Tips & Techniques for Compounding Capsules

“Fast is fine, but accuracy is everything.”

~ Wyatt Earp


While there’s a good chance that in this quote Mr. Earp was referring to gun fighting, his statement is also quite relevant for compounding capsules. Yes, as a pharmacist it’s good for you to be efficient in your actions. But what is most important when filling empty capsules is creating an accurate dosage for patients.


Empty capsules can be filled with powders, tablets, semisolids and liquids. Here are some tips and techniques that compounding pharmacies may find helpful:


  • Choose the right size capsules: Capsuline offers both gelatin capsules and vegetarian HPMC capsules in 10 standard sizes, with Size 000 being the largest and Size 5 the smallest. The capsule size chart provides detailed information regarding each size empty capsule. Smaller capsules are, of course, the easiest for patients to swallow.

Note that capsule capacity is not simply determined by how much material will physically fit into the capsules. Instead, it is a function of both volume and mass (i.e. weight, which depends on the density of the fill material). When calculating which size capsule to use, be sure to allow for both the active ingredients and any necessary excipients. All of the fill material must fit into the base half of the capsule; the cap is then used to keep the capsule closed.


  • Ensure homogeneity when blending powders: Getting a homogenous blend is vitally important for ensuring the correct dosage. To make this happen, powders must be mixed using proper geometric dilution (i.e. mixing a small amount of API with an appropriate amount of diluent) and for a sufficient amount of time.

    That said, many compounding pharmacies find that when compounding a mix of powders it can be extremely difficult to judge the homogeneity of the mix via visual inspection, especially when all or most of the ingredients are the same color. Adding a tracer dye (such as FD&C Blue No. 1 or FD&C Red No. 3) can help you overcome this challenge.
  • Use trituration to reduce the particle size of powdered ingredients. While most powders do not require further treatment before use, some do. In addition, tablets must be ground into a fine powder (comminuted) prior to encapsulation.

    All of this is most effectively done using a mortar and pestle. Always use a soft rubber spatula to remove powder from the mortar, as a hard plastic or metal spatula can cause problems. Be sure to weigh the powder after trituration, as some powder can be lost during the particle reduction process.
  • Use one of three methods to prepare liquids. Liquids can either be (a) filled in the capsules as a liquid, (b) evaporated and then used as a powder, or (c) soaked up by an adsorbent and then combined into the powder mix. Which is best will depend on the API and the compound being prepared.
  • Always weigh and measure all ingredients. Ideally you will be able to measure out enough for at least one extra capsule, in order to accommodate any powder lost during compounding. Be sure to account for the weight of the empty capsule itself.

    Be aware that the only reliable method of ensuring accurate dosage is to weigh each capsule individually. However, individually weighing a large quantity of capsules is not particularly practical! A common practice at many compounding pharmacies is to weigh some representative capsules individually, and weigh the other capsules in groups of 10.
  • Avoid spilling powder onto the scale when weighing. Instead of using a flat round-tip spatula to weigh powders, switch to a V-shaped lab scoop with a pointed tip instead, as this will better contain the material for you. Using a lab scoop instead of tapping or pouring powders onto the balance will also help reduce airborne particles.


  • Mask unpleasant tastes. Many APIs have extremely strong, bitter tastes that are not masked by standard capsules. While flavoring and sweetening agents have traditionally played a role in addressing this problem, there’s another solution that many pharmacists may not know about: flavored capsules. Capsuline, for example, sells gelatin capsules in the following popular flavored capsules like strawberry and mint


Patients depend on compounding pharmacies to help them get needed medications in custom dosages and combinations that are not commercially available. As a pharmacist it is your responsibility to accommodate any allergies, preferences and ensure that they receive exactly what was prescribed.