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RULES FOR PRESCRIBING CREAMS AND OINTMENTS
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On average, 30 g of cream will cover the body surface area of an adult. Ointments, despite being of a thicker consistency, do not penetrate into the deeper skin layers so readily, and the requirements are slightly less. Pastes are applied thickly, and the requirements are at least 3 to 4 times as great as for creams.
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The ‘rule of nines’, used routinely to determine the percentage of body surface area affected by burns (Fig. 16.1), may be used also to calculate the amount of a topical preparation that needs to be prescribed.
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If 9% of the body surface area is affected by eczema, approximately 3 g of cream is required to cover it.
Nine grams of cream is used per day if prescribed 3 times daily.
A 50 g tube will last 5 or 6 days.
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One gram of cream will cover an area approximately 10 cm × 10 cm, and this formula may be used for smaller lesions.
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Use creams or lotions for acute rashes.
Use ointments for chronic scaling rashes.
A thin smear only is necessary.
On average, 30 g:
will cover an adult body once
will cover hands twice daily for 2 weeks
will cover a patchy rash twice daily for 1 week.
On average, 200 g will cover a quite severe rash twice daily for 2 weeks.
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TOPICAL CORTICOSTEROIDS FOR SUNBURN
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When a patient with severe sunburn presents early, the application of 1% hydrocortisone ointment or cream can reduce significantly the eventual severity of the burn. This has been proved experimentally by covering one-half of the burnt area with hydrocortisone and comparing the outcome with the untreated area.
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The application can be repeated 2 to 3 hours after the initial application and then the next morning. The earlier the treatment is applied the better, as it may not be useful after 24 hours.
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Hydrocortisone should be used for unblistered erythematous skin, and not used on broken skin.
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SKIN EXPOSURE TO THE SUN
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There is evidence that our skin needs exposure to sunlight to provide a substantial dose of vitamin D. This is a preventive for osteoporosis. Hats and sunscreens prevent the natural synthesis of vitamin D in the body.
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There should be a balance between receiving enough sunlight exposure to prevent vitamin D deficiency on one hand and receiving too much, predisposing to skin cancer, on the other (see Table 16.1). A simpler guideline for most geographical areas ...