Basic Dispensing Calculation Of Medication Doses PDF

 CALCULATION OF MEDICATION DOSES Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  DOSE- quantitative amount administered or taken by a patient for the intended medicinal effect Expressed as: SINGLE DOSE - amount taken at one time DAILY...

 CALCULATION OF MEDICATION DOSES Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  DOSE- quantitative amount administered or taken by a patient for the intended medicinal effect Expressed as: SINGLE DOSE - amount taken at one time DAILY DOSE :can be subdivided into DIVIDED DOSES- two or more times per day TOTAL DOSE - the amount taken during the course of therapy DOSAGE REGIMEN - schedule of dosing 2021-9-30  weight and condition dosage form prescribed of the patient Age possible influence of other the frequency of drugs being taken administration Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  USP Dispensing Information : usual dosage and dosage ranges Manufacture’s Catalog, File Cards & Package : for dosage information for many drugs use Physician’s Desk Reference Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity   AMA Drug devaluations  American Hospital Formulary Services Drug Information, facts and Comparisons  Pediatric Dosage Hand Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  Factors affecting the Dose The increasing potency and complexity of modern drugs have increased the importance of exact determination of dosage. The optimum dose for a particular patient is highly individualistic, and must be determined by the physician after careful analysis of the patient’s history, examination, and diagnosis. Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity History and examination: age, sex, weight, body surface area, previous illnesses, emotional state, tolerance, and idiosyncrasy. Diagnosis : type and severity of the disease, presence of the pathological conditions. Patient’s environment: location, facilities, seasonal time and temperature. Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity Example: (a) Rx Sulfadiazine……………0.167 Sulfamerazine…………0.167 Sulfamethazine……….0.167 DTD cap. #24 Sig. 4 caps. Stat, then 2 caps q 4 h Each sulfa drug is prescribed in reduced the quantity since the combination is additive, and the total dose is reasonable. The initial dose is intended to bring an immediate effect. The antibacterial spectrum and therapeutic uses of sulfonamide mixtures are the same as those of the individual components but an advantage of such mixture is the lesser incidence of crystalluria and renal injury associated with their use. Collegeof Pharmacy | Central PhilippineUniversity | Jaro, IloiloCity  Example: (b)Rx Phenobarbital gr. iss tab No. xxiv Sig. One h.s s.o.s The usual adult dose of Phenobarbital is 30 mg, but single doses of 100 mg are prescribed occasionally. However, high doses of Phenobarbital should not be taken frequently because it has long term duration of action. the frequency of dose/ dosage form in which administration administered Age, weight or body surface area of the Px Sex of the Severity and type patient of illness CALCULATIONS  Over the past years various rules for that child is small calculating infants and children dosages have been devised adult are sometimes more susceptible than adults to certain drugs Doses for infants and children, where they are known, may be found in the USP, and APhA booklet entitled Pediatric Dosage Handbook and textbooks on the pediatrics. Doses should be calculated when it is possible to obtain the actual infant’s or child’s dose.  RULES FOR APPROXIMATE DOSES FOR INFANTS AND CHILDREN: 1. Young’s Rule (for children 2 years and older) 2. Clark’s Rule  3. Cowling’s Rule 2021-9-30 4. Deling’s Rule Age(year) xAdult Child’s dose 20 Dose approx. 5. Basteado’s Rule Age (year)+3 Child’s dose 30 xAdult Dose approx. 6. Fried’s Rule ( for infants up to 2yrs 7. The Square meter Square Surface Area Method - relates the surface are of individuals to dose. It is thought this is more realistic way of relating dosages. Body surface Area of child (m2) xAdult Child’s Body Surface are of Adult (m2) dose dose approx. Body surface Area of child (m2) xAdult Child’s Body Surface are of Adult (m2) dose dose approx. The average body surface area for an adult has been given as 1.73 m2 hence, Body surface Area of child (m2)x Adult Child’s 1.73 dose dose approx. 2021-9-30 2021-9-30 2021-9-30  : Drug dose are often stated mg/kg body weight and may be calculated as follows; Mg/kg x body weight= Individual’s dose This is the most common way of determining children doses. Drug doses also may be stated in units, as with vitamins A and D, penicillin, and hormones. This means that a certain quantity of biological activity of that drug is called 1 unit.  : The USP often standardizes the unit for such drugs, so the expression “USP Units” is used. This means the unit are calculated based on USP assay procedure and reference stated. Rules For Calculating Dosage On Prescription Orders  to find the amount of an ingredient/dose in a compound prescription order, divide the total amount of ingredient prescribed by the number of doses.  To find the total amount of an ingredient used to compound a prescription order, multiply the amount/dose prescribed by the total number of doses.On prescription orders, when the instructions to the pharmacists includes the expression D.T.D No… (such doses), it instructs the pharmacists to multiply the dose (amount of drug) stated in order by the number indicated in the expression, D.T.D No.. Rules For Calculating Dosage On Prescription Orders Remember: It is always better to look up the dose of drugs in textbooks or compendia than to rely on memory equations.  