The R-package lme4cens builds on lme4 to fit simple random effects models with a censored response.
It re-uses the formula-module from lme4 to facilitate model specification.
The censoring information is encoded via survival's Surv-object that allows for a flexible specification of
(a combination of) left-, right- and interval-censored responses with flexible censoring levels per observation.
The random effect structure is currently limited to the most simple case, namely models with a single random intercept.
Model fitting is via maximum likelihood (ML), residual maximum likelihood (REML) is not supported.
A good choice of starting values is helpful, although there is a heuristic in place if none are given. As with all non-trivial optimization problems it is good practice to check convergence with different start values.