Children are immature individuals, and their anatomical and physiological characteristics and metabolism of drugs are very different from those of adults, so their physiological characteristics and medication specificity must be considered when treating children. This article summarizes the main physiological characteristics of children and some precautions of commonly used dermatological drugs for clinical reference.
Children are growing and developing, and the clinical manifestations of their diseases as well as their tolerance and responsiveness to drugs are different from those of adults, and their conditions are more acute and fast-changing, which requires more precise and timely medication. Therefore, we must be familiar with drug selection, dose calculation, adverse drug reactions and drugs prohibited for children and other considerations.
1.Familiar with the physiological characteristics of children
The age range of children is generally considered to be from birth to 14 years old, including newborn, infancy, early childhood, preschool, school age and adolescence. Many organs (such as heart, liver, kidney) and the function of the nervous system are not yet well developed, the physiological function is not yet mature, the immune mechanism is not sound, and the detoxification function is also poor, so they have special reactions to drugs.
Children’s drug metabolism characteristics.
(1) Children’s liver enzyme level is only 30% – 50% of that of adults, and lack of enzymes for glucuronide generation, the oxidized products cannot form glucuronide derivatives, poor detoxification ability of drugs, and prolonged half-life.
(2) In children, especially in infancy, the blood-brain barrier is not yet developed and permeability is high, especially in hypoxia, and the concentration of drugs in cerebrospinal fluid is relatively higher.
(3) Children have imperfect renal function, lower effective blood flow and glomerular filtration rate than adults, slower drug excretion and longer biological half-life. Some adverse reactions that are rare in adults may also occur in children, and even serious adverse reactions. Therefore, the physiological characteristics of children need to be fully considered when using drugs.
2, master the calculation of children’s drug dose
Children’s reaction to drugs is different from that of adults, so the dosage of drugs must be more accurate than that of adults. The calculation method of pediatric drug dose includes calculation based on weight, body surface area and age. At present, the first two methods are mostly used.
(1) Calculation according to body weight.
The dose of medication per kilogram of body weight of the child is calculated by multiplying the number of kilograms of the child’s body weight as recommended in the drug instructions. If not provided, it can be estimated according to the formula (child dose = adult dose x child weight/70kg).
(2) Calculation by body surface area.
This method is the most reasonable and scientific, and is suitable for children of all ages. The dose per square meter of body surface area is the same regardless of age. The disadvantage of this method is that it is cumbersome to calculate. The formula for calculating body surface area: body surface area (m2) = body weight (kg) × 0.035 + 0.1. This formula is suitable for children under 30 kg. If the recommended dosage for children is not provided in the drug instruction but only the adult dosage is known, it can be estimated according to the formula (child dosage = adult dosage x child body surface area/1.73).
3. Clear diagnosis and rational drug selection
Clinicians should strictly grasp the indications for drug use, and select carefully and reasonably under clear diagnosis, and choose suitable dosage form, dose and route of administration according to age and condition. There should not be too many types of drugs, and drugs that can be used or not used should not be used as much as possible. In the combined application of several drugs, attention should be paid to the adverse effects of drug interactions or offsetting drug effects and other issues. The selection of several types of drugs commonly used in dermatology is listed below.
(1) antihistamines.
The first generation of H1 receptor antagonists due to the ability to pass the blood-brain barrier and anticholinergic effects, often cause drowsiness, sedation, drowsiness, fatigue or inattention, dry mouth, tachycardia and other adverse effects, and some reports of prolonged use can affect the development of cognitive function in infants and children’s memory and psychomotor. Due to the lack of controlled clinical studies in large samples of children, it is now less commonly used in clinical practice. Chlorpheniramine maleate (0.3-0.4 mg/(kg・d)), cycloheximide (0.3 mg/(kg・d)) and promethazine (1-3 mg/(kg・d)) are the main drugs that are relatively safe for use in children. These drugs are contraindicated in newborns and premature infants, and should be used with caution in children under 2 years of age. In recent years, a large number of multicenter, randomized double-blind and placebo-controlled clinical studies have proved that second-generation H1 receptor antagonists have definite effects in the treatment of common allergic diseases in children and alleviate clinical symptoms, and their efficacy and safety in children have been recognized. Cetirizine, levocetirizine, loratadine, desloratadine and fexofenadine are available for children. The dosage should be adjusted according to weight and age.
