Letermovir is contraindicated for allergy sufferers and those who use it in combination with pimozide/ergotamine; When used in combination with cyclosporine, the dosage should be halved to 240mg/day; When combined with tacrolimus, there is no need to adjust Letermovir, but it is necessary to strengthen the monitoring of tacrolimus blood concentration to ensure safe balance.

1、 Letermovir's taboo population

1.1 Absolute taboos

Individuals allergic to Letermovir or any of its excipients.

Patients taking pimozide or ergot alkaloids (such as dihydroergotamine) can experience serious or life-threatening toxic reactions when used in combination.

1.2 Relative contraindications/caution

Severe liver dysfunction (Child Pugh C grade): Lack of safety data, not recommended for use.

Pregnant and lactating women: Use should be avoided unless explicitly necessary.

2、 Dose adjustment in combination with cyclosporine

2.1 Mutual influence

Cyclosporine can significantly increase the blood concentration of Letermovir, so the dose of Letermovir needs to be halved when used in combination.

2.2 Specific Adjustment Plan

The standard dose (480mg once daily) should be reduced to 240mg once daily when combined with cyclosporine.

If cyclosporine is discontinued, Letermovir should be restored to 480mg once daily.

2.3 Impact on renal function

Cyclosporine itself can cause renal function damage. During combination use, serum creatinine and urine output should be closely monitored, and the immunosuppressive regimen should be adjusted if necessary.

3、 Dose adjustment in combination with tacrolimus

3.1 Mutual influence

Letermovir can slightly increase the blood concentration of tacrolimus, but there is no need to adjust the dosage of Letermovir.

3.2 Monitoring Requirements

During the combination period, the monitoring frequency of tacrolimus blood concentration should be increased (at least once a week) until the concentration stabilizes.

Adjust the dose of tacrolimus according to blood drug concentration to avoid excessive or insufficient immune suppression.

3.3 Renal function monitoring

When tacrolimus is combined with Letermovir, renal function and electrolytes need to be monitored, especially in elderly or patients with pre-existing kidney injury.