MELAN H

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

• Wound healing
• Skin irritations
• Dry skin conditions
• Eczema
• Psoriasis

Dosage

Children: Refer to the BNF for Children for appropriate dosing and formulation guidance for paediatric use.

Adults: Refer to specific product guidelines for application frequency and amount, as allantoin is typically used in topical formulations.

Mechanism of action

Although there is no well-controlled data to formally substantiate its method of action, studies suggest that allantoin may induce a histological wound healing profile. This profile includes increased vasodilation, inflammatory exudate presence, and enhanced numbers of inflammatory cells, angiogenesis, fibroblast proliferation, and collagen deposition in wound sites treated with allantoin compared to untreated ones.

Pharmacodynamics

Ongoing studies indicate that allantoin possesses moisturizing and keratolytic effects. It can increase the water content of the extracellular matrix and promote the desquamation of the upper layers of dead skin cells. These activities are believed to support cell proliferation and facilitate wound healing.

Pharmacokinetics

The pharmacokinetics of allantoin are not well characterized in controlled studies. However, its application as a topical agent suggests localized effects with minimal systemic absorption, facilitating its use in dermatological applications without significant systemic effects.

Pregnancy

There is limited data on the safety of allantoin in pregnancy. Use should be based on a risk-benefit assessment.

Breast-feeding

Limited data available, use with caution and consult a healthcare professional.

Storage

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

Formulations

• Topical cream
• Ointment
• Gel

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

There is no well controlled data that can formally substantiate the method of action. However, ongoing studies suggest that there may exist a histological wound healing profile induced by allantoin in rats that leads to the amelioration and fastening of the reestablishment of normal skin. This facilitation of wound healing is supported by observations that wounds inflicted to rat subjects to which topical allantoin preparations were applied histologically demonstrated increased vasodilation, presence of inflammatory exudates, number of inflammatory cells, angiogenesis, fibroblast proliferation, and increased collagen deposition when compared to rat subjects with wounds that did not receive any allantoin administration.

Pharmacodynamics

There is no well controlled and appropriate data that can formally substantiate the pharmacodynamic properties of allantoin. Nevertheless, ongoing studies suggest that allantoin possesses moisturizing and keratolytic effects, as well as abilities to increase the water content of the extracellular matrix and enhance the desquamation of upper layers of dead skin cells, all of which are activities that can promote cell proliferation and facilitate wound healing.

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.