Practical Pharmaceutical Orientation Strength of dosage Lab (2) Shahen S. Mohammed BSC pharmacy MSc Pharmaceutics

Strength of dosage Many dosage forms including capsules and tablets are available in more than one strength. If a capsule or a tablet of higher strength is prescribed but unavailable, two capsules or tablets of one-half the strength may be dispensed. Inversely, for example, if 300-mg tablets of ibuprofen are prescribed and only 600-mg ibuprofen tablets are available. In such a case, one- half of the total number of tablets required should be dispensed to the patients with clear instructions to take 1⁄2 tablet.

A few helpful tips for such calculations are provided below: Do not break the tablets that are not scored. Enteric coated tablets are designed to resist the acidic environment in the stomach and release the medication in the small intestine. If such tablets are broken, their enteric properties may be lost. Therefore, do not break them.

As a general rule, do not divide sustained/controlled release medications as they may lose their controlled release properties.

Examples: Tenormin® is available in strength of 50 mg. If a prescription is written for 100 mg daily for three weeks as directed, how many tablets should be dispensed? Two 50 mg tablets should be given in one day   Answer: for 21 days, 42 tablets should be dispensed

Rx Cephalexin Caps 500 mg   Sig. i cap tid, 10 days In the above problem, how many cephalexin 250 mg capsules should be dispensed totally? Answer: 60 capsules

Spironolactone tablets are available in 25 mg strength, but a drug order comes for 150 mg dose. How many tablets should be dispensed?

Calculations for filling powder prescriptions Pharmaceutical powder is a mixture of finely divided drugs and/or chemicals in dry form. They are dispensed as bulk powders or divided powders.   Bulk powders are provided as multiple doses in a container and the patient measures the dose as instructed at the time of administration. Divided powders are meant to be provided as single dose units in individually wrapped powder papers.

Procedure Reduce all the ingredients to a fine powder. Then by the geometric dilution method, mix all the ingredients with trituration. If bulk dispensing is required, fill the powder in a wide mouthed bottle. If divided powder papers are needed, weigh single doses and fill in the powder papers.