Pharmacogenomics in general practice

A structured GP reference for the common gene–drug pairs discussed in the RACGP Genomics in general practice guideline, plus the two MBS-funded pharmacogenomic tests. Pick a drug to see the gene, phenotype effects, clinical consequence, and MBS/testing status.

📋 Primary source: RACGP. Genomics in general practice — Pharmacogenomics. Last revised 19 December 2023. RACGP guideline page →
MBS items: item 73323 (HLA-B*57:01 before abacavir) and item 73327 (TPMT before thiopurines).
Extension source (where marked CPIC): Clinical Pharmacogenetics Implementation Consortium.
Verified June 2026. Reference material for registered medical professionals — not prescribing advice. Current TGA Product Information and CPIC guidelines are the authoritative sources for any prescribing decision.

Clinical judgement required. Pharmacogenomic testing may inform prescribing but does not replace clinical assessment, therapeutic drug monitoring, or standard indications and contraindications. RACGP notes the precise role of PGx testing in Australian general practice is still under consideration; evidence for clinical utility is strongest in a small number of gene–drug pairs and continues to evolve.

Drug lookup

Pick a drug to see the relevant gene, how variants affect the phenotype, and the clinical consequence. Entries marked RACGP are directly from RACGP Table 1. Entries marked MBS have an MBS-funded pharmacogenomic test. Entries marked CPIC are widely-cited CPIC pairs added for completeness.

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Clinical consequence of variants

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Phenotype effects

Testing status in Australia

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Alternatives / dose considerations mentioned in source

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Source

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Metaboliser phenotypes explained

Genetic variation in cytochrome P450 enzymes gives rise to four broad phenotypes. Click each to see what it means for drug response.

Poor metaboliser. Markedly reduced or absent enzyme activity. For drugs activated by the enzyme (prodrugs like codeine, clopidogrel), the patient may have no therapeutic response. For drugs cleared by the enzyme, the patient may accumulate the drug and have an increased risk of side effects — a lower dose or alternative agent may be considered.

Source: RACGP Genomics in general practice, Pharmacogenomics section.

MBS-funded pharmacogenomic tests

RACGP notes only two pharmacogenetic tests are currently funded through an MBS rebate. Most other PGx testing is available commercially at private cost.

Item 73323 — HLA-B*57:01 before abacavir. Detection of HLA-B*57:01 in a patient for whom abacavir is being considered as antiretroviral therapy. Testing is recommended because HLA-B*57:01 is strongly associated with abacavir hypersensitivity reaction. Once in a lifetime. MBS Online item 73323 →

Item 73327 — TPMT before thiopurines. Detection of genetic variants in the thiopurine S-methyltransferase (TPMT) gene for the prevention of dose-related toxicity during treatment with thiopurine drugs (azathioprine, mercaptopurine, thioguanine). Once in a lifetime. MBS Online item 73327 →

Everything else is private. Panel-based PGx testing (multiple genes at once — CYP2D6, CYP2C19, CYP2C9, VKORC1, SLCO1B1, others) is offered by several Australian commercial laboratories, typically for a few hundred dollars, with a 5–10 working day turnaround per RACGP. There is no Medicare rebate for these panels.

When to consider testing

Indications discussed in RACGP

RACGP notes pharmacogenomic testing may be considered for patients with:

Significant side effects from drugs for which pharmacogenomic variation in response is known (see the drug lookup above).
Poor therapeutic response to specific medications.
Potential suitability for using doses outside the usual range.

The guideline stops short of specific prescribing algorithms based on results — those are covered by CPIC guidelines internationally.

Source: RACGP Genomics in general practice, Pharmacogenomics — Genetic testing section.

Limitations to keep in mind

Cost. Only TPMT (item 73327) and HLA-B*57:01 (item 73323) are MBS-funded; commercial PGx panels are unfunded.
Turnaround. Results can take 5–10 working days per RACGP. In some clinical situations, standard trial-and-error dose adjustment would be complete within that window.
Evolving evidence. Understanding of gene–drug interactions is still developing. Evidence for clinical utility is stronger for some pairs (e.g. antidepressants — Bousman meta-analysis 2019) than others.
Not a substitute for TDM. Pharmacogenomics does not replace therapeutic drug monitoring where established (warfarin INR, lithium levels, tacrolimus levels, etc.).

Source: RACGP Genomics in general practice, Pharmacogenomics — Limitations section.

What genetic variation actually affects

Genetic variation can affect two things:

Pharmacokinetics — how the drug is handled by the body. Genetic variation in metabolising enzymes (e.g. the cytochrome P450 family) changes how quickly the drug is broken down or activated.
Pharmacodynamics — what effect the drug has on the body. Genetic variation in drug targets (e.g. receptors like VKORC1 for warfarin) changes sensitivity to a given drug concentration.

Cytochrome P450 enzymes account for an estimated 70–80% of enzymes involved in drug metabolism per RACGP.

Source: RACGP Genomics in general practice, Pharmacogenomics — How genetic polymorphisms/variants affect drug metabolism.

Patient resources cited by RACGP