title: Quantification of the spatial distribution of rectally applied surrogates for microbicide and semen in colon with SPECT and magnetic resonance imaging.
abstract: OBJECTIVE
  We sought to describe quantitatively the distribution of rectally administered gels and seminal fluid surrogates using novel concentration-distance parameters that could be repeated over time. These methods are needed to develop rationally rectal microbicides to target and prevent HIV infection.
  
  
  METHODS
  Eight subjects were dosed rectally with radiolabelled and gadolinium-labelled gels to simulate microbicide gel and seminal fluid. Rectal doses were given with and without simulated receptive anal intercourse. Twenty-four hour distribution was assessed with indirect single photon emission computed tomography (SPECT)/computed tomography (CT) and magnetic resonance imaging (MRI), and direct assessment via sigmoidoscopic brushes. Concentration-distance curves were generated using an algorithm for fitting SPECT data in three dimensions. Three novel concentration-distance parameters were defined to describe quantitatively the distribution of radiolabels: maximal distance (D(max) ), distance at maximal concentration (D(Cmax) ) and mean residence distance (D(ave) ).
  
  
  RESULTS
  The SPECT/CT distribution of microbicide and semen surrogates was similar. Between 1 h and 24 h post dose, the surrogates migrated retrograde in all three parameters (relative to coccygeal level; geometric mean [95% confidence interval]): maximal distance (D(max) ), 10 cm (8.6-12) to 18 cm (13-26), distance at maximal concentration (D(Cmax) ), 3.8 cm (2.7-5.3) to 4.2 cm (2.8-6.3) and mean residence distance (D(ave) ), 4.3 cm (3.5-5.1) to 7.6 cm (5.3-11). Sigmoidoscopy and MRI correlated only roughly with SPECT/CT.
  
  
  CONCLUSIONS
  Rectal microbicide surrogates migrated retrograde during the 24 h following dosing. Spatial kinetic parameters estimated using three dimensional curve fitting of distribution data should prove useful for evaluating rectal formulations of drugs for HIV prevention and other indications.
authors.affiliation: Department of Medicine, Division of Clinical Pharmacology, The Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
authors.forename: Ying J
authors.initials: YJ
authors.lastname: Cao
authors.forename: Brian S
authors.initials: BS
authors.lastname: Caffo
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Fuchs
authors.forename: Linda A
authors.initials: LA
authors.lastname: Lee
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.forename: Liye
authors.initials: L
authors.lastname: Li
authors.forename: Rahul P
authors.initials: RP
authors.lastname: Bakshi
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Macura
authors.forename: Wasif A
authors.initials: WA
authors.lastname: Khan
authors.forename: Richard L
authors.initials: RL
authors.lastname: Wahl
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Grohskopf
authors.forename: Craig W
authors.initials: CW
authors.lastname: Hendrix
mesh_terms: D000285:Administration, Rectal; D000328:Adult; D000890:Anti-Infective Agents / Q000493:pharmacokinetics; D002482:Cellulose / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D003106:Colon / Q000378:metabolism*; D005682:Gadolinium / Q000493:pharmacokinetics*; D019786:Gadolinium DTPA / Q000493:pharmacokinetics*; D005990:Glycerol / Q000493:pharmacokinetics*; D015658:HIV Infections / Q000517:prevention & control; D018451:Homosexuality, Male; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D004369:Pentetic Acid / Q000493:pharmacokinetics*; D010710:Phosphates / Q000493:pharmacokinetics*; D011409:Propylene Glycols / Q000493:pharmacokinetics*; D012661:Semen / Q000502:physiology; D012812:Sigmoidoscopy / Q000379:methods; D013671:Technetium Tc 99m Sulfur Colloid / Q000493:pharmacokinetics*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
chemical_list: D000890:Anti-Infective Agents; C042973:K-Y jelly; D010710:Phosphates; D011409:Propylene Glycols; D013671:Technetium Tc 99m Sulfur Colloid; D004369:Pentetic Acid; D002482:Cellulose; D005682:Gadolinium; D019786:Gadolinium DTPA; D005990:Glycerol