mortar and pestle
Robert P. Shrewsbury
ROBERT P. SHREWSBURY PhD
Beard Hall, Room # 202B
Email: bob_shrewsbury@unc.edu
  Resources

Lab Data

Devices That Dispense Measured Amounts of Ointment 2014

Several products are available that allow patients to easily dispense metered dosages of creams or ointments with a degree of accuracy. Among these are the AccuPen™, Topi-Click®, and Exact-a-Dose dispensers for Unguator® jars. An experiment in the student compounding laboratory compared a mock progesterone ointment dispensed from the AccuPen™ and the Topi-Click®. Students made the ointment composed of calamine, PEG 1450, diphenhydramine, and Emollient Cream™ and packaged the two dispensing devices according to the manufacturers’ instructions. The ointment was dispensed into weigh boats multiple times (n=5) and weighed with an electronic balance by each student (n=139). The tapped density of the ointment (approx. 0.97 g/mL) was used to convert the weight of ointment to the volume of ointment dispensed by the device. The AccuPen™ is designed to dispense 0.25 mL with 2 actuations, and the Topi-Click® is to dispense 0.25 mL with 1 click.

Average volume of ointment dispensed per actuation: a) within a range of volumes.


In this Excel histogram, the volume dispensed is given within a range of volumes. The largest number of students had volumes dispensed per actuation within the 0.08-0.10 mL for the AccuPen™ and 0.12-0.14 mL for the Topi-Click®.

Average volume of ointment dispensed per actuation: b) by percentage of volumes.

Data collected from the students shows that the AccuPen™ dispensed the stated volume only a few times, whereas the Topi-Click® did not meet its volume at all. From the AccuPen™, more than half of the students actuated an average volume between 0.08 to 0.1 mL (figure a), most of which were approximately 0.085 mL (figure b). The Topi-Click® showed more variation in dispensed volumes. The outcomes of this experiment cannot be directly compared to the manufacturers’ claims, however, because the viscosities and densities of the preparations used to calibrate the devices are not known. It is to be expected that differences in physical properties would yield different results. As with any metered dosing device, both dispensers should be calibrated before dispensing to patients.

Devices That Dispense Measured Amounts of Cream 2015

The data from fall semester 2014 was shared with the Topi-Click company because they had donated the Topi-Clicks to the compounding lab. Representatives from the company discussed with our laboratory that they had developed a testing protocol that was different than ours, and would be interested in reviewing the data when collected according to their protocol. The protocol was available to Schools of Pharmacy, and the company had recommended prototypical creams to use in the evaluation of the amounts dispensed by the device.

The protocol was discussed and demonstrated to the students via a pre-class video. The preparation was also changed in 2015 to more minic the prototypical creams the company was indicating they had used in evaluating their device. Our cream formulation was 6 g salicylic acid, 24 g propylene glycol, and qs to 60 g emollient cream™. Salicylic acid was used as the API since the students' compounded cream was to be analyzed for potency.

The cream was packaged into an AccuPen™ and the Topi-Click® according to the manufacturers’ instructions. The students primed the devices until their compounded preparation was consistently dispensed from the devices with each actuation, and then they measured the initial weight of the device. The students then actuated the device as instructed, and reweighed the device. They repeated this procedure to obtain 7 data samples and calculated the average volume dispensed actuation. The density of the cream (0.90 g/ml) was determined the method outlined in the protocol, and was used to convert the weight of cream to the volume of cream dispensed by the device.

Average volume of cream dispensed per actuation: a) within a range of volumes.


In this Excel histogram, the volume dispensed is given within a range of volumes. The largest number of students had volumes dispensed per actuation within the 0.125-0.150 mL for the AccuPen™ and 0.225-0.250 mL for the Topi-Click®.

Average volume of cream dispensed per actuation: b) by percentage of volumes.

For the AccuPen™, 45% of the collected values were between 0.125-0.150 mL, 24% was between 0.10-0.125 mL, and 24% was between 0.150-0.175 mL per actuation. Therefore, 93% of collected data was between 0.10 and 0.175 mL per actuation. For the Topi-Click®, 52.6% of the collected values were between 0.225-0.250 mL, 25.6% was between 0.20-0.225 mL, and 12.8% was between 0.250-0.275 mL per actuation. Therefore, 91% of collected data was between 0.20-0.275 mL per actuation.

When the results from 2015 were compared to the results from 2014, the results from both the AccuPen™ Topi-Click® were much closer to the manufacture’s claims. There are three possible reasons to explain the difference.

