Table 1.  Therapeutic Drug Monitoring Data for Small Animals Drug Usual Dosage Interval(hr) Therapeutic Range* Volume of Distribution (L/kg) Elimination Half-Life Time to Steady State Sample Collection Peak Sample Collection Trough Amikacin 7 to 20 mg/kg 12-24 2 to 25 µg/ml1 0.25 1-2 hrs 1 day 1 hr (plastic only) 2 half-lives (3 to 6 hrs)2 Asprin      (dog)      (cat) 10 mg/kg 10 mg/kg 8-12 72 50-100 µg/ml 0.19 0.19 8 hr 38 hr 40 hr 8 days 2-4 BND Benzodiazepines 1-2 mg/kg   100-200 ng3/ml   <8 hr 1 day 2-5 BND2 Bromide 15-20 mg/kg 12-24 1.0 to 3.5 mg/ml   24 days 2-34 months   BND Cyclosporine High: 6 0-8.5 mg/kg Moderate: 3.5-5.5 mg/kg Low: 0.75-3 mg/kg 12 12 12 Trough above 400  to 600 ng/ml   1.35 5.68 2-4 BND Digoxin      (dog)      (cat) .011 mg/kg .008 mg/kg 12 12-24 0.9-3.0 ng/ml 0.9-2.0 ng/ml 19 14.5 31.3 hr 33.5 hr 7 days 7 days Toxicity: 2-56 glass only Efficacy: BND Gentamicin      (dog)      (cat) 2-8 mg/kg 2-8 mg/kg 12-24 12-24 0.5-1.5 µg/ml1 5.0-8.0 µg/ml 0.3-0.4 0.9-1.3 hr 6.5 hr 1 hr (plastic only) 2 half-lives (3 to 6 hrs) Phenobarbital      (dog) 2 mg/kg 12 14-45 µg/ml 0.7 32-75 hr 14-16 days 4-57 BND Primidone      (dog)      (cat) 11-25 mg/kg 11-20 mg/kg 12-24 Based on phenobarbital3 0.7 6.1 hr 14-16 days 4-57 BND Procainamide      (dog) 15 mg/kg 12 8 1.4-2.1 2.9 hr 15 hr 2-4 BND Quinidine      (dog)      (cat) 6-20 mg/kg Not recommended   2.5-5.0 µg/ml 2.9 2.2 5.6 hr 1.9 hr 28 hr 10 hr 2-4 BND Theophylline 7-11 mg/kg 4 mg/kg 8-12 (D) 12-24 (C) 10-20 µg/ml 0.82 0.46 5.7 hr 7.9 hr 29 hr 40 hr 1-29 BND Thyroid Hormones T3, T4 T3: 4-6 µg/kg (d) 4.4 µg/kg (c) T4: 20 µg/kg (d) 50-100 µg/kg (c)   0.8-1.5 (d)10 1.5-3.5 (d) 1.5-5.0 (c)   5-6 (d) 12-15 (d) <24 hrs11 2-3 D11 4-5 BND * Therapeutic ranges are extrapolated from human patients unless noted otherwise. Note that ranges may also vary with the laboratory and specifically with the instrumentation used to assay the drug of interest. Values in this table may be superseded if the values for the instrument have been validated appropriately. Because samples sizes and assay methodologies vary, the specific laboratory that will be performing the assay should be contacted regarding sample volume, proper collection tubes, need of refrigeration and other sample handling specifics as well as "normal" ranges. BND = before next dose; C = cat; D = dog 1 "Target" peak concentration for aminoglycosides depend on infecting organism, and specifically the minimum inhibitory concentration (MIC) of the infecting organism. The target peak concentration should be 4 to 10 times the MIC. Trough concentration should equal or be below that recommended in order to minimize toxicity. 2 For drugs with very short half-life, trough sample may no longer have detectable drug. Wait 1 or 2 predicted elimination drug half-lives between peak and trough sample collections. 3 600 ng/ml listed in humans. Assay should measure all benzodiazepines (parent and active metabolites) relative to dosing interval. 4 Single sample post-load and 3 to 4 weeks later, or 3 to 4 weeks into therapy if a loading dose not used is recommended as therapy is begun. 5 In people; data not available for dogs. 6 Both peak and trough recommended because of short half-life; single peak acceptable if toxicity is a concern. 7 Peak and trough recommended if seizures are difficult to control. 8 As suggested in Papich ______. 9 For slow release preparations, one sample may be sufficient. 10 Values for ranges of thyroid hormones reflect an RIA assay. Values are likely to be different for each lab. Contact your laboratory, or if doing assays in house, establish your own normal ranges. Overlap between normal and abnormal is great, regardless of the lab, and interpretation should be based on clinical signs. 11 Monitoring should not take place until the body has had a chance to physiologically adapt to drug therapy (ie, 4 to 6 weeks after therapy is implemented). [back to top]