SB 8.8.34

sa vai bhagavataḥ sākṣād
 viṣṇor aṁśāṁśa-sambhavaḥ
dhanvantarir iti khyāta
 āyur-veda-dṛg ijya-bhāk
Synonyms: 
saḥ — he; vai — indeed; bhagavataḥ — of the Supreme Personality of Godhead; sākṣāt — directly; viṣṇoḥ — of Lord Viṣṇu; aṁśa-aṁśa-sambhavaḥ — incarnation of the plenary portion of a plenary portion; dhanvantariḥ — Dhanvantari; iti — thus; khyātaḥ — celebrated; āyuḥ-veda-dṛk — fully conversant in the medical science; ijya-bhāk — one of the demigods eligible to share the benefits of sacrifices.
Translation: 
This person was Dhanvantari, a plenary portion of a plenary portion of Lord Viṣṇu. He was very conversant with the science of medicine, and as one of the demigods he was permitted to take a share in sacrifices.
Purport: 

Śrīla Madhvācārya remarks:

teṣāṁ satyāc cālanārthaṁ
 harir dhanvantarir vibhuḥ
samartho ’py asurāṇāṁ tu
 sva-hastād amucat sudhām

Dhanvantari, who was carrying the jug containing nectar, was a plenary incarnation of the Supreme Personality of Godhead, but although he was very strong, the asuras were able to take the jug of nectar from his hands.