(2) Anti-infective drugs.
Children are prone to infectious diseases, and most of them are acute infections with rapid changes in condition, so drugs should be selected according to the disease type, severity and age. If the infection is clinically certain to be viral (such as measles, rubella, etc.), antiviral drugs or certain herbal preparations can be used instead of antibacterial drugs. Misuse of antibacterial drugs can cause adverse effects to the child due to various adverse reactions, so indications and adverse reactions need to be carefully considered. In the beginning, empirical use of drugs can be based on clinical signs and symptoms and relevant laboratory tests, and targeted selection after bacterial culture and drug sensitivity results. Try to choose narrow-spectrum antibiotics, to apply an antibacterial drug is appropriate. The dosing interval should not be too long (children are relatively fast metabolizers). The dosage should not be simply a fraction of the adult dosage, but should be calculated according to body weight and body surface area. The method of administration is mainly oral. Antimicrobial drugs prohibited in children: tetracyclines (under 8 years of age), sulfonamides (neonates), nitrofurans (neonates), bacitracin (neonates), ethambutol (neonates), fluoroquinolones (birth to 18 years of age).
(3) Glucocorticoids.
Mostly used for inflammatory skin diseases, allergic diseases, can be short courses of small doses of oral or local (such as the treatment of eczema) treatment, generally more short-term use. If long-term use is required, short-acting (e.g. hydrocortisone) or medium-acting preparations (e.g. prednisone, methylprednisolone) should be used, and long-acting preparations (e.g. dexamethasone) should be avoided. Reference dosage for children: 2-10 mg/kg.d for hydrocortisone, 1-2 mg/kg.d for prednisone, 0.5-2 mg/kg.d for methylprednisolone. long-term use in children may cause various adverse effects such as suppression of hypothalamic-pituitary-adrenal axis function, growth inhibition, osteoporosis, hypertension, gastric ulcer/hemorrhage, femoral necrosis, susceptibility to infection, and neuropsychiatric symptoms. Therefore, they should be used with caution and avoid abuse. Topical glucocorticosteroids are usually the main drugs for the treatment of allergic skin diseases in children. Since children have thin and tender skin, relatively large body surface area and higher sensitivity than adults, they should strictly control the indications and choose topical hormones of different concentrations and strengths according to the nature, type and location of skin lesions in children, and use them in small doses for a short period of time as much as possible to reduce adverse reactions. The use of strong hormone preparations for children should not exceed 2 weeks of continuous use, and should be used with caution especially for infant diaper dermatitis.
(4) Topical dermatological drugs.
Children, especially infants, have a relatively large skin mucous membrane area, thin skin stratum corneum and delicate mucous membrane, so the drug is absorbed more rapidly and extensively through the skin than adults, especially when the skin is inflamed or broken, more absorption, which can easily cause adverse reactions or even poisoning, and need to be alert. In addition to the general principles of topical medication, children should also pay attention to the following when using topical medication.
① The area of local topical medication should not be too large. Such as boric acid, generally small wet area is not very toxic, if the wet area is too large, it can be absorbed through the wound surface acute poisoning, or even cause circulatory failure, shock or death.
② Topical drug concentration should be lower than adults, children’s skin is thinner and more tender than adults, the body surface area is relatively large, so the drug absorption than adults for more. Topical drug concentrations such as close to the adult concentration is likely to cause erythema, burning sensation, pain and other local irritation. Such as vitamin A acid topical drugs, the concentration should not be too high, generally less than 0.03% is appropriate. When treating scabies, children should use 5% concentration of sulfur ointment, and adults should use l0% sulfur ointment.
③ try to choose mild, non-irritating topical drugs, should not use very strong irritant drugs, such as salicylic acid, iodine, etc., so as to avoid blistering, peeling or corrosion of the skin. If it must be used, it should be started from low concentration, and the irritation symptoms need to be stopped immediately.
④ Pay attention to the safety of the use of topical medication, need to prevent children from rubbing into the eyes or eating into the mouth with their hands.