Cyclosporine blood level in dogs and cats

What it shows

At least half of the cyclosporine in blood sits inside red blood cells, so labs measure it in whole blood rather than serum. Absorption varies between oral products, and the same regimen gives different levels in different animals; the test shows what this particular animal ends up with.

A first check can be done within days to a week of a new regimen. Two sampling points are used. The peak is taken about 1.5–2 hours after the capsule; the trough just before the next one. For immune-mediated disease with capsules every 12 hours, a lab describes a peak and a trough within 3–5 days of the start, and a single peak later for maintenance. When the capsule is given every 24–48 hours, as in atopic skin disease, the trough may be too low to detect, so a peak is preferred.

The method matters a great deal. Chromatography (HPLC) measures only the medicine itself. Immunoassays use antibodies that also pick up some breakdown products, and different kits pick up different amounts, so an immunoassay result tends to read higher than HPLC on the same blood.

Higher than reference — what it may be a sign of

• Peak sample. A sample 2 hours after the capsule is expected to be much higher than a trough.
• Other medicines. Some medicines that block the liver enzymes breaking down cyclosporine (an antifungal, ketoconazole, is the described example) markedly increase its effect and toxicity.
• Side effects. Described effects include vomiting, soft stool and diarrhea, overgrowth of the gums, more hair growth and warts; a higher exposure also means stronger suppression of immunity and more risk of infections.

A high result is not a signal to change anything at home: the vet decides what to do with it.

Lower than reference

A level below the target may mean the immune system is not suppressed enough for the disease the vet is managing. Practical reasons include a sample taken later than planned, missed capsules, a capsule given every 24–48 hours (the trough is then naturally very low), and a switch between products: absorption differs between brands, so a lab describes a peak before and a few days after a switch.

Look at together with

• The time of the last capsule and the lab method — without them the number cannot be compared with a target or with an earlier result.
• Toxoplasma — in cats the vet may check for hidden infection before starting.
• Bacteria in urine — urinary infections are among the effects described in dogs; the vet may also order other blood and urine tests during long use.

Units and conversion

Cyclosporine is reported in ng/mL (the same as µg/L). In the app this row is kept in ng/mL; if the form uses another unit, the row keeps the unit printed on the form. Results from different methods should not be put on one line as if they were the same scale — note the lab and method.

Reference range

The target range is on your lab’s form. For cyclosporine it is not a range of healthy animals: the target depends on the disease, on peak or trough, and on the method. As an example, Auburn University’s pharmacology lab gives, for its own antibody method in immune-mediated disease, a peak of about 800–1400 ng/mL and a trough of about 400–600 ng/mL, and a lower trough for chronic bowel inflammation. Another lab’s numbers may differ, and the target for a particular animal is set by the vet.

Cats and dogs

Sources

1. Auburn University Clinical Pharmacology Laboratory. Cyclosporine — therapeutic drug monitoring notes.
2. Auburn University Clinical Pharmacology Laboratory. Peak? Trough? — choosing the sampling time.
3. Auburn University College of Veterinary Medicine. Therapeutic Drug Monitoring (TDM): pricing and sample collection protocols (2023).
4. Immunomodulators for integumentary disease in animals. Merck Veterinary Manual, professional version.
5. Immunosuppressive drugs in animals. Merck Veterinary Manual, professional version.
6. ABCD (European Advisory Board on Cat Diseases). Guideline for vaccination of immunocompromised cats.
7. VCA Animal Hospitals. Cyclosporine — Oral (medication information for pet owners).