Pharmaceutical Calculations Ppt

[Channing Rupnick]

Thispresentation quotes various pharmaceutical calculations with examples. The following aspects like percentage calculations, alcoholic dilutions, Alligation method, proof spirit calculations, isotonicity adjustment, posology, temperature measurements, dialysis clearance, Pharmacokinetics calculations were covered with examples.Read less

Utilizing pharmacy calculations to administer therapeutics to patients correctly is vital to patient treatment. Health care professionals must dispense drugs in the accurate concentrations, calculate correct doses, and compound and prepare medications accurately to ensure that each particular drug is being administered correctly.

Dose refers to the amount of medication taken at a specific time, whereas the dosage of the drug refers to the administration of a frequency, amount, and the number of doses taken over a particular period of time.

The relationship between concentration and volume is inversely proportional. (See Figure 1 for a schematic of the inverse relationship between percent of concentration or ratio strength (decreases), and the total quantity of product (increases)).

It is important to note that when two solutions have equal osmotic pressure and salt concentration, they are said to be isotonic. Normal saline has a concentration of 0.90% w/v of NaCl in sterile water and therefore is an isotonic crystalloid.[5]

Additionally, pharmacy calculations require the knowledge of commonly used units; certain medications are dispensed in metric system units such as mg or mL, whereas others may be dispensed in other measurement systems. Vitamin D, for instance, is administered in International Units.[7]

Drugs may be administered through various routes of administration, oral, IV, IM, parenteral, etc.; these factors must be accounted for when computing calculations and consistency when converting units across different measurement systems is important in maintaining accuracy in pharmacy calculations. This issue also impacts patient care as patients may use the household and avoirdupois systems when using their medications (teaspoons and tablespoons), although the medication was dispensed in mL. It is important to know units within each system (such as 1 pound = 16 ounces). quantity, conversions are required between the US Customary System and the metric unit system.[8] Some commonly used conversions are:

Roman numerals are often used on prescriptions as they are challenging to alter, whereas decimals are also used elsewhere in pharmacy practices. Measurements requiring decimals are usually converted into fractions; thus, familiarity with converting measurements between various systems and a foundation in basic arithmetics in terms of fractions, ratios, proportions, and percent is necessary to perform pharmacy calculations.

The aliquot method consists of measuring out a small amount of drug, by diluting a larger amount. Aliquoting plays an essential role as a technique to separate a larger sample into smaller parts; it is also equally as important in temperature sensitivity of drugs.[9]

Lastly, stock solutions exist to dispense medications to patients. However, certain patients require different concentrations of drugs, and the Alliqation method exists to calculate and dispense correction concentrations of active ingredients for patients. (See Figure 2 for a schematic of the Alligation method).[10]

It may also be important to account for patients' weight when calculating the correct dose for certain drugs. The body surface area represents the patient's height and weight. In certain patient populations, specific drugs may be dosed based on BSA depending on drug properties. The average adult has a BSA of 1.73 m^2. The equation for BSA may be calculated as follows:

In regards to toxicity, understanding properties of certain drugs is important in order to eliminate them effectively. For acidic drugs: pH = pKa + log [A-]/[AH] and for basic drugs: pH = pKa + log[B]/[BH+].[15]

In addition to pharmacy calculations, other factors in pharmacology must also be a consideration. For instance, bioavailability is the amount of drug from the administered dose that reaches the systemic circulation and should be taken into account. Different routes of administrations can impact drug bioavailability.

It is essential to understand the relationship between pharmacokinetics and pharmacodynamics as these factors influence the drug effect and metabolism. (See Figure 3 for a schematic of the relationship between pharmacokinetics and pharmacodynamics.)

