Do we really get half dose after splitting a tablet into two equal halves?

Dosage involving splitting tablets: Common but unnecessary?

Its quiet common in our daily experience that patients are advised to use half a tablet, after splitting it into two equal halves. Sometimes prescribers tell their patients to do this for several reasons best known to them; and sometimes patients or their care takers "invents" this practice on their own.

It is so common that we even don't take notice of it!

Prescribers usually do this, when the desired dose strength is not available in the market. For example, A prescriber wish to prescribe a dose of 75mg (considering the weight, age and gender of patient) of a particular drug, but brands are available in the strengths of 100mg or 50mg. In this case he is likely to prescribe one and a half tablet of 50mg strength (in order to acheive the dose of 75mg)

Price is another rationale for this practice. Because if we check the price of any medicine, 2 tablets of 250mg will cost more than a single tablet of 500mg of same medicine. Some "clever" care takers of patients or patients themselves, uses this equation in their favor. What they do?, if they are prescribed the strength of 250mg; they purchase the 500mg strength of same medicine if available and use this tablet after splitting into two equal halves. It apparently looks strange that, how could they be able to get higher strength of the same drug when they are prescribed the lower strength, but in countries where, role of community and clinical pharmacist is neither developed nor emphasized; we should be prepared for any malpractice on retail drug stores.

Let's analyze this issue from a Pharmacist's perspective!

Each label of every dosage form bears label claim. For Example,

 Each tablet contains 50mg of API ( Active Pharmaceutical Ingredient)

 Each film coated tablet contains 50 mg of API

 Each ml of this syrup contains 50 mg of API

Matter of utmost concern is that, manufacturers claims the availability of 50mg API in a single tablet and this 50mg could be anywhere within that tablet; manufacturers does not claim that this 50mg API is evenly distributed throughout the tablet. This claim is supported by the fact that tablet is a unit dosage form, whole tablet when taken, ensures the supply of label claimed API. But when we split it into halves or takes one third or takes quarter of tablet, corresponding half dose or quarter dose cannot be ensured in the light of manufacturer claim.

During Manufacturing of tablets, Content uniformity test (for API) is conducted on the compressional weight of tablets, not on their fractions. For example, if a tablet contains 50mg of API, and its compressional weight is 200mg (remaining 150mg are excipients) then to check the adequate mixing, analysis  will not be performed on 50mg (quarter); nor on 100mg (half); but it will be performed on 200mg (full). In this particular example 200mg is also termed as "Scale of Scrutiny" - amount of the material within which the quality of mixing is important.

Keeping all these factors into consideration we are now able to conclude. As tablets are not checked for the uniformity of API at quarter or half size, therefore we can't be able to claim that quarter or half tablet will furnish the respective dose. It could be less or more than anticipated. This practice gets gravity, when we split tablets of potent drug (low strength drugs e.g, 2.5mg, 5 mg etc.)

This may not lead to a phenomenal change in drug effect, but this concept requires attention by prescribers and pharmacists at retail drug stores.

Kamran Zaheer

kamranzaheer.blogspot.com

Research on Tablet Splitting

• Teng and colleagues conducted a study of 11 commonly split tablets and evaluated the resulting half-tablets for content uniformity.¹ Eight of the 11 tablets, when split, failed to produce half-tablets that met a liberal adaptation of the content uniformity test for tablets from the United States Pharmacopeia. These half-tablets did not contain between 85% and 115% of the intended dosage. Notably, scoring of the tablet did not predict whether the tablet would pass or fail this test.

• McDevitt and colleagues evaluated the accuracy of tablet splitting by healthy volunteers.² Ninety-four volunteers each split 10 tablets of 25 mg of hydrochlorothiazide. The split tablets were weighed with an analytical balance to determine accuracy of splitting. Of the split tablet portions, 41.3% deviated by more than 10% from ideal weight, and 12.4% of the portions deviated by more than 20%. After this experience, 77.2% of the subjects stated a willingness to pay more for a standard tablet of the lower strength.

• Rosenberg and colleagues evaluated variability of tablet fragments dispensed by a pharmacy.³ In this study, 30 of 560 tablet fragments (5.4%) deviated by more than 15% from the ideal weight. This level of accuracy was higher than reported by McDevitt with healthy volunteers, but still represents a significant variation.

References:

1. Teng J, Song CK, Williams RL, et al. Lack of medication dose uniformity in commonly split tablets. J Am Pharm Assoc. 2002;42:195-9.
2. McDevitt JT, Gurst AH, Chen Y. Accuracy of tablet splitting. Pharmacotherapy 1998;18(1):193-7.
3. Rosenberg JM, Nathan JP, Plakogiannis F. Weight variability of pharmacist-dispensed split tablets. J Am Pharm Assoc. 2002;42:200-5.

What FDA says about Tablet Splitting

Tablet Splitting: A Risky Practice 

"Equal distribution of medicine in split tablets is questionable. Studies have shown that the actual dose in each half of a split tablet often is different. So while the two halves may look the same, they don't necessarily contain equal amounts of medicine. Even if the tablet is scored with a line that runs down the middle, one half may actually have more medicine than the other. "

(http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm171492.htm)

I would like to complete my blog with the words of  Daniel A. Hussar, Remington Professor of Pharmacy at the Philadelphia College of Pharmacy, stated: “Tablet splitting for economic reasons is bad patient care and bad pharmacy practice".  (In an editorial in Pharmacy Today)