  1. The cream for 2015 was composed of propylene glycol, salicylic acid, and Emollient Cream™. The ointment used in 2014 had the same density value, but included calamine as an ingredient. Calamine is a clay material, which can turn the preparation into a more solid material. The thick consistency of the ointment possibly contributed to an inconsistent amount dispensed from the AccuPen™ and Topi-Click®.
  2. The students in 2015 used a different method to determine the weight dispensed with each actuation or click. Previously (2014), the amount dispensed was collected in a weigh boat and the weigh boat was directly measured. In 2015, the amount of cream dispensed was removed from the device with a Kimwipe, and the weight difference in the device was determined.
  3. In 2015, the students were instructed to wait 30 seconds after an actuation or a "click" to allow the preparation to dispense fully leave the device. The process of waiting allowed the device to fully dispense the cream.

 

What Concentration of Flavoring Should be Used

Most drugs have disagreeable tastes, which can interfere with patient compliance. In order to aid in compliance, preparations can be flavored to increase the palatability of the medication. What is palatable to one person may not be palatable to another person, so there is variability in the amount of flavoring that may be required for a given patient.

Students (n = 129) made an enalapril suspension which they could flavor with banana crème, root beer, guava, peach, honey, or watermelon flavoring. First, students were instructed to flavor 15 mL of simple syrup to their desired taste with the flavoring of their choice and calculate the percentage of flavor added to the simple syrup.

Average volume and SD of flavor used to achieve desired taste in simple syrup

Flavor
(number of students that used the flavor)

Average volume added to 15 mL of simple syrup (mL)

Standard Deviation

Banana Crème (n=12)

0.264

0.185

Root Beer (n=15)

0.243

0.155

Honey (n=11)

0.444

0.361

Watermelon (n=40)

0.392

0.299

Guava (n=19)

0.520

0.440

Peach (n=29)

0.369

0.214

The table above shows the variation in flavor required to make 15 mL of simple syrup taste as desired for each student based on the flavor used. The standard deviation for the volume of flavor added to 15 mL of simple syrup was at least half of the average volume of flavor added, regardless of the flavor used. This data not only shows how unique each person’s taste preferences are, but also demonstrates the value of patient feedback when compounding flavored preparations for an individual.

Next, the students prepared their enalapril suspension using the same percentage of flavor that was used in their simple syrup. A 15 mL aliquot of the suspension was used to determine if any additional flavor was required to achieve the same flavor that was in the simple syrup.

Percent of students that required additional flavor in the enalapril suspension

Flavor
(number of students that used the flavor)

Number of Students that Added More Flavor

% of Students that Added More Flavor

Banana Crème (n=12)

1

8.3

Root Beer (n=15)

1

6.7

Honey (n=11)

1

9.1

Watermelon (n=40)

10

25

Guava (n=19)

3

15.8

Peach (n=29)

4

13.9

126 students

20

15.9

The majority of students did not have to add more flavor to their suspension in order to achieve the same flavor that was in the simple syrup. A common “rule of thumb” when compounding flavored preparations is to add 5 times the amount of flavor used in the “blank” when preparing the formulation that contains the drug. However, this student data suggests that increasing the amount of flavor used may not be necessary.


 

Number of Nasal Sprays of Dihydroergotamine (DHE)

Healthcare providers may choose to deliver a medication intranasally in order to achieve a faster onset of action or to increase drug delivery in cases where nausea and vomiting may be common. While metered dose inhaler (MDI) nasal pumps are designed to deliver a fixed amount of medication per actuation, the number of actuations that a patient needs depends on the concentration of the medication in the pump and the volume of medication delivered when that patient actuates the MDI device. But a different scenario occurs if the preparation is delivered by a nasal squeeze spray bottle.

Students (n=174) compounded a 2.5 mg/mL dihydroergotamine (DHE) nasal solution. The actual concentration of DHE in their preparation was determined using UV spectrophotometry (λ=270). Students also determined the average volume of medication dispensed with each actuation of an MDI nasal pump and a nasal squeeze spray bottle.  This information was used to determine the number of actuations required for the patient to dispense 0.5 mg of DHE.

Actuations required to deliver 0.5 mg DHE from a nasal squeeze spray bottle

There was wide variation in the number of actuations required by each student to deliver the desired 0.5 mg of DHE. Only 9 out of the 174 values provided were whole number actuations, which could also be a challenge when providing patients with actuation instructions. It is extremely important for a pharmacist to calibrate any metered dose devices a patient receives, and since there can be interpersonal variability in the amount of medication dispensed per actuation, it may be worthwhile for the pharmacist to have the patient perform the calibration procedure so that instructions can be provided based on the patient’s use of the device.


 

Average Weight of Tablet Triturates

Tablet triturates are small in size and allow for complete and rapid dissolution in water. Preparation of tablet triturates includes: a) preparing the powder mixture; b) wetting the powder mixture with a hydroalcoholic solution to some measureable end-point; c) pressing the powder into the cavity plate, filling one or two rows at a time; d) filling all of the cavities uniformly and to capacity; e) placing the cavity plate on the peg plate; f) removing the tablets from the cavity plate; g) allowing the tablets to dry on the pegs.