Pharmacodynamics is the study of drug effects and their metabolism of action.[16] Understanding potency of a drug (the amount of medication required to a given intensity of effect) and efficacy of the drug (maximum response achievable), and whether the drug has agonist or antagonist properties. Pharmacokinetics is the study of the time required for the drug to be absorbed, distributed, metabolized, and eliminated (ADME).[16]

Accurate pharmacy calculations are not only necessary for dispensing, dosing, and adequately medicating patients but also a vital component of pharmacological therapy, effect, and, ultimately, patient care. The interprofessional health care team must work together to determine and administer adequate pharmacological treatment to patients. Specifically, differing patient populations may have varying needs. Liver and kidney dysfunction can alter the metabolism of a drug, as can age.[17] Beers criteria are often used to determine which drugs to avoid in the elderly patient.[18] Thus, the accuracy of pharmacy calculations remains an important component of pharmacologic therapy and patient care.

The calculation paper is part 1 of the registration assessment, consisting of 40 questions that need to be completed within 120 minutes. That allows, on average, three minutes to complete each question. It is possible to complete some of the questions in under three minutes, which will provide valuable time to spend on the trickier questions.

It is essential that preregistration trainees are familiar with the types of questions mentioned, so there are no unpleasant surprises in the exam. Knowing what to expect will aid preparation. Good calculation skills are also important for the clinical paper, as it is likely that up to ten questions will require mathematical skills.

Some candidates prefer to fill in the answer sheet of the calculation paper as they progress through it. Others like to fill it all in towards the end of the assessment. Whichever method you choose, it is important to remember that careful transfer is essential.

Candidates are given a resource pack, which may contain extracts of the BNF, patient information leaflets or drug SPCs (summary of product characteristics). Be confident with navigating through the resource pack, and in particular with SPCs, as they are often filled with information that can be overwhelming.

There are a number of formulae that candidates are required to remember for certain questions. For the example below, you would need to know the equation for loading doses in order to manipulate the information provided.

As the June assessment is almost here, preregistration trainees should spend the time left wisely. Time should be spent practising the types of questions that candidates may feel weaker at. The number of steps in solving calculations should be reduced to save time and minimise the risk of making a mistake in the process.

If candidates encounter an unfamiliar question in the exam, it is advised an educated guess be made, as the exam is not negatively marked. As much as candidates should aim for 100% in the exam, not knowing the answers to some of the questions does not mean a fail.

Drug Calculation Questions

R Sinclair, Pharmacy 18.8.2005Drug calculation questions are a major concern for most pre-registration pharmacists and are also a worry for those involved in pre-registration training. When it is obvious that people are struggling with what are basic calculations, as part of a test exam or at their workdesk, one would be right to question their ability to accurately calculate doses in critical situations or environments such as on the Ward.

This Booklet is designed to accompany Booklet 1 and is structured to contain at the start some examples of calculations that students have stated they find difficult followed by a step by step approach to solving the problem

This handout covers a variety of numeracy based tasks which nurses and midwives may be required to perform in practice. These include drug calculations and setting drip rates on the controls of intravenous infusion controllers.

The handout covers the following: SI units and conversions, calculating drug quantities in both tablet and liquid form, and calculating intravenous flow rates and drip rates. Exercises are included at the end of each lesson. Answers are on the back page.

This e-learning from CPPE has been developed to support pharmacy technicians with dispensary-based calculations to ensure accuracy and safety when preparing, dispensing and checking prescriptions for patients.

The aim of this programme is to support pharmacy professionals with calculations in clinical settings when preparing, prescribing or checking medicines or when advising other healthcare professionals. The principles can be applied to any sector of pharmacy practice.

Formula sheet for nursing students including dosage, drop and infusion rates, unit conversion and BMI calculations contributed to the mathcentre Community Project by Shazia Ahmed, University of Glasgow. The leaflet is designed to be printed double-sided on A4 paper and folded into quarters lengthwise first.

A leaflet explaining how solid trituration calculations are performed for the dilution of drug powders. The resource is contributed to the mathcentre Community Project by Abigail Francis and reviewed by Bob Morris, Liverpool John Moores University

A leaflet showing how to calculate the freezing point depression of a solution. The resource is contributed to the mathcentre Community Project by Abigail Francis and reviewed by Bob Morris, Liverpool John Moores University

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