptors in the cytoplasm of target cells, leading to the translocation of the receptor-ligand complex into the nucleus. This complex then influences the expression of specific genes, resulting in decreased production of pro-inflammatory cytokines and increased production of anti-inflammatory proteins. This modulation of gene expression contributes to its anti-inflammatory and immunosuppressive effects.

Pharmacodynamics

The pharmacodynamics of acetonide involve its ability to inhibit the migration of leukocytes to sites of inflammation, reduce the production of inflammatory mediators such as prostaglandins and leukotrienes, and suppress the immune response. The potency and duration of action can vary based on the specific formulation and concentration used.

Pharmacokinetics

Acetonide is absorbed through the skin when applied topically, with systemic absorption depending on the formulation, application area, and duration of use. It undergoes hepatic metabolism, and its metabolites are excreted primarily through the urine. The half-life and clearance rates can vary based on individual patient factors and specific formulations.

Contra-indications

• Hypersensitivity to acetonide or any component of the formulation.
• Active or untreated infections at the site of application.

Adverse effects

• Local irritation or burning sensation at the application site.
• Skin thinning or atrophy with prolonged use.
• Systemic effects such as adrenal suppression with high doses or prolonged therapy.

Interactions

• Increased risk of systemic effects when used with other corticosteroids.
• Potentially altered metabolism when administered with CYP3A4 inhibitors or inducers.

Precautions

• Use with caution in patients with a history of tuberculosis or other infections.
• Monitor for signs of adrenal insufficiency in patients on high doses.
• Avoid application to large areas of the body or under occlusive dressings.

Pregnancy

Acetonide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Consult with a healthcare professional before use.

Breast-feeding

Limited data available. Use with caution as it may be excreted in breast milk. Consult with a healthcare professional before use.

Storage

Store at room temperature, away from direct sunlight and moisture. Keep out of reach of children.

Formulations

• Topical cream
• Topical ointment
• Topical solution

Indications

• Eczema
• Psoriasis
• Dermatitis
• Allergic skin reactions
• Lichen planus

Dosage

Children: For paediatric patients, dosage should be determined by a healthcare professional, considering the child's age, weight, and the specific condition being treated. Refer to the BNF for Children for specific dosing guidelines.

Adults: The dosage of fluocinolone varies based on the formulation and severity of the condition. It is typically applied as a thin layer to the affected area once or twice daily, as directed by a healthcare professional.

Mechanism of action

Fluocinolone binds to specific corticosteroid receptors in the cytoplasm of target cells, leading to the transcription of anti-inflammatory proteins and the repression of pro-inflammatory cytokines. This process ultimately results in a decrease in inflammation and an alteration of the immune response.

Pharmacodynamics

Fluocinolone exhibits strong anti-inflammatory and immunosuppressive effects. Its potency allows for effective management of conditions characterized by excessive inflammation. The drug helps to decrease the migration of leukocytes to sites of inflammation and inhibits the release of inflammatory mediators, thereby alleviating symptoms associated with inflammatory skin disorders.

Pharmacokinetics

Fluocinolone is absorbed through the skin when applied topically. The systemic absorption may vary depending on the formulation, the area of application, and the condition of the skin. Once absorbed, fluocinolone is metabolized in the liver and excreted primarily via urine. The half-life of fluocinolone is variable, influenced by factors such as the route of administration and individual patient characteristics.

Adverse effects

• skin irritation
• burning sensation
• dryness
• hypopigmentation
• striae
• telangiectasia
• folliculitis

Precautions

• Avoid use on broken skin
• Consider potential systemic absorption especially in large areas or under occlusion
• Caution in patients with diabetes or impaired adrenal function

Pregnancy

Fluocinolone is classified as Category C. Its use during pregnancy should be considered only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Fluocinolone is excreted in breast milk. Caution should be exercised when administering to nursing women, particularly on large areas of the skin.

Storage

Store below 25 degrees Celsius. Protect from light.