Students (n=173) prepared 10 mg enalapril triturates following the procedure described above. A 100 mg cavity mold was used, but the students did not calibrate the molds but used one set of data provided by the instructor (due to time limitations). The average weight of three of each student’s tablets was measured.

The weight variation of tablets compounded in a student laboratory

An acceptable tablet weight was considered 0.100 g ± 0.005g. Approximately two-thirds of the students had the average weight of their tablets within the range. The remaining students were likely out of range due to factors like the speed at which the student moved across the cavity plate as well as how much pressure was applied during the filling of each cavity. Those with lower than desired tablet weights probably moved across the cavity plate slower or did not apply sufficient pressure while filling the cavities. Those with tablet weights that were higher than desired probably applied too much pressure while filling the cavities. Another possible explanation is that the cavities in the 75 tablet triturate molds are not identical.

The standard deviation of the average weight of three tablets from all of the students was 9 mg. The average of the standard deviation between the three tablet weights from each student was 8 mg. This suggests there is notable variation in the tablet weights between students and within a cavity plate. The results indicate that when compounding tablet triturates with a mold, it is essential to utilize some type of quality control measure and mold calibration procedure to ensure the accuracy of the compounded preparation.


 

Rate of Mixing Promethazine PLO

If a small quantity of PLO preparation is to be made, each of the components (i.e., Poloxamer F-127 gel and the lecithin and isopropyl- palmitate solution) can be placed into a syringe and the two syringes connected by an adapter. The mixture is then forced between the two syringes and the shear caused by passing the mixture through the adapter creates the PLO.

In a student compounding laboratory exercise, promethazine 10% PLO gel was compounded by 136 pharmacy students using the two syringe technique described above. The gels were analyzed using approximately 0.1 mL of each student's preparation, dissolving the weighed sample in 20 mL of tetrahydrofuran or methanol, and reading on a spectrophotometer against a blank of PLO without promethazine.

Results of promethazine 10% PLO gel analysis

An acceptable preparation was considered 1.0 g ± 10%. Within that range, 50 students successfully compounded the preparation. There were 87 students within the range of 1.0 g ± 20%. In an attempt to understand parameters that might explain such a wide range of results, a second experiment was conducted by one student. The ingredients in one of the syringes were pushed into the other syringe in a fixed period of time to simulate a difference in the speed of mixing. The fixed times were 1, 5, 10, and 20 seconds per transfer from one syringe to the other which represents a 20-fold difference in mixing speeds. The samples were read on the day they were compounded (Day 0), and then three days after they were made (Day 3). The standards followed the time periods of the students' samples. Each time period had an n=4.

Promethazine PLO compounded at different rates of mixing

Analysis of the mean and standard deviation of the absorbance readings suggests that the rate (or speed) of mixing was not a significant factor in the final concentration of promethazine in the PLO emulsion.

The data was also assessed to see if gender played a role in the final concentration of promethazine in the PLO emulsion. Using 1.0 g ± 10% as the acceptable range, 34% of males were able to achieve that range on the first compounding, while 23% of females were within the range.


 

Determining Optimal Pouring Temperature to Maximize Product Uniformity and Consistency of a Semisolid Preparation

When compounding suppositories, it is important that each suppository has a similar API amount to ensure consistent dosing with each administration. It is thought that factors such as 1) the temperature at which the dispersion is poured into the suppository mold and 2) the amount of stirring that occurs immediately before the dispersion is poured can affect the API amount uniformity of the suppositories.

Small quantities of ingredients are sometimes required to compound some suppository prescriptions. In these cases, the compounder is not able to rely on the accuracy of a standard thermometer since the height of the materials in a beaker does not come to the calibration mark on the thermometer. One possible method of determining when to pour the semisolid dispersion used in our laboratory is for students to pour their preparations when the compounded dispersion was comfortable "to the back of the hand." This is a suboptimal method of deciding the right temperature because "the back of the hand" is interpreted differently by each student, and what may be comfortable for one student may not be comfortable for another student. If the hypothesis is correct - pouring temperature will influence the final API amount - variations in API amounts will result with this method.

Infrared thermometers (Manufacturer: Cen-tech) were used to see 1) if the variation between a single student's suppositories could be minimized and 2) if the API amount could be maximized by providing a specific temperature at which to pour the dispersion. An experiment was conducted in which a portion of the students (n=64) used the "back of the hand" method, and the remaining students (n=98) used the infrared thermometers. All infrared thermometer measurements were taken by laboratory personnel using the following protocol: 1) place the beaker containing the dispersion on the bench top 2) hold the infrared thermometer four fingers-width away from the top of the beaker 3) measure the temperature for 5 seconds, release the trigger, and use the stored number provided by the thermometer as the temperature. Students poured the dispersion when the temperature reached 46oC.

