W 4 Doses calculation PDF

Dose calculation Workshop 4 3°Medicine Professor: Vittoria Carrabs PhD Aa 2024-25 Calculation of doses You should perfectly manage units of volumen and mount and know the relationship between the different units The smallest error here could mean an error of p...

Dose calculation Workshop 4 3°Medicine Professor: Vittoria Carrabs PhD Aa 2024-25 Calculation of doses You should perfectly manage units of volumen and mount and know the relationship between the different units The smallest error here could mean an error of prescribing or using a dose ten times higher or lower, so it could be toxic or ineffective https://www.lasexta.com/noticias/socied ad/muere-bebe-darle-error-dosis- medicina-diez-veces-mayor-prescrita- gregorio- maranon_201910085d9c46d00cf26b4ee8b2 c751.html 2 Calculation of doses Drug dose for a particular patient depends on the patient’s: - age - weight - body surface area - general physical health - liver and kidney function (metabolism and elimination), - severity of the illness being treated Calculation of doses: Based on age Doses of drugs can be adjusted in terms of age. It could vary the amount in the dose and/or the frequency of administration Neonates Inmature hepatic and renal function Children Risk of Diminished organ function overdosage Elderly patients Issues with concomitant pathologies and toxicty Increased sensitivity to drugs Drug doses must be reduced to minimize the risk of adverse effects. Age is typically used in conjunction with other factors, such as weight, to determine the appropriate dosage. Dosage may vary due to individual differences.  CALCULATION OF DOSES GENERAL CONSIDERATIONS Dose definitions Dose measurement PATIENT PARAMETERS Patient parameters like age, weight, and health conditions influence the required dose. Different methods are used to express doses, ensuring personalized and accurate treatment. The aim is to adjust the dose to each individual to enhance effectiveness and reduce risks. Drug dosage based on age Drug dosage based on weight Drug dosage based on surface area DOSE PREPARATION: HOW TO CALCULATE THE CORRECT DOSE Concentrations can be expressed in %: Solid (p/p): % of drug A ➔ x g of A in 100 g of solid sample Liquid (p/vol): % of drug A ➔ x g of A in 100 ml of liquid sample 5  Calculation of doses: Weight Doses of the drugs could be mentioned in terms of mg(ml)/kg body weight A more accurate method of calculating an individual dose is based on body surface area  Calculation of doses: Body Surface Area (BSA) The body Surface area (BSA) is a method of calculating drug dose widely use in two patients groups: Oncology patients undergoing chemotherapy Pediatric patients BSA is expressed as m2 and it can be calculated by using: Equations Nomograms Calculation of doses: Body Surface Area (BSA) 8 Dose definitions DOSE of a drug (unit dose): amount (mg, ml, drops…) of a drug to be administered to a patient at a time to obtain a desired pharmacological effect DOSING INTERVAL: frequency of dose (how often is given the dose) Examples: every 8h➔ dosing interval 8h once a day➔dosing interval 24h twice a day ➔ dosing interval 12h DOSAGE REGIMEN: determination of the amount (dose), route, frequency and number of doses of medication for a patient. Examples: dose (mg or ml) twice a day for 5 days rectal route dose (mg or ml) p.o every 8 hours during 7 days p.o (oral route of administration) Dose definitions Single dose: is the dose for a treatment that just need to take the dose once e.g mebendazole for the treatment of pinworm infection. Maintenance dose: dose administered according to the dosage regimen (is the dose administered every dosing interval) to sustain the desired drug effects (without toxicity). 3 Loading dose: a larger-than-usual initial dose which is required for certain drugs to more rapidly achieve the desired blood drug level (effective and no toxic) Prophylactic dose: dose administered to achieve drug plasma levels to prevent a disease or infection (protection) Therapeutic dose: dose administered to achieve efficacy without toxicity Dose definitions Different types of expressing doses: Daily dose: recommended dose for one day (usually subdivided in divided doses) Examples: mg (ml)/ day in 3 divided doses mg (ml)/ kg/ day in 4 divided doses Usual dose range: range of dosage determined to be safe and effective in that same population group Low-dose therapy High-dose therapy Usual adult dose, usual pediatric dose: Amount of a drug that produce the desired therapeutic response in the population group Total dose: total amount of drug administered during all the treatment  Dose measurement An example of a calibrated medication cup for administering oral liquid medication An example of a calibrated oral dispenser for administering liquid medication to pediatric patients An example of scored tablets. The score is use to facilitate the splitting of the tablet into fractions so we can obtain a lower dose than the tablet one or multiple smaller doses Dose measurement The DROP as a unit of measure: The volume of a drop can vary depending on factors like the liquid's viscosity, surface tension, and the dropper used. Always check the specific relationship between volume and drops for each liquid medication to Calibrated dropper ensure accurate dosing.  United States Pharmacopeia (USP) defines the official medicine dropper with a 3 mm external diameter, which delivers 20 drops of water per mL.  The dropper should not be used to measure a specific liquid medication unless the volume per drop for that specific liquid has been determined.  Dose calculation How to calculate the medication amount if a concentration is known You have several 1 mL vials with a 10% concentrated drug (A). How would you prepare 30 mg of drug A? 15  Dose preparation: How to dilute solutions (specially for pediatrics) Beginning with a 20% concentrated solution (C1). How would you prepare 70 mL (V2) of a 5% diluted solution (C2)?  Where: C₁ = concentration of the starting solution V₁ = volume of the starting solution required Dose preparation: C₂ = concentration of the final solution V₂ = volume of the final solution How to dilute solutions (specially for pediatrics) C1 · V1 = C2 · V2 ; (C1/C2) · V1 = V2 Beginning with a 20% concentrated solution (C1). How would you prepare 70 mL (V2) of a 5% diluted solution (C2)? Solution: V1= C2 · V2 / C1 V1 =5 · 70/ 20 V1= 17.5 mL Desired final solution: (70 mL–17.5 mL) 52.5 mL solvent + 17.5 mL of 20% solution EXERCISE CORRECTION