Warning! The intended audience of this article is medical professionals and students. I am not your doctor. This article is not medical advice.

Notes

This discussion was prepared by examining items on the Australian Pharmaceutical Benefits Scheme (PBS) General Schedule, Repatriation PBS and Section 100 Highly Specialised Drugs (Public Hospital) programs, as at February 2023. I do not warrant that this will remain accurate in the future. Non-PBS drugs, including over-the-counter medications, are excluded from this discussion.

Also excluded from this discussion are:

  • complex preparations not normally dosed by mass (e.g. amino acid formula)
  • drugs in compound products, where the drug is only dosed in milligrams when not in a compounded product (e.g. indapamide)

Dosage units in this discussion are based on the dosage units listed on the PBS, rather than the dosage units printed on product packaging, or the dosage units the drug may actually be prescribed in. This will fail to capture situations where:

  • the PBS and manufacturer describe the dosage differently, e.g. clonazepam 500 microg (PBS) vs 0.5 mg (Paxam® manufacturer)
  • the dosage unit changes because of prescribing multiple tablets, or fractions of a tablet, e.g. paracetamol 500 mg 2 tabs = paracetamol 1 g

For salts of chemical elements, doses are considered in terms of the element (e.g. calcium) rather than the salt (e.g. calcium carbonate).

While reasonable efforts have been made to present correct information in this discussion, no warranty is provided as to its accuracy. You are advised to make your own enquiries through official sources when requiring information about drug dosages.

Inhalers

Almost all inhalers are dosed in micrograms. The exceptions are:

  • mannitol (40 mg)
  • sodium cromoglycate (5 mg)
  • tobramycin (28 mg)

Patches

The table below shows the dose units for drugs administered as patches:

Drug microg/hr mg/24 hr Other
buprenorphine ✓    
estradiol     microg/24 hr
fentanyl ✓    
glyceryl trinitrate   ✓  
nicotine   ✓ mg/16 hr
oxybutynin   ✓  
rivastigmine   ✓  
rotigotine   ✓  
testosterone   ✓  

As the table shows, all patches dosed ‘per hour’ are in micrograms, whereas all patches dosed ‘per 24 hours’ are in milligrams. The exception is estradiol, which is dosed in microg/24 hr.

Tablets, capsules and wafers

Almost all tablets, capsules and wafers are dosed in milligrams. The exceptions are discussed below.

Drugs listed in bold were prescribed more than 250,000 times between July 2021 and June 2022.

Dosed in micrograms

The following drugs in tablet, capsule or wafer form are dosed in micrograms only:

  • calcitriol (0.25 microg)
  • clonidine (hydrochloride 100/150 microg)
  • colchicine (500 microg)
  • colecalciferol (microg or units)
  • desmopressin (120/240 microg, acetate 200 microg)
  • digoxin (62.5/250 microg)
  • dutasteride (500 microg), tamsulosin (400 microg)
  • ethinylestradiol (20/30/35/50 microg)
  • fingolimod (250/500 microg)
  • fludrocortisone (acetate 100 microg)
  • levonorgestrel (30/50/75/100/125/150 microg)
  • levothyroxine (sodium 50/75/100/125/200 microg)
  • liothyronine (sodium 20 microg)
  • misoprostol (200 microg)
  • moxonidine (200/400 microg)
  • ozanimod (230/460/920 microg)
  • palonosetron (500 microg)
  • pizotifen (500 microg)
  • quinagolide (75 microg)

Dosed in grams

The following drugs in tablet, capsule or wafer form are dosed in grams only:

  • citrulline (1 g)
  • methenamine (1 g)

Dosed in both milligrams and grams

The following drugs in tablet, capsule or wafer form are dosed in either milligrams or grams:

  • amoxicillin (250/500 mg, 1 g)
  • deferiprone (500 mg, 1 g)
  • lanthanum (500/750 mg, 1 g)
  • levetiracetam (250/500 mg, 1 g)
  • mesalazine (250/500/800 mg, 1/1.2/1.6 g)
  • metformin (500/800 mg, 1 g)
  • naproxen (250/750 mg, 1 g, sodium 550 mg)
  • norethisterone (350/500 microg, 5 mg)

Dosed in both micrograms and milligrams

Some drugs in tablet, capsule or wafer form are dosed on the PBS in either micrograms or milligrams. However, in practice, dosages for many if not most drugs in this category are expressed in milligrams regardless. For completeness, the full list is:

  • alprazolam (250/500 microg, 1 mg)
  • budesonide (500 microg, 1/3 mg)
  • cabergoline (500 microg, 1/2 g)
  • clonazepam (500 microg, 2 g)
  • dexamethasone (500 microg, 4 mg)
  • everolimus (250/500/750 microg, 1/2/2.5/3/5/10 mg)
  • folic acid (500 microg, 5 mg)
  • haloperidol (500 microg, 1.5/5 mg)
  • pramipexole (125/250/375/750 microg, 1/1.5/2.25/3/3.75/4.5 mg)
  • riociguat (500 microg, 1/1.5/2/2.5 mg)
  • risperidone (500 microg, 1/2/3/4 mg)
  • selexipag (200/400/600/800 microg, 1/1.2/1.4/1.6 mg)
  • siponimod (250 microg, 2 mg)
  • sirolimus (500 microg, 1/2 mg)
  • tacrolimus (500/750 microg, 1/2/3/5 mg)
  • trametinib (500 microg, 2 mg)
  • trandolapril (500 microg, 1/2/4 mg)
  • varenicline (500 microg, 1 mg)