Suppositories containing enalapril as the API were compounded by students. Two suppositories were randomly selected from each student's preparation and analyzed by HPLC for the amount of enalapril. The expected amount per suppository was 1.25 mg. The percent variation in API amount between the 2 suppositories was calculated and categorized based on variation range of 0-9.99%, 10-19.99%, and >20%.

Percent variation of API amount between two suppositories from a single student

Additional analysis was performed to determine whether the use of the infrared thermometer resulted in an API amount that was closer to the expected amount of 1.25 mg per suppository.

Average amount of API per suppository

The use of the infrared thermometer did not reduce the variation in API amount between suppositories. The percentage of students in each variation range was nearly the same, so the back of the hand appears to be as reliable as the infrared thermometer in terms of suppository uniformity. However, the average amount of API per suppository is closer to the expected amount when the infrared thermometer is used (0.998 mg compared to 0.847 mg); the difference was not statistically significant.


 

Determining the Rate of Release from Modified Release Capsules

Modified released capsules can be used to decrease the rate of release compared to conventional dosage forms. This can be useful when longer dosing intervals are desired (i.e., pain medications). Changing the excipients, matrix, and composition of the capsule can aid in achieving the preferred rate of release.

The rate of release can be determined by plotting the amount of API released versus some function of time. For matrix diffusion controlled release, adaptations of the Higuchi equation are used; time is expressed as the square root of time and has units of minutes1/2. A linear trend line is fit through the points that occur after a lag time or before any asymptotic values are reached.

An experiment was performed to demonstrate the effects of Methocel E4M, a hydrophilic matrix material, on the release rate of salicylic acid from a capsule in 0.01 N HCl. A conventional "control" capsule was prepared with 4 mg of salicylic acid q.s. to 350 mg with lactose. The modified release capsule contained 40% Methocel E4M (140 mg), 4 mg salicylic acid, and 206 mg of lactose. Each capsule was placed into its own beaker that contained 100 mL of 0.01 N HCl. The solutions were stirred, and 3 mL of the solution was removed from each beaker every 15 minutes (exact time was recorded). Each 3 mL sample aliquot removed from the beaker was immediately replaced with 3 mL of fresh 0.01 N HCl. The absorbance of each sample was measured at 310 nm, and a Beer's Law plot was used to calculate the amount of drug released.

Release of salicylic acid into 0.01N HCl

The data show that the conventional capsule apparently released all of its contents by 30 minutes because after that time the amount released remained constant. The release rate of 1.55 mg/minutes1/2 was almost three times as fast as seen with the modified-release capsule (0.63 mg/minutes1/2). More important, the modified-release capsule released the drug continuously for hours, whereas the conventional capsule released all of the drug within 30 minutes.


 

Suspension Data - Degree of Flocculation

Suspensions are used when an oral or topical dosage form is needed and the API is not soluble in a suitable solvent or the stability of the drug is poor in solution. An ideal suspension should have a viscosity that allows it to pour/flow freely, while being able to redisperse rapidly and not settle quickly so that each dose is uniform.

Flocculating agents and viscosity enhancers can be added to suspensions to enhance particle "dispersability" and reduce sedimentation rate, respectively. There is a balance that must be achieved between the parameters to ensure that floccules are of sufficient size for adequate dispersion. Floccules are clusters of particles that assume the charge of the flocculating agent, therefore repelling each other as they settle and allowing for easier redispersion of the suspension when shaken. Well-flocculated suspensions have floccules of equal size to allow for rapid and uniform sedimentation; this results in a clear boundary between the settling particles and the suspension. Good suspensions also have larger sedimentation volumes because the floccules are not in intimate contact with each other and occupy more space.

An experiment was performed in which varying amounts of monobasic potassium phosphate was added to suspensions containing 4% bismuth subnitrate. The Sedimentation Rate was determined by measuring the time needed for the floccules to fall 10 mL in a graduate cylinder, and the Sedimentation Volume was recorded as the volume occupied by the settled bismuth subnitrate after 3-4 days divided by 100 mL. The Degree of Flocculation was calculated as the ratio of the Sedimentation Volume of each cylinder divided by the smallest Sedimentation Volume of all the cylinders. The Ease of Redispersion was based on the number of inversions necessary to resuspend the settled material off the bottom of the graduated cylinder.

Figure. Plot of Sedimentation Volume and Rate versus electrolyte concentration.

When plotting the Sedimentation Volume and Sedimentation Rate as a function of the logarithmic value of the electrolyte concentration, the electrolyte concentrations between 0.05% and 0.1% produced suspensions with faster sedimentation rates and larger sedimentation volumes. These electrolyte concentrations also had the highest degree of flocculation and showed the greatest ease of redispersion. Therefore, electrolyte concentrations between 0.05% and 0.1% produced the most acceptable suspension.