SAMPLE PROBLEM The adult dose of drug of a drug is 5 gr. What is the dose for a 3- year- old child? Using Young’s Rule: Child’s dose (approx)  SAMPLE PROBLEM What is the dose for a 40-lb child if the average adult dose of the medicament is 10mg? Using Clark’s Rule: Child’s dose (approx)  SAMPLE PROBLEM What is the dose for an 8-month-old infant if the average adult dose of a drug is 250mg? Using Fried’s Rule: Child’s dose (approx)  SIGN GIVEN BY PHYSICIANS TO INFORM THE PHARMACIST THAT HE IS AWARE OF THE OVERDOSE: Underlying the drug and the quantity. Writing Q.R. (quantum rectum) after the amount of the drug to show that the quantity has been verified and is correct. Writing both the apothecary and the metric system of the quantity involved.  SIGN GIVEN BY PHYSICIANS TO INFORM THE PHARMACIST THAT HE IS AWARE OF THE OVERDOSE: Writing both the Arabic figures and roman numerals for the quantities. Writing the amount of the medication in words. By initiating the amounts of the drugs desired. By placing exclamation marks before and after the quantity of the drug prescribed.  Measurement of liquid medication may lead to dosage variation caused by differences in the capacity of household spoons and interpretation of which measuring device to use by the patient. A standard teaspoon has been established by the American National Standards Institute as containing 4.93 ± 0.25mL.. A compounding and dispensing problem arises because of the continuing use of fz i, the symbol for one fluid dram. This represent one-eight of an apothecary fluid ounce but is frequently interpreted as one teaspoonful when the physician uses this designation in his instructions to the patient. When the following prescription is considered, the problem becomes evident.  It is important because usually infants and children generally (but not always) require a smaller dose than adults. AGE  Most of the average dose of drugs in the USP/NF is a quantity recommended for oral administration. Drugs administered by injection are given in smaller quantities than those orally and are tolerated safely. Usually hypodermic dose is considered ½ the oral dose and the intravenous dose is considerably less. Rectally the quantity is twice the oral although there are exceptions. Locally, in ointment or liniment form, absorption is general variable so no relationship to the oral dose can be stated. Dosage Form Administere d  If the drug has a fleeting action, there should be little concern about the short intervals of time between doses. They can be given more frequently than those with prolonged action. Frequency of Administration  On the other hand, potent drug with cumulative action may show toxic manifestation even though individual dose appears to be safe if frequency of administration is often. There should be more possible a large number of doses over a short time. Example of cumulative drug: Nux vomica, digitalis, mercury and its compounds, and arsenicals. Frequency of Administration The type of drug action determines frequency of administration. There are several factors that may require altered dosage of individual drugs. Examples: Quick acting and rapidly eliminated drugs may be given more frequently than those slowly eliminated or have prolonged action. Combination of drugs may require altered dosage of individual drugs, lower in case of additive or synergistic combination, higher in case of antagonistic combination.  Particularly good reason may lead a doctor to give an apparent overdose of a drug and perhaps intends the dose he has prescribed. Nevertheless, the pharmacist should consult the prescriber to clarify that the dose is safe. There many factors involved concerning the safety of a given dose that physician alone knows. Frequency of Administration Example: A nervous person usually requires a greater quantity of a sedative than a normal person. Phlegmatic person usually requires a quantity of a stimulant that seems abnormally large. Cross tolerance may exist in the patient who may have been taking one sedative for some time and has developed a tolerance for other member sedatives of the group as well as the one taken. Pathological conditions sometimes demand larger doses of certain drugs. There may be unusually large amount of pain accompany the condition and abnormally large doses of narcotic may be required Idiosyncrasy - is an unusual response to an average dose of a drug. It could be: Over-response which is abnormal susceptibility; under-response which is abnormal tolerance; different action which has opposite action than what is expected like stimulation instead of depression (e.g. morphine sometimes acts as a stimulant in young hysterical girls producing delirium); developments of abnormal symptoms. Cross tolerance – the development of tolerance for other drugs after taking certain drugs with similar effects for a certain period of time. An example is the tolerance developed for one sedative frequently leads to tolerance for another sedative. Alcoholics requiring larger amounts of anesthetic than the non- alcoholics. Synergism - when two drugs having similar actions are given together, one enhances the action of the other producing more pronounced effect than would be obtained with either drugs given alone. This permits the giving doses of each drug. Example Combination of codeine (30mg) and ASA (0.3g) will have a greater effect than codein (60mg) and ASA (0.6g) individually.  In general, women require smaller dosage of drugs than men and thin patients needs less dosage then heavy ones. Sex of the Patient  They may likewise alter the usual dosage requirements. For example extreme pain requires a higher degree of analgesia for relief than slight pain. Nature and Severity and Duration of Illness