Formulations

• Topical cream
• Topical ointment
• Topical solution

Indications

• Hyperpigmentation
• Melasma
• Post-inflammatory hyperpigmentation
• Age spots

Dosage

Children: Refer to the BNF for Children for appropriate dosing information, as pediatric dosing may differ significantly from adult recommendations.

Adults: Topical application of hydroquinone is typically applied to the affected areas twice daily. Patients should follow specific product guidelines and consult healthcare professionals for individualized treatment plans.

Mechanism of action

Hydroquinone reduces melanin pigment production through inhibition of the tyrosinase enzyme, which is involved in the initial step of the melanin pigment biosynthesis pathway. This inhibition decreases the overall production of melanin, leading to a lighter skin appearance.

Pharmacodynamics

The pharmacodynamic effects of hydroquinone are largely related to its ability to modulate melanin synthesis in melanocytes by inhibiting tyrosinase activity. Prolonged exposure to hydroquinone can lead to a gradual lightening of the skin. However, the drug's efficacy may vary among individuals based on skin type and the extent of hyperpigmentation.

Pharmacokinetics

Hydroquinone is absorbed through the skin, reaching systemic circulation to some extent. The metabolic pathways of hydroquinone include its conversion to various reactive metabolites, which can generate reactive oxygen species and may lead to oxidative stress. Hydroquinone has a half-life that varies based on the route of administration and individual metabolism, but specific pharmacokinetic parameters are not well defined in the literature.

Adverse effects

• Skin irritation
• Erythema
• Hypopigmentation
• Allergic contact dermatitis

Precautions

• Use with caution in individuals with a history of skin sensitivity or allergy
• Avoid prolonged exposure to sunlight or ultraviolet light during treatment
• Not for use on broken or inflamed skin

Pregnancy

Hydroquinone should be used during pregnancy only if clearly needed, as safety in pregnancy has not been established.

Breast-feeding

Caution is advised when using hydroquinone while breastfeeding, as it is not known whether it is excreted in human milk.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Cream
• Gel
• Lotion

Mechanism of action

The exact mechanism of action of tretinoin in skin conditions and acute promyelocytic leukemia (APL) has not been fully elucidated; however, several proposed mechanisms exist. Tretinoin is believed to exert its pharmacological actions by binding to and activating two types of nuclear receptors - retinoic acid receptors (RARs) alpha, beta, and gamma and retinoid X receptors (RXRs). In the human skin, RARs (especially RAR-alpha) form heterodimers with RXR to act as inducible transcription regulators of genes involved in cell differentiation by binding to retinoic acid response elements. Tretinoin binds to RXRs to promote epidermal proliferation. It also blocks the actions of inflammatory mediators, enhancing procollagen production and collagen type I and III formations. Some animal and human studies suggest that tretinoin induces the expression of transforming growth factor beta (TGF-β), which stimulates the transcription of several types of collagen messenger RNA. Collagen formation curtails further solar UV-induced skin damage and aging processes. Acne is associated with abnormal follicular formation from excessive keratinization of epithelial cells. Tretinoin promotes cornified cell detachment and enhances keratinocyte shedding. It also stimulates mitotic activity and loosely-adherent corneocyte turnover to expel comedo contents, reducing microcomedo precursor lesions of acne vulgaris. Tretinoin may reduce epidermal melanin and pigmentation by increasing keratinocyte turnover and reducing tyrosinase activity. RAR-alpha and -beta have also been implicated in APL. APL is characterized by a t(15;17) chromosomal translocation, which fuses the promyelocytic myeloid leukemia (PML) gene with the RAR-alpha gene. The resulting PML-RAR-alpha fusion protein plays a role in the pathogenesis of APL by aberrating promyelocyte differentiation. The PML-RAR-alpha fusion protein is found to be predominant in leukemic cells, exerting a dominant negative effect on RAR, RXR and PML function. Tretinoin induces terminal differentiation in hemopoietic precursor cell lines and APL cells. Tretinoin is believed to promote caspase-mediated cleavage and proteasome-dependent degradation to cause apoptosis and degradation of the PML-RAR-alpha fusion protein. It may also convert the fusion protein from a transcription repressor to an activator. Although the precise mechanism(s) of action of tretinoin has not been fully elucidated, it is known that the drug is not a cytolytic agent. Tretinoin induces cellular differentiation and decreases the proliferation of acute promyelocytic leukemia (APL) cells. The PML/RAR-a fusion protein resulting from the chromosomal translocation appears to block myeloid differentiation at the promyelocyte stage, possibly by complexing and inactivating wild-type PML or by inhibiting the normal retinoic acid signaling pathway. In patients with APL who achieve a complete remission with tretinoin therapy, the drug causes an initial maturation of the primitive promyelocytes derived from the cellular leukemic clone followed by a repopulation of the bone marrow and peripheral blood by normal, polyclonal hematopoietic cells. Observations supporting cellular differentiation effects as a mechanism of tretinoin include the absence of bone marrow hypoplasia during induction, the appearance of immunophenotypically unique "intermediate cells" expressing both mature and immature cell surface antigens, and the presence of both Auer rods and the translocation in morphologically mature granulocytes until a late stage of induction. The mechanism by which the population of malignant cells is eliminated is not fully understood but appears to involve apoptosis (programmed cell death). Following induction therapy, the PML/RAR-a fusion protein can be detected in the majority of patients, suggesting that tretinoin alone does not eradicate the leukemic clone.

