Toxicity of a novel HMG-CoA reductase inhibitor in the common marmoset (Callithrix jacchus).

1. GR95030X, a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was administered daily to marmosets by gavage. In a Maximum Repeatable Dose (MRD) study, doses of up to 30 mg kg-1 day-1 were administered for 49 days. In a chronic study, animals received dosages equivalent to 0, 1, 2.5, 7.5 and 20 mg kg-1 day-1 for 204 or 205 days. Some animals were maintained without treatment for a recovery period of 29 or 30 days. 2. Clinical signs included poor coat condition, weakness with impaired coordination, lethargy and other behavioural changes. There was also alimentary disturbance, and some deaths occurred at doses of 20 mg kg-1 day-1 and above. 3. Adverse effects upon body weight were seen although some recovery was apparent after the cessation of treatment. 4. Serum cholesterol concentrations were reduced. Very large increases in serum ALT, AST and CK activities were recorded with CK-MM isoenzymes accounting for 80% or more of the total CK enzyme activity. 5. Treatment was associated with muscle fibre atrophy and a sarcolemmal response with little evidence of regeneration. Histological examination revealed vascular changes, glial proliferation and cell death in the brain, with no consistent distribution. Alveolar capillary congestion and alveolar proteinosis indicated that there may have been a reduction in cardiac function. 6. HMG-CoA reductase inhibitors have evident potential to cause myopathy in marmosets. This is believed to be the first report of such an effect.