Pharmacodynamics

Tretinoin is a vitamin A derivative that promotes cell production, proliferation, and differentiation. When used topically, tretinoin regulates epidermal cell turnover and collagen production. It also prevents collagen loss, reduces inflammation, and blocks the induction of matrix metalloproteinase (MMP), which are enzymes that disrupt collagen and elastic fibres. In short-term and long-term studies, topical application of tretinoin at doses ranging from 0.001% to 0.1% was associated with improvements in clinical signs of photoaging and fine wrinkles, increased epidermal thickness, compaction of the stratum corneum, and decreased melanin content. It also improved melanocyte differentiation and distribution, promotion of epidermal hyperplasia, and angiogenesis. Tretinoin exhibits antineoplastic activities when given orally. Tretinoin was shown to induce differentiation in tumour cells. It induced cytodifferentiation and decreased acute promyelocytic leukemia (APL) cell proliferation in culture and _in vivo_. In patients with APL, tretinoin promoted the initial maturation of the primitive promyelocytes derived from the leukemic clone, followed by a repopulation of the bone marrow and peripheral blood by normal, polyclonal hematopoietic cells in patients achieving complete remission.

Mechanism of action

Hydroquinone reduces melanin pigment production through inhibition of the tyrosinase enzyme, which is involved in the initial step of the melanin pigment biosynthesis pathway. Hydroquinone takes several months to take effect. Benzene is a well-established human carcinogen. Benzene metabolites hydroquinone (HQ) and benzoquinone (BQ) are highly reactive molecules capable of producing reactive oxygen species and causing oxidative stress. /This study/ investigated the role of the Nrf2, a key nuclear transcription factor that regulates antioxidant response element (ARE)-containing genes, in defense against HQ- and BQ-induced cytotoxicity in cultured human lung epithelial cells (Beas-2B). When the cells were exposed to HQ or BQ the activity of an ARE reporter was induced in a dose-dependent manner, meanwhile Nrf2 protein levels were elevated and accumulated in the nucleus. Increased expression of well-known Nrf2-dependent proteins including NQO1, GCLM, GSS and HMOX was also observed in the HQ/BQ-treated cells. Moreover, transient overexpression of Nrf2 conferred protection against HQ- and BQ-induced cell death, whereas knockdown of Nrf2 by small interfering RNA resulted in increased apoptosis. /This study/ also found that the increased susceptibility of Nrf2-knockdown cells to HQ and BQ was associated with reduced glutathione levels and loss of inducibility of ARE-driven genes, suggesting that deficiency of Nrf2 impairs cellular redox capacity to counteract oxidative damage. Altogether, these results suggest that Nrf2-ARE pathway is essential for protection against HQ- and BQ-induced toxicity.